Refrigerant circulation system

Abstract

To provide a refrigerant circulation system which provides a motor with a gas-phase refrigerant whose degree of superheat is suppressed to a small value.SOLUTION: A refrigerant circulation system S for cooling a motor 20 in a vehicle by circulating a CO2 refrigerant R includes upstream side expansion valves 14a-14c for outputting an input refrigerant in a gas phase state having an input pressure PIN. The controller 40 is configured to estimate a corresponding pressure P C of the refrigerant R at a corresponding point H having the same specific enthalpy as that of the input refrigerant on a saturated vapor line L2 and at a lower pressure side than the maximum pressure PM (S10), set the corresponding pressure P C as a target output pressure P T, and control the downstream expansion valve 16 so that the output pressure POUT of the downstream expansion valve 16 becomes the target output pressure P T (S11 to S13).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a refrigerant circulation system, and more particularly to a refrigerant circulation system for cooling a motor of a vehicle. [Background technology]

[0002] Conventionally, a refrigerant circulation system using a refrigeration cycle has been used in a vehicle (see, for example, Patent Document 1). The refrigerant circulation system described in Patent Document 1 is used in an in-vehicle air conditioning device, and a condenser, an expansion valve, an evaporator, and a compressor are provided in this order in the circulation flow path.

[0003] In general, in a refrigerant circulation system, a gas-liquid mixed-phase refrigerant is fed to the evaporator, but to prevent the liquid refrigerant from returning to the compressor, it is necessary to supply the refrigerant in the form of vaporized superheated vapor. Therefore, the gas-liquid mixed-phase refrigerant becomes completely vapor-phase refrigerant in the evaporator.

[0004] In the system of Patent Document 1, the compressor is an electric compressor equipped with an inverter, an electric motor, and a compression section, and the refrigerant that flows from the evaporator into the electric compressor absorbs heat from the inverter and the electric motor before flowing into the compression section. Therefore, in the system of Patent Document 1, if the electric compressor consumes a lot of power, there is a risk that the refrigerant flowing into the compression section will become overheated.

[0005] For this reason, in the system of Patent Document 1, when power consumption is high, the refrigerant flow rate or valve opening is adjusted by the expansion valve, and the refrigerant is not completely gasified in the evaporator, but rather the refrigerant in a gas-liquid mixed phase state is supplied to the inverter and electric motor of the electric compressor, where it is completely gasified by the inverter and electric motor. This makes it possible to prevent the refrigerant flowing into the compression section from becoming overly superheated.

[0006] Thus, in the system of Patent Document 1, in addition to a normal evaporator, the inverter and the electric motor also become part of the evaporator, and a refrigerant in a gas-liquid mixed phase state can be supplied to these evaporators. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-186209 Summary of the Invention [Problem to be solved by the invention]

[0008] In response to this, the present inventors are attempting to develop a new refrigerant circulation system for vehicles such as electric vehicles that includes a relatively large motor used for driving the vehicle as an evaporator in addition to a normal evaporator (for example, a heat exchanger in an on-board air conditioning system).This new system is configured so that the refrigerant flows directly into the motor (i.e., the space between the rotor and stator).

[0009] In this case, if a liquid-phase refrigerant flows into the motor, the relatively high viscosity of the liquid refrigerant creates agitation resistance between the rotor and stator as the motor rotates. Because agitation resistance increases quadratically with rotation speed, it becomes particularly significant in ultra-high-speed motors. Therefore, the inventors discovered a technical problem: in a refrigerant circulation system that directly cools the motor's interior with a refrigerant, a completely vaporized refrigerant, or a gas-liquid mixture with a small liquid fraction and primarily vapor refrigerant, must be introduced into the motor.

[0010] The inventors also discovered a technical problem: to ensure that the refrigerant gasified by the increase in specific enthalpy still has sufficient cooling capacity, it is necessary to maintain the degree of superheat of the gasified refrigerant at a small value. Note that superheating refers to a state in which the refrigerant temperature rises above the saturation temperature during the process in which the refrigerant absorbs heat at a constant pressure and changes from a gas-liquid mixed phase state to a gas phase state, and the degree of superheat refers to the temperature rise above the saturation temperature.

[0011] The present invention has been made to solve the above-mentioned technical problems, and aims to provide a refrigerant circulation system that supplies a gas-phase refrigerant with a low degree of superheat to a motor. [Means for solving the problem]

[0012] In order to achieve the above object, the refrigerant circulation system of the present invention is a refrigerant circulation system for circulating a CO2 refrigerant to cool a motor in a vehicle, and includes a refrigerant circulation circuit forming a refrigeration cycle including a compressor that compresses the refrigerant, a first heat exchanger that dissipates heat from the compressed refrigerant, an upstream expansion valve that expands the heat-dissipating refrigerant, a second heat exchanger that causes the refrigerant expanded by the upstream expansion valve to absorb heat, a downstream expansion valve that expands the refrigerant flowing out from the second heat exchanger, and a motor that causes the refrigerant expanded by the downstream expansion valve to absorb heat, a first sensor that detects at least the pressure and temperature of an input refrigerant that is the refrigerant supplied to the downstream expansion valve, and a second sensor that detects at least the pressure and temperature of an output refrigerant that is the refrigerant discharged from the downstream expansion valve. The system is equipped with a second sensor that detects pressure, and a controller that controls the upstream expansion valve to output an input refrigerant in a gas phase state having the input pressure, and the downstream expansion valve to reduce the pressure of the input refrigerant and output an output refrigerant having the output pressure, wherein the input pressure is set higher than the maximum pressure at the maximum point on the saturated vapor line of the refrigerant's pH diagram where the specific enthalpy is maximized, and the controller estimates the corresponding pressure of the refrigerant at a corresponding point on the saturated vapor line that has the same specific enthalpy as the input refrigerant and is lower in pressure than the maximum pressure, sets the corresponding pressure to a target output pressure, and controls the downstream expansion valve based on the detection signal of the second sensor so that the output pressure of the downstream expansion valve becomes the target output pressure.

