Cooling system

Abstract

To provide a cooling system for circulating a refrigerant containing CO2 to cool a battery or the like in the vehicle, capable of securing the maximum coolability when the battery abnormally generates heat.SOLUTION: The cooling system 100 includes the compressor 1 that compresses the refrigerant, the heat exchangers 2 that cool the refrigerant from the compressor 1, the heat exchangers 5a and 6a that use the refrigerant cooled by the heat exchangers 2, the refrigerant line 17 that supplies the refrigerant from the heat exchangers 2 to the battery 6 and returns the refrigerant to the compressor 1, and the expansion valves E2 provided in the refrigerant line 17. Lim1 E2, when abnormal heat generation of the battery 6 occurs, the opening of the expansion value E2 is set to a limit opening Lim1 larger than the limit opening Lim2.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a cooling system that circulates a refrigerant containing CO2 to cool the interior of a vehicle. [Background technology]

[0002] Conventionally, systems that circulate a refrigerant through a compressor, a heat exchanger, etc. have been used in refrigeration cycles used in air conditioners. In recent years, such refrigerant circulating systems have also been used to cool components inside vehicles, such as the batteries of electric vehicles and hybrid vehicles. In one example, Patent Document 1 describes a system that cools or heats battery cells by connecting a compressor, a first heat exchanger, and a second heat exchanger through a refrigerant flow path and performing heat exchange between the refrigerant and the battery cells using the second heat exchanger. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-180455 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the demand for battery cooling has increased with the rapid charging and higher output of batteries. To address this, battery cooling technologies using insulating coolants that can directly cool the inside of the battery have been developed. While such battery cooling technologies using coolants offer high cooling capacity, they suffer from pressure loss due to the viscosity of the oil. In response, the present inventors have devised a method for efficiently cooling batteries while reducing pressure loss by using an insulating, low-viscosity refrigerant containing CO2 (hereinafter referred to as a "CO2 refrigerant"). Because such CO2 refrigerants are so-called natural refrigerants, they are also environmentally friendly and considerate of the impact on the human body.

[0005] Here, in a cooling system that cools a battery using a refrigerant, it is desirable to ensure a sufficient amount of refrigerant is supplied to the battery in order to improve the cooling capacity of the battery using the refrigerant. However, if the amount of refrigerant supplied to the battery is increased, the efficiency of the entire system (i.e., the efficiency of the refrigeration cycle) will decrease.

[0006] On the other hand, batteries can sometimes generate abnormal heat due to thermal runaway (caused by various reactions or thermal decomposition within the battery) caused by an internal short circuit, etc. When such abnormal heat generation occurs, it is desirable to prioritize cooling the battery and maximize the cooling capacity of the refrigerant.

[0007] The present invention has been made to solve the problems of the conventional technology described above, and aims to ensure the efficiency of the entire system in a cooling system that circulates a refrigerant containing CO2 to cool a battery or other components inside a vehicle, while maximizing the cooling capacity of the refrigerant for the battery when the battery abnormally heats up. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a cooling system for cooling the interior of a vehicle by circulating a refrigerant containing CO2, the cooling system comprising: a compressor for compressing the refrigerant; a first heat exchanger for cooling the refrigerant compressed by the compressor; a second heat exchanger for at least air-conditioning the vehicle using the refrigerant cooled by the first heat exchanger; a refrigerant passage for supplying the refrigerant to the battery and for supplying the refrigerant after being used for cooling in the battery to the compressor, in order to cool a battery in the vehicle using the refrigerant cooled by the first heat exchanger; an expansion valve provided in the refrigerant passage upstream of the battery for expanding the refrigerant; and a control device configured to acquire the temperature of the battery and control the expansion valve based on the battery temperature, wherein the control device is configured to increase the opening degree of the expansion valve as the battery temperature increases within a range equal to or less than a predetermined first opening degree when abnormal heat generation is not occurring in the battery, and to set the opening degree of the expansion valve to a second opening degree greater than the first opening degree when abnormal heat generation is occurring in the battery.

[0009] According to the present invention configured as described above, a single system (cooling system) that circulates a refrigerant can appropriately achieve vehicle air conditioning and battery cooling. Furthermore, according to the present invention, when the battery is not overheating, the opening of the expansion valve is increased within a range equal to or less than a first opening as the battery temperature increases, thereby ensuring the refrigerant's ability to cool the battery while suppressing a decrease in overall system efficiency. On the other hand, according to the present invention, when the battery is overheating, the opening of the expansion valve is set to a second opening greater than the first opening, thereby maximizing the refrigerant's ability to cool the battery and giving top priority to battery cooling. As a result, it is possible to suppress abnormal battery overheating and avoid the worst-case scenario of the battery catching fire.

[0010] In the present invention, the control device is preferably configured to first set the opening degree of the expansion valve to a first opening degree when abnormal heat generation occurs in the battery, and then, if the battery temperature continues to rise, to set the opening degree of the expansion valve to a second opening degree. According to the present invention configured in this manner, when abnormal heat generation occurs in the battery, the expansion valve is controlled in stages from the first opening to the second opening, thereby increasing the cooling capacity of the battery by the refrigerant while minimizing the increase in temperature of the refrigerant discharged from the compressor.

[0011] In the present invention, preferably, when the refrigerant passage is a first refrigerant passage and the expansion valve is a first expansion valve, the cooling system further has a second refrigerant passage for supplying the refrigerant after being used for cooling in the second heat exchanger to the compressor without passing through the first refrigerant passage, and a second expansion valve provided on the second refrigerant passage for expanding the refrigerant, and the control device is configured to increase the opening of the second expansion valve as the opening of the first expansion valve increases when abnormal heat generation is not occurring in the battery, and to decrease the opening of the second expansion valve as the opening of the first expansion valve increases when abnormal heat generation is occurring in the battery. According to the present invention configured as described above, when the battery is not overheating, the flow rate of refrigerant supplied to the compressor from the second refrigerant passage via the second expansion valve is increased in response to an increase in the flow rate of refrigerant supplied to the compressor from the first refrigerant passage via the first expansion valve, thereby suppressing an increase in the temperature of the refrigerant discharged from the compressor. As a result, for example, deterioration or degradation of the oil in the refrigerant can be suppressed. On the other hand, when the battery is overheating, the flow rate of refrigerant supplied to the compressor from the second refrigerant passage via the second expansion valve is reduced, allowing an increase in the temperature of the refrigerant discharged from the compressor, thereby giving top priority to cooling the battery.

