Cooling device

Abstract

And the simplification of the device and the high cooling efficiency of the heated insulating oil are both considered. The cooling device cools the power semiconductor device. The cooling device is provided with a tank for accommodating the power semiconductor device, an insulating oil, and a refrigerant fluid having a boiling point temperature lower than the boiling point temperature of the insulating oil and a specific gravity greater than the specific gravity of the insulating oil. The insulating oil and the refrigerant fluid are stored in a mixed state in the tank and cool the power semiconductor device.

Description

Technical Field

[0001] The invention relates to a cooling device. Background Art

[0002] Patent Document 1 discloses a cooling device in which a semiconductor stack is immersed in insulating oil and contained in an oil-immersed tank, and a working fluid is sealed in a heat pipe type heat sink on both sides of the semiconductor element, and cooling is performed by boiling and condensing cycles of the sealed working fluid. In this cooling device, the insulating oil and the working fluid are in an immiscible state, and the insulating oil heated by the heat from the heat sink undergoes natural convection or forced convection by a pump in the oil-immersed tank, and dissipates heat to the atmosphere through a radiator attached to the tank, thereby being cooled.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: (Japanese) Patent Publication No. 8-97338 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] Compared with the case of forced convection, the case of allowing the heated insulating oil to circulate naturally can simplify the cooling device, but it is difficult to obtain high cooling efficiency compared with the case of forced convection. Conversely, compared with the case of natural convection, the case of allowing the heated insulating oil to circulate forced convection can obtain high cooling efficiency, but it is necessary to add a device such as a pump for forced convection of the insulating oil, which may hinder the simplification of the cooling device.

[0008] The present invention has been made in view of the above technical problems, and an object of the present invention is to achieve both simplification of the device and high cooling efficiency of heated insulating oil.

[0009] Technical solutions for solving technical problems

[0010] A cooling device according to one embodiment of the present invention is a cooling device for cooling a power semiconductor device, the cooling device comprising: a tank that contains the power semiconductor device; insulating oil; and a refrigerant having a boiling point temperature lower than that of the insulating oil and a specific gravity greater than that of the insulating oil. The insulating oil and the refrigerant are stored in the tank in a mixed state and cool the power semiconductor device.

[0011] Effects of the Invention

[0012] According to this method, the insulating oil and the refrigerant stored in the tank in a mixed state are located at different positions in the height direction due to the difference in specific gravity. As a result, the refrigerant with a higher specific gravity is located below the insulating oil. Therefore, even without adding a device for forced convection, by using the refrigerant for vaporization heat cooling, the insulating oil above can be stirred by the vaporized refrigerant, thereby forcing the heated insulating oil to convect. Therefore, it is possible to achieve both simplification of the device and high cooling efficiency of the heated insulating oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the cooling device.

[0014] Figure 2 It is a diagram showing the state of the cooling device when the circuit is operating.

[0015] Figure 3 It is a diagram showing a first modified example of the electric circuit and the cooling device.

[0016] Figure 4 It is a diagram showing a second modified example of the electric circuit and the cooling device. DETAILED DESCRIPTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0018] Figure 1 1 is a schematic diagram of the configuration of the cooling device 100 . Figure 1 The circuit 50 is shown in a static state in which it is not in operation and is in an ambient temperature state. The ambient temperature is the outside air temperature or atmospheric temperature, for example, when it is room temperature. Figure 1 The up and down direction corresponds to the vertical direction (height direction).

[0019] The cooling device 100 cools the circuit 50. The circuit 50 is, for example, an inverter (a circuit that functions as an inverter), which corresponds to a semiconductor device for power. The circuit 50 includes a first substrate 51, a second substrate 52, and a circuit unit 55. The first substrate 51 and the second substrate 52 are printed substrates, and the first substrate 51 is stacked on the second substrate 52. The circuit unit 55 is mounted on the first substrate 51 and the second substrate 52, and is electrically connected to the first substrate 51 and the second substrate 52 by being connected to the circuit patterns of the first substrate 51 and the second substrate 52.

[0020] The circuit unit 55 includes a semiconductor element 55a, a wire 55b, a lead frame 55c, and a capacitor 55d. The semiconductor element 55a, the wire 55b, and the lead frame 55c are mounted on the first substrate 51, and the capacitor 55d is mounted on the second substrate 52. The semiconductor element 55a is a power element and is set as a switching element such as an IGBT or a power MOSFET. A plurality of semiconductor elements 55a are provided. In this embodiment, the semiconductor elements 55a are arranged along the Figure 1 The inward and outward directions (with Figure 1 It should be noted that the configuration of the plurality of semiconductor elements 55a is not necessarily limited to this.

