JP2014184862A - Cooling system of electric vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology which quickly discharges air bubbles as necessary in a cooling system for an electric vehicle where a reserve tank is placed at a position lower than cooling target units.SOLUTION: A cooling system 20 disclosed by the specification includes: a circulation passage 16 for circulating a coolant; a pump 15; a reserve tank 17; temperature sensors 24; and a cooling controller 31. The circulation passage circulates the coolant to multiple cooling target units (a motor 9 and a power control unit 13). The reserve tank 17 is provided at a position in the circulation passage which is located lower than the multiple cooling target units. The temperature sensors 24 measure temperatures in two different positions in the multiple cooling target units. The cooling controller 31, which controls the output of the pump 15, adjusts the output of the pump 15 according to a difference between the temperatures measured by the two temperature sensors 24 when air bubbles mixed in the circulation passage are detected.

Description

  The present invention relates to a cooling system for an electric vehicle. The electric vehicle in this specification includes a so-called hybrid vehicle including both an engine and a motor, and a fuel cell vehicle.

  The electric vehicle includes a plurality of units that generate a large amount of heat. Typical units that generate a large amount of heat are a motor for traveling, a battery that stores electric power to be supplied to the motor, and a power converter that converts the DC power of the battery into AC power and supplies it to the motor. Many electric vehicles are equipped with a cooling system that circulates liquid refrigerant in the plurality of units. Hereinafter, a unit to be cooled by the cooling system is referred to as a cooling target unit.

  It is desirable to replace the liquid refrigerant periodically. When the liquid refrigerant is replaced, bubbles may be mixed into the refrigerant circulation path. Air bubbles cause a reduction in cooling capacity. A cooling system using a liquid refrigerant is usually provided with a reserve tank in the refrigerant circulation path, and bubbles are discharged from the circulation path in the reserve tank. Therefore, even if bubbles are mixed, if the cooler is operated, the bubbles can be eliminated.

  However, in order to shorten the period during which the cooling capacity is reduced, it is desired to quickly discharge the bubbles from the circulation path. Alternatively, when the pump for pumping the refrigerant is operated at a low output, the bubbles may not be easily eliminated. Even in such a case, it is desirable to discharge the bubbles from the circulation path as quickly as possible. It is. For example, Patent Document 1 discloses a technique for quickly discharging bubbles by driving a pump that pumps a refrigerant in a specific pattern.

  On the other hand, Patent Document 2 discloses a technique for quickly discharging bubbles in an electric vehicle in which a reserve tank is disposed at a position higher than a fuel cell having a large calorific value. In this technique, an air storage space is provided in the refrigerant circulation path at a position lower than the reserve tank, such as near the refrigerant outlet of the fuel cell. Then, the air reservoir space and the reserve tank are connected by an air vent pipe. Since the reserve tank is arranged at a position higher than the air reservoir space, the bubbles reach the reserve tank through the air vent pipe and are discharged to the outside from there. This technique does not move the bubbles in the circulation path according to the flow of the liquid refrigerant, but collects air (bubbles) in the air storage space and sends the air to the reserve tank through a dedicated pipe.

JP 2008-180160 A JP 2005-129387 A

  The technique of Patent Document 2 is effective when the reserve tank is arranged at a position higher than the fuel cell (that is, the cooling target unit). However, depending on the layout, there is a case where it is desired to arrange the reserve tank at a position lower than the cooling target unit. In such a case, the technique of Patent Document 2 cannot be used. Further, as in Patent Document 1, it is preferable to drive the pump with a specific drive pattern, but it is not always necessary to drive the pump with such a specific pattern when bubbles are present. Typically, if high cooling capacity is not required, such as when the temperature of the unit to be cooled is low, the bubbles may be discharged slowly.

  The technology disclosed in this specification has been created in view of the above problems. The present specification provides a technique for quickly discharging bubbles as necessary in a cooling system for an electric vehicle in which a reserve tank is arranged at a position lower than a unit to be cooled.

