JP6101936B2 - Cooling device and electric vehicle equipped with the same - Google Patents

Description

  The present invention relates to a cooling device and an electric vehicle equipped with the same.

  A conventional cooling device for an electric vehicle has been mounted on a power conversion circuit. In an electric vehicle, an electric motor serving as a driving power source is switched by an inverter circuit that is a power conversion circuit. Here, a plurality of semiconductor switching elements represented by power transistors are used in the inverter circuit. A large current of several tens of amperes or more flowed through each semiconductor switching element. Therefore, the semiconductor switching element generates a large amount of heat and needs to be cooled.

  For example, as in Patent Document 1, the cooling of the inverter circuit disposed in the lower part is performed in a boiling cooling device having a refrigerant radiator and a refrigerant tank at the top and bottom.

  In such a conventional cooling device, the refrigerant that has vaporized the semiconductor switching element is cooled and condensed by the refrigerant radiator disposed on the upper part. Then, the cycle in which the refrigerant is dropped again in the lower part is repeated. However, since the refrigerant reciprocates up and down, the circulation efficiency of the refrigerant is poor and the heat dissipation is also poor.

JP-A-8-126125

  The present invention includes a heat receiving part to which heat released from the heating element is transferred, and a heat radiating part connected to the heat receiving part via a heat dissipation path and a feedback path, and the refrigerant is from the heat receiving part to the heat dissipation path, the heat dissipation part, and A cooling device that returns to the heat receiving part from the inlet of the return path through the return path, the heat receiving part contacting the heating element to absorb the heat, and the heat receiving part that covers the heat receiving plate and evaporates the flowing refrigerant And a heat receiving cover that forms a space, and the return path includes a first check valve that is opened at the head pressure of the refrigerant condensed and retained at the inlet.

  The liquefied refrigerant in the heat receiving space takes the heat of vaporization from the heating element and vaporizes. And a refrigerant | coolant flows through a thermal radiation path and is condensed in a thermal radiation part. Furthermore, the refrigerant opens the first check valve by the water head pressure of the refrigerant condensed through the return path, and flows into the heat receiving space again from the inlet. At this time, the refrigerant flows in one direction by the action of the first check valve. Due to the water head pressure of the condensed refrigerant, a regular cycle of heat reception and heat release occurs, and a cooling device with improved cooling performance is provided.

FIG. 1 is a schematic diagram of an electric vehicle according to Embodiment 1 of the present invention. FIG. 2A is a diagram showing a configuration of the cooling device. 2B is a cross-sectional view taken along line 2B-2B of FIG. 2A. FIG. 3 is a diagram showing a configuration of the heat radiator of the cooling device according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating the basic operation of the cooling device. FIG. 5 is a diagram showing a different configuration of the cooling device. FIG. 6 is a diagram showing the configuration of the cooling device according to the second embodiment of the present invention. FIG. 7 is a diagram illustrating the operation of the liquid sealing unit in the bypass path and the boundary state of the cooling device. FIG. 8 is a diagram illustrating an operation when the bypass path and the liquid seal portion of the cooling device are in communication. FIG. 9 is a diagram showing different bypass paths of the cooling device.

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

(Embodiment 1)
FIG. 1 is a schematic diagram of an electric vehicle according to Embodiment 1 of the present invention. As shown in FIG. 1, the electric motor 3 is connected to an inverter circuit 5. Here, the electric motor 3 drives the axle 2 of the electric vehicle 1. The inverter circuit 5 is a power conversion device that is arranged in the passenger compartment front 4 of the electric vehicle 1. The inverter circuit 5 includes a plurality of semiconductor switching elements 6 that supply power to the electric motor 3. The inverter circuit 5 includes a cooling device 7 that cools the semiconductor switching element 6.

  2A is a diagram illustrating a configuration of the cooling device according to the first exemplary embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along line 2B-2B of FIG. 2A. As shown in FIG. 2A, the cooling device 7 includes a heat receiving portion 8, a heat radiating portion 9, and a circulation path 11. In the heat receiving part 8, heat 6 a emitted from a heating element such as the semiconductor switching element 6 is delivered. The heat radiating part 9 radiates the heat 6 a absorbed in the heat receiving part 8. Further, the heat dissipating part 9 is connected to the heat receiving part 8 via the circulation path 11. In the circulation path 11, the refrigerant 10 serving as a heat medium circulates between the heat receiving unit 8 and the heat radiating unit 9. The circulation path 11 and the heat receiving part 8 are connected by an inflow port 15 and an exhaust port 16.