[0021] The semiconductor element 55a is electrically connected to the lead frame 55c via the wire 55b. The semiconductor element 55a is sealed by a molding resin, and heat dissipation from the semiconductor element 55a is performed via the molding resin. Heat dissipation from the semiconductor element 55a can also be performed via the lead frame 55c. The semiconductor element 55a is provided on the lower side (back side) of the second substrate 52 together with the wire 55b and the lead frame 55c, and the capacitor 55d is provided on the upper side (front side) of the second substrate 52.

[0022] The semiconductor element 55a and the capacitor 55d are examples of multiple electronic components included in the circuit 50, and the semiconductor element 55a and the capacitor 55d have different heat densities. The circuit 50 may have electronic components other than the semiconductor element 55a and the capacitor 55d. In the present embodiment, the capacitor 55d is an example of other electronic components other than the semiconductor element 55a among the multiple electronic components, and represents other electronic components other than the semiconductor element 55a. Compared with the capacitor 55d, the heat density of the semiconductor element 55a is relatively high, and the semiconductor element 55a and the capacitor 55d are equivalent to multiple electronic components with different heat densities.

[0023] The cooling device 100 includes a tank 10 and a sub-tank 20. The tank 10 accommodates a circuit 50. A boss 10a is provided on the inner surface of the side wall of the tank 10, and a second substrate 52 is fixed to the boss 10a. The second substrate 52 divides the tank 10 into an upper space and a lower space. A plurality of through holes 52a are formed in the second substrate 52, and the upper space and the lower space in the tank 10 are connected to each other via the plurality of through holes 52a. The plurality of through holes 52a can be provided, for example, at a position that does not overlap with the first substrate 51 when viewed in the vertical direction.

[0024] The tank 10 includes a first frame portion 11, a second frame portion 12, and a sealing member 13. The first frame portion 11 and the second frame portion 12 each have a box-like shape with one side open. The first frame portion 11 and the second frame portion 12 are combined by bolt fastening in a state where the joint surfaces of the open ends are joined to each other via the sealing member 13. The first frame portion 11 is disposed on the second frame portion 12, and the boss 10a is provided on the second frame portion 12.

[0025] The insulating oil OL and the refrigerant liquid LQ are stored in a mixed state in the tank 10. The mixed state refers to a state in which they are not isolated but mixed in the same space, including a state in which they are separated according to specific gravity in a static state. The insulating oil OL is a hydrocarbon oil, for example, the same oil as that used for cooling and lubrication in the continuously variable transmission mechanism is used. The refrigerant liquid LQ is a fluorine-based refrigerant (fluorine-based inactive liquid), and as the refrigerant LQ, for example, perfluorocarbon (PFC) is used. The specific gravity of the refrigerant LQ as a fluorine-based refrigerant is greater than that of the insulating oil OL. Therefore, if the insulating oil OL and the refrigerant liquid LQ are stored in a mixed state in the tank 10, in the tank 10, the insulating oil OL exists on the upper side and the refrigerant liquid LQ exists on the lower side.

[0026] The storage amount of the refrigerant liquid LQ stored in the tank 10 is smaller than the capacity of the second frame portion 12. Therefore, the refrigerant liquid LQ is stored at the bottom of the tank 10 in the second frame portion 12 in a static state. In the tank 10, the remaining space other than the space occupied by the refrigerant liquid LQ is filled with the insulating oil OL. Therefore, the insulating oil OL exists at the joint position of the first frame portion 11 and the second frame portion 12 in the height direction.

[0027] The sealing member 13 seals the first frame portion 11 and the second frame portion 12 that are connected to each other. The sealing member 13 is provided within a range where the insulating oil OL is stored in the height direction according to specific gravity, and prevents leakage of the insulating oil OL. The sealing member 13 can be formed of a gasket, for example.

[0028] The tank 10 has a cooling liquid passage 10b and a through hole 10c. The cooling liquid passage 10b is formed inside the upper wall of the tank 10 formed by the first frame portion 11. The cooling liquid flows through the cooling liquid passage 10b, and the cooling liquid is heated by the insulating oil OL and the refrigerant LQ in the tank 10 to cool the insulating oil OL and the refrigerant LQ. The through hole 10c penetrates the side wall of the tank 10 formed by the first frame portion 11. Therefore, the through hole 10c is provided in a range in which the insulating oil OL is stored in the height direction according to the specific gravity (in the range in the height direction where the insulating oil OL exists in a static state). The through hole 10c extends in the horizontal direction and penetrates the side wall of the tank 10.