[0012] In the present invention, the first opening degree is preferably set based on the opening degree of the expansion valve for keeping the temperature of the refrigerant discharged from the compressor at or below a predetermined temperature. According to the present invention configured in this manner, when abnormal heat generation is not occurring in the battery, the opening degree of the expansion valve can be regulated to a first opening degree or less, thereby making it possible to keep the temperature of the refrigerant discharged from the compressor below a predetermined temperature.

[0013] In the present invention, the control device is preferably configured to determine whether or not abnormal heat generation is occurring in the battery by detecting an internal short circuit in the battery. According to the present invention configured as described above, it is possible to accurately determine whether abnormal heat generation has occurred in the battery.

[0014] In the present invention, preferably, the cooling system further includes a battery heat exchanger for causing the refrigerant in the refrigerant passage to flow around the plurality of cells in the battery to directly cool the plurality of cells with the refrigerant, and the battery heat exchanger is supplied with refrigerant whose pressure has been reduced by an expansion valve. According to the present invention configured as described above, the battery heat exchanger directly cools the multiple cells with the refrigerant, thereby effectively cooling the multiple cells. In this case, since the pressure resistance of the battery pack and the like is relatively low, it is not desirable to supply the high-pressure refrigerant from the compressor directly to the battery heat exchanger. Therefore, in the present invention, the refrigerant from the compressor is decompressed by an expansion valve before being supplied to the battery heat exchanger. This effectively protects the inside of the battery (multiple cells, etc.).

[0015] In the present invention, preferably, the second heat exchanger includes an air conditioning heat exchanger for air conditioning the vehicle, and further includes a battery heat exchanger for supplying refrigerant to the outside of a battery pack including a plurality of cells in a battery, thereby indirectly cooling the plurality of cells with the refrigerant. According to the present invention configured in this manner, by using a battery heat exchanger that supplies refrigerant to the outside of the battery pack, the battery can be appropriately cooled and relatively large heat exchange can be achieved between the battery and the refrigerant.

[0016] In the present invention, the first heat exchanger is preferably configured as a cascade heat exchanger that exchanges heat between a first heat cycle circuit including at least a compressor, a second heat exchanger, a refrigerant passage, and an expansion valve, and a second heat cycle circuit that is separate from the first heat cycle circuit and includes an outside air heat exchanger that exchanges heat with outside air. According to the present invention configured in this manner, by performing heat exchange (cascade heat exchange) between the first heat cycle circuit and the second heat cycle circuit, which performs heat exchange with outside air, the efficiency of the entire system of the first heat cycle circuit can be improved, in other words, the work of the compressor in the first heat cycle circuit can be reduced.

[0017] In the present invention, the cooling system is preferably configured to further cool a motor that drives the vehicle using electric power from the battery, with the refrigerant cooled by the first heat exchanger. According to the present invention configured in this manner, it is possible to appropriately cool various components within a vehicle, such as the motor, using a single system (cooling system) that circulates a refrigerant. [Effects of the Invention]

[0018] According to the present invention, in a cooling system that circulates a refrigerant containing CO2 to cool a battery or other device inside a vehicle, it is possible to ensure the efficiency of the entire system while maximizing the cooling capacity of the refrigerant for the battery when the battery abnormally heats up. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic configuration diagram of a vehicle to which a cooling system according to an embodiment of the present invention is applied; [Figure 2] 1 is a schematic configuration diagram of a cooling system according to an embodiment of the present invention. [Figure 3] 3(a) and 3(b) are schematic configuration diagrams of a first battery heat exchanger and a second battery heat exchanger according to an embodiment of the present invention, respectively. [Figure 4]FIG. 2 is a block diagram showing the electrical configuration of the cooling system according to the embodiment of the present invention. [Figure 5] 5(a) and 5(b) respectively show the control of the E2 opening and the E3 opening that is performed during steady running or during slow charging in the embodiment of the present invention. [Figure 6] 6(a) and 6(b) respectively show the control of the E2 opening and the E3 opening performed during rapid charging in the embodiment of the present invention. [Figure 7] 7(a) and 7(b) respectively show the control of the E2 opening and the E3 opening that is performed when the battery is abnormally heated in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, a cooling system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0021] [Overall configuration] First, the overall configuration of the cooling system according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of a vehicle to which the cooling system according to this embodiment is applied.

[0022] 1, vehicle 200 is, for example, an electric vehicle, and has a cooling system 100 that circulates a refrigerant in a refrigeration cycle. This cooling system 100 mainly has a compressor 1 for compressing the refrigerant, a heat exchanger 2 for cooling the refrigerant compressed by compressor 1, a motor 4 for generating power to drive vehicle 200, an air conditioner 5 for conditioning the interior of vehicle 200, and a battery 6 for supplying power to drive motor 4.

[0023] The cooling system 100 circulates a CO2 refrigerant (hereinafter sometimes simply referred to as "refrigerant") as a natural refrigerant. Typically, CO2 refrigerant is a refrigerant containing refrigeration oil (oil) such as PAG and additives. To use this CO2 refrigerant, the compressor 1 is configured to compress the refrigerant to extremely high pressures. The motor 4 uses the refrigerant (liquid (typically supercritical) refrigerant) compressed by the compressor 1 to cool its rotor and stator. In addition, the motor 4 is configured to use the refrigerant to lubricate the sliding bearings that support the rotating shaft. The refrigerant compressed by the compressor 1 is used for air conditioning in the air conditioner 5 and for cooling the battery 6. For example, in the cooling system 100, a high-temperature, high-pressure gas refrigerant is supplied from the compressor 1 to the heat exchanger 2, a low-temperature, high-pressure liquid refrigerant is supplied from the heat exchanger 2 to the motor 4, and a room-temperature, low-pressure gas refrigerant is supplied from the motor 4 to the compressor 1.