[0013] In the present invention configured as described above, a motor is incorporated in addition to the second heat exchanger as a heat source for increasing the specific enthalpy of the refrigerant during the refrigeration cycle. That is, in the present invention, a gas-liquid mixed-phase refrigerant is supplied to the second heat exchanger as in a conventional refrigeration cycle, but the refrigerant that absorbs heat in the second heat exchanger further cools the motor. In this case, the present invention estimates the corresponding pressure of the refrigerant at a corresponding point on the saturated vapor line that has the same specific enthalpy as the gas-phase refrigerant (input refrigerant) that absorbs heat in the second heat exchanger and is located lower than the maximum pressure, and sets this corresponding pressure as the target output pressure of the downstream expansion valve. This allows the downstream expansion valve to supply the motor with gas-phase output refrigerant with zero superheat and sufficient cooling capacity.

[0014] In the present invention, the controller preferably controls the flow rate of the upstream expansion valve based on the detection signal of the first sensor so that the specific enthalpy of the input refrigerant becomes smaller than the specific enthalpy at the maximum point. According to the present invention configured in this manner, it is possible to supply input refrigerant with a low degree of superheat to the downstream expansion valve.

[0015] In the present invention, preferably, when the controller determines, based on the detection signal of the first sensor, that the specific enthalpy of the input refrigerant is equal to or greater than the specific enthalpy at the maximum point, it sets the target output pressure to a predetermined set pressure. According to the present invention configured in this manner, when the degree of superheat of the input refrigerant is high and no corresponding point exists, the target output pressure is set to a predetermined set pressure (for example, a lower limit pressure), thereby ensuring the cooling capacity of the output refrigerant.

[0016] In the present invention, preferably, when the specific enthalpy at the corresponding point is less than a predetermined lower limit specific enthalpy, the controller sets the target output pressure to a predetermined lower limit pressure instead of the corresponding pressure, the lower limit pressure being a pressure higher than the sublimation pressure at which dry ice can exist in the wet vapor region of the pH diagram. According to the present invention configured in this way, when a corresponding point exists but there is a risk that the refrigerant at the corresponding point may become dry ice, the target output pressure can be set to the predetermined lower limit pressure so that the output refrigerant does not contain refrigerant in a solid phase.

[0017] In the present invention, preferably, the refrigerant circulation circuit further includes a gas-liquid separator in a flow path between the downstream expansion valve and the motor, and the refrigerant separated into liquid by the gas-liquid separator is supplied to the motor. According to the present invention configured in this manner, when the output refrigerant is in a gas-liquid mixed phase state (for example, when the target output pressure is not the corresponding pressure but the lower limit pressure), the liquid can be recovered from the output refrigerant by the gas-liquid separator, and only the gas-phase refrigerant can be supplied to the motor.

[0018] In the present invention, the motor preferably has a refrigerant passage formed therein to supply refrigerant to the space between the stator and rotor of the motor. According to the present invention configured in this manner, refrigerant is supplied in gas phase to the space within the motor, thereby suppressing an increase in stirring resistance during operation of the motor.

[0019] In the present invention, the second heat exchanger preferably includes a heat exchanger for an on-board air conditioning system and / or a heat exchanger for an on-board battery. According to the present invention configured in this manner, a normal heat exchanger for a vehicle can be incorporated into the refrigerant circulation system. [Effects of the Invention]

[0020] According to the refrigerant circulation system of the present invention, it is possible to provide the motor with a gas phase refrigerant whose degree of superheat is suppressed to a small value. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic configuration diagram of a refrigerant circulation system according to an embodiment of the present invention. [Figure 2] FIG. 2 is an electrical block diagram of a refrigerant circulation system according to an embodiment of the present invention. [Figure 3A] FIG. 2 is a perspective view of a motor of a refrigerant circulation system according to an embodiment of the present invention. [Figure 3B] 1 is a cross-sectional view of a motor of a refrigerant circulation system according to an embodiment of the present invention. [Figure 3C] 1 is a longitudinal cross-sectional view of a motor in a refrigerant circulation system according to an embodiment of the present invention. [Figure 4] 1 is an explanatory diagram of a refrigeration cycle of a refrigerant circulation system according to an embodiment of the present invention. [Figure 5] 1 is an explanatory diagram of a refrigeration cycle in a steady state of a refrigerant circulation system according to an embodiment of the present invention. [Figure 6A] 1 is an explanatory diagram of a refrigeration cycle of a refrigerant circulation system according to an embodiment of the present invention. [Figure 6B] 1 is an explanatory diagram of a refrigeration cycle of a refrigerant circulation system according to an embodiment of the present invention. [Figure 6C] 1 is an explanatory diagram of a refrigeration cycle of a refrigerant circulation system according to an embodiment of the present invention. [Figure 7] 3 is a process flow of a refrigerant circulation system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, a motor system according to an embodiment of the present invention will be described with reference to the accompanying drawings. [System Configuration] First, the overall configuration of a refrigerant circulation system according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a schematic diagram of the refrigerant circulation system according to this embodiment, and Figure 2 is an electrical block diagram of the refrigerant circulation system. The refrigerant circulation system S shown in Figure 1 is mounted on a vehicle such as an electric vehicle, and is configured to cool a motor 20 used to drive the vehicle.