[0029] The tank 10 also includes a shielding plate 14 and a shielding plate 15. The shielding plate 14 and the shielding plate 15 are disposed on the inner surface of the side wall of the tank 10 provided with the through hole 10c. The shielding plate 14 is disposed at the lower portion of the periphery of the opening of the through hole 10c into the tank 10, and the shielding plate 15 is disposed at the upper portion of the periphery of the opening. The shielding plate 14 extends obliquely upward in a manner that the farther away from the through hole 10c is from the through hole 10c along the extension direction of the through hole 10c, the more upward it is. The shielding plate 15 extends obliquely downward in a manner that the farther away from the through hole 10c is from the through hole 10c along the extension direction of the through hole 10c, the more downward it is. A gap is formed between the front end portion of the shielding plate 14 and the front end portion of the shielding plate 15. Therefore, the communication state between the tank 10 and the through hole 10c is not hindered by the shielding plate 14 and the shielding plate 15.

[0030] The shielding plates 14 and 15 each have a deformed L-shaped cross-section with an angle greater than a right angle, and can be provided by fixing one of the plate-shaped portions as a fixing portion to the inner surface of the side wall of the tank 10 with bolts or the like. Figure 1 In the inner and outer directions, the shielding plates 14 and 15 may be replaced with a tapered pipe member whose tip becomes thinner as it moves away from the through hole 10c along the extending direction of the through hole 10c.

[0031] The sub-tank 20 is provided on the tank 10. The sub-tank 20 has a tank portion 21 and a connection portion 22. The tank portion 21 has a cylindrical shape. The tank portion 21 extends in the vertical direction and is open at the upper end. The connection portion 22 has a tubular shape and extends in the horizontal direction. The connection portion 22 has a flange as a fixing portion at the open end, for example, and the sub-tank 20 is fixed to the tank 10 by bolting the flange to the side wall of the tank 10.

[0032] The connecting portion 22 is connected to the lower portion of the tank portion 21 in the radial direction at the base end portion and is open in the tank portion 21, and is connected to the through hole 10c at the open end portion. Therefore, the insulating oil OL stored in a manner that fills the tank 10 fills the through hole 10c and the connecting portion 22, and fills a part of the tank portion 21. In order to prevent leakage of the insulating oil OL, a sealing member can be provided between the connecting portion 22 and the side wall of the tank 10.

[0033] The subtank 20 further includes an air chamber AR. The air chamber AR is formed in the tank portion 21 just above the insulating oil OL. The air chamber AR communicates with the tank portion 21 via a communication path C. The communication path C is composed of the portion of the tank portion 21 filled with the insulating oil OL, the connection portion 22, and the through hole 10c.

[0034] The auxiliary tank 20 is also provided with a vent cover 23. The vent cover 23 is provided at the upper end of the tank portion 21. The vent cover 23 has a main body 23a and an umbrella portion 23b. The main body 23a has a cylindrical shape, and a thread is formed on the outer periphery of one end of the main body 23a. The main body 23a is screwed into the thread formed on the inner periphery of the upper end of the tank portion 21. The main body 23a is screwed until the flange portion provided on the outer periphery abuts against the tank portion 21, thereby fixing the vent cover 23 to the tank portion 21.

[0035] The umbrella portion 23b is provided at the other end of the main body 23a. The umbrella portion 23b has a bottomed cylindrical shape, and prevents the infiltration of water from the outside by covering the main body 23a from above. A gap is formed in the circumferential direction between the main body 23a and the umbrella portion 23b, and the gap is open to the outside air toward the bottom. A communication hole that communicates the inside and the outside is formed in the peripheral wall of the other end of the main body 23a. Therefore, the vent cover 23 communicates the air chamber AR with the outside air outside the auxiliary tank 20 via the communication hole and the gap.

[0036] A labyrinth flow path L is formed in the main body 23a. The labyrinth flow path L allows air to pass through and blocks the passage of the insulating oil OL. Each wall portion forming the labyrinth flow path L may be arranged, for example, to be inclined downward toward the front end, thereby promoting the falling of the insulating oil OL by its own weight. The vent cover 23 corresponds to a vent mechanism.