  The heat radiating section 9 includes a heat radiating body 17 that releases heat 6a to the outside air. The heat dissipating unit 9 includes a blower 17 a that blows outside air to the heat dissipating body 17. That is, as shown in FIG. 1, the inverter circuit 5 is arranged in the middle of the vehicle front side 4 close to the driver's seat side. And the circulation path 11 is extended, and the heat radiator 17 is attached to the front grille 4a side which is easy to let outside air pass.

  As shown in FIG. 2A, the heat receiving unit 8 includes a heat receiving plate 12, a heat receiving cover 14, and a discharge port 16. Here, the heat receiving plate 12 contacts the semiconductor switching element 6 that is a heating element and absorbs the heat 6a. The heat receiving cover 14 covers the heat receiving plate 12 and forms a heat receiving space 13 in which the flowing refrigerant 10 evaporates. The condensed refrigerant 10 is poured into the heat receiving space 13 from the inlet 15. The gasified refrigerant 10 is discharged from the discharge port 16 of the heat receiving space 13.

  The circulation path 11 includes a heat dissipation path 11a and a return path 11b. The heat radiation path 11a and the return path 11b are respectively connected to the heat radiator 17 of the heat radiation portion 9. That is, the heat radiation path 11 a connects the discharge port 16 and the heat radiator 17, and the return path 11 b connects the heat radiator 17 and the inlet 15. In the cooling device 7, the refrigerant 10 returns from the heat receiving part 8 to the heat receiving part 8 from the inlet 15 of the return path 11 b through the heat dissipation path 11 a, the heat dissipation part 9, and the return path 11 b.

  FIG. 3 is a diagram showing a configuration of the heat radiator of the cooling device according to the first embodiment of the present invention. As shown in FIG. 3, in the heat dissipating body 17, a plurality of pipe lines 18 penetrates through a block body in which fins 19 are stacked at a predetermined interval. The heat radiator 17 is connected to the heat radiation path 11a at the entrance. The heat radiation path 11 a is divided into a plurality of pipe lines 18. The radiator 17 is connected to the return path 11b at the outlet. A plurality of pipelines 18 merge to form a return path 11b. Here, the fins 19 are formed in a thin strip shape of aluminum.

  In addition, as shown in FIG. 2A, the inlet 15 is provided with a first check valve 20 that is opened by the water head pressure of the refrigerant 10. The water head pressure of the refrigerant 10 condensed and retained causes the first check valve 20 to be easily opened. Here, the inflow pipe 24 is formed vertically on the upstream side of the first check valve 20. A first check valve 20 is disposed immediately below the inflow pipe 24. Thus, the first check valve 20 is provided in the return path 11b. Moreover, the side connected to the heat receiving part 8 of the return path 11 b is an inflow pipe 24 extending vertically from the inflow port 15.

  The heat receiving unit 8 further includes a refrigerant dropping unit 21 and an introduction pipe 23. Here, the refrigerant dripping portion 21 is located at the center of the heat receiving plate 12. As shown in FIG. 2B, the heat receiving plate 12 includes slits 22 that are radially expanded from the refrigerant dropping portion 21 toward the outer periphery 12 a of the heat receiving plate 12. The slit 22 forms a flow path 22 a of the refrigerant 10. The introduction pipe 23 is a pipe from the inlet 15 to the refrigerant dropping unit 21, and drops the condensed refrigerant 10 at the center of the heat receiving plate 12.

  Further, the inflow pipe 24 and the introduction pipe 23 are conduits having the same inner diameter. The inflow pipe 24 is longer than the introduction pipe 23. That is, the internal volume of the inflow pipe 24 is larger than the internal volume of the introduction pipe 23. Therefore, the refrigerant 10 that remains in the inflow pipe 24 is larger than the amount of the refrigerant 10 that flows into the introduction pipe 23 at a time when the first check valve 20 is opened.

