Cooling structure for electric unit

Abstract

To provide an electric unit capable of improving strength or NV characteristics together with cooling performance.SOLUTION: A cooling structure for an electric unit in which an electric motor, a transmission mechanism that transmits torque output by the electric motor, and a controller that controls the electric motor are housed inside a casing having a liquid-tight structure, wherein the casing has reinforcing ribs and a thin plate portion between the reinforcing ribs, oil that lubricates the electric motor or the transmission mechanism is sealed inside the casing, a heat exchanger 10 that cools the inside of the casing by performing heat exchange between the oil and cooling water is provided in the thin plate portion, and the heat exchanger includes a plurality of fins 14 that stand vertically with respect to the thin plate portion and define a flow path for one of the oil and the cooling water.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a structure for cooling an electric unit that includes a motor or a motor with a power generating function (motor generator), a transmission mechanism that transmits the output torque, and a power control unit (PCU). [Background technology]

[0002] This type of electric unit is sometimes mounted on a vehicle and used as a driving force source. Because of the limited mounting space, it is common for the entire unit to be housed in a casing, or for the mechanical drive and electrical control components to be housed in separate casings, which are then connected and housed in an engine compartment or other location. On the other hand, when mounted on an electric vehicle as a driving force source, it is required that vibration and noise be minimized to ensure ride comfort. Such vibration and noise are primarily generated by moving parts, but can be exacerbated by resonance or sympathetic vibration. Patent Document 1 describes an on-board unit in which an electric unit and an electromechanical integrated unit, each housed in a casing, are connected via an air gap. The unit provides a surface seal between the electric unit and the electromechanical integrated unit at the connection between the electric unit and the electromechanical integrated unit. This configuration is said to suppress resonance in the air gap and the resulting deterioration of vibration and noise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-152851 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, the electric unit is generally housed in a casing, and it is preferable that the casing be as light as possible while still maintaining the required strength. While reducing the casing's thickness is one way to reduce weight, the electric unit contains mechanically moving parts such as a motor and a transmission mechanism inside the casing. As power is generated and transmitted, membrane vibrations may occur in parts of the casing, which may cause deterioration of the so-called NV characteristics. While the configuration described in Patent Document 1 can suppress resonance in the air layer, it is unable to reduce other vibrations or noise.

[0005] Furthermore, while the interior of the electric unit is sealed for lubrication with oil, heat is generated due to Joule loss and iron loss in the electrical components, friction in the moving parts, and other factors, so active cooling is required. When installed in a vehicle, it is conceivable to use a cooling system that utilizes the wind generated by the vehicle while the electric unit is running. However, adding new cooling equipment to the electric unit presents new challenges, such as worsening vibration and noise and increasing the size and weight of the electric unit.

[0006] The present invention has been made in view of the above technical problems, and aims to improve the strength or NV characteristics in addition to the cooling performance. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present invention provides a cooling structure for an electric unit in which an electric motor, a transmission mechanism that transmits the torque output by the electric motor, and a controller that controls the electric motor are housed inside a liquid-tight casing, wherein the casing has reinforcing ribs and thin plate portions between the reinforcing ribs, oil that lubricates the electric motor or the transmission mechanism is sealed inside the casing, a heat exchanger that exchanges heat between the oil and cooling water to cool the inside of the casing is provided in the thin plate portion, and the heat exchanger has a plurality of fins that stand vertically relative to the thin plate portion and separate the flow paths for either the oil or the cooling water. [Effects of the Invention]

[0008] According to the present invention, a casing containing an electric motor, a power transmission mechanism, and a controller, which generate heat during operation, is partially reinforced with reinforcing ribs, and the area between the reinforcing ribs forms a thin plate portion susceptible to membrane vibration. A heat exchanger is provided in the thin plate portion, which exchanges heat between the interior of the casing and the coolant to cool the interior of the casing. The heat exchanger has multiple fins that define the oil or coolant flow paths, thereby expanding the heat exchange area. In addition, these fins are arranged vertically relative to the thin plate portion, functioning similarly to ribs to increase the rigidity of the thin plate portion. In other words, the heat exchanger not only improves cooling performance, but also increases rigidity, thereby improving strength or NV characteristics. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram conceptually showing the configuration of an electric unit according to the present invention; [Figure 2] FIG. 2 is an exploded perspective view of an example of a heat exchanger. [Figure 3] FIG. 2 is a schematic view showing the appearance of the electric unit. [Figure 4] FIG. 2 is a partial perspective view showing a part of a casing having a reinforcing rib and a thin plate portion. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiment described below is merely an example of how the present invention can be implemented, and is not intended to limit the present invention.

[0011] The electric unit in an embodiment of the present invention is, for example, a device mounted on a vehicle to serve as a driving force source, and one example of such a device is conceptually shown in the block diagram of Figure 1. The example shown here has two motors (electric motors), a first motor / generator 2 and a second motor / generator 3, and is equipped with a transmission mechanism 4 that increases or decreases the torque output from these motors 2, 3. There is also provided a power control unit (PCU) 5 that is a controller that controls the output torque and power generation amount (charge amount for the battery) of these motors 2, 3. A battery (not shown) that supplies power to the motors 2, 3 and charges the power generated by either motor 2, 3 is mounted on the vehicle together with the electric unit 1.

[0012] The motors 2 and 3, the power transmission mechanism 4, and the PCU 5 are housed inside a casing 6, and together they constitute a single electric unit 1. The casing 6 has a liquid-tight structure, and oil 7 that lubricates the motors 2 and 3 and the power transmission mechanism 4 is sealed inside the casing 6, and is configured to circulate the oil 7 around rotating and sliding parts, etc.

