Cooling system

Abstract

To provide a cooling system for circulating a refrigerant containing CO2 to cool a battery or the like in the vehicle, in which the temperature of the refrigerant is prevented from becoming high due to the pressure rise of a compressor.SOLUTION: A cooling system 100 includes a compressor 1 for compressing a refrigerant in two stages by first and second compressors 1a, 1b, heat exchangers 2 for cooling the refrigerant from the compressor 1, and heat exchangers 5a, 6a using the refrigerant from the heat exchangers 2. The cooling system includes the refrigerant line 17 that supplies the refrigerant to the first compressor 1a, the refrigerant lines 18 and 19 that supply the refrigerant from the heat exchangers 5a and 6a to the second compressor 1b, the expansion valve E2 provided in the refrigerant line 17, and the expansion valve E3 provided in the refrigerant line 18, and the controller 80 performs control to increase the opening degree of the expansion valve 1b when the temperature of the refrigerant discharged from the second compressor E3 is equal to or higher than a predetermined temperature.SELECTED DRAWING: Figure 2

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] When a CO2 refrigerant is used to cool a battery, it is typically considered that the CO2 refrigerant is pressurized by a compressor, then significantly reduced in pressure by an expansion valve before being supplied to the battery. This is because it may not be desirable to supply high-pressure CO2 refrigerant directly to the battery. For example, it is not desirable to supply high-pressure CO2 refrigerant to multiple cells in a battery.

[0006] As described above, after the CO2 refrigerant is used to cool the battery after being significantly decompressed by the expansion valve, it is returned to the compressor. In this case, the compressor significantly increases the pressure of the CO2 refrigerant, which is already at a fairly low pressure. As a result, the CO2 refrigerant discharged from the compressor becomes very hot. This causes the oil in the CO2 refrigerant to malfunction, leading to seizure of the sliding surfaces, a decrease in sealing performance, and oil deterioration.

[0007] The present invention has been made to solve the problems of the conventional technology described above, and aims to prevent the refrigerant from becoming too hot due to a compressor pressure increase in a cooling system that circulates a refrigerant containing CO2 to cool a battery or other components inside a vehicle. [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 system including a first compressor and a second compressor provided downstream of the first compressor, the compressor being configured to compress the refrigerant in two stages by the first and second compressors, a first heat exchanger for cooling the refrigerant compressed by the compressor, a second heat exchanger for cooling a predetermined cooling target within the vehicle with the refrigerant cooled by the first heat exchanger, and a cooling medium for supplying the refrigerant to the battery and using the refrigerant cooled by the first heat exchanger to cool the battery within the vehicle. the compressor includes a first refrigerant passage for supplying the refrigerant after being used for cooling in the second heat exchanger to the first compressor of the compressor, a second refrigerant passage for supplying the refrigerant after being used for cooling in the second heat exchanger to the second compressor of the compressor, a first expansion valve provided on the first refrigerant passage for expanding the refrigerant, a second expansion valve provided on the second refrigerant passage for expanding the refrigerant, and a control device configured to control at least the first expansion valve and the second expansion valve, wherein the control device is configured to obtain the temperature of the refrigerant discharged from the second compressor of the compressor, and if the temperature is equal to or higher than a predetermined temperature, to control the second expansion valve to increase the opening degree.

[0009] According to the present invention, the compressor is configured to pressurize the refrigerant in two stages using the first and second compressors. The upstream first compressor is supplied with refrigerant decompressed by the first expansion valve, while the downstream second compressor is supplied with a mixture of refrigerant discharged from the first compressor and refrigerant in a relatively low enthalpy state decompressed by the second expansion valve (i.e., refrigerant with a lower enthalpy than the refrigerant pressurized by the first compressor). This prevents the refrigerant from becoming too hot after being pressurized by the second compressor. In particular, the present invention controls the opening of the second expansion valve to increase when the temperature of the refrigerant discharged from the second compressor is equal to or higher than a predetermined temperature (i.e., the opening of the second expansion valve is not increased when the refrigerant temperature is below the predetermined temperature), thereby increasing the amount of refrigerant supplied to the second compressor from the second refrigerant passage. This allows the temperature of the refrigerant discharged from the second compressor to be kept below the predetermined temperature while minimizing a decrease in efficiency of the cooling system. As a result, the function of the oil in the refrigerant can be maintained and deterioration of the oil can be suppressed.