  The return path 11 b includes an inflow pipe 24 and a bypass path 26. The bypass path 26 connects the heat receiving space 13 or the heat radiation path 11 a and the upstream portion 25 of the inflow pipe 24. In the inflow pipe 24, the condensed refrigerant 10 stops on the first check valve 20. The bypass path 26 according to the first embodiment of the present invention connects the heat receiving space 13 and the return path 11b.

  The bypass path 26 is provided with a second check valve 27. The second check valve 27 opens to the inflow pipe 24 side by the pressure of the refrigerant 10 vaporized in the heat receiving space 13. The second check valve 27 has a larger operating pressure than the first check valve 20. The second check valve 27 applies the pressure in the heat receiving space 13 to the condensed refrigerant 10 in the inflow pipe 24.

  Moreover, the heat receiving space 13 and the circulation path 11 are sealed, the internal pressure is lower than atmospheric pressure, and the inside is saturated. For example, when the refrigerant 10 is water, the internal initial pressure is about −97 KPa at room temperature.

  In the configuration of the cooling device 7 shown in FIG. 1, when the semiconductor switching element 6 of the inverter circuit 5 starts operating, electric power is supplied to the electric motor 3 and the electric vehicle 1 starts moving. At this time, a large current flows through the semiconductor switching element 6, and at least several percent of the total power is lost, and a large heat 6a is generated.

  FIG. 4 is a diagram illustrating the basic operation of the cooling device according to the first embodiment of the present invention. As shown in FIG. 4, the heat 6a generated from the semiconductor switching element 6 is transferred from the heat receiving plate 12 to the condensed refrigerant 10 in the heat receiving space 13, and the refrigerant 10 is vaporized instantly. Then, the refrigerant 10 flows through the heat radiation path 11a from the discharge port 16, and the heat 6a is released to the outside air in the heat radiator 17. The refrigerant 10 that has released the heat 6 a in the heat radiating body 17 is condensed and flows through the return path 11 b, and accumulates on the first check valve 20 of the inlet 15 in the inflow pipe 24. The condensed refrigerant 10 gradually increases in the inflow pipe 24. The first check valve 20 is pushed down and opened by the water head pressure of the refrigerant 10. Then, the refrigerant 10 flows into the heat receiving space 13 again.

  In this way, the refrigerant 10 repeatedly circulates in the cooling device 7 and the semiconductor switching element 6 is cooled.

  Here, the cooling mechanism in the heat receiving space 13 will be described. In the heat receiving space 13, the refrigerant 10 is dropped as droplets from the introduction pipe 23 by the refrigerant dropping unit 21. The dropped refrigerant 10 is diffused to the outer periphery 12 a of the heat receiving plate 12 through the gap between the opening of the introduction pipe 23 and the heat receiving plate 12. At this time, since the slits 22 that are radially expanded in the heat receiving plate 12 form the flow path 22a of the refrigerant 10, the refrigerant 10 spreads on the heat receiving plate 12 as a thin film. Since the heat receiving plate 12 is in contact with the semiconductor switching element 6, the thin film of the refrigerant 10 is heated and vaporized in an instant.

  Since the pressure in the heat receiving space 13 is set lower than the atmospheric pressure, the refrigerant 10 is vaporized at a temperature lower than the boiling of water in the atmospheric pressure even if water is used. As in the first embodiment of the present invention, when the atmospheric pressure is set to -97 KPa and the inside of the circulation path 11 is saturated, the boiling temperature corresponding to the outside air temperature is determined, and water is easily vaporized. At this time, the heat 6a of the semiconductor switching element 6 is taken and cooled. That is, the heat 6a of the semiconductor switching element 6 is taken away by the latent heat of vaporization of water. Also, since water is heated and vaporized in an instant, the amount of heat it takes is greater than when water is heated and boiled.

  Moreover, when the refrigerant | coolant 10 vaporizes, the pressure in the heat receiving space 13 increases. However, the refrigerant 10 does not flow back to the inflow pipe 24 side by the action of the first check valve 20, but is reliably discharged from the discharge port 16 to the heat radiation path 11a.

  By operating the cooling device 7 in this way, a regular cycle of heat reception and heat dissipation is created. Therefore, the refrigerant 10 is continuously vaporized in the heat receiving space 13 and the semiconductor switching element 6 is cooled.