[0024] [Cooling system configuration] Next, the cooling system 100 according to this embodiment will be specifically described with reference to Fig. 2. Fig. 2 is a schematic diagram of the cooling system 100 according to this embodiment.

[0025] As shown in Fig. 2, the cooling system 100 includes a first heat cycle circuit (low-temperature circuit) 100a that circulates the CO2 refrigerant described above, and a second heat cycle circuit (high-temperature circuit) 100b that includes an outside-air heat exchanger 30 that exchanges heat with outside air and circulates a refrigerant such as propane or a fluorine-based refrigerant, and is configured to realize a cascade refrigeration cycle. Specifically, the first heat cycle circuit 100a and the second heat cycle circuit 100b perform cascade heat exchange in a heat exchanger 2 (hereinafter, the heat exchanger 2 will be referred to as the "cascade heat exchanger 2" as appropriate). This cascade heat exchanger 2 corresponds to the "first heat exchanger" in this invention.

[0026] The first heat cycle circuit 100a of the cooling system 100 mainly includes, in addition to the compressor 1 and motor 4 described above, an air conditioning heat exchanger 5a (specifically, an evaporator that generates cool air to be supplied to the vehicle interior) for performing heat exchange in the air conditioner 5, a first battery heat exchanger 6a and a second battery heat exchanger 6b for performing heat exchange to cool the battery 6, refrigerant passages 11 to 20 through which the refrigerant flows, a compressor 23 that compresses the refrigerant, flow control valves V1, V2, and V3 that adjust the flow rate of the refrigerant, and expansion valves E1, E2, and E3 that expand the refrigerant to reduce its pressure.

[0027] In this embodiment, the compressor 1 has a first compressor 1a on the upstream side and a second compressor 1b on the downstream side, and is configured to compress the refrigerant in two stages. The first compressor 1a increases the refrigerant pressure P3 to pressure P2 (pressure P2 > pressure P3), and the second compressor 1b increases the refrigerant pressure P2 to pressure P1 (pressure P1 > pressure P2). In one example, pressure P1 is about 3 MPa, pressure P2 is about 1.5 MPa, and pressure P3 is about 0.1 MPa.

[0028] In this embodiment, the battery 6 is configured to be cooled by two heat exchangers: a first battery heat exchanger 6a and a second battery heat exchanger 6b. The configurations of the first battery heat exchanger 6a and the second battery heat exchanger 6b will be described with reference to FIGS. 3(a) and 3(b). FIGS. 3(a) and 3(b) schematically show examples of the first battery heat exchanger 6a and the second battery heat exchanger 6b, respectively. More specifically, FIG. 3(a) shows a plan view of a battery pack 61 of the battery 6 as seen from the outside, and FIG. 3(b) shows a plan view of the battery pack 61 seen through.

[0029] As shown in FIG. 3(a), the first battery heat exchanger 6a is configured to supply a refrigerant to the outside (typically, the surface of the case) of a battery pack 61 including a plurality of cells 62 in the battery 6, and more specifically, to flow the refrigerant through a meandering flow path 63, thereby indirectly cooling the plurality of cells 62 in the battery 6 with the refrigerant. Note that the configuration for indirectly cooling the cells 62 in the battery 6 with the refrigerant is not limited to the configuration shown in FIG. 3(a), and various known configurations are applicable. In contrast, as shown in FIG. 3(b), the second battery heat exchanger 6b is configured to flow the refrigerant around the plurality of cells 62 in the battery 6, that is, to flow the refrigerant inside the battery pack 61, thereby directly cooling the plurality of cells 62 with the refrigerant. Note that the first battery heat exchanger 6a and the above-described air-conditioning heat exchanger 5a correspond to the "second heat exchanger" in the present invention. In this case, the air conditioning heat exchanger 5a cools the evaporator (object to be cooled) of the air conditioner 5 with the refrigerant, and the first battery heat exchanger 6a cools the battery 6 (object to be cooled) with the refrigerant.

[0030] Returning to FIG. 2 , the flow of refrigerant within the first heat cycle circuit 100a will be specifically described. Refrigerant compressed by compressor 1 is supplied to cascade heat exchanger 2 through refrigerant passage 11, and the refrigerant cooled by cascade heat exchanger 2 is supplied to air conditioning heat exchanger 5a, first battery heat exchanger 6a, and motor 4 through refrigerant passages 12, 13, and 15 connected to refrigerant passage 11. Refrigerant passages 12 and 13 join at a junction C1 and are connected to refrigerant passage 16, whereby the refrigerant that has exchanged heat in air conditioning heat exchanger 5a and first battery heat exchanger 6a is supplied to refrigerant passage 16. Refrigerant cooled by cascade heat exchanger 2 is supplied directly to refrigerant passage 16 through refrigerant passage 14 connected to refrigerant passage 11 without passing through air conditioning heat exchanger 5a and first battery heat exchanger 6a (i.e., bypassing refrigerant passages 12, 13, and 15). In this case, refrigerant passage 14 and refrigerant passage 16 merge at junction C2 downstream of junction C1. Refrigerant passages 12, 13, and 14 are provided with flow control valves V1, V2, and V3, respectively, for adjusting the flow rate of the refrigerant flowing through each passage, and refrigerant passage 15 is provided with expansion valve E1 for expanding the refrigerant supplied to motor 4. Expansion valve E1 functions to reduce the pressure of the refrigerant from pressure P1 to pressure P2.

[0031] A refrigerant passage 17 is connected to the refrigerant passage 16, and the refrigerant in the refrigerant passage 16 is supplied from the refrigerant passage 17 to the second battery heat exchanger 6b. An expansion valve E2 for expanding the refrigerant is provided in the refrigerant passage 17 upstream of the second battery heat exchanger 6b, and the refrigerant decompressed by the expansion valve E2 is supplied to the second battery heat exchanger 6b. The expansion valve E2 functions to decompress the refrigerant from pressure P1 to pressure P3. An internal heat exchanger (IHX) 6c having a known double-pipe structure is provided in the refrigerant passage 17 downstream of the second battery heat exchanger 6b, and its downstream side is connected to the first compressor 1a of the compressor 1. The refrigerant decompressed to pressure P3 by the expansion valve E2 is supplied to the first compressor 1a.

