Refrigerant circulation system

Abstract

To prevent liquid refrigerant from flowing into a compressor in a refrigerant circulation system, in which the refrigerant is used to lubricate a sliding bearing of a motor and is also expanded in the motor for cooling.SOLUTION: A refrigerant circulation system 100 which circulates a refrigerant containing CO2 comprises: a compressor 3 which compresses the refrigerant; a rotor 11 and a stator 12; a rotating shaft 13 connected to the rotor; and a sliding bearing 14 which is lubricated by the refrigerant compressed by the compressor and supports the rotating shaft. The refrigerant circulation system also has a motor 1 configured such that the refrigerant passing through the motor expands after flowing out of the sliding bearing 14 and is used to cool the stator and a control device 50 configured to control at least the motor. The motor has a flow regulating valve 20 capable of adjusting a flow rate of the refrigerant. The control device controls the flow regulating valve of the motor to adjust a degree of superheating in a refrigeration cycle of the refrigerant.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a refrigerant circulation system that circulates a refrigerant. [Background technology]

[0002] Conventionally, refrigerant circulation systems that circulate refrigerant have been used in refrigeration cycles used in air conditioners, etc. Generally, in this type of refrigerant circulation system, the refrigerant is circulated between a compressor, a heat exchanger (condenser), an expansion valve, and an evaporator while changing its state.

[0003] In such a refrigerant circulation system, in order to prevent compressor failure due to liquid refrigerant flowing into the compressor (liquid backflow / liquid return), the refrigerant heated in the evaporator is heated with a margin and controlled so that a fully gasified refrigerant is supplied to the compressor. In the refrigeration cycle, the degree of heating with a margin is called the "degree of superheat," and the degree of superheat is determined from the saturated vapor temperature corresponding to the pressure before the compressor (i.e., the pressure of the evaporator) and the refrigerant temperature before the compressor. A technology for controlling the degree of superheat in such a refrigeration cycle is disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-023780 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, rolling bearings and sliding bearings have traditionally been used as bearings to support the rotating shaft of, for example, a vehicle's power source (engine or motor). However, when rolling bearings are used in motors such as electric vehicles, the rotating shaft of the motor rotates at high speeds of, for example, over 30,000 rpm, causing problems with rolling fatigue and shortening the bearing's lifespan. On the other hand, when a typical sliding bearing that uses oil as a lubricant is used in a motor, loss due to oil agitation resistance caused by the motor's rotating shaft increases.

[0006] Therefore, the present inventors considered applying a motor to a refrigerant circulation system such as the one described above and using a sliding bearing that uses, as a lubricant, the refrigerant circulated in the system—particularly a CO2 refrigerant that liquefies when compressed by a compressor—as the motor's rotating shaft. At the same time, the present inventors considered having the motor perform part of the refrigeration cycle of the refrigerant circulation system, specifically functioning as an expansion valve and evaporator in the refrigeration cycle. In other words, the refrigerant passing through the motor would be expanded after flowing out of the sliding bearing (expansion valve) and used to cool the rotor and stator (evaporator). Even in a refrigerant circulation system including such a motor, it is necessary to prevent liquid refrigerant from flowing into the compressor downstream of the motor (liquid backflow).

[0007] The present invention has been made to solve the problems of the conventional technology described above, and has an object to prevent liquid refrigerant from flowing into a compressor in a refrigerant circulation system in which the sliding bearings of a motor are lubricated with a refrigerant, and the refrigerant is expanded within the motor and used for cooling. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a refrigerant circulation system that circulates a refrigerant containing CO2, the system comprising a motor having a compressor that compresses the refrigerant, a rotor and a stator, a rotating shaft connected to the rotor, and a sliding bearing that supports the rotating shaft and is lubricated using the refrigerant compressed by the compressor, wherein the refrigerant passing through the motor is expanded after flowing out of the sliding bearing and is used to cool the rotor or the stator, and a control device configured to control at least the motor, the motor further comprising a flow rate adjustment mechanism that can adjust the flow rate of the refrigerant, and the control device configured to control the flow rate adjustment mechanism of the motor to adjust the degree of superheat in the refrigeration cycle of the refrigerant realized by the refrigerant circulation system.

[0009] In this refrigerant circulation system, the motor's sliding bearing is lubricated with refrigerant, and the motor functions as an expansion valve and evaporator for the refrigeration cycle. By controlling the flow rate of the refrigerant to the motor with a flow rate adjustment mechanism, the superheat level of the refrigeration cycle can be accurately adjusted. Therefore, this invention can prevent liquid refrigerant from flowing into the compressor downstream of the motor (liquid back).