  Further, the inflow pipe 24 is formed longer than the introduction pipe 23. Therefore, the supply of the refrigerant 10 to the introduction pipe 23 by the operation of the first check valve 20 is continuously performed without interruption, and a stable cooling performance is exhibited.

  Further, the refrigerant 10 vaporized by the increased pressure in the heat receiving space 13 is caused to flow through the heat radiation path 11a. Therefore, the moving speed of the refrigerant 10 is faster than that of the liquid, and the heat receiving unit 8 and the heat radiating unit 9 may be arranged apart from each other. The inverter circuit 5 shown in FIG. 1 is vulnerable to dust and water droplets. Further, it is desired that the heat dissipating unit 9 be efficiently cooled by outside air. Therefore, the inverter circuit 5 and the heat radiating portion 9 can be installed separately from the front grille 4a and the passenger compartment front 4 of the electric vehicle 1, respectively. Therefore, the electric vehicle 1 can ensure good running performance.

  As described above, the basic part of the cooling device 7 according to Embodiment 1 of the present invention has been described. The most important features of the cooling device 7 will be described below with reference to FIG. 2A. As shown in FIG. 2A, the cooling device 7 includes a bypass path 26 that connects the heat receiving space 13 and the upstream portion 25 of the inflow pipe 24. The bypass path 26 includes a second check valve 27 that opens to the inflow pipe 24 side. Hereinafter, the operation will be described.

  As described above, the refrigerant 10 is vaporized by taking the heat 6 a of the semiconductor switching element 6, releases the heat 6 a in the heat radiating portion 9, is condensed, and stops in the inflow pipe 24 through the circulation path 11. Then, the first check valve 20 is pushed down by the water head pressure of the condensed refrigerant 10, and the refrigerant 10 flows into the heat receiving space 13 again.

  By the way, when the calorific value of the semiconductor switching element 6 increases, the pressure in the heat receiving space 13 increases. Therefore, the first check valve 20 may not be pushed down only by the water head pressure of the refrigerant 10 retained in the inflow pipe 24. When such a phenomenon occurs, the inflow of the refrigerant 10 into the heat receiving space 13 stops, heat removal cannot be performed, and the cooling capacity decreases.

  Therefore, a bypass path 26 is provided as shown in FIG. 2A. Therefore, when the pressure in the heat receiving space 13 becomes high, the second check valve 27 is opened, and the pressure in the heat receiving space 13 is applied to the upstream portion 25 of the inflow pipe 24. As a result, the pressure in the heat receiving space 13 is applied to the first check valve 20. That is, even if the pressure in the heat receiving space 13 increases, the cooling device 7 can be realized in which the cooling capacity does not decrease. As described above, as described in the first embodiment of the present invention, the cooling device 7 having an extremely high cooling capacity is provided.

  Further, the first check valve 20 is opened more easily by the action of the bypass path 26. Therefore, the amount of the refrigerant 10 retained in the inflow pipe 24 can be reduced. That is, since the height of the inflow pipe 24 is low and the amount of the refrigerant 10 can be reduced, a small cooling device 7 can be realized.

  In the first embodiment of the present invention, the configuration in which the bypass path 26 connects the heat receiving space 13 and the upstream portion 25 of the inflow pipe 24 has been described. FIG. 5 is a diagram showing another configuration of the cooling device according to the first embodiment of the present invention. As shown in FIG. 5, the bypass path 26 may be configured to connect the heat dissipation path 11 a and the upstream portion 25 of the inflow pipe 24.

(Embodiment 2)
In the second embodiment of the present invention, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The second embodiment of the present invention is different from the first embodiment in that the flow path cross-sectional area 26a of the bypass path is formed to be sufficiently smaller than the flow path cross-sectional area 11c of the heat dissipation path, and the second reverse The stop valve 27 is not provided.