[0032] Furthermore, refrigerant passage 16 branches into refrigerant passages 18 and 20 downstream of the connection point with refrigerant passage 17. Refrigerant passage 18 is provided with an expansion valve E3 for expanding the refrigerant. The expansion valve E3 functions to reduce the pressure of the refrigerant from pressure P1 to pressure P2. Refrigerant passage 18 also merges with refrigerant passage 15, which includes the motor 4, at a junction C3 downstream of the expansion valve E3, and these refrigerant passages 15 and 18 are connected to refrigerant passage 19. Refrigerant passage 19 is connected between the first compressor 1a and the second compressor 1b of compressor 1, and supplies the refrigerant at pressure P2 reduced by the expansion valve E1 and the expansion valve E3 to the second compressor 1b. Meanwhile, refrigerant passage 20 is connected to refrigerant passage 11 between compressor 1 and cascade heat exchanger 2 at a junction C4 downstream of refrigerant passage 20. The refrigerant passage 20 is provided with a compressor 23 and an internal heat exchanger (IHX) 24 having a known double-pipe structure. Such refrigerant passage 20 allows the refrigerant from the refrigerant passage 16 to be supplied to the cascade heat exchanger 2 by the compressor 23 without passing through the compressor 1 (i.e., by bypassing the compressor 1).

[0033] The refrigerant passage 17 corresponds to the "first refrigerant passage" in the present invention, and the refrigerant passages 18 and 19 correspond to the "second refrigerant passage" in the present invention. The expansion valve E2 corresponds to the "first expansion valve" in the present invention, and the expansion valve E3 corresponds to the "second expansion valve" in the present invention.

[0034] Next, the second heat cycle circuit 100b of the cooling system 100 is a high-temperature circuit that circulates a refrigerant such as propane or a fluorine-based refrigerant, as described above, and includes an outside air heat exchanger 30 that exchanges heat with outside air, a refrigerant passage 31 through which the refrigerant flows, a compressor 32 that compresses and feeds the refrigerant, and an expansion valve 33 that expands the refrigerant. In the cooling system 100 according to this embodiment, the second heat cycle circuit 100b is provided separately from the first heat cycle circuit 100a, thereby improving the efficiency of the entire system of the first heat cycle circuit 100a, in other words, reducing the work of the compressor 1.

[0035] Next, the electrical configuration of the cooling system 100 according to this embodiment will be described with reference to Fig. 4 in addition to Fig. 2. Fig. 4 is a block diagram showing the electrical configuration of the cooling system 100 according to this embodiment.

[0036] 4, the cooling system 100 has a control device 80 configured to perform various controls in the system. The control device 80 is configured by a computer including one or more processors 80a (typically a CPU) and memory 80b such as a ROM or RAM that stores various programs interpreted and executed on the processor 80a (including basic control programs such as an OS and application programs that are started on the OS and realize specific functions) and various data.

[0037] The cooling system 100 also has refrigerant temperature sensors 41, 42, 43, 44 that detect the temperature of the refrigerant and refrigerant pressure sensors 51, 52, 53 that detect the pressure of the refrigerant (see Figure 2), a passenger compartment temperature sensor 71 that detects the temperature of the passenger compartment (cabin), a battery temperature sensor 72 that detects the temperature of the battery 6 (hereinafter referred to as "battery temperature"), and a motor temperature sensor 73 that detects the temperature of the motor 4, all of which are provided in the first heat cycle circuit 100a. 2, refrigerant temperature sensor 41 is provided in refrigerant passage 11 between compressor 1 and cascade heat exchanger 2 (more specifically, upstream of junction C4 of refrigerant passage 11 and 20), refrigerant temperature sensor 42 is provided at junction C2 of refrigerant passage 14 and 16, refrigerant temperature sensor 43 is provided at junction C3 of refrigerant passage 15 and 18, and refrigerant temperature sensor 44 is provided in refrigerant passage 17 downstream of second battery heat exchanger 6b and IHX 6c. In addition, refrigerant pressure sensor 51 is provided in refrigerant passage 11 downstream of cascade heat exchanger 2, refrigerant pressure sensor 52 is provided in refrigerant passage 15 downstream of motor 4, and refrigerant pressure sensor 53 is provided in refrigerant passage 17 downstream of second battery heat exchanger 6b and IHX 6c.

[0038] The control device 80 supplies control signals to the compressor 1, the flow rate control valves V1, V2, V3, and the expansion valves E1, E2, E3 based on the detection signals from the above sensors 41-44, 51-53, 71-73 to control them. In particular, in this embodiment, the control device 80 controls the openings of the expansion valves E2 and E3 (hereinafter referred to as "E2 opening" and "E3 opening" as appropriate) based on the battery temperature detected by the battery temperature sensor 72 so as to ensure the cooling capacity of the battery 6 by the refrigerant while suppressing a decrease in the efficiency of the cooling system 100 (particularly the first heat cycle circuit 100a) (details will be described later).

[0039] [Control method] The following describes the control performed by the control device 80 in this embodiment. First, the basic concept of the control according to this embodiment will be described.

[0040] The balance between the efficiency (COP: Coefficient of Performance) and cooling capacity of the cooling system 100 changes depending on various conditions such as the driving state of the vehicle 200, whether or not air conditioning is used while the vehicle 200 is driving, and the charging rate (slow charging, fast charging) of the battery 6. Therefore, in order to improve the driving range of the vehicle 200 and reduce the charging time of the battery 6, it is desirable to adjust the balance between the cooling capacity and the efficiency taking these conditions into consideration.