[0023] The refrigerant circulation system S forms a refrigeration cycle using a refrigerant and includes a refrigerant circulation circuit 10, various sensors 30, and a controller 40. The refrigerant circulation circuit 10 includes, in a pipe or flow path 3 for the refrigerant R, a compressor 11, a first heat exchanger 12 serving as a condenser including a condenser and a fan, a receiver 13 for receiving the refrigerant R, upstream expansion valves 14a and 14b (first expansion valves) and an expansion valve 14c (second expansion valve or bypass expansion valve), second heat exchangers 15a and 15b serving as evaporators, a downstream expansion valve 16 (third expansion valve), a gas-liquid separator 17, a motor 20, and an accumulator 18. The refrigerant R in this embodiment is a mixture of a natural refrigerant (e.g., CO2) and lubricating oil.

[0024] Flow path 3 branches into flow paths 3a and 3b downstream of receiver 13, which communicate with second heat exchangers 15a and 15b. The refrigerant from receiver 13 is supplied via flow paths 3a and 3b from upstream expansion valves 14a and 14b to second heat exchangers 15a and 15b. Second heat exchangers 15a and 15b are a heat exchanger for an in-vehicle air conditioner and a heat exchanger for a lithium battery that supplies power to motor 20, etc. Flow paths 3a and 3b merge at a junction C1.

[0025] In addition, flow path 3 is provided with flow path 3c that bypasses second heat exchangers 15a and 15b. No heat exchanger is provided in flow path 3c, and the refrigerant discharged from expansion valve 14c is supplied downstream without absorbing heat from the heat exchanger. In this embodiment, flow path 3c merges with flow path 3 at junction C2, which is downstream of junction C1.

[0026] Furthermore, the gas-liquid separator 17 separates liquid from the refrigerant R containing lubricating oil flowing through the flow path 3. The separated liquid is lubricating oil, but may also contain refrigerant R in a liquid phase. The separated liquid is supplied to the accumulator 18 through the separation flow path 3d. Therefore, the gas-liquid separator 17 passes only the refrigerant R in a gas phase to the downstream flow path 3, and only the gasified refrigerant R is used to cool the motor 20. The separated liquid is sent to the accumulator 18 and mixed with the refrigerant R (in a gas phase) after cooling the motor 20.

[0027] The sensor 30 includes a pressure sensor 31 and a temperature sensor 32 arranged between the junction C2 and the expansion valve 16, a liquid level sensor 34 arranged between the junction C1 and the junction C2, and a pressure sensor 33 arranged between the expansion valve 16 and the motor 20. The pressure sensors 31 and 33 detect the pressure of the refrigerant R in the flow path 3. The temperature sensor 32 detects the temperature of the refrigerant R in the flow path 3. The liquid level sensor 34 includes a refrigerant storage chamber 34a arranged in the flow path 3 and a level meter 34b that detects the liquid level of the refrigerant R in the refrigerant storage chamber 34a. The level meter 34b can continuously measure the liquid level of the refrigerant R in the refrigerant storage chamber 34a. The level meter 34b can be configured using a known method such as a conductivity type, a radio wave type, or a float type.

[0028] In addition to the above, additional pressure sensors and temperature sensors may be provided. For example, a temperature sensor may be provided between the expansion valve 16 and the motor 20, or an additional pressure sensor and temperature sensor may be provided between the junction C1 and the junction C2, or a pressure sensor and temperature sensor may be provided within the liquid level sensor 34. The liquid level sensor 34 may also be disposed between the junction C2 and the expansion valve 16.

[0029] The controller 40 is a computer device having a processor, memory, input / output devices, etc. The memory stores a database including a predetermined control program and information on the pH diagram of the refrigerant R. The controller 40 receives a detection signal from the sensor 30, a power switch signal (on / off signal) from the vehicle power switch 41, and other signals, and controls the expansion valves 14a, 14b, 14c, the expansion valve 16, etc. based on these signals and by referring to the database.

[0030] [Motor configuration] The configuration of motor 20 according to this embodiment will be described with reference to Figures 3A to 3C. Figures 3A, 3B, and 3C are a perspective view, a cross-sectional view, and a longitudinal-sectional view of the motor, respectively. In each figure, some components have been omitted for ease of understanding. Motor 20 is an ultra-high-speed motor, and is configured to operate at a high rotation speed of, for example, over 30,000 rpm.

[0031] The motor 20 comprises a stator 21 wound with a motor coil, a rotor 22 on which a permanent magnet is arranged, a rotor shaft (rotating shaft) 23 fixed to the rotor 22 and extending in the axial direction, a bearing (not shown), and a housing 24 having an approximately cylindrical shape with a bottom that accommodates and supports these components.

[0032] The housing 24 has a storage passage 24a formed within its cylindrical portion. The stator 21 also has a plurality of capillary tubes 24b, which function as refrigerant passages, radially penetrating each tooth. The capillary tubes 24b have an extremely small cross-sectional diameter so as not to degrade the electromagnetic performance of the stator 21. In this embodiment, the small cross-sectional area of ​​the capillary tubes 24b increases flow resistance for liquid refrigerant R, making it difficult for the liquid refrigerant R to pass through the capillary tubes 24 efficiently. Therefore, it is highly preferable to supply gaseous refrigerant R to the capillary tubes 24b. The refrigerant R supplied from the flow path 3 to the motor 20 is supplied to each capillary tube 24b and discharged from the openings 24c of the capillary tubes 24b into the internal space F between the stator 21 and the rotor 22. After cooling the motor coil and other components, the refrigerant returns to the flow path 3 and is sent to the accumulator 18. In this embodiment, the storage passage 24a of the housing 24 can be used as a refrigerant storage chamber 34a of the liquid level sensor 34.