[0010] In the present invention, the control device is preferably configured to control the opening of the first expansion valve to be smaller when the temperature of the refrigerant discharged from the second compressor is higher than a predetermined temperature and the second expansion valve is fully open. According to the present invention configured as described above, by throttling the first expansion valve in the first refrigerant passage, the amount of refrigerant flowing through the second refrigerant passage can be increased, and the amount of refrigerant supplied from the second refrigerant passage to the second compressor can be secured. Therefore, according to the present invention, even if the second expansion valve is fully open, the temperature of the refrigerant discharged from the second compressor can be appropriately reduced.

[0011] In the present invention, preferably, the cooling system further includes a battery heat exchanger for causing the refrigerant in the first 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 the first expansion valve and then supplied to the battery heat exchanger. This allows the interior of the battery (including the multiple cells) to be adequately protected.

[0012] In the present invention, the second heat exchanger preferably includes an air conditioning heat exchanger for air conditioning the vehicle, and / or 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 as described above, a single system (cooling system) that circulates a refrigerant can adequately achieve vehicle air conditioning and battery cooling. In particular, by using a battery heat exchanger that supplies refrigerant to the outside of the battery pack, the battery can be adequately cooled and a relatively large amount of heat can be exchanged between the battery and the refrigerant.

[0013] 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, first and second refrigerant passages, and first and second expansion valves, 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.

[0014] 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.

[0015] In the present invention, preferably, the second refrigerant passage is further supplied with the refrigerant that has been used for cooling the motor. According to the present invention configured as described above, refrigerant in a relatively low enthalpy state from the motor can be supplied to the second compressor. In this case, the enthalpy of the refrigerant supplied from the second refrigerant passage to the second compressor changes depending on the cooling demands of the motor, but as described above, the present invention monitors the temperature of the refrigerant discharged from the second compressor and controls the opening of the second expansion valve in accordance with this temperature, thereby suppressing the effects of changes in the enthalpy of the refrigerant due to the cooling demands of the motor, etc. [Effects of the Invention]

[0016] According to the present invention, in a cooling system that circulates a refrigerant containing CO2 to cool a battery or the like in a vehicle, it is possible to prevent the refrigerant from becoming too hot due to pressure increase in a compressor. [Brief explanation of the drawings]

[0017] [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] FIG. 1 is an explanatory diagram illustrating a basic concept of control according to an embodiment of the present invention. [Figure 6] 4 is a flowchart illustrating a control according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a cooling system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0019] [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.

[0020] 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.

[0021] The cooling system 100 circulates a CO2 refrigerant (hereinafter sometimes simply referred to as "refrigerant") as a natural refrigerant. Typically, the CO2 refrigerant contains refrigeration oil (oil) such as PAG and additives to lubricate and seal various devices within the cooling system 100. 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, high-temperature, high-pressure gas refrigerant is supplied from the compressor 1 to the heat exchanger 2, low-temperature, high-pressure liquid refrigerant is supplied from the heat exchanger 2 to the motor 4, and room-temperature, low-pressure gas refrigerant is supplied from the motor 4 to the compressor 1.

[0022] [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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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).

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The cooling system 100 also includes refrigerant temperature sensors 41, 42, 43, and 44 that detect the temperature of the refrigerant and refrigerant pressure sensors 51, 52, and 53 that detect the pressure of the refrigerant (see FIG. 2), a vehicle interior temperature sensor 71 that detects the temperature of the vehicle interior (cabin), a battery temperature sensor 72 that detects the temperature of the battery 6, and a motor temperature sensor 73 that detects the temperature of the motor 4. Specifically, as shown in FIG. 2, the refrigerant temperature sensor 41 is provided in the refrigerant passage 11 between the compressor 1 and the cascade heat exchanger 2 (more specifically, upstream of a junction C4 of the refrigerant passage 11 and the refrigerant passage 20), the refrigerant temperature sensor 42 is provided at a junction C2 of the refrigerant passage 14 and the refrigerant passage 16, the refrigerant temperature sensor 43 is provided at a junction C3 of the refrigerant passage 15 and the refrigerant passage 18, and the refrigerant temperature sensor 44 is provided in the refrigerant passage 17 downstream of the second battery heat exchanger 6b and the IHX 6c. In addition, the refrigerant pressure sensor 51 is provided on the refrigerant passage 11 downstream of the cascade heat exchanger 2, the refrigerant pressure sensor 52 is provided on the refrigerant passage 15 downstream of the motor 4, and the refrigerant pressure sensor 53 is provided on the refrigerant passage 17 downstream of the second battery heat exchanger 6b and the IHX 6c.