[0010] In the present invention, the control device is preferably configured to calculate the current degree of superheat in the refrigeration cycle, and if the degree of superheat is greater than a reference value, control the flow rate adjustment mechanism to increase the flow rate of the refrigerant, and if the degree of superheat is less than the reference value, control the flow rate adjustment mechanism to decrease the flow rate of the refrigerant. In the present invention configured as described above, when the degree of superheat is greater than the reference value, the refrigerant flow rate is increased to decrease the degree of superheat, and when the degree of superheat is less than the reference value, the refrigerant flow rate is decreased to increase the degree of superheat. This makes it possible to maintain the degree of superheat at a predetermined reference value (target value) and reliably prevent liquid backflow into the compressor.

[0011] In the present invention, preferably, the refrigerant circulation system further includes a first pressure sensor that detects the pressure of the refrigerant after it has been compressed by the compressor, and a first temperature sensor that detects the temperature of the refrigerant before it is supplied to the sliding bearing of the motor, and the control device is configured to determine a target cooling capacity to be achieved in the refrigeration cycle based on the heat generation amount of the coil applied to the rotor or stator to be cooled, calculate a target expansion pressure after the refrigerant expands based on the target cooling capacity, the pressure detected by the first pressure sensor, and the temperature detected by the first temperature sensor, determine a target flow rate of the refrigerant by the flow rate adjustment mechanism to achieve the target expansion pressure, and correct the target flow rate to increase if the degree of superheat is greater than a reference value, while correcting the target flow rate to decrease if the degree of superheat is less than the reference value, and control the flow rate adjustment mechanism based on the corrected target flow rate. According to the present invention configured as described above, it is possible to accurately achieve both cooling of the inside of the motor with the refrigerant and prevention of liquid backflow to the compressor.

[0012] In the present invention, preferably, the refrigerant circulation system further includes a second pressure sensor that detects the pressure of the refrigerant after it has flowed out of the sliding bearing, and a second temperature sensor that detects the temperature of the refrigerant after it has been used to cool the rotor or stator, and the control device is configured to calculate the current degree of superheat in the refrigeration cycle based on the pressure detected by the second pressure sensor and the temperature detected by the second temperature sensor. According to the present invention configured as described above, the current degree of superheat (actual degree of superheat) in the refrigeration cycle can be determined with high accuracy.

[0013] In the present invention, the control device is preferably configured to calculate a second superheat degree estimated based on the heat generation amount of the coil and the target cooling capacity separately from the first superheat degree, when the first superheat degree is calculated based on the pressure detected by the second pressure sensor and the temperature detected by the second temperature sensor, and to correct the target flow rate according to the difference between the first superheat degree and the second superheat degree. According to the present invention configured in this manner, the flow rate adjustment mechanism can be accurately feedback-controlled according to the difference between the first superheat degree (actual superheat degree) and the second superheat degree (estimated superheat degree), i.e., the estimation error of the superheat degree.

[0014] In the present invention, the motor preferably further comprises a guide portion that directs the refrigerant immediately after it flows out of the sliding bearing towards a coil that is applied to the rotor or stator to be cooled, and the flow rate adjustment mechanism is configured to be able to adjust the flow rate of the refrigerant by moving the guide portion or sliding bearing in the axial direction so as to change the size of the gap through which the refrigerant flows out, which is located between the guide portion and the end of the sliding bearing on the guide portion side. According to the present invention configured in this manner, the flow rate adjustment mechanism can change the size of the gap between the guide portion and the end of the sliding bearing, thereby accurately adjusting the flow rate of the refrigerant supplied to cool the rotor or stator of the motor. [Effects of the Invention]

[0015] According to the present invention, in a refrigerant circulation system in which the sliding bearing of a motor is lubricated with a refrigerant, the refrigerant is expanded within the motor, and is used for cooling, it is possible to prevent liquid refrigerant from flowing into the compressor. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram of a vehicle to which a refrigerant circulation system according to an embodiment of the present invention is applied; [Figure 2] 1 is a schematic configuration diagram of a motor according to an embodiment of the present invention. [Figure 3] 1 is a block diagram showing an electrical configuration of a refrigerant circulation system according to an embodiment of the present invention. [Figure 4] FIG. 1 is an explanatory diagram illustrating a basic concept of a flow rate control method according to an embodiment of the present invention. [Figure 5] 3 is a flowchart illustrating a flow control method according to an embodiment of the present invention. [Figure 6]4 is a time chart showing a flow rate control method according to an embodiment of the present invention. [Figure 7] 10A and 10B are explanatory diagrams of a flow rate adjusting mechanism according to a modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, a refrigerant circulation system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0018] [Overall configuration] First, the overall configuration of a refrigerant circulation 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 refrigerant circulation system according to this embodiment is applied.