  A cooling system disclosed in the present specification includes a circulation path for circulating liquid refrigerant to a plurality of cooling target units, a pump for pumping liquid refrigerant in the circulation path, a controller for controlling the output of the pump, a reserve tank, A plurality of temperature sensors are provided. In other words, the unit to be cooled is the heat generating unit described above. Typically, the motor for traveling, a battery for storing electric power to be supplied to the motor, and DC power of the battery are converted into AC power and supplied to the motor. Power conversion device. The reserve tank is connected to the circulation path at a position lower than the cooling target unit. The reserve tank is arranged at a position lower than at least one cooling target unit. The technique disclosed in this specification focuses on a cooling target unit disposed at a position higher than the reserve tank, but another cooling target unit may exist at a position lower than the reserve tank.

  The plurality of sensors detect the temperature of the cooling target unit disposed at a position higher than the reserve tank. The cooling system typically includes two temperature sensors and measures temperatures at two different locations of the cooling target unit. The two locations may be different positions in one cooling target unit (or different devices in the cooling target unit), or may be temperatures of different cooling target units. Alternatively, the refrigerant temperature at a specific location in the circulation path may be measured as the estimated value of the temperature of the cooling target unit. In the system described above, when it is detected that air bubbles are mixed in the circulation path, the controller pumps according to the temperature difference measured by a plurality of temperature sensors (two of the plurality of temperature sensors). Adjust the output of. Typically, the controller drives the pump at the first output when the temperature difference is lower than a predetermined temperature difference threshold, and first when the temperature difference is higher than the temperature difference threshold. The pump is driven with a second output greater than one output.

  The reason why the temperature sensors are attached to two different places of the cooling target unit (including the circulation path) arranged at a position higher than the reserve tank is as follows. Air bubbles tend to stay in the cooling target unit located higher than the reserve tank. The cooling capacity is locally reduced at the locations where the bubbles remain. Therefore, the location is locally hotter than other locations. That is, when bubbles are present, a large temperature difference between two different locations indicates that there are locations where the bubbles continue to stay and the cooling capacity is locally reduced. The greater the temperature difference, the more significant the local cooling capacity declines. Therefore, the larger the temperature difference is, the more the pump output is increased and the bubbles are quickly moved to the reserve tank. Note that the presence of bubbles may be typically determined as the occurrence of bubbles when the pump rotation speed with respect to the target output given to the pump by the controller exceeds a predetermined rotation speed threshold. This is because when the bubbles are generated, the load on the pump is reduced, and the pump rotational speed with respect to the target output is increased.

  In many cases, the electric automatic cooling system includes, as one of the cooling target units, a battery that stores electric power to be supplied to the traveling motor. In such a case, the reserve tank may be provided integrally with the battery. A typical example of “the reserve tank and the battery are integrated” is a mode in which the reserve tank and the battery are accommodated in one housing. Such an embodiment can cool the battery efficiently. When the reserve tank and the battery are provided integrally, the other cooling target unit of the battery is located above the reserve tank.

  Details and further improvements of the technology disclosed in this specification will be described in detail in the section of Detailed Description.

It is a block diagram of the electric power system of the electric vehicle of an Example. It is a block diagram of a cooling system. FIG. 3 is a schematic layout diagram of units to be cooled in the vehicle. It is a flowchart which shows the process which a controller performs.

  Initially, the electric power system of the electric vehicle of an Example is demonstrated. In FIG. 1, the system diagram of the electric power system of the electric vehicle 2 of an Example is shown. The electric vehicle 2 has two batteries (main battery 3 and sub-battery 4) for supplying electric power to the driving motor. The main battery 3 is a battery used during normal traveling. The sub-battery 4 is used together with the main battery 3 to increase the electric power supplied to the motor when a high torque is required temporarily. The case where a high torque is required temporarily is, for example, a case where the driver suddenly steps on the accelerator or a case where the vehicle travels on an uphill road with a large gradient. The sub battery 4 has a smaller capacity (maximum charging power) than the main battery 3, but has an output voltage higher than that of the main battery 3.