[0036] The control device 80 supplies control signals to the compressor 1, the flow rate adjustment valves V1, V2, V3, and the expansion valves E1, E2, E3 to control them based on the detection signals from the sensors 41 to 44, 51 to 53, 71 to 73. In particular, in this embodiment, the control device 80 controls the expansion valves E2 and E3 so as to prevent the refrigerant from becoming too hot due to the pressure increase of the compressor 1 (details will be described later).

[0037] [Control method] Next, the control performed by the control device 80 in this embodiment will be described. First, the basic concept of control according to this embodiment will be described with reference to FIG. 5. In FIG. 5, the horizontal axis represents the specific enthalpy (enthalpy per unit mass) of the CO2 refrigerant, and the vertical axis represents the pressure of the CO2 refrigerant. Specifically, FIG. 5 shows a portion of a Mollier diagram (ph diagram) realized by the first heat cycle circuit 100a of the cooling system 100. Note that the specific enthalpy illustrated in FIG. 5 is defined based on the liquid side of the saturated vapor pressure line at 0°C (200 kJ / kg).

[0038] As described above, in this embodiment, in the second battery heat exchanger 6b, the refrigerant flows around the multiple cells 62 in the battery pack 61 to directly cool the multiple cells 62 (FIG. 3(b)). However, in this case, because the pressure resistance of the battery pack 61 is relatively low, it is not desirable to directly supply the refrigerant compressed by the compressor 1 to the second battery heat exchanger 6b. Therefore, in this embodiment, the refrigerant compressed by the compressor 1 is significantly reduced in pressure (from pressure P1 to pressure P3) by the expansion valve E2 provided upstream of the second battery heat exchanger 6b in the refrigerant passage 17, and then supplied to the second battery heat exchanger 6b.

[0039] The refrigerant supplied to the second battery heat exchanger 6b as described above is then returned to the compressor 1 and pressurized. At this time, the refrigerant changes from the state indicated by point X1 to the state indicated by point X2 (arrow A1), as shown in FIG. 5. Here, we consider an example in which the compressor 1 pressurizes the refrigerant in a single stage. In this case, the compressor 1 significantly pressurizes a fairly low-pressure refrigerant in a single stage (pressure P3 → pressure P1). For example, if pressure P1 is about 3 MPa and pressure P3 is about 0.1 MPa, a 30-fold pressure difference occurs between the upstream and downstream of the compressor 1. As a result, the refrigerant discharged from the compressor 1 reaches a high temperature (e.g., 280°C or higher). This causes the oil in the refrigerant to malfunction, resulting in seizure of the sliding surfaces, deterioration of sealing performance, and oil deterioration.

[0040] Therefore, in this embodiment, the compressor 1 is configured to increase the pressure of the refrigerant in two stages using the first and second compressors 1a and 1b, and low-pressure (pressure P3) refrigerant is supplied to the upstream first compressor 1a, while medium-pressure (pressure P2 > pressure P3) refrigerant in a relatively low enthalpy state is supplied to the downstream second compressor 1b, thereby lowering the temperature of the refrigerant discharged from the compressor 1 (second compressor 1b).

[0041] The control according to this embodiment will be described in more detail with reference to Fig. 5. First, in the first heat cycle circuit 100a of the cooling system 100, the refrigerant supplied from refrigerant passage 11 to refrigerant passage 18 via refrigerant passages 12, 13, and 14 and refrigerant passage 16 is in the state indicated by point X3. The refrigerant changes as indicated by arrow A3 due to the pressure reduction (from pressure P1 to pressure P2) of expansion valve E3 in refrigerant passage 18. The refrigerant supplied from refrigerant passage 11 to refrigerant passage 15 changes from the state indicated by point X4 to the states indicated by arrows A41 and A42 due to the pressure reduction (from pressure P1 to pressure P2) of expansion valve E3 in refrigerant passage 15 and heat exchange in motor 4. The refrigerant flowing through refrigerant passages 18 and 15 merge at confluence C3 and flows into refrigerant passage 19 (in this case, the state indicated by point X5) and is supplied from refrigerant passage 19 to the second compressor 1b. On the other hand, in the refrigerant passage 17 in which the second battery heat exchanger 6b is provided, the refrigerant reaches the state shown at point X1 due to the pressure reduction (pressure P1 → pressure P3) of the expansion valve E2 and the heat exchange in the second battery heat exchanger 6b, as described above. After this, the refrigerant changes from the state shown at point X1 to the state shown at point X6, as indicated by arrow A6, due to the pressure increase by the first compressor 1a.