[0019] 1, vehicle 200 is, for example, an electric vehicle, and has a refrigerant circulation system 100 that circulates a refrigerant in a refrigeration cycle. This refrigerant circulation system 100 has a motor (electric motor) 1 that generates power to drive vehicle 200, a compressor (compressor) 3 that compresses the refrigerant to be supplied to motor 1, and a heat exchanger (condenser) 5 that includes a condenser, a fan, etc., and that cools the refrigerant compressed by compressor 3.

[0020] The refrigerant circulation system 100 circulates a CO2 refrigerant (which may contain refrigeration oil or additives) as a natural refrigerant. To this end, the compressor 3 is configured to compress the refrigerant to extremely high pressures. The motor 1 is configured to function as an expansion valve and an evaporator in a refrigeration cycle by using the refrigerant compressed by the compressor 3 to lubricate the sliding bearings that support the rotating shaft and to cool the rotor and stator (details will be described later). For example, in the refrigerant circulation system 100, a high-temperature liquid refrigerant is supplied from the compressor 3 to the heat exchanger 5, a low-temperature liquid refrigerant is supplied from the heat exchanger 5 to the motor 1, and a high-temperature gaseous refrigerant is supplied from the motor 1 to the compressor 3. In this case, the motor 1 is cooled by the latent heat of vaporization of the refrigerant. The refrigerant circulated by the refrigerant circulation system 100 may also be used for an air conditioner that conditions the interior of the vehicle 200.

[0021] [Motor configuration] Next, the configuration of the motor 1 according to this embodiment will be described with reference to Fig. 2. Fig. 2 is a schematic diagram of the motor 1 according to this embodiment. Specifically, Fig. 2 is a cross-sectional view of the motor 1 as seen along the axial direction.

[0022] As shown in Figure 2, the motor 1 is a system that mainly includes a rotor 11, a stator 12, a rotating shaft 13 that is connected to the rotor 11 and has one end connected to a transaxle (not shown) of the vehicle 200, a pair of plain bearings 14 that support the rotating shaft 13, and a housing 15 that houses the rotor 11, stator 12, rotating shaft 13, plain bearings 14, etc.

[0023] The motor 1 also has a refrigerant supply passage 16 that supplies the refrigerant compressed by the compressor 3 to the sliding bearing 14. More specifically, the refrigerant supply passage 16 supplies the refrigerant to the gap between the rotating shaft 13 and the sliding bearing 14. The sliding bearing 14 is configured to be lubricated using the refrigerant (CO2 refrigerant) supplied from the refrigerant supply passage 16 in this way as a lubricant. Typically, the sliding bearing 14 is lubricated using a liquid refrigerant.

[0024] If a rolling bearing is applied to the motor 1, for example in an electric vehicle, the rotating shaft 13 of the motor 1 rotates at a high rotation speed of, for example, over 30,000 rpm, causing a problem of reduced lifespan due to rolling fatigue. On the other hand, if a typical sliding bearing that uses oil is applied to the motor 1, the loss of oil agitation resistance caused by the rotating shaft 13 becomes large. Therefore, in this embodiment, a sliding bearing 14 that uses a refrigerant (CO2 refrigerant) that has been liquefied by compression by the compressor 3 is applied to the motor 1. This solves problems such as rolling fatigue and oil agitation resistance.

[0025] The refrigerant used as a lubricant in the sliding bearing 14 is then supplied to the rotor 11 and stator 12 and used for cooling. Specifically, in the motor 1, a coil (not shown) is provided on the stator 12, and the refrigerant is used to cool the coil of the stator 12. In particular, the motor 1 has a pair of guide sections 19, each of which has a substantially truncated cone shape, provided on the rotating shaft 13 (penetrating the rotating shaft 13) so as to face each of the pair of sliding bearings 14, and these guide sections 19 direct the refrigerant that flows out (sprays) from the gap between the rotating shaft 13 and the sliding bearing 14 toward the coil of the stator 12 (see the arrows in FIG. 2 ). The surface of the guide sections 19 that faces the gap between the rotating shaft 13 and the sliding bearing 14 is inclined, i.e., the guide sections 19 have an inclined surface, and this inclined surface directs the refrigerant toward the coil of the stator 12 (particularly the coil ends), causing the refrigerant to be sprayed onto the coil and evaporate.

[0026] This motor 1 functions as an expansion valve because the refrigerant is supplied from the gap between the rotating shaft 13 and the sliding bearing 14 into a space 15a in the housing 15, where the rotor 11 and the stator 12 are located, and reduced in pressure, and also functions as an evaporator because the refrigerant exchanges heat with the relatively high-temperature stator 12 (the refrigerant evaporates as it is sprayed onto the coil of the stator 12). The refrigerant used for cooling (heat exchange) is then discharged from a refrigerant discharge passage 17 of the motor 1 and returned to the compressor 3 (Fig. 1).