[0033] [Refrigerant refrigeration cycle] Next, with reference to FIG. 4, the refrigeration cycle of refrigerant R in this embodiment will be described. FIG. 4 shows the refrigeration cycle of refrigerant R. The refrigeration cycle is shown on a pH diagram of refrigerant R. In FIG. 4, the horizontal axis represents specific enthalpy [kJ / kg] and the vertical axis represents absolute pressure [MPaA]. Some isotherms are also shown in FIG. 4. The critical point of CO2 refrigerant is 7.4 MPaA at 31°C. In the wet vapor region Zm surrounded by the saturated liquid line L1 on the left side of the critical point CP and the saturated vapor line L2 on the right side, refrigerant R is in a gas-liquid mixed phase state. Note that within the wet vapor region Zm, refrigerant R may become dry ice at pressures below a predetermined pressure (0.52 MPaG). On the other hand, in the superheated vapor region Zv on the right side of the saturated vapor line L2, refrigerant R is in a gas phase state.

[0034] First, in the refrigeration cycle (ABCDEF) of this embodiment, a compression stroke (AB) is performed by the compressor 11. The compressor 11 receives high-temperature, low-pressure refrigerant R (gas) from the accumulator 18 via the flow path 3 (point A), compresses the received refrigerant R, and discharges high-temperature, high-pressure refrigerant R (supercritical fluid) (point B). Next, a condensation stroke (BC) is performed by the first heat exchanger 12. The first heat exchanger 12 receives the high-temperature, high-pressure refrigerant R (point B), and condenses and releases heat from the refrigerant R through heat exchange with the external environment (cold air, cooling water, etc.), generating medium-temperature, high-pressure refrigerant R (supercritical fluid) (point C).

[0035] Next, an expansion stroke (CD) is performed by the expansion valves 14a and 14b. The expansion valves 14a and 14b reduce the pressure of the medium-temperature, high-pressure refrigerant R to generate a low-temperature, medium-pressure refrigerant R (gas-liquid mixture) (point D). Then, an evaporation stroke (DE) is performed in the second heat exchangers 15a and 15b. The second heat exchangers 15a and 15b exchange heat with the low-temperature, medium-pressure refrigerant R, evaporating and absorbing heat from the refrigerant R, ideally resulting in a low-temperature, medium-pressure refrigerant R (gas) with a degree of superheat of zero. The temperatures at points C and D may vary depending on factors such as the outside air temperature.

[0036] Furthermore, this embodiment is characterized by having a second expansion stroke (EF) and a second evaporation stroke or second heat absorption stroke (FA). In the second expansion stroke (EF), the expansion valve 16 further reduces the pressure of the low-temperature, medium-pressure refrigerant R to generate low-temperature, low-pressure refrigerant R (gas). Finally, in the second evaporation stroke (FA), the motor 20 exchanges heat with the low-temperature, low-pressure refrigerant R (gas), cooling the motor 20 and generating high-temperature, low-pressure refrigerant R. This high-temperature, low-pressure refrigerant R is returned to the accumulator 18 (point A).

[0037] As described above, the refrigeration cycle of this embodiment has an evaporation stroke (DE) and a second evaporation stroke (FA). In the evaporation stroke (DE), gas-liquid mixed-phase refrigerant R is used, as in a general refrigeration cycle. On the other hand, in the second evaporation stroke (FA), gas-phase refrigerant R is used. That is, in the second evaporation stroke (FA), gas-phase refrigerant R is supplied to the motor 20 to suppress stirring resistance caused by liquid-phase refrigerant R in the internal space F of the motor 20. In addition, in the second evaporation stroke (FA), the refrigerant R is supplied to the internal space F of the motor 20 via the thin tube 24b, and therefore, gas-phase refrigerant R is used to efficiently supply the refrigerant R.

[0038] In this embodiment, the superheat degree control is executed so that the refrigerant R is completely gasified in the evaporation stroke (DE) (i.e., so that the superheat degree is equal to or greater than zero). The superheat degree d is the difference between the temperature T of the refrigerant R and the saturation temperature Ts (d=T-Ts). In this heating degree control, the controller 40 is configured to control the valve opening or flow rate of the expansion valves 14a-14c in response to a cooling request from the second heat exchanger 15.

[0039] In general, when the cooling demand is small, the controller 40 reduces the flow rates of the expansion valves 14a to 14c to control the point E not to be located to the left of the saturated vapor line L2. For example, the controller 40 adjusts the flow rates to maintain a predetermined target superheat degree (e.g., 0 to 1°C) at point E (junction C2). If point E is expected to be located to the left of the saturated vapor line L2 (e.g., when the liquid level sensor 34 detects a positive liquid level or when the liquid level is rising), the controller 40 can reduce the flow rates of the expansion valves 14a to 14c to control the point E to be located on or to the right of the saturated vapor line L2.

[0040] [Outline of flow rate adjustment using expansion valves] Next, with reference to Figures 5 and 6A to 6C, the flow rate adjustment control of the refrigerant R by the upstream expansion valves 14a, 14b, and 14c and the downstream expansion valve 16 will be described. Figure 5 shows a refrigeration cycle in an ideal steady state, and Figures 6A to 6C show refrigeration cycles that deviate from the ideal steady state.

[0041] 5, the saturated vapor line L2 has a maximum point M where the specific enthalpy E becomes maximum with respect to the pressure P. At the maximum point M, the refrigerant R is M and maximum specific enthalpy E M On the saturated vapor line L2, there may be two points (points G and H) with equal specific enthalpy on the high-pressure side and the low-pressure side of the maximum point M.