  The main battery 3 is connected to the voltage converter 6 via the system main relay 5. The output side of the voltage converter 6 is connected to the inverter 7. The high-power sub battery 4 is connected to the inverter 7 via a relay 8. The main battery 3 has an output voltage lower than that of the sub-battery 4. Therefore, the voltage converter 6 boosts the output voltage of the main battery 3 and aligns it with the output voltage of the sub-battery 4.

  The inverter 7 converts the DC power of the main battery 3 (and the sub-battery 4) into AC and outputs it to the traveling motor 9. The travel controller 10 opens and closes the system main relay 5 and the relay 8 according to the situation, and selects a battery to be supplied to the inverter 7. Specifically, the travel controller 10 calculates the target output of the motor 9 from sensor data such as an accelerator opening sensor and a vehicle speed sensor (not shown), and if the target output is higher than a predetermined threshold output, the system main Relay 5 and relay 8 are closed. That is, the travel controller 10 supplies power to the inverter 7 from two batteries. When the target output is lower than the threshold output, the travel controller 10 closes the system main relay 5 and opens the relay 8. That is, only the power of the high-capacity main battery 3 is supplied to the inverter 7. The main battery 3 and the sub-battery 4 are charged by generating electricity with the motor 9 using the deceleration energy of the vehicle speed. Moreover, although illustration of a charger etc. is omitted, the electric vehicle 2 can also charge the main battery 3 and the sub battery 4 by receiving power supply from an external power source.

  The voltage converter 6 and the inverter 7 are housed in one casing, and the casing is referred to as a power control unit. Hereinafter, the power control unit is simply referred to as PCU. The PCU housing also houses a circuit board, which is the substance of the travel controller 10, and a relay 8. In FIG. 2 to be described later, reference numeral 13 is assigned to the PCU.

  Since the main battery 3, the motor 9, and the PCU 13 generate a large amount of heat, they are cooled by liquid cooling. That is, in this embodiment, the main battery 3, the motor 9, and the PCU 13 correspond to the cooling target unit. FIG. 2 shows a block diagram of a cooling system 20 that cools the main battery 3, the motor 9, and the PCU 13, and a sub-battery cooler 40 that cools the sub-battery 4. The cooling system 20 includes a main battery case 22, a reserve tank 17, a circulation path 16, an electric pump 15, and a radiator 14. The circulation path 16 is connected to a main battery 3, a motor 9, and a PCU 13 that are units to be cooled. The circulation path 16 is also connected with a reserve tank 17 for temporarily storing the refrigerant. As described above, the cooling system 20 is liquid-cooled, and the reserve tank 17 stores a liquid that cools the motor 9 and the PCU 13. The liquid is typically LLC (Long Life Coolant), but may be water. Hereinafter, the liquid refrigerant used by the cooling system 20 is referred to as cooling water. The cooling water is sucked out of the reserve tank 17 by the electric pump 15, flows through the circulation path 16, exchanges heat with these devices in the order of the main battery 3, the radiator 14, the PCU 13, and the motor 9, and returns to the reserve tank 17.

  A sub-battery cooler 40 that cools the sub-battery 4 includes a sub-battery case 21 that houses the sub-battery 4 and the fan 18.

  The cooling water exiting the reserve tank 17 first passes through the inside of the main battery case 22 that houses the main battery 3. The inside of the main battery case 22 is a heat exchanger, where the cooling water flowing through the circulation path 16 exchanges heat with the main battery 3. The main battery case 22 is in contact with the inside of the main battery 3 while cooling water passes through the inside. The main battery case 22 corresponds to a so-called water jacket.

  The cooling water that has passed through the main battery case 22 is pumped by the electric pump 15 and reaches the radiator 14. After the cooling water is cooled by the radiator 14, the PCU 13 is cooled (that is, the voltage converter 6 and the inverter 7 are cooled), and then the motor 9 is cooled. The cooling water absorbs heat from the PCU 13 and the motor 9 and returns to the reserve tank 17. That is, the cooling water stored in the reserve tank 17 has a corresponding amount of heat (the amount of heat absorbed from the PCU 13 and the motor 9).