[0027] 2, the refrigerant is not limited to being supplied to stator 12 via slide bearing 14, but may also be supplied directly to stator 12. In this case, it is preferable to supply the refrigerant to stator 12 via an expansion valve. In addition, in a motor in which a coil is provided on rotor 11 instead of stator 12, the refrigerant may be used to cool the coil of rotor 11.

[0028] Motor 1 also has a seal member 18 for sealing sliding bearing 14 provided on the side of rotating shaft 13 that is connected to a transaxle or the like. This seal member 18 is provided in housing 15 so as to prevent refrigerant from leaking to the outside from the gap between sliding bearing 14 and rotating shaft 13. On the other hand, such a seal member 18 is not provided on sliding bearing 14 on the opposite side to the side of rotating shaft 13 that is connected to a transaxle or the like, and the gap between sliding bearing 14 and rotating shaft 13 is sealed by being covered by housing 15.

[0029] Furthermore, motor 1 further has, in refrigerant supply passage 16, a flow rate adjustment valve 20 serving as a "flow rate adjustment mechanism" that can adjust the flow rate of refrigerant supplied into motor 1. Motor 1 is also provided with a first temperature sensor 22 that detects the temperature of the refrigerant before it is supplied to plain bearing 14 (i.e., the temperature of the refrigerant supplied from heat exchanger 5 to motor 1), a second pressure sensor 23 that detects the pressure of the refrigerant after it has flowed out of plain bearing 14 (i.e., the pressure of the refrigerant in space 15a of housing 15), and a second temperature sensor 24 that detects the temperature of the refrigerant after it has been used to cool stator 12 (i.e., the temperature of the refrigerant supplied from motor 1 to compressor 3). Specifically, first temperature sensor 22 is provided in refrigerant supply passage 16, second pressure sensor 23 is provided in space 15a of housing 15, and second temperature sensor 24 is provided in refrigerant discharge passage 17. The locations where the first temperature sensor 22, the second pressure sensor 23, and the second temperature sensor 2 are provided are not limited to the locations shown in FIG. 2, as long as they can detect the temperatures and pressures described above.

[0030] [Electrical configuration of the refrigerant circulation system] Next, the electrical configuration of the refrigerant circulation system 100 will be described with reference to Fig. 3. Fig. 3 is a block diagram showing the electrical configuration of the refrigerant circulation system 100 according to this embodiment.

[0031] 4, the refrigerant circulation system 100 includes, in addition to the above-described flow rate control valve 20, first temperature sensor 22, second pressure sensor 23, and second temperature sensor 24, a first pressure sensor 21 that detects the pressure of the refrigerant after being compressed by the compressor 3 (i.e., the pressure of the refrigerant supplied from the compressor 3 to the heat exchanger 5), and a control device 50. The control device 50 is configured by a computer that includes one or more processors 50a (typically, a CPU) and a memory 50b such as a ROM or RAM that stores various programs interpreted and executed on the processor 50a (including basic control programs such as an OS and application programs that are started on the OS and realize specific functions) and various data.

[0032] Specifically, the control device 50 controls the flow rate adjustment valve 20 of the motor 1 based on the pressure and temperature detected by the first pressure sensor 21, the first temperature sensor 22, the second pressure sensor 23, and the second temperature sensor 24. In particular, in this embodiment, the control device 50 controls the opening of the flow rate adjustment valve 20 to adjust the flow rate of the refrigerant so as to adjust the degree of superheat in the refrigeration cycle realized by the refrigerant circulation system 100, in order to prevent the refrigerant in a liquid state from flowing from the motor 1 to the compressor 3 (liquid back).

[0033] [Flow control method] Next, a control method (flow rate control method) that the control device 50 performs on the flow rate adjustment valve 20 of the motor 1 in this embodiment will be specifically described.

[0034] First, the basic concept of the flow rate control method according to this embodiment will be described with reference to Fig. 4. Fig. 4 shows the refrigeration cycle of a refrigerant (CO2 refrigerant), with enthalpy and pressure plotted on the horizontal and vertical axes, respectively. Fig. 4 also includes regions representing the states that the refrigerant can take, specifically, liquid, gas, gas-liquid mixed phase, and supercritical states. In Fig. 4, the area surrounded by curve L1 represents the gas-liquid mixed phase. In other words, curve L1 corresponds to the boundary between the gas-liquid mixed phase and the supercritical, liquid, and gas states.