[0042] The refrigerant pressurized by first compressor 1a, i.e., the refrigerant discharged from first compressor 1a, merges with the refrigerant supplied from refrigerant passage 19 to second compressor 1b as described above, between first compressor 1a and second compressor 1b. At this time, the refrigerant from first compressor 1a in the state indicated by point X6 changes as indicated by arrow A71, and the refrigerant from refrigerant passage 19 in the state indicated by point X5 changes as indicated by arrow A72, resulting in the refrigerant after the merger becoming the state indicated by point X7. In this case, the refrigerant (point X6) that has become a relatively high-enthalpy state due to the pressurization by first compressor 1a is mixed with the refrigerant (point X5) in a relatively low-enthalpy state from refrigerant passage 19, and the refrigerant (point X7) with a lowered specific enthalpy is supplied to second compressor 1b. The refrigerant supplied to the second compressor 1b, which is in the state indicated by point X7, changes to the state indicated by point X8, as indicated by arrow A8, as a result of being pressurized by the second compressor 1b. In this state indicated by point X8, the specific enthalpy of the refrigerant is significantly lower than the state indicated by point X2 when the refrigerant is pressurized in a single stage as described above (arrow A1), i.e., the temperature of the refrigerant is significantly lower. Therefore, according to this embodiment, the temperature of the refrigerant discharged from the compressor 1 (second compressor 1b) can be lowered.

[0043] Here, if the amount of refrigerant decompressed in the expansion valve E3 in the refrigerant passage 19 is large, work is generated to compress the decompressed refrigerant, which increases the compressor work in the compressor 1, i.e., reduces the efficiency of the cooling system 100 (particularly the first heat cycle circuit 100a). Therefore, it is undesirable to supply an unnecessarily large amount of refrigerant from the refrigerant passage 19 to the second compressor 1b. On the other hand, the specific enthalpy state (point X5) at the junction C3 is affected by factors such as the cooling demand of the motor 4. This influence changes the specific enthalpy (point X7) of the refrigerant supplied from the refrigerant passage 19 to the second compressor 1b, and the specific enthalpy (point X8) of the refrigerant discharged from the second compressor 1b, i.e., the temperature of the refrigerant, fluctuates.

[0044] Therefore, in this embodiment, the control device 80 monitors the temperature of the refrigerant discharged from the second compressor 1b and controls the expansion valve E3 on the refrigerant passage 18 to adjust the amount of refrigerant supplied from the refrigerant passage 19 to the second compressor 1b. Specifically, in this embodiment, when the temperature of the refrigerant discharged from the second compressor 1b is equal to or higher than a predetermined temperature (e.g., 180°C), the control device 80 controls the expansion valve E3 to increase its opening (in other words, when the refrigerant temperature is below the predetermined temperature, the control device 80 does not increase the opening of the expansion valve E3), thereby keeping the refrigerant temperature below the predetermined temperature. This makes it possible to appropriately reduce the temperature of the refrigerant discharged from the second compressor 1b while suppressing a decrease in efficiency in the cooling system 100 (particularly the first heat cycle circuit 100a).

[0045] Furthermore, in this embodiment, when the temperature of the refrigerant discharged from the second compressor 1b is equal to or higher than a predetermined temperature and the expansion valve E3 is fully open, the control device 80 controls the expansion valve E2 in the refrigerant passage 17 to reduce the opening degree. This reduces the opening degree of the expansion valve E2 in the refrigerant passage 17, thereby increasing the amount of refrigerant flowing through the refrigerant passages 18 and 19 and ensuring the amount of refrigerant supplied from the refrigerant passage 19 to the second compressor 1b. Therefore, according to this embodiment, even when the expansion valve E3 is fully open, it is possible to appropriately reduce the temperature of the refrigerant discharged from the second compressor 1b.