[0013] The PCU 5 is equipped with electrical converters (not shown), such as inverters and converters, and is water-cooled to maintain the temperature of the converters at or below a predetermined temperature. That is, the vehicle is equipped with a radiator 8 that dissipates heat into the outside air, such as the wind while the vehicle is running, and the cooling water 9, whose temperature has been lowered by the radiator 8, is circulated through the PCU 5 to cool the converters, such as the inverter and converter.

[0014] The electric unit 1 shown in FIG. 1 further includes a heat exchanger 10 that exchanges heat between the oil 7 and the coolant 9 to cool the oil 7 and the interior of the casing 6. An example of the heat exchanger 10 is schematically shown in FIG. 2. The heat exchanger 10 shown here has a flow path 11 formed inside a rectangular container. The main body 12 is shaped like a thin box, and inside the main body 12, multiple fins 14 are arranged parallel to each other at regular intervals, standing perpendicular to the inner surface of the bottom plate 13. These fins 14 are plate pieces that extend linearly from one side of the opposing inner wall surfaces to the other, with their tips spaced apart from the other inner wall surface. The spaced apart points are opposite each other for adjacent fins 14. The flow paths between the fins 14 are connected at the points where they are spaced apart from the other inner wall surfaces. The main body 12 also has an opening on the side opposite the bottom plate 13, and a lid 15 is provided to close this opening. These fins 14 thus define and form a zigzag-shaped flow path 11. An inlet 16 connected to one end of the flow path 11 and an outlet 17 connected to the other end are provided on the side surface of the main body portion 12 .

[0015] The external appearance of the electric unit 1 is shown schematically in Figure 3. The motors 2 and 3 are housed in the section of the casing 6 that has the largest volume, and the power transmission mechanism 4 is housed in the section extending axially from that section. The PCU 5 is housed in the uppermost section. The casing 6 is a cast product made of aluminum alloy or the like, and as shown in an enlarged partial view in Figure 4, reinforcing ribs 18 are provided in necessary locations to reduce weight, and the portions between these reinforcing ribs 18 form thin plate sections 19.

[0016] The heat exchanger 10 is provided on the thin plate portion 19. The heat exchanger 10 is provided in a portion between the reinforcing ribs 18 on the surface side (e.g., the outer surface side) from which the reinforcing ribs 18 protrude, or on the opposite surface side (e.g., the inner surface side), in a portion spanning two thin plate portions 19 so as to straddle the portion corresponding to the reinforcing ribs 18. The heat exchanger 10 is provided with its bottom plate portion 13 in close contact with or integrated with the thin plate portion 19. Therefore, the fins 14 are integrated with the thin plate portion 19 in a state where they stand perpendicular to the thin plate portion 19, and as a result, the fins 14 function to reinforce the thin plate portion 19, increasing the rigidity or strength of the thin plate portion 19.

[0017] When the heat exchanger 10 is provided on the outer surface of the casing 6, the oil 7 sealed inside the casing 6 exchanges heat with the heat exchanger 10 via the thin plate portion 19. Meanwhile, since cooling water 9 flows inside the heat exchanger 10, the heat of the oil 7 is absorbed by the cooling water 9, thereby cooling the oil 7 and the inside of the casing 6. When the heat exchanger 10 is provided on the inner surface of the casing 6, the heat exchanger 10 is immersed in the oil 7, or the oil 7 flows in contact with the outer surface of the heat exchanger 10. Meanwhile, inside the heat exchanger 10, the cooling water 9 flows along the flow path 11, contacting not only the bottom plate portion 13 of the heat exchanger 10 but also the fins 14, and absorbs heat from the heat exchanger 10. Therefore, the heat exchange area for the cooling water 9 is increased, allowing the oil 7 and the inside of the casing 6 to be efficiently cooled.

[0018] As described above, according to the embodiment of the present invention, the heat exchange area is increased by the heat exchange fins 14, so that the electric unit 1 can be cooled efficiently. In addition, the fins 14 increase the rigidity or strength of the thin plate portion 19, which is prone to membrane vibration, so that vibration of the thin plate portion 19 or the casing 6 can be suppressed, thereby improving the NV characteristics of the electric unit 1.

[0019] The present invention is not limited to the structure of the above-described embodiment, and the key point is that the fins for heat exchange are configured to reinforce the thin plate portion of the casing. For example, when the heat exchanger 10 is provided between the reinforcing ribs 18 described above, the reinforcing ribs 18 and the thin plate portion 19 between them can be used as the side wall and bottom plate portions of the main body 12, and the fins can be installed vertically on the thin plate portion and a lid can be provided to cover them to form the heat exchanger. Furthermore, the present invention may include multiple heat exchangers. Furthermore, the present invention may be configured so that oil flows inside the heat exchanger and the heat exchanger is cooled from the outside with cooling water. [Explanation of symbols]

[0020] 1 Electric unit 2,3 Motor-generator (motor) 4 Transmission mechanism 6 Casing 7. Oil 8 Radiator 9 Cooling water 10 Heat exchanger 11 Flow path 12 Main body part 13 Bottom plate part 14 Finn 15 Lid 16 Inlet 17 Outlet 18 Reinforcing rib 19 Thin plate part

Claims

[Claim 1] A cooling structure for an electric unit in which an electric motor, a transmission mechanism that transmits torque output by the electric motor, and a controller that controls the electric motor are housed inside a casing with a liquid-tight structure, The casing has reinforcing ribs and thin plate portions between the reinforcing ribs, oil for lubricating the electric motor or the transmission mechanism is sealed inside the casing; a heat exchanger that exchanges heat between the oil and cooling water to cool the inside of the casing is provided in the thin plate portion; The heat exchanger has a plurality of fins that stand perpendicular to the thin plate portion and define a flow path for either the oil or the cooling water. A cooling structure for an electric unit.

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