[0035] 4, the refrigeration cycle realized by the refrigerant circulation system 100 is repeated in the order of point A → point B → point C → point D. Specifically, this refrigeration cycle includes a compression process performed by the compressor 3 from point A to point B, a condensation process performed by the heat exchanger 5 from point B to point C, an expansion process performed by the motor 1 from point C to point D (i.e., expansion of the refrigerant from the sliding bearing 14 to the space 15a of the housing 15 within the motor 1), and an evaporation process performed by the motor 1 from point D to point A (i.e., cooling (heat exchange) of the stator 12 by the refrigerant within the motor 1).

[0036] Here, during the evaporation process from point D to point A, the enthalpy (heat quantity) from point D to point X on curve L1 (the intersection of line segment DA and curve L1) corresponds to the cooling capacity (cooling amount) of the refrigeration cycle of the refrigerant circulation system 100, and the enthalpy (heat quantity) from point X to point A corresponds to the superheat of the refrigeration cycle of the refrigerant circulation system 100. Generally, in the evaporator of a refrigeration cycle, a state in which the refrigerant temperature is higher than the saturated vapor temperature is called "superheat," and the temperature difference between these is called the "degree of superheat." Therefore, the degree of superheat can be calculated by subtracting the saturated vapor temperature corresponding to the pressure at point D (the pressure at the start of the evaporation process) from the temperature at point A (the temperature at the start of the compression process). Increasing the degree of superheat ensures that the refrigerant is in a gaseous state at the start of the compression process, i.e., before the compressor 3, and prevents the liquid backflow. However, if the degree of superheat is too high, the cooling capacity decreases, meaning that the stator 12 cannot be effectively cooled by the refrigerant.

[0037] Such a degree of superheat can be adjusted by controlling the flow rate of the refrigerant with the flow rate control valve 20 of the motor 1. That is, as shown in Fig. 4, when the flow rate control valve 20 is controlled to open to increase the flow rate of the refrigerant, the cooling capacity increases but the degree of superheat decreases. Conversely, when the flow rate control valve 20 is controlled to close to decrease the flow rate of the refrigerant, the cooling capacity decreases but the degree of superheat increases. On the other hand, the degree of superheat changes appropriately depending on the operating state of the vehicle 1, that is, the operating state of the refrigerant circulation system 100. Typically, the degree of superheat tends to change depending on the amount of heat generated in the coil of the stator 12 of the motor 1 (coil heat generation amount).

[0038] For the above reasons, in this embodiment, the control device 50 adjusts the degree of superheat in the refrigeration cycle by controlling the flow rate control valve 20 of the motor 1 to prevent liquid backflow to the compressor 3 while ensuring the cooling capacity of the refrigerant. Specifically, the control device 50 calculates the current degree of superheat in the refrigeration cycle (hereinafter referred to as the "actual degree of superheat"), and when the actual degree of superheat is greater than a target degree of superheat (hereinafter simply referred to as the "reference value"), the control device 50 controls the flow rate control valve 20 to the opening side so as to increase the flow rate of the refrigerant, and when the actual degree of superheat is smaller than the reference value, the control device 50 controls the flow rate control valve 20 to the closing side so as to decrease the flow rate of the refrigerant. In this way, the degree of superheat is maintained at the reference value. The reference value is determined in advance from the viewpoint of realizing both the cooling capacity of the refrigerant and preventing liquid backflow. Alternatively, a reference value having a certain range may be used, and the refrigerant flow rate may be increased when the actual degree of superheat exceeds this range, and decreased when the actual degree of superheat falls below this range.

[0039] Next, the flow rate control method according to this embodiment will be described in more detail with reference to Fig. 5. Fig. 5 is a flowchart showing the flow rate control method according to this embodiment. This flow is repeatedly executed at a predetermined cycle by the control device 50. More specifically, the processor 50a in the control device 50 reads a program stored in the memory 50b and executes the program, thereby realizing the flow rate control method according to this flow.

[0040] First, in step S10, the control device 50 acquires various information such as pressure and temperature detected by each of the first pressure sensor 21, the first temperature sensor 22, the second pressure sensor 23, and the second temperature sensor 24. Then, in step S11, the control device 50 calculates the coil heat generation amount corresponding to the amount of current (coil current amount) supplied to the stator 12 of the motor 1. The coil current amount is the amount of current corresponding to the control signal supplied from the control device 50 to the motor 1 (more specifically, the amount of current input to the stator 12 of the motor 1 via the inverter), and the coil heat generation amount is a heat generation amount that is uniquely determined from this coil current amount.

[0041] Next, in step S12, based on the heat generation amount of the coil calculated in step S11, the control device 50 determines a target cooling capacity (in other words, a required cooling amount) to be achieved by the refrigeration cycle in order to adequately cool the stator 12 of the motor 1. For example, the target cooling capacity is a value to be applied (amount of heat to be removed by cooling) determined in advance according to the heat generation amount of the coil.