[0037] In a static state, the refrigerant LQ has a liquid level H, and the second substrate 52 is provided so that the liquid level H is located between its upper surface and lower surface. Therefore, the semiconductor element 55a provided on the back side of the second substrate 52 is accommodated in a state immersed in the refrigerant LQ at the lower part (below the insulating oil OL) in the tank 10, and the capacitor 55d provided on the front side of the second substrate 52 is accommodated in a state immersed in the insulating oil OL. As a result, the circuit 50 is cooled in the cooling device 100 as follows.

[0038] Figure 2 1 is a diagram showing the state of the cooling device 100 when the circuit 50 is operating. When the circuit 50 is operating, the semiconductor element 55a and the capacitor 55d generate heat. In the cooling device 100, the circuit 50 is cooled by the vaporization heat cooling of the refrigerant LQ and the heating of the insulating oil OL. Since the semiconductor element 55a is immersed in the refrigerant LQ, the refrigerant LQ vaporizes when the semiconductor element 55a generates heat. As a result, the semiconductor element 55a having a relatively high heat density is cooled by the vaporization heat cooling, and the circuit 50 is effectively cooled.

[0039] The capacitor 55d immersed in the insulating oil OL is cooled by dissipating heat to the insulating oil OL. This is because the capacitor 55d, which has a lower heat density than the semiconductor element 55a, can be sufficiently cooled by the insulating oil OL. As a result, the storage amount of the refrigerant LQ can be reduced, and thus the storage amount of the expensive fluorine-based refrigerant can be reduced. As a result, cost reduction can be achieved compared to, for example, the case where only the refrigerant LQ is used for cooling the circuit 50. The insulating oil OL is cooled in a liquid state without being vaporized.

[0040] The vaporized refrigerant liquid LQ moves from the lower space to the upper space in the tank 10 through the through hole 52a. The insulating oil OL is also heated by the vaporized refrigerant liquid LQ. As a result, a part of the vaporized refrigerant liquid LQ is liquefied by heat dissipation to the insulating oil OL. The heated insulating oil OL and the refrigerant liquid LQ that remains in a vaporized state are cooled by the coolant near the top of the tank 10. As a result, the refrigerant liquid LQ that remains in a vaporized state is also liquefied. The specific gravity of the liquefied refrigerant liquid LQ is greater than that of the insulating oil OL. Therefore, the liquefied refrigerant liquid LQ gradually sinks in the insulating oil OL and returns to the lower space from the upper space in the tank 10 through the through hole 52a.

[0041] The insulating oil OL is stirred by the vaporized refrigerant liquid LQ. As a result, even without adding a device for forced convection such as a pump, the insulating oil OL generates forced convection, thereby improving the cooling efficiency of the heated insulating oil OL compared with the case of natural convection. In the tank 10, the refrigerant liquid LQ circulates between the lower space and the upper space due to the vaporization and liquefaction of the refrigerant liquid LQ. At this time, the vaporized refrigerant liquid LQ passes through a part of the through holes 52a of the plurality of through holes 52a, and the liquefied refrigerant liquid LQ passes through the remaining through holes 52a. As a result, the forced convection becomes a flow shown by, for example, an arrow.

[0042] The air chamber AR is connected to the tank 10 via the connecting passage C. Therefore, the increase in the internal pressure of the tank 10 caused by the vaporization of the refrigerant liquid LQ is suppressed by the sub-tank 20. As a result, the sealing of the sealing component 13 becomes easier accordingly. In addition, since the increase in the boiling point of the refrigerant liquid LQ is also suppressed, the difficulty in performing vaporization heat cooling is also suppressed accordingly. Furthermore, the air chamber AR set in this way is a different chamber from the tank 10. Therefore, a structure in which it is difficult for the refrigerant liquid LQ to enter the air chamber AR is also obtained at the same time. The refrigerant liquid LQ is prevented from entering the sub-tank 20 in a vaporized state by the baffle plate 14, and is also prevented from entering the sub-tank 20 in a liquefied state by the baffle plate 15.