[0042] The expansion valves 14a, 14b, and 14c on the upstream side are capable of adjusting the flow rate and pressure, and the refrigerant R is supplied to the refrigerant chamber at a maximum pressure P M Higher input pressure P IN (In Figure 5, P G ) (point D0). The expansion valve 16 on the downstream side is also capable of adjusting the flow rate and pressure, and reduces the refrigerant R to a maximum pressure P M Lower output pressure P OUT (In Figure 5, P H) (point F0). In this specification, the refrigerant R flowing into the expansion valve 16 on the downstream side may be referred to as the "input refrigerant," and the refrigerant R output from the expansion valve 16 may be referred to as the "output refrigerant."

[0043] The input pressure P IN When the flow rate of the refrigerant R decompressed to the point C2 is balanced with the cooling demand of the second heat exchangers 15a and 15b, the refrigerant R at the confluence point C2 (point E0) is in a completely vaporized state with a heating degree of zero. In other words, point E0 coincides with point G on the saturated vapor line L2. The refrigerant R at point G has a maximum specific enthalpy E M Smaller specific enthalpy E G (E G <E M ) Also, on the saturated vapor line L2, there exists a corresponding point H whose specific enthalpy is equal to that of point G. The corresponding pressure P at the corresponding point H is C is the target output pressure P of the downstream expansion valve 16. T (P T =P C ).

[0044] The downstream expansion valve 16 converts the refrigerant R (input refrigerant) flowing in from the confluence C2 into an output pressure P OUT (=P H ), point F0 coincides with point H on the saturated vapor line L2, so the refrigerant R (output refrigerant) decompressed by the expansion valve 16 is in a gas phase state with a degree of superheat of zero. Because the degree of superheat of this refrigerant R is zero, it provides a large cooling capacity to the motor 20, and the specific enthalpy of the refrigerant R increases due to the absorption of heat from the motor 20 (point A0). Point A0 exists, for example, on the 40°C isothermal line.

[0045] In addition, the refrigerant R has a predetermined sublimation pressure P D It can become dry ice below the saturated vapor line L2. D The lower limit pressure P is higher than the specified safety margin. J (P J >P D ) and point J is set corresponding to the lower limit pressure P Jis set to be equal to or higher than the sublimation pressure of the lubricating oil contained in the refrigerant R. In this embodiment, the lower limit pressure P J is preset to a predetermined pressure (for example, 0.6 MPaA). The refrigerant R at point J has a lower limit specific enthalpy E J In this embodiment, in order to prevent the refrigerant R from becoming dry ice due to the pressure reduction by the expansion valve 16, the output pressure P OUT is the lower limit pressure P J In Figure 5, the lower limit pressure P J Dry ice areas or prohibited areas are set in the following areas (shaded areas).

[0046] 6A shows a case where the cooling demand by the second heat exchangers 15a and 15b increases, and the cooling capacity of the refrigerant R supplied from the expansion valves 14a to 14c becomes slightly smaller. In this case, the refrigerant R at the confluence point C2 (the input refrigerant at point E1) has a specific enthalpy E A1 and has a positive superheat. A1 is the maximum specific enthalpy E M Less than (E A1 <E M In this case, the saturated vapor line L2 has a specific enthalpy E A1 There exists a point K where the maximum pressure P M The smaller corresponding pressure P C In this situation, the corresponding pressure P at point K C is the target output pressure P of the downstream expansion valve 16. T (P T =P C ).

[0047] The downstream expansion valve 16 operates at an output pressure P OUT The target output pressure P TWhen the refrigerant R (input refrigerant at point E1) flowing in from junction C2 is decompressed (point F1) so that point F1 coincides with point K on the saturated vapor line L2, the refrigerant R (output refrigerant at point F1) decompressed by expansion valve 16 is in a gas phase state with a degree of superheat of zero. Because the degree of superheat of this refrigerant R is zero, it provides a large cooling capacity to motor 20, and the specific enthalpy of refrigerant R increases due to the heat absorption from motor 20 (point A1).

[0048] 6B shows a case where the cooling demand from the second heat exchangers 15a and 15b further increases, and the cooling capacity of the refrigerant R supplied from the expansion valves 14a to 14c becomes relatively small. In this case, the refrigerant R at the confluence point C2 (the input refrigerant at point E2) has a specific enthalpy E A2 and has a positive superheat. Furthermore, the specific enthalpy E A2 is the maximum specific enthalpy E M The magnitude is greater than or equal to (E A2 ≧E M ) In this case, on the saturated vapor line L2, there is a specific enthalpy E A2 There is no point with the maximum pressure P at point J (except for the maximum point M). J is the target output pressure P of the downstream expansion valve 16. T (P T =P J ).

[0049] The downstream expansion valve 16 operates at an output pressure P OUT The target output pressure P T The refrigerant R flowing in from the junction C2 (the input refrigerant at point E2) is set at the lower limit pressure P J The pressure of the refrigerant R (output refrigerant) is reduced to (point F2). This refrigerant R (output refrigerant) is supplied to the motor 20, and the specific enthalpy of the refrigerant R increases due to the heat absorption from the motor 20 (point A2). J is the output pressure P of the expansion valve 16 OUT This is the lowest pressure within the pressure control range, and this lower limit pressure P J Now, in the situation of Figure 6B, the target output pressure P T The lower limit pressure P JWhen a higher pressure is set, a larger difference in specific enthalpy (i.e., cooling capacity) between point F2 and point A2 (40°C isotherm) can be ensured.