[0041] In the cooling system 100 according to this embodiment, the temperature of the refrigerant discharged from the compressor 1 (hereinafter referred to as the "compressor discharge temperature"), the cooling capacity of the entire system, and the efficiency of the entire system change depending on the balance between the ratio of the refrigerant supplied from the junction C2 via the refrigerant passage 17, the expansion valve E2, and the second battery heat exchanger 6b to the compressor 1 (first compressor 1a) (hereinafter referred to as the "first refrigerant ratio") and the ratio of the refrigerant supplied from the junction C2 via the refrigerant passage 18, the expansion valve E3, the junction C3, and the refrigerant passage 19 to the compressor 1 (second compressor 1b) (hereinafter referred to as the "second refrigerant ratio"). In this case, the first and second refrigerant ratios are adjusted by the expansion valve E2 in the refrigerant passage 17 and the expansion valve E3 in the refrigerant passage 18, respectively. Basically, the compressor discharge temperature tends to increase as the proportion of the first refrigerant increases and decrease as the proportion of the second refrigerant increases, the cooling capacity of the entire system tends to increase as the proportion of the first refrigerant increases, and the efficiency of the entire system tends to decrease as the proportion of the first refrigerant increases and decrease as the proportion of the second refrigerant increases.

[0042] In one example, when the vehicle 200 is traveling, the control device 80 controls the expansion valves E2 and E3 to make the ratio of the first to the second refrigerant relatively small so as to suppress the cooling capacity and ensure efficiency in order to extend the cruising distance. In another example, when the battery 6 is being externally charged, the control device 80 controls the expansion valves E2 and E3 to make the cooling capacity large so as to complete charging in a short time, and to set the ratio of the first to the second refrigerant to a medium value so as to keep the compressor discharge temperature at or below a predetermined temperature (for example, 180°C) and to make the efficiency at or above a predetermined value (for example, 1 or above).

[0043] Next, specific control that the control device 80 performs on the expansion valves E2 and E3 in this embodiment will be described.

[0044] (Control during steady-state driving or slow charging) First, with reference to Figures 5(a) and (b), the control performed during steady-state driving or slow charging in this embodiment will be described. Figure 5(a) shows the control of the E2 opening (vertical axis) performed in response to the battery temperature (horizontal axis), and Figure 5(b) shows the control of the E3 opening (vertical axis) performed in response to the E2 opening (horizontal axis). Figures 5(a) and (b) correspond to control maps for the E2 opening and E3 opening applied during steady-state driving or slow charging.

[0045] In this embodiment, the control device 80 performs control as shown in FIGS. 5(a) and 5(b) when the vehicle 200 is running at a steady state or when the battery 6 is being slowly charged (which means external charging; the same applies below). For example, steady state running refers to when the acceleration / deceleration (absolute value) of the vehicle 200 is less than a predetermined value, and slow charging refers to when the battery 6 is being charged at a C rate (1C, in one example) that is less than a predetermined value. During such steady state running or slow charging, the battery 6 generates heat gradually (about 0.4 kW). The C rate refers to the charging rate of the battery 6, and is basically defined as the ratio of the charging current value to the battery capacity.

[0046] Specifically, during steady-state driving or slow charging, as shown in FIG. 5(a), when the battery temperature is within a first region R1 on the low-temperature side, the control device 80 maintains the E2 opening at 0 (fully closed). This allows the overall system efficiency to be ensured by suppressing the proportion of the first refrigerant when the battery temperature is relatively low. The first region R1 corresponds to a battery temperature range in which the battery 6 (cell 62) can be sufficiently cooled by the first battery heat exchanger 6a, which indirectly cools the cell 62, without using the second battery heat exchanger 6b, which directly cools the cell 62. When the control device 80 sets the E2 opening to 0 (fully closed), it also sets the E3 opening to 0 (fully closed) (FIG. 5(b)). This also suppresses the proportion of the second refrigerant, effectively ensuring the overall system efficiency.

[0047] On the other hand, as shown in FIG. 5(a), when the battery temperature is within a second region R2, which is higher than the first region R1, the control device 80 linearly increases the E2 opening as the battery temperature increases. This increases the proportion of the first refrigerant, ensuring the refrigerant's ability to cool the battery 6. More specifically, when increasing the E2 opening in response to the battery temperature, the control device 80 restricts the E2 opening to a predetermined limit Lim1 or less to keep the compressor discharge temperature below a predetermined temperature (e.g., 180°C). In other words, the E2 opening is increased within a range below the limit Lim1. The predetermined compressor discharge temperature is set based on a temperature above which the oil in the refrigerant will no longer function, causing seizure of the sliding surfaces, deterioration of sealing, or oil degradation. The limit Lim1 is set in advance based on this predetermined temperature.

[0048] Furthermore, when the control device 80 controls the E2 opening as described above during steady-state driving or low-speed charging, the control device 80 linearly increases the E3 opening as the E2 opening increases, as shown in Fig. 5(b). This increases the second refrigerant proportion in accordance with an increase in the first refrigerant proportion, thereby suppressing an increase in the compressor discharge temperature.

[0049] The reason why increasing the proportion of the second refrigerant (i.e., increasing the amount of refrigerant supplied to compressor 1 via refrigerant passages 18 and 19) as described above can suppress an increase in the compressor discharge temperature is as follows. In this embodiment, compressor 1 is configured to pressurize the refrigerant in two stages using first and second compressors 1a and 1b. Refrigerant decompressed by expansion valve E2 is supplied to upstream first compressor 1a, while refrigerant discharged from first compressor 1a is mixed with refrigerant in a relatively low enthalpy state decompressed by expansion valve E3 (i.e., refrigerant with an enthalpy lower than that of the refrigerant pressurized by first compressor 1a) and supplied to downstream second compressor 1b. This prevents the refrigerant pressurized by second compressor 1b from becoming too hot, thereby suppressing an increase in the compressor discharge temperature.

[0050] (Control during fast charging) Next, the control performed during rapid charging in this embodiment will be described with reference to Figures 6(a) and 6(b). Figure 6(a) shows the control of E2 opening (vertical axis) performed in response to battery temperature (horizontal axis), and Figure 6(b) shows the control of E3 opening (vertical axis) performed in response to E2 opening (horizontal axis). Figures 6(a) and 6(b) correspond to control maps of E2 opening and E3 opening applied during rapid charging.