[0043] The vent cap 23 maintains the tank 10 at atmospheric pressure. Therefore, the fluctuation of the boiling point of the refrigerant LQ is suppressed, and the boiling point is prevented from rising due to the increase in the internal pressure of the tank 10. Therefore, it is possible to avoid the situation where the vaporization heat cooling cannot be performed unless the temperature is higher. In addition, by maintaining the tank 10 at atmospheric pressure, the sealing of the sealing member 13 becomes easier than when the pressure is higher. The viscosity and surface tension of the refrigerant LQ, which is a fluorine-based refrigerant, are smaller than those of the insulating oil OL, and it is easy to pass through the sealing member 13. Therefore, even if the insulating oil OL is to be prevented from leaking, the sealing of the sealing member 13 becomes easier.

[0044] Next, the main effects of this embodiment will be described.

[0045] (1) The cooling device 100 cools the circuit 50 which is a power semiconductor device. The cooling device 100 includes a tank 10 for accommodating the circuit 50, insulating oil OL, and a refrigerant LQ having a lower boiling point temperature than the insulating oil OL and a higher specific gravity than the insulating oil OL. The insulating oil OL and the refrigerant LQ are stored in the tank 10 in a mixed state and cool the circuit 50.

[0046] According to such a configuration, the insulating oil OL and the refrigerant LQ stored in the tank 10 in a mixed state are located at different positions in the height direction due to the difference in specific gravity. As a result, the refrigerant LQ with a larger specific gravity is located below the insulating oil OL. Therefore, even without adding a device for forced convection, by cooling the refrigerant LQ using the vaporization heat, the insulating oil OL above can be stirred using the vaporized refrigerant LQ, thereby forcing the heated insulating oil OL to convect. Therefore, both simplification of the device and high cooling efficiency of the heated insulating oil OL can be achieved.

[0047] (2) In the present embodiment, the refrigerant LQ is a fluorine-based refrigerant. According to such a configuration, the refrigerant LQ having a lower boiling point than the insulating oil OL and a higher specific gravity can be cooled by the heat of vaporization.

[0048] (3) The cooling device 100 further includes: a sub-tank 20 having an air chamber AR; and a connecting passage C that connects the air chamber AR with the inside of the tank 10. According to such a configuration, it is possible to suppress the increase in the internal pressure in the tank 10 caused by the vaporization of the refrigerant liquid LQ. Therefore, the sealing of the sealing member 13 becomes easier accordingly. In addition, since the increase in the boiling point of the refrigerant liquid LQ is also suppressed, it is also possible to suppress the difficulty in performing vaporization heat cooling accordingly. Furthermore, since the air chamber AR is provided as a chamber different from the inside of the tank 10, these effects can be obtained, and a structure in which the refrigerant liquid LQ is difficult to enter the air chamber AR can be obtained.

[0049] (4) The sub-tank 20 is provided with a vent cap 23, which allows the air chamber AR to communicate with the atmosphere outside the sub-tank 20. According to such a configuration, the inside of the tank 10 is maintained at atmospheric pressure, so that the fluctuation of the boiling point of the refrigerant LQ can be suppressed. Therefore, it is possible to avoid a situation where the boiling point rises due to the increase in the internal pressure of the tank 10, and the vaporization heat cooling cannot be performed unless the temperature reaches a higher level. In addition, since the inside of the tank 10 is maintained at atmospheric pressure, the sealing of the sealing member 13 is also easier.

[0050] (5) The circuit 50 includes a semiconductor element 55a and a capacitor 55d. The semiconductor element 55a, which is an electronic component with a relatively high heat density among the semiconductor element 55a and the capacitor 55d, is accommodated in a state immersed in the refrigerant LQ at the lower part of the tank 10. According to such a configuration, the circuit 50 can be effectively cooled by using the refrigerant LQ to cool the semiconductor element 55a with a relatively high heat density by vaporization heat. In addition, since the capacitor 55d can be cooled by the insulating oil OL, a plurality of electronic components can be appropriately cooled according to the heat density, and the cost can be reduced by suppressing the storage amount of the refrigerant LQ.

[0051] (6) The tank 10 includes a first frame portion 11, a second frame portion 12, and a sealing member 13 that seals the first frame portion 11 and the second frame portion 12 that are coupled to each other. The sealing member 13 is provided within a range in the height direction where the insulating oil OL is stored according to its specific gravity. With such a configuration, since the insulating oil OL is prevented from leaking, sealing of the sealing member 13 becomes easy.

[0052] The electric circuit 50 may be accommodated in the cooling device 100 as described below.