[0046] Next, a flowchart showing specific control according to this embodiment will be described with reference to Fig. 6. This flow is repeatedly executed at a predetermined cycle by the control device 80. In detail, the processor 80a in the control device 80 reads a program stored in the memory 80b and executes the program, thereby realizing the control related to this flow.

[0047] First, in step S10, the control device 80 acquires various information such as the detection values ​​detected by the above-mentioned sensors 41 to 44, 51 to 53, 71 to 73 (FIG. 4).

[0048] Next, in step S11, the control device 80 determines the opening degree of the expansion valve E2 on the refrigerant passage 17 (hereinafter referred to as "E2 opening degree" as appropriate) in accordance with the cooling request of the battery 6. In this case, the control device 80 determines the E2 opening degree based on the current temperature of the battery 6 detected by the battery temperature sensor 72.

[0049] Next, in step S12, the control device 80 calculates the temperature (hereinafter referred to as the "estimated first temperature") downstream of the second battery heat exchanger 6b in the refrigerant passage 17 based on the E2 opening degree and other factors determined in step S11. For example, the control device 80 calculates the estimated first temperature using a map or an arithmetic expression that is defined in advance based on the E2 opening degree and other factors.

[0050] Next, in step S13, the control device 80 acquires the temperature of the refrigerant (hereinafter referred to as the "actual first temperature") detected by the refrigerant temperature sensor 44 provided on the refrigerant passage 17 downstream of the second battery heat exchanger 6b.

[0051] Next, in step S14, the control device 80 determines whether the difference between the estimated first temperature calculated in step S12 and the actual first temperature acquired in step S13 (hereinafter referred to as the "first temperature error") is equal to or greater than a predetermined value. As a result, if the control device 80 determines that the first temperature error is equal to or greater than the predetermined value (step S14: Yes), the control device 80 proceeds to step S15, corrects the E2 opening based on the first temperature error, and returns to step S11. In step S11, the control device 80 determines the E2 opening corrected in step S15 as the opening to be applied. On the other hand, if the control device 80 does not determine that the first temperature error is equal to or greater than the predetermined value (step S14: No), that is, if the first temperature error is less than the predetermined value, the control device 80 proceeds to step S16 without performing the processing of step S15 as described above.

[0052] Next, in step S16, the control device 80 determines the opening degree of the expansion valve E1 on the refrigerant passage 15 (hereinafter referred to as the "E1 opening degree") in accordance with the cooling requirement of the motor 4. In this case, the control device 80 determines the E1 opening degree based on the current temperature of the motor 4 detected by the motor temperature sensor 73.

[0053] Next, in step S17, the control device 80 determines the specific enthalpy of the refrigerant at the confluence C3 of the refrigerant passages 15 and 18 based on the E1 opening determined in step S16, etc. (hereinafter referred to as the "C3 estimated enthalpy" where appropriate. The C3 estimated enthalpy corresponds to the specific enthalpy at point X5 in FIG. 5.) For example, the control device 80 determines the C3 estimated enthalpy using a map or an arithmetic expression that is defined in advance based on the E1 opening, etc.

[0054] Next, in step S18, the control device 80 determines the opening degree of the expansion valve E3 on the refrigerant passage 18 (hereinafter referred to as "E3 opening degree" as appropriate) based on the actual first temperature acquired in step S13 and the C3 estimated enthalpy calculated in step S17. For example, the control device 80 calculates the flow rate from the refrigerant passage 18 required to set the temperature of the refrigerant discharged from the second compressor 1b to a value lower than a predetermined temperature based on the actual first temperature downstream of the second battery heat exchanger 6b and the C3 estimated enthalpy at the junction C3, and determines the E3 opening degree that achieves this flow rate.

[0055] Next, in step S19, the control device 80 calculates the temperature of the refrigerant discharged from the second compressor 1b (hereinafter referred to as the "estimated second temperature") based on the E3 opening etc. determined in step S18. For example, the control device 80 calculates the estimated second temperature using a map or an arithmetic expression that is defined in advance based on the E3 opening etc.

[0056] Next, in step S20, the control device 80 acquires the temperature of the refrigerant detected by the refrigerant temperature sensor 41 provided in the refrigerant passage 11 between the compressor 1 and the cascade heat exchanger 2 (hereinafter referred to as the "actual second temperature" as appropriate).