[0050] FIG. 6C shows the input pressure P IN (P IN =P G1 ) is the steady-state pressure P G In this case, the refrigerant R at the junction C2 (the input refrigerant at point E3) has a specific enthalpy E A3 The point E3 overlaps with the point G1 on the saturated vapor line L2. The specific enthalpy E A3 is the maximum specific enthalpy E M Less than (E A3 <E M ) In this case, there is a specific enthalpy E on the saturated vapor line L2, which is equal to point E3. A3 In the example of FIG. 6C, the corresponding point H1 has the lower limit pressure P J The smaller corresponding pressure P C The specific enthalpy E at the corresponding point H1 A3 is the lower limit specific enthalpy E J In this situation, the lowest pressure in the pressure control range, the lower limit pressure P J is the target output pressure P of the downstream expansion valve 16. T (P T =P J ).

[0051] The downstream expansion valve 16 operates at an output pressure P OUT The target output pressure P T The refrigerant R flowing in from the junction C2 (the input refrigerant at point E3) is set at the lower limit pressure P JThe refrigerant R is depressurized to (point F3). Point F3 is located slightly to the left of the saturated vapor line L2 and is within the wet vapor region Zm, so the refrigerant R (output refrigerant) depressurized by the expansion valve 16 is in a gas-liquid mixed-phase state containing a small proportion of liquid-phase refrigerant. When this refrigerant R passes through the gas-liquid separator 17, the small proportion of liquid-phase refrigerant R is recovered from the gas-liquid mixed-phase refrigerant R, and most of the gas-phase refrigerant R is supplied to the motor 20. In this case, the gas-phase refrigerant R can provide a greater cooling capacity to the motor 20. The specific enthalpy of the gas-phase refrigerant R increases due to the heat absorption from the motor 20 (point A2).

[0052] [Processing flow] Next, the processing flow of the refrigerant circulation system S of this embodiment will be described with reference to FIG. 7. When the processing starts, the controller 40 reads a vehicle power switch signal from the vehicle power switch 41 (S1), and determines based on the vehicle power switch signal whether the vehicle power is on and the vehicle motor 20 is operating (S2). If the determination is negative (S2; NO), the processing ends, but the controller 40 repeatedly executes the processing of FIG. 7 at predetermined time intervals. On the other hand, if the determination is positive (S2; YES), the controller 40 determines based on a predetermined signal input whether vehicle startup control has been completed (S3), and after startup control is completed (S3; YES), starts steady-state control of the refrigeration cycle (S4). The steady-state control is repeatedly executed until it is determined based on the vehicle power switch signal that the vehicle power has been turned off (S18 to S20).

[0053] When the steady state control is started, the controller 40 starts the expansion valve control (S5) and reads the detection signal of the sensor 30 (S5). Based on the detection signal, the controller 40 estimates the degree of superheat d and specific enthalpy E of the refrigerant R (input refrigerant) at an intermediate position (corresponding to the junction C2) between the expansion valve 16 and the second heat exchangers 15a, 15b (S7). For this purpose, the controller 40 first calculates the input pressure P of the refrigerant R supplied to the expansion valve 16 based on the detection signals of the pressure sensor 31 and the temperature sensor 32. IN and temperature T, and the input pressure P of the refrigerant R INFrom the temperature T, the degree of superheat d and specific enthalpy E of refrigerant R are estimated by referring to the information on the pH diagram of refrigerant R.

[0054] The controller 40 calculates the input pressure P from the temperature T of the refrigerant R. IN The degree of superheat d can be calculated by subtracting the saturation temperature Ts at T (d=T-Ts≧0). Furthermore, the controller 40 can estimate the specific enthalpy E based on the temperature T (T≧Ts) by referring to information on the pH diagram of the refrigerant R.

[0055] In the wet vapor region Zm, even if the specific enthalpy of the refrigerant R changes, the temperature T of the refrigerant R remains equal to the saturation temperature Ts until the refrigerant R is completely gasified. However, in this embodiment, the flow rate of the upstream expansion valves 14a to 14c is controlled by the heating degree control as described above so that the refrigerant R at the intermediate position does not exist in the wet vapor region Zm. Therefore, in this embodiment, in the process flow of Figure 7, the refrigerant R at the intermediate position is completely gasified and is in the superheated vapor region Zv. In the superheated vapor region Zv, the temperature T of the refrigerant R increases as the specific enthalpy increases.

[0056] Next, the controller 40 calculates whether the estimated specific enthalpy E is equal to the maximum specific enthalpy E at the maximum point M. M (S8) and the lower limit pressure P J Lower limit specific enthalpy E J It is determined whether the maximum specific enthalpy E at the maximum point M is equal to or greater than the maximum specific enthalpy E at the maximum point M (S9). M and lower limit pressure P J Lower limit specific enthalpy E J are known values ​​from the pH diagram, and the controller 40 can read these values ​​from the database. If the determination is affirmative in both cases (S8 and S9: YES, corresponding to the situation in FIG. 5 or FIG. 6A), the controller 40 determines the maximum pressure P on the saturated vapor line L2 that has a specific enthalpy equal to the specific enthalpy E. M The smaller corresponding pressure P C(See FIG. 5, FIG. 6A, or FIG. 6C) (S10). The controller 40 calculates the corresponding pressure P C The target output pressure P of the downstream expansion valve 16 T Set to (P T =P C ).

[0057] Next, the controller 40 calculates the output pressure P of the refrigerant R (output refrigerant) supplied by the downstream expansion valve 16 based on the detection signal of the sensor 30 (pressure sensor 33). OUT and obtain the output pressure P OUT The target output pressure P T (P C ), the controller 40 controls the expansion valve 16 to match the output pressure P OUT is the target output pressure P T (P C ) or more (S11; YES), the valve opening of the expansion valve 16 is narrowed by a predetermined valve opening to reduce the flow rate, and the output pressure P OUT is the target output pressure P T (P C ) (S11; NO), the valve opening of the expansion valve 16 is opened by a predetermined valve opening to increase the flow rate. As a result, when the flow rate is low, the output pressure P OUT When the flow rate increases, the output pressure P OUT rises, and in either case the output pressure P OUT is the target output pressure P T (P C ) is approaching.