  As well represented in FIG. 2, in the reserve tank 17, the water intake 16 a of the circulation path 16 is located in the cooling water, but the drainage outlet 16 b through which the circulating water is discharged from the circulation path is: It exists in the position higher than the water surface of a cooling water (refer also FIG. 3 mentioned later). When the cooling water is replaced, bubbles may remain in the circulation path 16 or the cooling target unit. However, the bubbles are carried by the cooling water, pushed out from the drain port 16b by the reserve tank 17, and discharged from the circulation path 16. If the cooling system 20 is operated in this manner, the bubbles are eventually discharged. However, since the bubbles cause a decrease in the cooling capacity, it is desirable to quickly discharge the bubbles when the temperature of the cooling target unit is high. Alternatively, while the electric pump 15 is being driven at a low output, the flow rate of the refrigerant may be small and the bubbles may not be pushed out, so it is desirable to discharge the bubbles quickly. A mechanism for quickly discharging bubbles will be described later.

  The radiator 14, the PCU 13, and the motor 9 are attached with temperature sensors 24 that measure respective temperatures. During normal travel, the cooling controller 31 adjusts the output of the electric pump 15 based on the measured value of the temperature sensor 24. Specifically, as the temperature of the motor 9 or the PCU 13 is higher, the output of the electric pump 15 is increased, the flow rate of cooling water flowing through the circulation path 16 is increased per unit time, and the cooling capacity is increased. A booster circuit 32 is incorporated between the cooling controller 31 and the electric pump 15, and when the electric pump is driven at a high output, the voltage of the electric power supplied to the electric pump 15 is increased by the booster circuit 32. How to use the booster circuit 32 will be described later. The electric pump 15 is provided with a rotation speed sensor 25 for measuring the rotation speed of the pump, and the cooling controller 31 determines the cooling water from the relationship between the electric power (drive power) supplied to the electric pump 15 and the rotation speed. Check if air bubbles are mixed in the flow path. This check will also be described later.

  The sub battery 4 is air-cooled. The sub battery cooler 40 sends external air into the sub battery case 21 by the fan 18. The sub battery cooler 40 is cooled by the air sent by the fan 18.

  The main battery case 22 and the reserve tank 17 are made integrally. In other words, the main battery case 22 and the reserve tank 17 are in contact with each other, and when the main battery 3 is at a high temperature, the cooling water stored in the reserve tank 17 also contributes to the cooling of the main battery 3 in an auxiliary manner.

  The reserve tank 17 is also integrally formed with the sub battery case 21. That is, the reserve tank 17 is in contact with the sub battery case 21. When the temperature of the sub battery 4 is lower than the temperature of the cooling water stored in the reserve tank 17, the cooling water stored in the reserve tank 17 keeps the sub battery 4 warm. This function is effective when, for example, the sub-battery 4 is below a temperature suitable for starting in a cold region.

  As described above, the reserve tank 17 is formed integrally with the main battery case 22 and the sub battery case 21. In other words, the reserve tank 17 is formed integrally with the main battery 3 and the sub battery 4.

  Next, the positional relationship between the cooling target unit and the reserve tank 17 in the vehicle will be described with reference to FIG. In particular, the vertical positional relationship between the cooling target unit and the reserve tank 17 will be described. The reserve tank 17, the main battery case 22 (main battery 3), and the sub battery case 21 (sub battery 4) that are integrally formed are installed on the floor of the vehicle. There is a relatively large space under the floor, which is suitable for placing a large battery. In the electric vehicle 2 of the embodiment, not only the battery but also the reserve tank 17 is arranged using the space.

  The radiator 14 is disposed in front of the vehicle, and then the PCU 13 and the motor 9 are disposed. As shown in FIG. 3, the position of the reserve tank 17 is the lowest, and the motor 9 and the PCU 13 that are units to be cooled are located higher than the reserve tank 17. The electric pump 15 and the radiator 14 constituting the cooling system 20 are also located higher than the reserve tank 17. Further, FIG. 3 shows that the intake port 16a in the reserve tank is located in the cooling water, and the drain port 16b is located above the water surface.