  FIG. 6 is a diagram showing the configuration of the cooling device according to the second embodiment of the present invention. FIG. 6 shows a case where the cooling device 37 is in a normal operation state. As shown in FIG. 6, the bypass path 26 connects the heat receiving space 13 or the heat radiation path 11a and the upstream portion 25 of the inflow pipe 24 of the return path 11b. Since the flow path cross-sectional area 26a of the bypass path is formed sufficiently small with respect to the flow path cross-sectional area 11c of the heat dissipation path, the pipe resistance of the bypass path 26 is larger than the pipe resistance of the heat dissipation path 11a. ing. Therefore, in a normal operation state, a liquid sealing part 29 that seals the bypass path 26 with the condensed refrigerant 10 is formed in a portion near the heat receiving space 13 of the bypass path 26. Since the bypass path 26 has a larger pressure loss than the heat dissipation path 11a, the liquid sealing portion 29 in the bypass path 26 is held without moving. Therefore, the bypass path 26 and the inflow pipe 24 do not communicate with each other. That is, in the normal operation state, the presence of the bypass path 26 is irrelevant to the basic operation of the cooling device 37.

However, in a state where the heat generation amount of the semiconductor switching element 6 increases and exceeds the normal operating range, the downstream pressure P _{B of} the first check valve 20 provided by the heat receiving space 13 increases, and the valve opening / closing conditions in normal operation No longer holds. Then, the downstream side pressure P _B of the first check valve 20, so much higher than state upstream pressure P _u in the first check valve 20 is sustained. This state means that the first check valve 20 is closed, and the supply of the refrigerant 10 is also stopped. Therefore, it eventually becomes aired (dry out) and eventually the cooling capacity is lost.

  In order to prevent this, it is extremely important to provide the bypass path 26 shown in FIG. Hereinafter, the relationship between the bypass path 26 and the operation of the first check valve 20 will be described in a little more detail.

FIG. 7 is a diagram illustrating the operation of the liquid sealing unit in the bypass path and the boundary state of the cooling device according to the second embodiment of the present invention. FIG. 7 shows a state where the heat generation amount slightly exceeds the level of normal operation. The downstream pressure P _B of the first check valve 20 given by the pressure in the heat receiving space 13 is equal to the upstream pressure P _{u of} the first check valve 20 (pressure in the return path 11b + retention in the inflow pipe 24). Or higher (P _B ≧ P _u ). In such a state, the pressure in the heat receiving space 13 becomes larger than the pressure obtained by adding the pipe line resistance of the bypass path 26 and the surface tension of the liquid seal portion 29. The liquid sealing portion 29 gradually moves in the bypass path 26 toward the return path 11b.

  FIG. 8 is a diagram illustrating an operation when the bypass path and the liquid seal portion of the cooling device according to the second embodiment of the present invention communicate with each other. When the calorific value further increases, as shown in FIG. 8, the liquid sealing portion 29 is pushed toward the return path 11b, and the bypass path 26 communicates with the return path 11b. At this moment, a part of the pressure in the heat receiving space 13 is released to the return path 11 b side, and the pressure balance before and after the first check valve 20 returns to a state in which the first check valve 20 is operable. For this reason, it is prevented that the first check valve 20 is closed and the air blower (dry out) state is reached. In this way, the liquid sealing portion 29 is broken by the increase in the pressure in the heat receiving space 13, and opens the bypass path 26 toward the inflow pipe 24. That is, by the bypass path 26, the stable operation state of the cooling device 37 can be maintained even when the heat generation amount exceeds the normal operation level.

  As described above, as described in the second embodiment of the present invention, the provision of the bypass path 26 provides the cooling device 37 that maintains stable performance even when the heat generation amount exceeds the normal operation level.

  Further, the first check valve 20 can be opened more easily by the action of the bypass path 26, so that the amount of the refrigerant 10 retained in the inflow pipe 24 can be reduced. That is, the inflow pipe 24 can be reduced in height and the amount of the refrigerant 10 can be reduced, and the cooling device 37 can be downsized.

FIG. 9 is a diagram illustrating different bypass paths of the cooling device according to the second embodiment of the present invention. As shown in FIG. 9, the bypass path 26 connects the middle of the heat dissipation path 11 a and the upstream portion 25 of the inflow pipe 24. When the heat generation amount exceeds the level of normal operation the bypass passage 26, the internal pressure P _S of similarly heat dissipation path 11a and FIG. 7 is greater than the upstream pressure P _u in the first check valve 20. And the pressure in the heat receiving space 13 becomes larger than the surface tension of the liquid sealing part 29, and the bypass path 26 is in a state of communicating with the return path 11b. Since the internal pressure P _S of the radiation path 11a is opened to the return path 11b side, and the upstream pressure P _u in the first check valve 20, and the downstream pressure P _B of the first check valve 20 The pressure balance returns to the operable state of the first check valve 20. Therefore, even when the heat generation amount of the semiconductor switching element 6 increases to a state exceeding the normal state, the dry check state in which the first check valve 20 is closed is easily avoided and stable. Cooling performance is maintained.