[0058] On the other hand, if the determination in step S8 is negative (S8; NO, which corresponds to the situation in FIG. 6B), or if the determination in step S9 is negative (S9; NO, which corresponds to the situation in FIG. 6C), the controller 40 sets the lower limit pressure P J The target output pressure P of the downstream expansion valve 16 T Set to (P T =P J ), and the output pressure P of the downstream expansion valve 16 based on the detection signal of the sensor 30 (pressure sensor 33). OUT and obtain the output pressure P OUTThe target output pressure P T (P J ), the expansion valve 16 is controlled so that the pressure difference (P) coincides with the pressure difference (P), and then the process proceeds to step S20.

[0059] That is, the controller 40 controls the output pressure P OUT is the target output pressure P T (P J ) (S14; YES), the valve opening of the expansion valve 16 is opened by a predetermined valve opening to increase the flow rate, and the output pressure P OUT is the target output pressure P T (P J ) or more (S14; NO), the valve opening of the expansion valve 16 is narrowed by a predetermined valve opening to reduce the flow rate. OUT When the flow rate decreases, the output pressure P OUT decreases, and in both cases the output pressure P OUT is the target output pressure P T (P J ) is approaching.

[0060] [Action and effect] Next, the operation and effects of the refrigerant circulation system S according to this embodiment will be described. The refrigerant circulation system S according to this embodiment is a refrigerant circulation system S for circulating a CO2 refrigerant R to cool a motor 20 in a vehicle, and includes a compressor 11 for compressing the refrigerant R, a first heat exchanger 12 for dissipating heat from the compressed refrigerant R, upstream expansion valves 14a to 14c for expanding the refrigerant R that has dissipated heat, second heat exchangers 15a and 15b for absorbing heat into the refrigerant R expanded by the upstream expansion valves 14a to 14c, and a second heat exchanger 15b for expanding the refrigerant R that has flowed out of the second heat exchangers 15a and 15b. The refrigerant circulation circuit 10 forms a refrigeration cycle including a downstream expansion valve 16 that expands the refrigerant R, and a motor 20 that absorbs heat in the refrigerant R expanded by the downstream expansion valve 16; a first sensor (pressure sensor 31, temperature sensor 32) that detects at least the pressure P and temperature T of the input refrigerant, which is the refrigerant R supplied to the downstream expansion valve 16; a second sensor (pressure sensor 33) that detects at least the pressure P of the output refrigerant, which is the refrigerant R discharged from the downstream expansion valve 16; and a second sensor (pressure sensor 34) that detects at least the pressure P of the output refrigerant, which is the refrigerant R discharged from the downstream expansion valve 16. IN The input refrigerant is then output in a gas phase state having a pressure P OUT and a controller 40 for controlling the input pressure P IN is the maximum pressure P at the maximum point M where the specific enthalpy E is maximum on the saturated vapor line L2 of the pH diagram of refrigerant R. M The controller 40 controls the refrigerant on the saturated vapor line L2 to have the same specific enthalpy as the input refrigerant and have a maximum pressure. PM The corresponding pressure P of refrigerant R at the corresponding point H on the lower pressure side C (S10) and the corresponding pressure P C The target output pressure P T and based on the detection signal of the second sensor (pressure sensor 33), the output pressure P OUT is the target output pressure P T The downstream expansion valve 16 is controlled so as to satisfy the above condition (S11 to S13).

[0061] In this embodiment configured as above, in addition to the second heat exchangers 15a and 15b, a motor 20 is incorporated as a heat source for increasing the specific enthalpy of the refrigerant R during the refrigeration cycle. That is, in this embodiment, the refrigerant R in a gas-liquid mixed phase is supplied to the second heat exchangers 15a and 15b as in a normal refrigeration cycle, but the refrigerant R that has absorbed heat by the second heat exchangers 15a and 15b further cools the motor 20. At this time, in this embodiment, the refrigerant R has a specific enthalpy equal to that of the refrigerant R (input refrigerant) in a gas phase that has absorbed heat by the second heat exchangers 15a and 15b on the saturated vapor line L2, and is at a maximum pressure P M The corresponding pressure P of refrigerant R at the corresponding point H on the lower pressure side C and the corresponding pressure P C The target output pressure P of the downstream expansion valve 16 T As a result, in this embodiment, it is possible to supply output refrigerant in a gaseous state with a degree of superheat of zero and sufficient cooling capacity from the downstream expansion valve 16 to the motor 20.

[0062] Furthermore, according to this embodiment, the controller 40 determines whether the specific enthalpy E of the input refrigerant is equal to or greater than the maximum specific enthalpy E at the maximum point M based on the detection signals of the first sensors (pressure sensor 31, temperature sensor 32). M In this embodiment, the flow rates of the upstream expansion valves 14a to 14c are controlled so that the degree of superheat of the input refrigerant is small.

[0063] Furthermore, according to this embodiment, the controller 40 determines whether the specific enthalpy E of the input refrigerant is equal to or greater than the maximum specific enthalpy E at the maximum point M based on the detection signals of the first sensors (pressure sensor 31, temperature sensor 32). M If it is determined that the target output pressure P T to a predetermined set pressure (for example, the lower limit pressure P J In this embodiment configured as above, when the degree of superheat of the input refrigerant is high and no corresponding point H exists, the target output pressure P T to the specified set pressure (lower limit pressure P J) to ensure the cooling capacity of the output refrigerant.