[0042] Next, in step S13, the control device 50 calculates the target expansion pressure to be set after the refrigerant expands, based on the target cooling capacity determined in step S12. Specifically, from the refrigeration cycle realized by the refrigerant circulation system 100 shown in Fig. 4, the control device 50 calculates the target expansion pressure (pressure at point D) for achieving the target cooling capacity (amount of heat between points D and X) based on the pressure of the refrigerant after it has been compressed by the compressor 3 (pressure at point B), detected by the first pressure sensor 21, and the temperature of the refrigerant before it is supplied to the sliding bearing 14 (temperature at point C), detected by the first temperature sensor 22.

[0043] Next, in step S14, the control device 50 determines a target valve opening of the flow rate adjustment valve 20 of the motor 1 to achieve the target expansion pressure calculated in step S13. For example, the target valve opening is a value (opening) that should be applied depending on the target expansion pressure, which is determined in advance.

[0044] Next, in step S15, the control device 50 calculates the current degree of superheat (actual degree of superheat) in the refrigeration cycle based on the pressure of the refrigerant after it has flowed out of the sliding bearing 14 (pressure at point D; this is the current actual pressure and is different from the target expansion pressure) detected by the second pressure sensor 23 and the temperature of the refrigerant after it has been used to cool the stator 12 (temperature at point A) detected by the second temperature sensor 24. Specifically, the control device 50 calculates the actual degree of superheat by determining the saturated steam temperature according to the pressure detected by the second pressure sensor 23 and subtracting the saturated steam temperature from the temperature detected by the second temperature sensor 24.

[0045] Next, in step S16, the control device 50 calculates an estimated degree of superheat (second degree of superheat) based on the coil heat value calculated in step S11 and the target cooling capacity determined in step S12, separately from the actual degree of superheat (first degree of superheat). Specifically, the control device 50 calculates the estimated degree of superheat by subtracting the heat value corresponding to the target cooling capacity from the coil heat value.

[0046] Next, in step S17, the control device 50 calculates an estimation error (absolute value) by subtracting the actual superheat degree calculated in step S15 from the estimated superheat degree calculated in step S16. Then, in step S18, the control device 50 determines whether this estimation error is less than a predetermined value. As a result, if the control device 50 does not determine that the estimation error is less than the predetermined value (step S18: No), that is, if the estimation error is equal to or greater than the predetermined value, the control device 50 proceeds to step S19. In step S19, the control device 50 corrects the target valve opening determined in step S14 in accordance with the magnitude of the estimation error (absolute value). Thereafter, the control device 50 returns to step S13 and performs the processes from step S13 onwards again.

[0047] On the other hand, if the control device 50 determines that the estimation error is less than the predetermined value (step S18: Yes), the process proceeds to step S20. In step S20, the control device 50 determines whether the actual degree of superheat calculated in step S15 is greater than the above-mentioned reference value. As a result, if the control device 50 determines that the actual degree of superheat is greater than the reference value (step S20: Yes), the process proceeds to step S21, where the control device 50 corrects the target valve opening to the open side in accordance with the difference (absolute value) between the actual degree of superheat and the reference value. Then, the control device 50 proceeds to step S24, where the control device 50 controls the flow rate adjustment valve 20 so as to set the flow rate adjustment valve 20 to the target valve opening corrected in step S21.

[0048] On the other hand, if the control device 50 does not determine that the actual superheat degree is greater than the reference value (step S20: No), the process proceeds to step S22. In step S22, the control device 50 determines whether the actual superheat degree is smaller than the reference value. As a result, if the control device 50 determines that the actual superheat degree is smaller than the reference value (step S22: Yes), the process proceeds to step S23, where the control device 50 corrects the target valve opening to the closing side according to the difference (absolute value) between the actual superheat degree and the reference value. Then, the control device 50 proceeds to step S24, where the control device 50 controls the flow rate adjustment valve 20 so as to set the flow rate adjustment valve 20 to the target valve opening corrected in step S23.

[0049] On the other hand, when the control device 50 does not determine that the actual superheat degree is smaller than the reference value (step S22: No), the process proceeds to step S24. In this case, since the actual superheat degree is maintained at the reference value, the control device 50 controls the flow rate adjustment valve 20 to set the target valve opening degree to the target valve opening degree without correcting the target valve opening degree.