  Furthermore, as in the case of the basic cooling device 7 shown in FIG. 4, the heat transport principle in the second embodiment of the present invention is the difference between the pressure in the heat receiving space 13 due to boiling and the internal pressure of the radiator 17 cooled by the outside air. It is the pressure difference generated between. However, in the case of the basic cooling device 7 as shown in FIG. 4, the maximum heat transport capacity depends on the opening / closing conditions of the first check valve 20. Therefore, even if the refrigerant 10 exists on the inlet side of the first check valve 20, the refrigerant will eventually become dry (dryout) unless the first check valve 20 is opened. On the other hand, Embodiment 2 of the present invention provides a cooling device 37 in which the refrigerant 10 is circulated to the limit heat amount at which all of the refrigerant 10 enclosed in the circulation system is boiled.

  In the second embodiment of the present invention, the flow path cross-sectional area 26a of the bypass path is made sufficiently smaller than the flow path cross-sectional area 11c of the heat dissipation path to form the liquid sealing portion 29. However, the liquid seal portion 29 is also formed by providing a U-shaped portion in the bypass path 26.

  The cooling device of the present invention is useful for cooling a power conversion device, a high-speed arithmetic processing device, and the like as a drive device of an electric vehicle.

DESCRIPTION OF SYMBOLS 1 Electric vehicle 2 Axle 3 Electric motor 4 Car front 4a Front grille 5 Inverter circuit 6 Semiconductor switching element 6a Heat 7,37 Cooling device 8 Heat receiving part 9 Heat radiation part 10 Refrigerant 11 Circulation path 11a Heat radiation path 11b Return path 11c Flow of heat radiation path Road cross-sectional area 12 Heat receiving plate 12a Outer periphery 13 Heat receiving space 14 Heat receiving cover 15 Inlet 16 Outlet 17 Radiator 18 Multiple pipes 19 Fin 20 First check valve 21 Refrigerant dripping portion 22 Slit 22a Flow path 23 Introducing pipe 24 Inflow pipe 25 Upstream part 26 Bypass path 26a Channel cross-sectional area of bypass path 27 Second check valve 28 Blockade 29 Liquid seal part

Claims (6)

A heat receiving part to which heat released from the heating element is transferred;
A heat dissipating part connected to the heat receiving part via a heat dissipating path and a return path;
A cooling device in which the refrigerant passes from the heat receiving section through the heat radiation path, the heat radiation section, and the feedback path to the heat receiving section from the inlet of the feedback path,
The heat receiving portion includes a heat receiving plate that contacts the heat generating body and absorbs the heat, and a heat receiving cover that covers the heat receiving plate and forms a heat receiving space for evaporating the refrigerant that has flowed.
The return path includes a first check valve that is opened by a water head pressure of the refrigerant condensed and retained at the inlet,
The side connected to the heat receiving part of the return path is an inflow pipe extending vertically from the inflow port, and includes a bypass path that connects the heat receiving space or the heat radiation path and the upstream part of the inflow pipe,
A cooling device comprising a second check valve that opens to the inflow pipe side in the bypass path. The second check valve has a larger operating pressure than the first check valve, and applies the pressure in the heat receiving space to the refrigerant condensed in the inflow pipe. Cooling system. The heat receiving portion includes a refrigerant dropping portion at the center of the heat receiving plate, a slit that radially expands the flow path from the refrigerant dropping portion toward the outer periphery of the heat receiving plate, and the inlet for dropping the condensed refrigerant. The cooling device according to claim 1, further comprising an introduction pipe extending from the coolant to the refrigerant dropping portion. The cooling device according to claim 3, wherein the inflow pipe has a larger internal volume than the introduction pipe. The cooling device according to claim 1, wherein a pressure between the heat receiving space and the heat radiation path is lower than an atmospheric pressure. An electric vehicle comprising the cooling device according to claim 1, wherein the cooling device cools a power conversion device connected to an electric motor that drives an axle.

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