[0064] Furthermore, according to this embodiment, the controller 40 calculates the specific enthalpy (E A3 ) is the lower limit of the specific enthalpy E J If it is less than (S9; NO), the target output pressure P T The corresponding pressure P C Instead of the predetermined lower limit pressure P J and set the lower limit pressure P J is the sublimation pressure P at which dry ice can exist in the wet vapor region Zm of the pH diagram. D In this embodiment configured as above, when the corresponding point H exists but there is a risk that the refrigerant R at the corresponding point H may become dry ice, the target output pressure P T The predetermined lower limit pressure P J so that the output refrigerant does not contain any solid-phase refrigerant.

[0065] According to this embodiment, the refrigerant circuit 10 further includes a gas-liquid separator 17 in the flow path 3 between the downstream expansion valve 16 and the motor 20, and the refrigerant R separated into liquid by the gas-liquid separator 17 is supplied to the motor 20. In this embodiment configured as above, when the output refrigerant is in a gas-liquid mixed phase state (for example, when the target output pressure P T The corresponding pressure P C Instead, the lower limit pressure P J In this case, the liquid is recovered from the output refrigerant by the gas-liquid separator 17, and only the gas-phase refrigerant can be supplied to the motor 20.

[0066] Furthermore, according to this embodiment, the motor 20 is formed with a refrigerant passage (thin tubes 24b) so as to supply the refrigerant R to the space F between the stator 21 and the rotor 22 of the motor 20. In this embodiment configured as above, the refrigerant R in gas phase is supplied to the space F within the motor 20, so that an increase in stirring resistance during operation of the motor 20 can be suppressed.

[0067] In addition, according to this embodiment, the second heat exchangers 15a, 15b include a heat exchanger for an in-vehicle air conditioner and / or a heat exchanger for an in-vehicle battery. In this embodiment configured as described above, a normal heat exchanger for a vehicle can be incorporated into the refrigerant circulation system S. [Explanation of symbols]

[0068] 3,3a~3c flow path 10 Refrigerant circulation circuit 11 Compressor 12 1st heat exchanger 14 Second heat exchanger 14a, 14b, 14c Upstream expansion valve 15a,15b 2nd heat exchanger 16 Downstream expansion valve 17 Gas-liquid separator 20 Motor 21 Stator 22 rotor 24 Housing 24b tubule 31,33 Pressure sensors 32 Temperature Sensor 34 Liquid level sensor 40 Controller F space R refrigerant S Refrigerant Circulation System

Claims

1. CO 2 A refrigerant circulation system for circulating a refrigerant to cool a motor in a vehicle, a refrigerant circulation circuit forming a refrigeration cycle including, in a flow path for circulating the refrigerant, a compressor for compressing the refrigerant, a first heat exchanger for dissipating heat from the compressed refrigerant, an upstream expansion valve for expanding the heat-dissipating refrigerant, a second heat exchanger for causing the refrigerant expanded by the upstream expansion valve to absorb heat, a downstream expansion valve for expanding the refrigerant flowing out from the second heat exchanger, and the motor for causing the refrigerant expanded by the downstream expansion valve to absorb heat; a first sensor for detecting at least the pressure and the temperature of an input refrigerant that is supplied to the downstream expansion valve; a second sensor for detecting at least the pressure of the output refrigerant, which is the refrigerant discharged from the downstream expansion valve; a controller that controls the upstream expansion valve to output the input refrigerant in a gas phase state having an input pressure, and the downstream expansion valve to reduce the pressure of the input refrigerant and output the output refrigerant having an output pressure, The input pressure is set higher than the maximum pressure at the maximum point where the specific enthalpy is maximized on the saturated vapor line of the refrigerant's pH diagram, The controller estimates the corresponding pressure of the refrigerant at a corresponding point on the saturated vapor line that has the same specific enthalpy as the input refrigerant and is lower in pressure than the maximum pressure, sets the corresponding pressure to a target output pressure, and controls the downstream expansion valve based on the detection signal of the second sensor so that the output pressure of the downstream expansion valve becomes the target output pressure.

2. 2. The refrigerant circulation system according to claim 1, wherein the controller controls the flow rate of the upstream expansion valve based on the detection signal of the first sensor so that the specific enthalpy of the input refrigerant is smaller than the specific enthalpy at the maximum point.

3. 2. The refrigerant circulation system according to claim 1, wherein the controller sets the target output pressure to a predetermined set pressure when it determines, based on the detection signal of the first sensor, that the specific enthalpy of the input refrigerant is equal to or greater than the specific enthalpy at the maximum point.

4. 2. The refrigerant circulation system of claim 1, wherein when the specific enthalpy at the corresponding point is less than a predetermined lower limit specific enthalpy, the controller sets the target output pressure to a predetermined lower limit pressure instead of the corresponding pressure, and the lower limit pressure is a pressure higher than a sublimation pressure at which dry ice can exist within the wet vapor region of the p-h diagram.

5. 2. The refrigerant circulation system according to claim 1, wherein the refrigerant circulation circuit further includes a gas-liquid separator in the flow path between the downstream expansion valve and the motor, and the refrigerant from which the liquid has been separated by the gas-liquid separator is supplied to the motor.

6. The refrigerant circulation system according to claim 1 , wherein the motor has a refrigerant passage formed therein to supply the refrigerant to a space between a stator and a rotor of the motor.

7. The refrigerant circulation system according to claim 1 , wherein the second heat exchanger includes a heat exchanger of an on-board air conditioning system and / or a heat exchanger of an on-board battery.

Images