[0057] Next, in step S21, the control device 80 determines whether the difference between the estimated second temperature calculated in step S19 and the actual second temperature acquired in step S20 (hereinafter referred to as the "second temperature error") is equal to or greater than a predetermined value. As a result, if the control device 80 determines that the second temperature error is equal to or greater than the predetermined value (step S21: Yes), the control device 80 proceeds to step S22, corrects the E3 opening based on the second temperature error, and returns to step S18. In step S18, the control device 80 determines the E3 opening corrected in step S22 as the opening to be applied. On the other hand, if the control device 80 does not determine that the second temperature error is equal to or greater than the predetermined value (step S21: No), that is, if the second temperature error is less than the predetermined value, the control device 80 proceeds to step S23 without performing the processing of step S22 as described above.

[0058] Next, in step S23, the control device 80 determines whether the actual second temperature acquired in step S20 is equal to or higher than a predetermined temperature (e.g., 180°C). As a result, if the control device 80 determines that the actual second temperature is equal to or higher than the predetermined temperature (step S23: Yes), the control device 80 proceeds to step S24 and performs control to increase the E3 opening of the expansion valve E3 (expansion control) in order to increase the amount of refrigerant supplied from the refrigerant passages 18 and 19 to the second compressor 1b.

[0059] Then, the control device 80 proceeds to step S25 to determine whether the E3 opening is fully open, that is, whether the E3 opening is already fully open due to the expansion control of the expansion valve E3. As a result, if the control device 80 determines that the E3 opening is fully open (step S25: Yes), the control device 80 proceeds to step S26 to perform control to reduce the E2 opening of the expansion valve E2 (reduction control). In this case, by throttling the expansion valve E2 in the refrigerant passage 17, the amount of refrigerant flowing through the refrigerant passages 18 and 19 is increased, and the amount of refrigerant supplied from the refrigerant passage 19 to the second compressor 1b is ensured.

[0060] Thereafter, the control device 80 returns to step S23 and performs the processes from step S23 onwards again. Note that, before determining the actual second temperature in step S23, the control device 80 again acquires the temperature (actual second temperature) detected by the refrigerant temperature sensor 41 in the same manner as in step S20 (same below). Also, by repeating steps S23 to S26, if the E2 opening degree becomes fully closed due to the reduction control of the expansion valve E2 (step S26), the process shown in the flow of Fig. 6 may be ended.

[0061] On the other hand, if the control device 80 does not determine in step S23 that the actual second temperature is equal to or higher than the predetermined temperature (step S23: No), the actual second temperature is lower than the predetermined temperature, and therefore ends the processing shown in the flow of Fig. 6. Also, if the control device 80 does not determine in step S25 that the E3 opening is fully open (step S25: No), the process returns to step S23.

[0062] In the above-described flow, processing was performed using specific enthalpy, but instead of this specific enthalpy, processing of the above flow may also be performed using the degree of superheat defined from the specific enthalpy and the saturated vapor line.

[0063] [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 100, which cools the interior of the vehicle 200 by circulating a refrigerant containing CO2 (CO2 refrigerant), includes a first compressor 1a and a second compressor 1b provided downstream of the first compressor 1a, and is configured to compress the refrigerant in two stages by the first and second compressors 1a and 1b, a cascade heat exchanger 2 for cooling 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 a supply unit for supplying the refrigerant to the battery 6 to cool the battery 6 with the refrigerant cooled by the cascade heat exchanger 2. the refrigerant passage 17 for supplying the refrigerant to the first compressor 1a after being used for cooling in the battery 6, and for supplying the refrigerant to the first compressor 1a after being used for cooling in the air conditioning heat exchanger 5a and the first battery heat exchanger 6a, the refrigerant passages 18 and 19 for supplying the refrigerant to the second compressor 1b after being used for cooling in the air conditioning heat exchanger 5a and the first battery heat exchanger 6a, an expansion valve E2 provided in the refrigerant passage 17 for expanding the refrigerant, an expansion valve E3 provided in the refrigerant passage 18 for expanding the refrigerant, and a control device 80 configured to control at least the expansion valves E2 and E3, and the control device 80 controls to increase the opening of the expansion valve E3 when the temperature of the refrigerant discharged from the second compressor 1b is equal to or higher than a predetermined temperature.