  Although the cooling water is periodically replaced, bubbles may be mixed into the circulation path 16 or the cooling target unit during the replacement. As shown in FIG. 3, when at least one cooling target unit (in this embodiment, the motor 9 and the PCU 13) is arranged at a position higher than the reserve tank 17, the bubbles enter the refrigerant flow path in the cooling target unit. In such a case, it is difficult to move to the reserve tank with a weak flow of cooling water. In such a case, the cooling controller 31 increases the output of the electric pump 15 to push out bubbles from the unit to be cooled. Next, a mechanism for discharging bubbles will be described.

  FIG. 4 shows a flowchart of processing executed by the cooling controller 31. The process of FIG. 4 is executed every time the main switch (ignition switch) of the vehicle is turned on.

  First, the cooling controller 31 drives the electric pump 15 with LO for a certain period (for example, 1 minute) (S2). The drive mode of the electric pump 15 has three patterns of LO, MID (Middle), and HI for each output, and the output is LO <MID <HI. That is, “LO” corresponds to the smallest pump output, and “HI” corresponds to the largest pump output.

  The cooling controller 31 monitors the rotational speed of the electric pump 15 after rotating the electric pump 15 for a certain period (S3). The rotational speed is acquired by the rotational speed sensor 25. If a certain amount or more of air bubbles are present in the circulation path 16 or the refrigerant flow path in the cooling target unit, the load on the electric pump 15 is reduced. Therefore, the rotation speed of the electric pump 15 is the rotation speed expected for the LO output. Higher than. When the cooling controller 31 drives the pump for a certain period of time at the LO output and the rotational speed of the electric pump 15 is higher than the rotational speed expected from the LO output plus a margin (the rotational speed threshold), It is determined that bubbles are generated (S3: YES). In addition, when the rotation speed of the electric pump 15 is lower than a rotation speed threshold value (S3: NO), the cooling controller 31 complete | finishes this routine without doing anything. After this routine, the cooling controller 31 shifts to normal cooling control. The normal cooling control is a control for driving the electric pump according to the temperature of the cooling target unit such as the motor 9 or the PCU 13. Description of the normal control is omitted.

  If the determination in step S3 is YES, that is, if it is determined that there are bubbles of a certain amount or more, the cooling controller 31 acquires the temperature of the motor 9 and the temperature of the PCU 13 by the temperature sensor 24, and the absolute value of the difference ( Temperature difference). When the temperature difference is larger than a predetermined value (temperature difference threshold value) (S4: YES), it is confirmed that the air bubbles are locally staying somewhere in the refrigerant flow path, and the cooling performance is locally reduced. It is likely that this is the cause. In particular, there is a high possibility that a location where the temperature is high is a location where bubbles remain. In such a case, the cooling controller 31 drives the electric pump 15 with the HI output in order to quickly push out the bubbles to the reserve tank 17 (S6). At this time, the cooling controller 31 uses the booster circuit 32 to increase the voltage of the electric power supplied to the electric pump 15 to be higher than normal and increase the output of the electric pump 15. The cooling controller 31 continues the pump drive with the HI output until the temperature difference becomes smaller than the temperature difference threshold (S6, S4).

  When the temperature difference becomes smaller than the temperature difference threshold (S4: NO), the cooling controller 31 determines that the local decrease in cooling performance has been eliminated, and drives the electric pump 15 with the LO output (S5). Terminate the process. After the process of FIG. 4, the cooling controller 31 moves to the normal cooling control described above.

  The processes of steps S4, S5, and S6 can be expressed as follows. That is, the cooling controller 31 drives the pump with the first output (LO output) when the difference between two different temperatures (temperature difference) in the refrigerant flow path is lower than a predetermined temperature difference threshold, When the difference is higher than the temperature difference threshold, the pump is driven with a second output (HI output) larger than the first output (LO output). The magnitudes of “LO output” and “HI output” are determined in advance. In addition, the temperature difference threshold is individually and specifically determined according to the characteristics of the cooling system and the cooling target unit, and an example thereof is about 10 ° C.