[0050] Next, FIG. 6 is a time chart showing the flow rate control method according to this embodiment. FIG. 6 shows the time variations of the coil heat generation amount, the valve opening of the flow rate control valve 20 of the motor 1, and the superheat degree (actual superheat degree) of the refrigeration cycle. As shown in FIG. 6, the coil heat generation amount increases from time t1, causing the flow rate control valve 20 to be set to the open side. Accordingly, the superheat degree changes, but the opening of the flow rate control valve 20 is adjusted so that the superheat degree is quickly maintained at the reference value. Subsequently, the coil heat generation amount decreases from time t2, causing the flow rate control valve 20 to be set to the closed side. Accordingly, the superheat degree changes, but the opening of the flow rate control valve 20 is adjusted so that the superheat degree is quickly maintained at the reference value. Thereafter, a similar flow rate control method is executed.

[0051] [Action and effect] Next, the operation and effects of the refrigerant circulation system 100 according to this embodiment will be described.

[0052] In this embodiment, a refrigerant circulation system 100 that circulates a refrigerant containing CO2 includes a motor 1 equipped with a compressor 3 that compresses the refrigerant, a rotor 11 and a stator 12, a rotating shaft 13 connected to the rotor 11, and a plain bearing 14 that supports the rotating shaft 13 and is lubricated using the refrigerant compressed by the compressor 3, wherein the refrigerant passing through the motor 1 is expanded after flowing out of the plain bearing 14 and is used to cool the stator 12, and a control device 50 configured to control at least the motor 1, wherein the motor 1 further includes a flow control valve 20 that can adjust the flow rate of the refrigerant, and the control device 50 controls the flow control valve 20 of the motor 1 to adjust the degree of superheat in the refrigeration cycle of the refrigerant realized by the refrigerant circulation system 100.

[0053] According to this embodiment, in the refrigerant circulation system 100 in which the sliding bearing 14 of the motor 1 is lubricated with refrigerant and the motor 1 functions as an expansion valve and an evaporator of the refrigeration cycle, the degree of superheat of the refrigeration cycle can be accurately adjusted by controlling the flow rate of the refrigerant to the motor 1 with the flow control valve 20. This makes it possible to prevent liquid refrigerant from flowing into the compressor 3 (liquid back).

[0054] Furthermore, according to this embodiment, the control device 50 calculates the current degree of superheat (actual degree of superheat) in the refrigeration cycle, and if the actual degree of superheat is greater than a reference value, controls the flow rate control valve 20 to increase the refrigerant flow rate. If the actual degree of superheat is less than the reference value, the control device 50 controls the flow rate control valve 20 to decrease the refrigerant flow rate. That is, if the actual degree of superheat is greater than the reference value, the control device 50 increases the refrigerant flow rate to decrease the degree of superheat. If the actual degree of superheat is less than the reference value, the control device 50 decreases the refrigerant flow rate to increase the degree of superheat. This makes it possible to maintain the degree of superheat at a predetermined reference value and reliably prevent liquid backflow to the compressor 3.

[0055] According to this embodiment, the refrigerant circulation system 100 further includes a first pressure sensor 21 that detects the pressure of the refrigerant after compression by the compressor 3 and a first temperature sensor 22 that detects the temperature of the refrigerant before it is supplied to the sliding bearing 14 of the motor 1. The control device 50 determines a target cooling capacity to be achieved by the refrigeration cycle based on the coil heat value, calculates a target expansion pressure after the refrigerant expands based on the target cooling capacity, the pressure detected by the first pressure sensor 21, and the temperature detected by the first temperature sensor 22, determines a target refrigerant flow rate for the flow control valve 20 to achieve the target expansion pressure, and controls the flow control valve 20 based on the corrected target flow rate by increasing the target flow rate when the actual superheat degree is greater than a reference value and decreasing the target flow rate when the actual superheat degree is less than the reference value. This allows the refrigerant to cool the motor 1 (stator 12) while preventing liquid backflow in the compressor 3.

[0056] Furthermore, according to this embodiment, the refrigerant circulation system 100 further includes a second pressure sensor 23 that detects the pressure of the refrigerant after it has flowed out of the sliding bearing 14, and a second temperature sensor 24 that detects the temperature of the refrigerant after it has been used to cool the stator 12, and the control device 50 calculates the current degree of superheat (actual degree of superheat) in the refrigeration cycle based on the pressure detected by the second pressure sensor 23 and the temperature detected by the second temperature sensor 24. This makes it possible to accurately determine the actual degree of superheat.

[0057] Furthermore, according to this embodiment, the control device 50 calculates an estimated degree of superheat based on the coil heat generation amount and the target cooling capacity, separately from the actual degree of superheat calculated based on the pressure detected by the second pressure sensor 23 and the temperature detected by the second temperature sensor 24, and corrects the target flow rate according to the difference between the actual degree of superheat and the estimated degree of superheat. This makes it possible to accurately feedback control the flow rate of the flow control valve 20 according to the estimation error of the degree of superheat.