[0051] In this embodiment, the control device 80 performs control as shown in Figures 6(a) and 6(b) during rapid charging of the battery 6. For example, rapid charging refers to charging the battery 6 at a C rate equal to or higher than a predetermined rate (for example, 2C, 3C, or 4C). During such rapid charging, the amount of heat generated inside the cells 62 in the battery 6 is greater than the amount of heat dissipated from the end faces of the cells 62. Therefore, during rapid charging, there is a greater need to directly cool the cells 62 in order to suppress local temperature increases in the battery 6 than during slow charging.

[0052] Specifically, in Fig. 6(a), reference numeral G1 indicates the graph (similar to Fig. 5(a)) used during the above-described steady running or low-speed charging, and reference numerals G2 and G3 indicate the graphs used during rapid charging. Specifically, graph G3 is the graph used when charging at a C-rate larger than that of graph G2. For example, graph G2 is used when the C-rate during charging is 3C, and graph G3 is used when the C-rate during charging is 4C.

[0053] As shown in graphs G2 and G3, when the battery temperature is within the first region R1 on the low-temperature side during rapid charging, the control device 80 maintains the opening degree of E2 at 0 (fully closed). When the battery temperature is within the second region R2 on the higher-temperature side than the first region R1, the control device 80 linearly increases the opening degree of E2 as the battery temperature rises. When the battery temperature is within the third region R3 on the even higher-temperature side than the second region R2, the control device 80 maintains the opening degree of E2 at the limit opening degree Lim1. In particular, as the C-rate during charging increases, the control device 80 reduces the first region R1 (R13 < R12 < R11), expands the third region R3 (R33 > R32), and further increases the change rate (increase rate) of the opening degree of E2 with respect to the battery temperature in the second region R2. Thereby, when the C-rate when charging the battery 6 is large, the first refrigerant ratio can be increased to improve the cooling capacity of the battery 6 by the refrigerant. Specifically, the cells 62 of the battery 6 can be effectively cooled.

[0054] Furthermore, when the control device 80 controls the opening degree of E2 as described above during rapid charging, as shown in Fig. 6(b), the opening degree of E3 is also linearly increased as the opening degree of E2 increases. Thereby, by increasing the second refrigerant ratio in response to the increase in the first refrigerant ratio, the rise in the compressor discharge temperature can be suppressed. The reason why the rise in the compressor discharge temperature can be suppressed in this way is as described above.

[0055] (Control during abnormal heat generation of the battery) Next, with reference to Figures 7(a) and (b), a description will be given of the control performed in this embodiment when the battery 6 abnormally heats up. Figure 7(a) shows the control of the E2 opening (vertical axis) performed in response to the battery temperature (horizontal axis), and Figure 7(b) shows the control of the E3 opening (vertical axis) performed in response to the E2 opening (horizontal axis).

[0056] In this embodiment, the control device 80 performs control as shown in Figures 7(a) and (b) when the battery 6 generates abnormal heat. Abnormal heat generation in the battery 6 refers to heat generation caused by thermal runaway due to an internal short circuit or the like in the battery 6 (this thermal runaway is caused by various reactions and thermal decomposition within the battery 6). In this case, the control device 80 determines the occurrence of such abnormal heat generation by detecting an internal short circuit in the battery 6 from the current value or voltage value of the battery 6 or by detecting gas generated within the battery 6. Alternatively, the control device 80 may determine the occurrence of abnormal heat generation from changes in the battery temperature over time.

[0057] Specifically, as shown in Fig. 7(a), when the battery 6 is not abnormally heated, as described above (see Fig. 5(a)), the control device 80 maintains the E2 opening at 0 (fully closed) when the battery temperature is within the first region R1 on the low-temperature side, and linearly increases the E2 opening as the battery temperature rises when the battery temperature is within the second region R2 on the higher side than the first region R1. However, when the battery 6 is abnormally heated (arrow A1), for example, when the control device 80 detects an internal short circuit in the battery 6, the control device 80 first quickly (in a stepwise manner) increases the E2 opening to the limit opening (first opening) Lim1, as shown by arrow A2. This quickly increases the cooling capacity of the refrigerant for the battery 6, thereby suppressing abnormal heat generation in the battery 6.

[0058] If the battery temperature continues to rise even after the E2 opening is set to the limit opening Lim1 as described above, the control device 80 quickly (in a stepwise manner) increases the E2 opening to a limit opening (second opening) Lim2 that is even greater than the limit opening Lim1, as indicated by arrow A3. The limit opening Lim2 is a large E2 opening that may cause the compressor discharge temperature to exceed the predetermined temperature (i.e., may cause oil performance degradation or oil deterioration). Therefore, by setting the E2 opening to this limit opening Lim2, the compressor discharge temperature is allowed to exceed the predetermined temperature, maximizing the cooling capacity of the refrigerant for the battery 6, thereby making it possible to prioritize cooling of the battery 6. This suppresses abnormal heat generation in the battery 6 and avoids the worst-case scenario of the battery catching fire.

[0059] On the other hand, when the control device 80 controls the E2 opening as described above when the battery 6 is abnormally heated, the control device 80 controls the E3 opening according to the E2 opening, as shown in FIG. 7(b). First, when the E2 opening is less than the limit Lim1 (when the battery 6 is not abnormally heated), the control device 80 linearly increases the E3 opening as the E2 opening increases, as in FIGS. 5(b) and 6(b). Then, when the E2 opening is equal to or greater than the limit Lim1, that is, when the battery 6 is abnormally heated and the E2 opening is increased above the limit Lim1 to deal with this (FIG. 7(a)), the control device 80 linearly decreases the E3 opening as the E2 opening increases. This allows the compressor discharge temperature to rise, and allows the cooling of the battery 6 to be given top priority.

