Power control unit

Abstract

To provide a power control unit mounted in a vehicle.SOLUTION: The power control unit includes: a switching element; a heat sink that absorbs heat from the switching element; a cooling flow path that circulates cooling medium so as to pass through the heat sink; a pair of valves that are provided in the cooling flow path and arranged on opposite sides of the heat sink; and a control device configured to execute boiling cooling processing when an abnormality of the cooling flow path is detected. The boiling cooling processing includes a process of closing the pair of valves when the temperature of the switching element exceeds a predetermined temperature threshold. The temperature threshold is lower than the boiling point of the cooling medium. The boiling point of the cooling medium is lower than the heat-resistant temperature of the switching element.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a power control unit, and in particular to a power control unit mounted on a vehicle. [Background technology]

[0002] Patent Document 1 describes a power control unit mounted on a vehicle. The vehicle includes an inverter and a cooling passage through which a cooling medium circulates to absorb heat from the inverter's switching elements. The inverter converts electric power supplied from a power source into drive power supplied to a motor for running the vehicle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-137157 Summary of the Invention [Problem to be solved by the invention]

[0004] When a vehicle is driven or used, cooling medium leakage from the cooling path may occur. In this case, the cooling performance of the cooling path may be reduced, which may result in overheating of the switching elements. In this regard, Patent Document 1 describes a technique for suppressing temperature increases in the switching elements by lowering the upper output limit of the motor and raising the motor's output limit start temperature. However, even if such a technique is adopted, the reduction in cooling performance due to cooling medium leakage will not be improved. As a result, the operation of the power control unit is significantly restricted, which results in a significant reduction in the vehicle's driving performance. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, this specification provides a power control unit to be mounted on a vehicle. The power control unit includes a switching element, a heat sink that absorbs heat from the switching element, a cooling flow path that circulates a cooling medium through the heat sink, a pair of valves that are provided in the cooling flow path and arranged on opposite sides of the heat sink, and a control device configured to execute a boiling cooling process when an abnormality in the cooling flow path is detected. The boiling cooling process includes closing the pair of valves when the temperature of the switching element exceeds a predetermined temperature threshold. The temperature threshold is lower than the boiling point of the cooling medium. The boiling point of the cooling medium is lower than the heat resistance temperature of the switching element. The boiling point here refers to the boiling point under atmospheric pressure (i.e., 1 atmosphere).

[0006] In the above-described configuration, a boil-off cooling process is executed when an abnormality in the cooling flow path is detected. In this boil-off cooling process, when the temperature of the switching element exceeds a predetermined temperature threshold, it is determined that sufficient circulation of the cooling medium cannot be expected, and a pair of valves is closed. With the pair of valves closed, the temperature of the cooling medium confined in the heat sink rises due to heat absorption from the switching element. However, because the boiling point of the cooling medium is lower than the heat resistance temperature of the switching element, the cooling medium begins to boil before the switching element becomes overheated.

[0007] When the cooling medium begins to boil, a large amount of heat generated by the switching element is absorbed by the cooling medium as heat of vaporization. This halts or suppresses the temperature rise of the cooling medium, preventing overheating of the switching element. By utilizing the boiling of the cooling medium in this way, relatively high cooling performance can be maintained even when, for example, a cooling medium leak occurs from the cooling flow path and sufficient circulation of the cooling medium cannot be expected. Therefore, even when an abnormality in the cooling flow path is detected, a situation in which the vehicle's driving performance is significantly restricted can be avoided by relaxing the operational restrictions on the power control unit. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a schematic configuration of a power control unit 1 according to an embodiment of the present invention. [Figure 2] 4 is a flowchart for explaining the operation of the power control unit 1 of the embodiment. [Figure 3] 2 is a graph illustrating the temperature change over time of the switching element 11 in the power control unit 1 of the embodiment. The element temperature T on the vertical axis represents the temperature of the switching element 11. DETAILED DESCRIPTION OF THE INVENTION

[0009] An electric power control unit 1 according to an embodiment will be described with reference to the drawings. The electric power control unit 1 according to the embodiment can be mounted on a vehicle. Although not particularly limited, the electric power control unit 1 controls the power supplied to a drive motor that drives the wheels of the vehicle. The vehicle referred to here is not particularly limited and may be, for example, a battery electric vehicle (BEV), a hybrid electric vehicle (HEV), or a fuel cell electric vehicle (FCEV). In another embodiment, the electric power control unit 1 may be, for example, a power control unit (i.e., a charge control unit) that controls charging power to an on-board battery.