  Points to be noted regarding the cooling system of the embodiment will be described. The cooling system of the embodiment is effective for a vehicle in which a unit to be cooled (the motor 9 and the PCU 13) is located above the reserve tank 17 that can eliminate bubbles. In such an arrangement, bubbles accumulated in the unit to be cooled are difficult to move to the reserve tank 17, and there is a possibility that local cooling capacity may be lowered at the location where the bubbles are accumulated. The cooling system according to the embodiment determines the presence of bubbles of a certain amount or more based on the pump rotation speed with respect to the electric power supplied to the electric pump 15, and increases the output of the electric pump 15 when bubbles are present. Air bubbles are pushed out to the reserve tank 17 by increasing the output of the electric pump 15. When the presence of bubbles is not detected, the output of the electric pump 15 is not increased and the power consumption is suppressed.

  The motor 9 and the PCU 13 connected to the circulation path 16 are an example of a cooling target unit. The technology disclosed in this specification is also preferably applied to a cooling system that targets a cooling target unit different from the motor 9 and the PCU 13. Moreover, at least one should just be located above a reserve tank among several cooling object units.

  In the embodiment, the output of the electric pump 15 is controlled according to the difference between the temperature of the motor 9 and the temperature of the PCU 13. The temperature of interest may be other than the motor 9 and the PCU 13. For example, as shown in FIG. 2, the cooling system 20 includes a temperature sensor 24 in the radiator 14. The temperature difference in step S4 in the flowchart of FIG. 4 may be the difference between the temperature of the radiator 14 and the temperature of the PCU 13, or the difference between the temperature of the radiator 14 and the temperature of the motor 9.

  The temperature difference between the temperature sensors is not limited to the temperature difference between the units to be cooled. For example, when a plurality of temperature sensors are provided inside the PCU, the temperature difference between the plurality of temperature sensors inside the PCU may be used. That is, a plurality of temperature sensors may be provided inside the cooling target unit, and the output of the electric pump may be controlled based on the temperature difference therebetween.

  The vehicle of the example was an electric vehicle equipped with one motor for traveling. It should be noted that the “electric vehicle” in this specification includes a hybrid vehicle that uses both a motor and an engine for traveling, and a fuel cell vehicle.

  In the embodiment, the process of FIG. 4 is performed every time the main switch (ignition switch) of the vehicle is turned on. However, the present invention is not limited to this, and the process of FIG.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Electric vehicle 3: Main battery 4: Sub battery 5: System main relay 6: Voltage converter 7: Inverter 8: Relay 9: Motor 10: Travel controller 13: PCU (power control unit)
14: Radiator 15: Electric pump 16: Circulation path 16a: Intake port 16b: Drain port 17: Reserve tank 18: Fan 20: Cooling system 21: Sub battery case 22: Main battery case 24: Temperature sensor 25: Revolution sensor 31 : Cooling controller 32: Booster circuit 40: Sub battery cooler

Claims (3)

A circulation path for circulating a liquid refrigerant to a plurality of cooling target units;
A pump for pumping liquid refrigerant;
A reserve tank connected to the circulation path at a position lower than the cooling target unit;
A plurality of temperature sensors for detecting the temperature of the cooling target unit;
A controller for controlling the output of the pump;
With
The controller adjusts the output of the pump according to the temperature difference detected by the plurality of temperature sensors when it is detected that bubbles are mixed in the circulation path, and the cooling system for the electric vehicle is characterized in that .   The controller drives the pump with a first output when the temperature difference is lower than a predetermined temperature difference threshold, and is greater than the first output when the temperature difference is higher than the temperature difference threshold. The cooling system according to claim 1, wherein the pump is driven with the second output.   The cooling system according to claim 1, wherein the reserve tank is provided integrally with a battery that stores electric power to be supplied to a traveling motor.

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