[0060] [Action and effect] Next, the operation and effect of the cooling system 100 according to this embodiment will be described. In this embodiment, the cooling system circulates a refrigerant containing CO2 (CO2 refrigerant) to cool the interior of the vehicle 200, and includes a compressor 1 that compresses the refrigerant, a cascade heat exchanger 2 that cools the refrigerant compressed by the compressor 1, an air conditioning heat exchanger 5a and a first battery heat exchanger 6a that use the refrigerant cooled by the cascade heat exchanger 2, and supplies the refrigerant to the battery 6 in order to cool the battery 6 in the vehicle 200 with the refrigerant cooled by the cascade heat exchanger 2, and supplies the refrigerant after being used for cooling in the battery 6 to the compressor 1. the battery 6 is not generating abnormal heat, the control device 80 is configured to increase the opening of the expansion valve E2 as the battery temperature increases within a range equal to or less than the limit opening Lim1, and when the battery 6 is generating abnormal heat, the control device 80 is configured to set the opening of the expansion valve E2 to the limit opening Lim2 which is greater than the limit opening Lim1.

[0061] According to this embodiment, both the air conditioning of the vehicle 200 and the cooling of the battery 6 can be appropriately achieved using the refrigerant circulated through the cooling system 100. Furthermore, according to this embodiment, when the battery 6 is not generating abnormal heat, the opening of the expansion valve E2 is increased within a range equal to or less than the limit opening Lim1 as the battery temperature increases, thereby ensuring the cooling capacity of the battery 6 by the refrigerant while suppressing a decrease in the efficiency of the entire system. On the other hand, according to this embodiment, when the battery 6 is generating abnormal heat, the opening of the expansion valve E2 is set to the limit opening Lim2, which is greater than the limit opening Lim1, thereby maximizing the cooling capacity of the battery 6 by the refrigerant and making the cooling of the battery 6 a top priority. As a result, abnormal heat generation in the battery 6 can be suppressed, and the worst-case scenario of the battery catching fire can be avoided.

[0062] Furthermore, according to this embodiment, the control device 80 is configured to first set the opening of the expansion valve E2 to the limit opening Lim1 when abnormal heat generation occurs in the battery 6, and then, if the battery temperature continues to rise, set the opening of the expansion valve E2 to the limit opening Lim2. This controls the opening of the expansion valve E2 in stages from the limit opening Lim1 to the limit opening Lim2, thereby increasing the cooling capacity of the battery 6 by the refrigerant while minimizing the rise in the compressor discharge temperature.

[0063] According to this embodiment, the cooling system 100 further includes refrigerant passages 18 and 19 for supplying the refrigerant used for cooling in the air-conditioning heat exchanger 5a and the first battery heat exchanger 6a to the compressor 1 without passing through the refrigerant passage 17, and an expansion valve E3 provided in the refrigerant passage 18 for expanding the refrigerant. The control device 80 is configured to increase the opening of the expansion valve E3 as the opening of the expansion valve E2 increases when the battery 6 is not overheating, and to decrease the opening of the expansion valve E3 as the opening of the expansion valve E2 increases when the battery 6 is overheating. As a result, when the battery 6 is not overheating, the flow rate of the refrigerant supplied to the compressor 1 from the refrigerant passages 18 and 19 via the expansion valve E3 increases in response to an increase in the flow rate of the refrigerant supplied to the compressor 1 from the refrigerant passage 17 via the expansion valve E2, thereby suppressing an increase in the compressor discharge temperature. As a result, functional degradation and deterioration of the oil in the refrigerant can be suppressed. On the other hand, when abnormal heat generation occurs in the battery 6, the flow rate of the refrigerant supplied to the compressor 1 from the refrigerant passages 18 and 19 via the expansion valve E3 is reduced, allowing the compressor discharge temperature to rise and giving top priority to cooling the battery 6.

[0064] Furthermore, according to this embodiment, the limit opening Lim1 is set based on the opening of the expansion valve E2 for keeping the compressor discharge temperature at or below a predetermined temperature. As a result, when abnormal heat generation is not occurring in the battery 6, the opening of the expansion valve E2 is restricted to be equal to or less than the limit opening Lim1, thereby making it possible to keep the compressor discharge temperature at or below the predetermined temperature. As a result, functional deterioration and degradation of the oil in the refrigerant can be effectively suppressed.

[0065] Furthermore, according to this embodiment, the control device 80 is configured to determine whether or not abnormal heat generation has occurred in the battery 6 by detecting an internal short circuit in the battery 6. This allows accurate determination of whether or not abnormal heat generation has occurred in the battery 6.

[0066] According to this embodiment, the cooling system 100 further includes a second battery heat exchanger 6b for circulating the refrigerant in the refrigerant passage 17 around the plurality of cells 62 in the battery 6 to directly cool the plurality of cells 62 with the refrigerant. The second battery heat exchanger 6b is supplied with refrigerant decompressed by an expansion valve E2. According to this embodiment, the plurality of cells 62 of the battery 6 are directly cooled with the refrigerant in the second battery heat exchanger 6b, so the plurality of cells 62 can be effectively cooled. In this case, since the pressure resistance of the battery pack 61 and the like is relatively low, it is undesirable to directly supply the high-pressure refrigerant from the compressor 1 to the second battery heat exchanger 6b. Therefore, in this embodiment, the refrigerant from the compressor 1 is decompressed by the expansion valve E2 and supplied to the second battery heat exchanger 6b. This allows the interior of the battery 6 (the plurality of cells 62, etc.) to be adequately protected.

[0067] Furthermore, according to this embodiment, the heat exchangers using the refrigerant cooled by the cascade heat exchanger 2 include an air conditioning heat exchanger 5a for air conditioning the vehicle 200 and a first battery heat exchanger 6a that supplies refrigerant to the outside of a battery pack 61 including a plurality of cells 62 in the battery 6 to indirectly cool the plurality of cells 62 with the refrigerant. Thus, by using the first battery heat exchanger 6a that supplies refrigerant to the outside of the battery pack 61 to indirectly cool the plurality of cells 62, the battery 6 can be appropriately cooled and a relatively large amount of heat exchange can be achieved between the battery 6 and the refrigerant.