[0058] [Variations] In the above-described embodiment, the flow rate adjustment valve 20 provided in the refrigerant supply passage 16 was shown as an example of a "flow rate adjustment mechanism" capable of adjusting the flow rate of the refrigerant in the motor 1. However, the use of the flow rate adjustment valve 20 as a flow rate adjustment mechanism is not limited to this. A modified flow rate adjustment mechanism will be described with reference to FIG. 7 . FIG. 7 is an enlarged cross-sectional view of the plain bearing 14 and guide portion 19 of the motor 1. As shown in FIG. 7 , a modified flow rate adjustment mechanism 30 is configured to adjust the flow rate of the refrigerant by either moving the guide portion 19 axially (arrow A1) or moving the plain bearing 14 axially (arrow A2) to change the size of the gap SP through which the refrigerant flows, which is located between the guide portion 19 and the end of the plain bearing 14 on the guide portion 19 side. The flow rate adjustment mechanism 30 is configured to move the guide portion 19 or the plain bearing 14 axially using various known actuators (not shown). [Explanation of symbols]

[0059] 1 motor 3 Compressor 5 Heat exchanger 11 rotor 12 Stator 13 Rotation axis 14 Plain bearings 16 Refrigerant supply passage 19 Guide section 20 Flow control valve 30 Flow rate adjustment mechanism 50 Control device 100 Refrigerant Circulation System 200 vehicles

Claims

1. CO 2 A refrigerant circulation system that circulates a refrigerant including: a compressor that compresses the refrigerant; a motor including a rotor and a stator, a rotating shaft connected to the rotor, and a sliding bearing that supports the rotating shaft and is lubricated using the refrigerant compressed by the compressor, wherein the refrigerant passing through the motor is expanded after flowing out of the sliding bearing and is used to cool the rotor or the stator; a controller configured to control at least the motor; and the motor further includes a flow rate adjusting mechanism that adjusts the flow rate of the refrigerant; The control device is configured to control the flow rate adjustment mechanism of the motor to adjust the degree of superheat in the refrigeration cycle of the refrigerant realized by the refrigerant circulation system. A refrigerant circulation system.

2. 2. The refrigerant circulation system of claim 1, wherein the control device is configured to calculate the current degree of superheat in the refrigeration cycle, and when the degree of superheat is greater than a reference value, control the flow rate adjustment mechanism to increase the flow rate of the refrigerant, and when the degree of superheat is less than the reference value, control the flow rate adjustment mechanism to decrease the flow rate of the refrigerant.

3. the refrigerant circulation system further includes a first pressure sensor that detects a pressure of the refrigerant after being compressed by the compressor, and a first temperature sensor that detects a temperature of the refrigerant before being supplied to the sliding bearing of the motor, The control device determining a target cooling capacity to be realized by the refrigeration cycle based on a heat generation amount of a coil applied to the rotor or the stator to be cooled; calculating a target expansion pressure after the refrigerant expands based on the target cooling capacity, the pressure detected by the first pressure sensor, and the temperature detected by the first temperature sensor; determining a target flow rate of the refrigerant by the flow rate adjustment mechanism to achieve the target expansion pressure; When the degree of superheat is greater than the reference value, a correction is made to increase the target flow rate, and when the degree of superheat is less than the reference value, a correction is made to decrease the target flow rate, and the flow rate adjustment mechanism is controlled based on the corrected target flow rate. The refrigerant circulation system according to claim 2 , wherein the refrigerant circulation system is configured as follows:

4. the refrigerant circulation system further includes a second pressure sensor that detects the pressure of the refrigerant after it has flowed out of the sliding bearing, and a second temperature sensor that detects the temperature of the refrigerant after it has been used to cool the rotor or the stator, 4. The refrigerant circulation system according to claim 2, wherein the control device is configured to calculate the current degree of superheat in the refrigeration cycle based on the pressure detected by the second pressure sensor and the temperature detected by the second temperature sensor.

5. The control device The superheat degree calculated based on the pressure detected by the second pressure sensor and the temperature detected by the second temperature sensor is defined as a first superheat degree. A second superheat degree estimated based on the heat generation amount of the coil and the target cooling capacity is calculated separately from the first superheat degree. correcting the target flow rate in accordance with a difference between the first degree of superheat and the second degree of superheat; The refrigerant circulation system according to claim 4, which is configured as follows:

6. The motor further includes a guide portion configured to direct the refrigerant immediately after flowing out of the sliding bearing toward a coil applied to the rotor or the stator to be cooled, The flow rate adjustment mechanism is configured to be able to adjust the flow rate of the refrigerant by axially moving the guide part or the plain bearing so as to change the size of the gap through which the refrigerant flows out, which is between the guide part and the end of the plain bearing on the guide part side. The refrigerant circulation system according to any one of claims 1 to 3.

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