[0010] As shown in FIG. 1, the power control unit 1 includes a switching element 11, a heat sink 12, a cooling channel 13, a pair of valves 14, and a control device 15. Although not particularly limited, the switching element 11 is a component of an inverter 10 mounted on a vehicle (not shown). In other embodiments, the switching element 11 may be a heat-generating element included in a drive motor or a battery pack mounted on the vehicle. A relatively large current flows through the switching element 11 when the vehicle is running. This causes the temperature of the switching element 11 to rise.

[0011] The heat sink 12 is disposed in the cooling flow path 13 and abuts against the switching element 11. The heat sink 12 absorbs heat from the switching element 11 and releases the heat to the cooling flow path 13. The cooling flow path 13 circulates the cooling medium so that the cooling medium passes through the heat sink 12. A radiator (not shown) is provided in the cooling flow path 13. The cooling medium heated in the heat sink 12 is removed in the radiator and then sent back to the heat sink 12. As a result, the switching element 11 is maintained at a constant temperature.

[0012] The pair of valves 14 are provided in the cooling flow path 13 and are arranged on opposite sides of the heat sink 12. The pair of valves 14 are configured to open and close the cooling flow path 13. Although not particularly limited, the pair of valves 14 are electronic valves that receive signals from the control device 15 and operate accordingly.

[0013] Although not particularly limited, the control device 15 is disposed within the inverter 10. The control device 15 controls the operation of the power control unit 1, particularly the operation of the switching element 11 and the pair of valves 14. In addition, the control device 15 monitors the presence or absence of an abnormality in the cooling flow path 13 and the temperature of the switching element 11. An abnormality in the cooling flow path 13 here refers to, for example, a cooling medium leak, which can be detected by monitoring the amount of cooling medium. An abnormality in the cooling flow path 13 may be detected by the control device 15 itself, or may be detected by another on-board device. The power control unit 1 may be appropriately equipped with various sensors so that the control device 15 can monitor the presence or absence of an abnormality in the cooling flow path 13 and the temperature of the switching element 11.

[0014] The operation of the power control unit 1 will be described below with reference to Figures 2 and 3. In step S0, the power control unit 1 starts up. Although not particularly limited, the power control unit 1 of this embodiment is a power control unit that controls the power supplied to the drive motor, and therefore starts up when the vehicle starts up. In other embodiments, the power control unit 1 may be started up at an appropriate timing depending on the function and use of the power control unit 1. After the power control unit 1 starts up, the power control unit 1 proceeds to step S1.

[0015] In step S1, the control device 15 of the power control unit 1 determines whether or not an abnormality has been detected in the cooling flow path 13. If no abnormality has been detected, the control device 15 continues to monitor for the presence or absence of an abnormality. Although not particularly limited, the control device 15 repeatedly performs this determination at a predetermined cycle. If an abnormality in the cooling flow path 13 is detected, the power control unit 1 proceeds to step S2.

[0016] In step S2, the vehicle starts evacuation running. In evacuation running, for example, the torque and rotation speed of the drive motor are limited more than in normal running. In the power control unit 1, the current flowing through the switching element 11 is reduced, thereby suppressing heat generation in the switching element 11 and mitigating the temperature rise of the switching element 11. Here, it is assumed that evacuation running is started at time t1, for example. That is, as shown in FIG. 3, the rate of temperature rise of the switching element 11 between times t1 and t2 (the slope of the graph) is smaller than that just before time t1. Next, the power control unit 1 proceeds to step S3.

[0017] In step S3, the control device 15 determines whether the temperature of the switching element 11 has exceeded a predetermined first temperature threshold T1. If the temperature of the switching element 11 has not exceeded the first temperature threshold T1, the control device 15 continues to monitor the temperature of the switching element 11. Although not particularly limited, the control device 15 repeats this determination at predetermined intervals. If the temperature of the switching element 11 has exceeded the first temperature threshold T1, the power control unit 1 proceeds to step S4.

[0018] In step S4, the control device 15 starts the boil cooling process. Once the boil cooling process is started, in step S5, the control device 15 closes the pair of valves 14. Here, it is assumed that the pair of valves 14 are closed at time t2, for example. By closing the pair of valves 14, the cooling medium in the heat sink 12 is sealed within the heat sink 12. As a result, the temperature of the heat sink 12 rises, and as shown in FIG. 3, the temperature rise of the switching element 11 also increases. Here, the first temperature threshold T1 described above is lower than the boiling start temperature T2, which is the boiling point of the cooling medium. Furthermore, the boiling start temperature T2 is lower than the element damage temperature T3, which is the heat resistance temperature of the switching element 11. Therefore, the cooling medium in the heat sink 12 starts boiling before the switching element 11 becomes overheated (step S6).