[0053] Figure 3 , Figure 4 1 is a diagram showing a modified example of the circuit 50 and the cooling device 100. Figure 3 In the example shown, the first substrate 51 is provided on the bottom surface of the tank 10 and is electrically connected to the second substrate 52 via a connector and wiring. A plurality of through holes 52a may also be provided at a position overlapping the first substrate 51 in the vertical direction. The second substrate 52 is provided together with the boss 10a. Figure 1 , Figure 2In the case of the present embodiment shown in FIG. 1 , the liquid level H of the refrigerant LQ is the same as that of the present embodiment. As a result, in this example, the semiconductor element 55a is also located below the liquid level H, and the capacitor 55d is also located above the liquid level H. Therefore, the semiconductor element 55a is accommodated in a state of being immersed in the refrigerant LQ at the bottom of the tank 10, and the capacitor 55d is accommodated in a state of being immersed in the insulating oil OL. In the case of such a configuration, the insulating oil OL at the top can also be stirred by the vaporized refrigerant LQ, thereby forcing convection of the heated insulating oil OL, so that both the simplification of the device and the high cooling efficiency of the heated insulating oil OL can be achieved.

[0054] exist Figure 4 In the example shown, Figure 3 Compared with the example shown in the figure, the circuit 50 further includes a third substrate 53, and the tank 10 further includes a boss 10d. The boss 10d is provided on the first frame portion 11, and the third substrate 53 is fixed to the boss 10d from the opening side of the first frame portion 11. Therefore, the third substrate 53 is provided at a position above the second substrate 52. The third substrate 53 is provided at a position below the through hole 10c. A diode 55e is mounted on the third substrate 53. A plurality of diodes 55e are provided, and they become components of the circuit portion 55. Therefore, in this example, the circuit portion 55 is mounted on the first substrate 51, the second substrate 52, and the third substrate 53, and the third substrate 53 is electrically connected to the first substrate 51 and the second substrate 52 via a connector and wiring. The diode 55e, like the capacitor 55d, has a lower heat density than the semiconductor element 55a, and is accommodated in a state of being immersed in the insulating oil OL. That is, in this example, the diode 55e and the capacitor 55d are a plurality of electronic components included in the circuit 50, and are examples of other electronic components other than the semiconductor element 55a. Even in such a configuration, the insulating oil OL above can be stirred by the vaporized refrigerant LQ, thereby forcing the heated insulating oil OL to convect, thereby achieving both simplification of the device and high cooling efficiency of the heated insulating oil OL.

[0055] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate a part of application examples of the present invention and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0056] For example, the sub-tank 20 may include a vent mechanism that is integrally formed with the tank portion 21 instead of the vent cap 23 .

[0057] Description of Reference Numerals

[0058] 10: tank; 10c: through hole; 11: first frame portion; 12: second frame portion; 13: sealing member; 20: sub-tank; 21: tank portion; 22: connecting portion; 23: ventilation cover (ventilation mechanism); 11: housing; 12: circuit; 50: circuit 50; 55: circuit portion; 55a: semiconductor element; 55d: capacitor; 100: cooling device; AR: air chamber; C: connecting path; LQ: refrigerant (fluorine-based refrigerant); OL: insulating oil.

Claims

1. A cooling device for cooling a semiconductor device for electric power, the cooling device comprising: a tank that accommodates the power semiconductor device; Insulating oil; a refrigerant having a boiling point temperature lower than that of the insulating oil and a specific gravity greater than that of the insulating oil; The insulating oil and the refrigerant are stored in the tank in a mixed state and cool the power semiconductor device.

2. The cooling device according to claim 1, characterized in that: The refrigerant is a fluorine-based refrigerant.

3. The cooling device according to claim 1, characterized in that: Also features: a secondary tank having an air chamber; A communication passage connects the air chamber with the inside of the tank.

4. The cooling device according to claim 3, characterized in that: The sub-tank includes a vent mechanism that allows the air chamber to communicate with the atmosphere outside the sub-tank.

5. The cooling device according to any one of claims 1 to 4, characterized in that: The power semiconductor device has a plurality of electronic components with different heat generation densities. Among the plurality of electronic components, electronic components having relatively high heat generation density are accommodated in a state of being immersed in the cooling liquid at the lower portion of the tank.

6. The cooling device according to any one of claims 1 to 4, characterized in that: The tank comprises: a first frame portion, a second frame portion, and a sealing member, the sealing member sealing the first frame portion and the second frame portion which are coupled to each other. The sealing member is provided in a range in which the insulating oil is stored in accordance with specific gravity in a height direction.

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