[0064] According to this embodiment, the compressor 1 is configured to pressurize the refrigerant in two stages using the first and second compressors 1a and 1b. The upstream first compressor 1a is supplied with refrigerant decompressed by the expansion valve E2, while the downstream second compressor 1b is supplied with a mixture of the refrigerant discharged from the first compressor 1a and a relatively low-enthalpy refrigerant decompressed by the expansion valve E3 (i.e., a refrigerant with a lower enthalpy than the refrigerant pressurized by the first compressor 1a). This prevents the refrigerant pressurized by the second compressor 1b from becoming too high. In particular, this embodiment increases the aperture of the expansion valve E3 when the temperature of the refrigerant discharged from the second compressor 1b is equal to or higher than a predetermined temperature (in other words, does not increase the aperture of the expansion valve E3 when the refrigerant temperature is below the predetermined temperature), thereby increasing the amount of refrigerant supplied from the refrigerant passage 19 to the second compressor 1b. This makes it possible to appropriately lower the temperature of the refrigerant discharged from the second compressor 1b while suppressing a decrease in efficiency in the cooling system 100 (particularly the first heat cycle circuit 100a). As a result, the function of the oil in the refrigerant can be maintained and oil deterioration can be suppressed.

[0065] Furthermore, according to this embodiment, when the temperature of the refrigerant discharged from the second compressor 1b is equal to or higher than a predetermined temperature and the expansion valve E3 is fully open, the control device 80 controls the expansion valve E2 to reduce its opening. This reduces the opening of the expansion valve E2 in the refrigerant passage 17, thereby increasing the amount of refrigerant flowing through the refrigerant passages 18 and 19 and ensuring the amount of refrigerant supplied from the refrigerant passage 19 to the second compressor 1b. Therefore, according to this embodiment, even when the expansion valve E3 is fully open, it is possible to appropriately reduce the temperature of the refrigerant discharged from the second compressor 1b.

[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. 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 in the cooling system 100. In particular, 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, a relatively large amount of heat exchange can be achieved with 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] Furthermore, according to this embodiment, the refrigerant passage 19 is further supplied with refrigerant that has been used to cool the motor 4. This allows refrigerant in a relatively low enthalpy state from the motor 4 to be supplied to the second compressor 1b. In this case, the specific enthalpy of the refrigerant supplied from the refrigerant passage 19 to the second compressor 1b changes depending on the cooling request of the motor 4, but in this embodiment, as described above, the temperature of the refrigerant discharged from the second compressor 1b is monitored and the opening of the expansion valve E3 is controlled in accordance with this temperature, so that the effects of changes in the specific enthalpy of the refrigerant due to the cooling request of the motor 4, etc., can be suppressed.

[0071] [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.

[0072] 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]

[0073] 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 including a first compressor and a second compressor provided downstream of the first compressor, the compressor being configured to compress the refrigerant in two stages by the first and second compressors; a first heat exchanger for cooling the refrigerant compressed by the compressor; a second heat exchanger for cooling a predetermined cooling target within the vehicle by the refrigerant cooled by the first heat exchanger; a first refrigerant passage for supplying the refrigerant cooled by the first heat exchanger to the battery in order to cool the battery in the vehicle with the refrigerant, and for supplying the refrigerant after being used for cooling the battery to the first compressor of the compressor; a second refrigerant passage for supplying the refrigerant after being used for cooling in the second heat exchanger to the second compressor of the compressor; a first expansion valve provided in the first refrigerant passage for expanding the refrigerant; a second expansion valve provided in the second refrigerant passage for expanding the refrigerant; a control device configured to control at least the first expansion valve and the second expansion valve; and The control device is configured to acquire the temperature of the refrigerant discharged from the second compressor of the compressor, and, when the temperature is equal to or higher than a predetermined temperature, perform control to increase the opening degree of the second expansion valve. A cooling system characterized by:

2. 2. The cooling system of claim 1, wherein the control device is configured to control the opening of the first expansion valve to be smaller when the temperature of the refrigerant discharged from the second compressor is higher than the predetermined temperature and the second expansion valve is fully open.

3. the cooling system further includes a battery heat exchanger for causing the refrigerant in the first 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 first expansion valve is supplied to the battery heat exchanger.

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

4. 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 / or 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.

5. 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 first and second refrigerant passages, and the first and second expansion valves, 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.

6. 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.

7. The cooling system according to claim 6 , wherein the second refrigerant passage is further supplied with the refrigerant after being used for cooling the motor.

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