[0019] In step S6, the cooling medium in the heat sink 12 starts to boil, and a large amount of heat generated by the switching element 11 is absorbed by the cooling medium as heat of vaporization. This stops or suppresses the temperature rise of the switching element 11, preventing overheating of the switching element 11. For example, assume that the cooling medium starts to boil at time t3. In this case, as shown in FIG. 3, the temperature of the switching element 11 starts to decrease after time t3. This prevents the temperature of the switching element 11 from reaching the element damage temperature T3.

[0020] In this way, by utilizing the boiling of the cooling medium, it is possible to maintain a relatively high cooling performance even when sufficient circulation of the cooling medium cannot be expected, for example, due to leakage of the cooling medium from the cooling flow path 13. Therefore, even when an abnormality in the cooling flow path 13 is detected, it is possible to avoid a situation in which the driving performance of the vehicle is significantly restricted by relaxing the operational restrictions on the power control unit 1.

[0021] Thereafter, the power control unit 1 performs an operation to stop the boil cooling process. As shown in FIG. 2, after step S6, the power control unit 1 proceeds to step S7. In step S7, the control device 15 determines whether the temperature of the switching element 11 has fallen below a predetermined second temperature threshold (not shown). If the temperature of the switching element 11 has fallen below the second temperature threshold, the power control unit 1 proceeds to step S8. Here, the second temperature threshold is set to a value lower than the first temperature threshold T1 described above.

[0022] In step S8, the control device 15 determines to stop the boil-cooling process. In this case, in step S9, the control device 15 opens the pair of valves 14. This causes the vaporized cooling medium to flow out of the heat sink 12, and a relatively low-temperature cooling medium is replenished in the heat sink 12. As a result, in step S10, boiling of the refrigerant is stopped. Thereafter, the power control unit 1 returns to step S3. As a result, the boil-cooling process is repeatedly started and stopped depending on the temperature of the switching element 11. Note that by setting the second temperature threshold to a value lower than the first temperature threshold T1, unnecessary frequent starting and stopping of the boil-cooling process (the occurrence of so-called hunting) is avoided. In another embodiment, the power control unit 1 does not need to return to step S3 after executing step S10. In other words, the boil-cooling process does not necessarily need to be repeated. (Variation)

[0023] As a modified example, the control device 15 may monitor the pressure between the pair of valves 14. In this case, although not particularly limited, the power control unit 1 may further include a pressure sensor that detects the pressure between the pair of valves 14. Then, the power control unit 1 may perform an operation to stop or end the boil cooling process based on the pressure between the pair of valves 14.

[0024] In this case, as an example, in addition to or instead of determining the temperature in step S7 described above, the control device 15 may determine whether the pressure between the pair of valves 14 exceeds a predetermined pressure threshold. If the pressure exceeds the predetermined pressure threshold, the control device 15 may proceed to step S8 and open the pair of valves 14. With this configuration, it is possible to prevent the pressure between the pair of valves 14 from becoming excessive.

[0025] As another modification, the control device 15 does not necessarily have to execute the evacuation running described in step S2. That is, the boil cooling process of this embodiment does not necessarily have to be executed during evacuation running. As another modification, the control device 15 may execute the boil cooling process when the temperature of the switching element 11 exceeds the first temperature threshold T1, regardless of whether an abnormality in the cooling flow path is detected or not.

[0026] As another modification, the power control unit 1 may have three or more valves. In this case, the user or the control device 15 may select the valve that performs the boil cooling process depending on the location of the cooling medium leak. Also, the user or the control device 15 may refer to the pressure in the cooling flow path where the vaporized cooling medium is located and change the valve that performs the boil cooling process as needed to reduce the pressure. [Explanation of symbols]

[0027] 1: power control unit; 11: switching element; 12: heat sink; 13: cooling channel; 14: pair of valves; 15: control device; T1: first temperature threshold; T2: boiling point of cooling medium; T3: heat resistance temperature of switching element

Claims

[Claim 1] A power control unit mounted on a vehicle, A switching element; a heat sink that absorbs heat from the switching element; a cooling flow path for circulating a cooling medium through the heat sink; a pair of valves provided in the cooling flow path and arranged on opposite sides of the heat sink; a control device configured to execute a boiling cooling process when an abnormality in the cooling flow path is detected; Equipped with the boil-cooling process includes a process of closing the pair of valves when the temperature of the switching element exceeds a predetermined temperature threshold; the temperature threshold is lower than the boiling point of the cooling medium; The boiling point of the cooling medium is lower than the heat resistance temperature of the switching element. Power control unit.

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