[0068] Furthermore, according to this embodiment, the cascade heat exchanger 2 is configured to exchange heat between a first heat cycle circuit 100a including at least the compressor 1, the air conditioning heat exchanger 5a, and the first battery heat exchanger 6a, and a second heat cycle circuit 100b including an outside air heat exchanger 30 that exchanges heat with outside air, separate from the first heat cycle circuit 100a. This allows the first heat cycle circuit 100a to exchange heat (cascade heat exchange) with the second heat cycle circuit 100b that exchanges heat with outside air, thereby improving the efficiency of the entire system of the first heat cycle circuit 100a, or in other words, reducing the work of the compressor 1.

[0069] Furthermore, according to this embodiment, the cooling system 100 further cools the motor 4, which drives the vehicle 200 using power from the battery 6, with the refrigerant cooled by the cascade heat exchanger 2. This makes it possible to appropriately cool various components in the vehicle 200, such as the motor 4, using the refrigerant circulated in the cooling system 100.

[0070] [Variations] In the above-described embodiment, the cooling system 100 is configured with the first heat cycle circuit 100a and the second heat cycle circuit 100b. However, in other examples, the cooling system 100 may be configured with only the first heat cycle circuit 100a. In this case, the cascade heat exchanger 2 may be configured as an outside air heat exchanger. Note that, when the cooling system 100 is configured with the first heat cycle circuit 100a and the second heat cycle circuit 100b, the system efficiency is increased (i.e., the work of the compressor 1 can be reduced), but the configuration becomes more complex. Therefore, when prioritizing a simple configuration over system efficiency, it is preferable to configure the cooling system 100 with only the first heat cycle circuit 100a.

[0071] Furthermore, in the above-described embodiment, the temperature of the battery 6 is detected by the battery temperature sensor 72, but in other examples, the temperature of the battery 6 may be estimated based on the current value, voltage value, output requirement of the battery 6, or charging speed requirement of the battery 6. In still another example, the temperature of the battery 6 may be estimated based on the temperature of the refrigerant detected by a refrigerant temperature sensor 44 provided in the refrigerant passage 17 downstream of the second battery heat exchanger 6b. [Explanation of symbols]

[0072] 1 Compressor 1a First compressor 1b Second compressor 2 Heat exchanger (cascade heat exchanger) 4 motors 5. Air Conditioning 5a air conditioning heat exchanger 6 Battery 6a First battery heat exchanger 6b Second battery heat exchanger 11~20 Refrigerant passage 41, 42, 43, 44 Refrigerant temperature sensors 51, 52, 53 Refrigerant pressure sensors 61 Battery pack 62 cells 80 Control device 100 Cooling System 100a First thermal cycle circuit 100b Second thermal cycle circuit 200 vehicles E1, E2, E3 expansion valves V1, V2, V3 flow adjustment valve

Claims

1. CO 2 A cooling system for cooling a vehicle interior by circulating a refrigerant containing a compressor that compresses the refrigerant; a first heat exchanger for cooling the refrigerant compressed by the compressor; a second heat exchanger for at least air-conditioning the vehicle using the refrigerant cooled by the first heat exchanger; a refrigerant passage for supplying the refrigerant cooled by the first heat exchanger to the battery in order to cool the battery in the vehicle using the refrigerant, and for supplying the refrigerant after being used for cooling in the battery to the compressor; an expansion valve provided in the refrigerant passage upstream of the battery for expanding the refrigerant; a control device configured to acquire a temperature of the battery and control the expansion valve based on the temperature of the battery; and The control device When abnormal heat generation does not occur in the battery, the opening degree of the expansion valve is increased within a range equal to or less than a predetermined first opening degree as the temperature of the battery increases; When abnormal heat generation occurs in the battery, the opening degree of the expansion valve is set to a second opening degree that is larger than the first opening degree. The cooling system is characterized by being configured as follows.

2. 2. The cooling system according to claim 1, wherein the control device is configured to first set the opening degree of the expansion valve to the first opening degree when abnormal heat generation occurs in the battery, and then, if the temperature of the battery continues to rise, set the opening degree of the expansion valve to the second opening degree.

3. Assuming that the refrigerant passage is a first refrigerant passage and the expansion valve is a first expansion valve, the cooling system further includes a second refrigerant passage for supplying the refrigerant after being used for cooling in the second heat exchanger to the compressor without passing through the first refrigerant passage, and a second expansion valve provided on the second refrigerant passage for expanding the refrigerant, The control device is configured to increase the opening degree of the second expansion valve as the opening degree of the first expansion valve increases when abnormal heat generation is not occurring in the battery, and to decrease the opening degree of the second expansion valve as the opening degree of the first expansion valve increases when abnormal heat generation is occurring in the battery.

3. The cooling system according to claim 1 or 2.

4. The cooling system according to claim 1 or 2, wherein the first opening degree is set based on an opening degree of the expansion valve for keeping the temperature of the refrigerant discharged from the compressor equal to or lower than a predetermined temperature.

5. 3. The cooling system according to claim 1, wherein the control device is configured to determine whether or not abnormal heat generation is occurring in the battery by detecting an internal short circuit in the battery.

6. the cooling system further includes a battery heat exchanger for causing the refrigerant in the refrigerant passage to flow around a plurality of cells in the battery to directly cool the plurality of cells with the refrigerant; The refrigerant decompressed by the expansion valve is supplied to the battery heat exchanger.

3. The cooling system according to claim 1 or 2.

7. 3. The cooling system according to claim 1, wherein the second heat exchanger includes an air conditioning heat exchanger for air conditioning the vehicle, and further includes a battery heat exchanger for supplying the refrigerant to the outside of a battery pack including a plurality of cells in the battery, thereby indirectly cooling the plurality of cells with the refrigerant.

8. 3. The cooling system according to claim 1, wherein the first heat exchanger is configured as a cascade heat exchanger that exchanges heat between a first heat cycle circuit including at least the compressor, the second heat exchanger, the refrigerant passage, and the expansion valve, and a second heat cycle circuit that is separate from the first heat cycle circuit and includes an outside air heat exchanger that exchanges heat with outside air.

9. 3. The cooling system according to claim 1, wherein the cooling system is configured to further cool a motor that drives the vehicle using power from the battery with the refrigerant cooled by the first heat exchanger.

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