Refrigerant circulation system

Abstract

To perform control properly in consideration of frictional heat generation occurring in a slide bearing in a refrigerant circulation system which lubricates the slide bearing of a motor with a refrigerant.SOLUTION: A refrigerant circulation system 100 circulates a refrigerant containing a CO2 and includes: a compressor 3 which compresses the refrigerant; a motor 1 including a rotor 11 and a stator 12, a rotary shaft 13 connected to the rotor, and a slide bearing 14 which is lubricated with the refrigerant compressed by the compressor and supports the rotary shaft, the motor being configured so that the refrigerant passing through the motor flows out from the slide bearing and then is expanded to be used to cool the stator; and a control device 50 configured to control at least the motor. The motor 1 further includes a flow regulating valve 20 capable of regulating a flow rate of the refrigerant. The control device 50 controls the flow regulating valve 20 so as to regulate the flow rate of the refrigerant based on a slide surface temperature detected by a third temperature sensor 25.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 have been used in refrigeration cycles used in air conditioners, in which a refrigerant is circulated through a compressor, a heat exchanger, etc. In recent years, such refrigerant circulation systems have also been used to cool components inside vehicles, for example, the batteries of electric vehicles and hybrid vehicles. As one example, Patent Document 1 discloses a vehicle that shares a single compressor and supplies the refrigerant flowing out from the compressor to the air conditioner and battery, thereby achieving a smaller and less expensive system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-037294 Summary of the Invention [Problem to be solved by the invention]

[0004] 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.

[0005] Therefore, the present inventors considered applying a motor to a refrigerant circulation system such as the one described above, and applying a sliding bearing to the motor's rotating shaft that uses, as a lubricant, the refrigerant circulated in this system - in particular, a CO2 refrigerant that is liquefied when compressed by a compressor. At the same time, the present inventors considered having this motor perform part of the function of the refrigeration cycle of the refrigerant circulation system, specifically functioning as an expansion valve and evaporator in the refrigeration cycle. In other words, they considered expanding the refrigerant passing through the motor after it leaves the sliding bearing (expansion valve) and using it to cool the rotor and stator (evaporator).

[0006] In refrigerant circulation systems that include such motors, heat is generated due to friction in the sliding bearings, and this frictional heat can have a variety of effects. For example, if the refrigerant heats up in the sliding bearings, the refrigerant may not be able to sufficiently cool the rotor or stator, or the sliding bearings may wear out or seize. Therefore, refrigerant circulation systems must be controlled in a way that takes into account the frictional heat generated in the sliding bearings.

[0007] The present invention has been made to solve the problems of the conventional technology described above, and has an object to provide accurate control in a refrigerant circulation system that lubricates the sliding bearings of a motor with a refrigerant, taking into account the frictional heat generated in the sliding bearings. [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 including 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 is configured to obtain the sliding surface temperature of the sliding bearing of the motor, and control the flow rate adjustment mechanism of the motor to adjust the flow rate of the refrigerant in accordance with the sliding surface temperature.

[0009] According to the present invention configured in this way, in a refrigerant circulation system that lubricates a motor's sliding bearing with a refrigerant, the cumulative frictional heat generated by fluid lubrication in the sliding bearing can be determined based on the sliding surface temperature of the sliding bearing. Therefore, according to the present invention, the motor's flow rate adjustment mechanism can be accurately controlled by taking into account the frictional heat generated by fluid lubrication in the sliding bearing. For example, when frictional heat is high, the flow rate adjustment mechanism can increase the refrigerant flow rate, thereby ensuring the refrigerant's cooling performance for the motor.

[0010] In the present invention, the control device is preferably configured to control the flow rate adjustment mechanism so that the flow rate of the coolant increases as the sliding surface temperature increases. According to the present invention configured as described above, it is possible to effectively prevent insufficient cooling of the motor caused by heating of the refrigerant due to frictional heat.

[0011] In the present invention, preferably, the refrigerant circulation system further includes a motor rotation speed sensor that detects the rotation speed of the motor, and the control device is configured to control the flow rate adjustment mechanism based on the sliding surface temperature only when the rotation speed detected by the motor rotation speed sensor is equal to or greater than a predetermined threshold value. According to the present invention configured in this manner, in the high rotation speed range where cumulative frictional heat due to fluid lubrication occurs, this frictional heat can be accurately grasped based on the sliding surface temperature and the flow rate adjustment mechanism can be controlled.

[0012] In the present invention, the control device is preferably configured to calculate the amount of frictional heat generated in the sliding bearing according to the sliding surface temperature and the amount of heat generated by a coil applied to the rotor or stator to be cooled, calculate the required cooling capacity to be achieved by the refrigerant circulation system based on the amount of frictional heat generated and the amount of heat generated by the coil, and control the flow rate adjustment mechanism based on the required cooling capacity. According to the present invention configured in this manner, the required cooling capacity of the entire refrigerant circulation system is set taking into account the amount of frictional heat generated in the sliding bearing, thereby ensuring appropriate cooling of the motor by the refrigerant.

[0013] In the present invention, preferably, the refrigerant circulation system further includes a pressure sensor that detects the pressure of the refrigerant after it has been compressed by the compressor, and a 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 calculate a target expansion pressure after the refrigerant has expanded based on the required cooling capacity, the pressure detected by the pressure sensor, and the temperature detected by the temperature sensor, determine a target flow rate of the refrigerant by the flow rate adjustment mechanism to achieve the target expansion pressure, and control the flow rate adjustment mechanism so that the refrigerant flows at the target flow rate. According to the present invention configured in this manner, the target expansion pressure is accurately calculated from the required cooling capacity, and the flow rate adjustment mechanism is controlled based on the target flow rate corresponding to this target expansion pressure, so that the required cooling capacity can be accurately achieved.

[0014] In the present invention, the motor preferably further comprises a guide portion configured to direct the refrigerant immediately after it flows out of the sliding bearing towards a coil 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.

[0015] In a preferred example of the present invention, the refrigerant circulation system further includes a temperature sensor that detects the sliding surface temperature, and the control device is configured to acquire the sliding surface temperature detected by the temperature sensor and control the flow rate adjustment mechanism based on the sliding surface temperature. [Effects of the Invention]

[0016] According to the present invention, in a refrigerant circulation system that lubricates the sliding bearings of a motor with a refrigerant, it is possible to perform accurate control taking into account the frictional heat generated in the sliding bearings. [Brief explanation of the drawings]

[0017] [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] 1 is an explanatory diagram of a refrigeration cycle in a refrigerant circulation system according to an embodiment of the present invention. [Figure 5] 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 6] 3 is a flowchart illustrating a flow control method according to an embodiment of the present invention. [Figure 7] 4 is a time chart showing a flow rate control method according to an embodiment of the present invention. [Figure 8] 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

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

[0019] [Overall configuration] First, the overall configuration of 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.

[0020] 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.

[0021] 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.

[0022] [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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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).

[0028] 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.

[0029] 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.

[0030] Furthermore, motor 1 is provided with a flow rate adjustment valve 20, located in refrigerant supply passage 16, 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), 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), and a third temperature sensor 25 that detects the temperature of the sliding surface of plain bearing 14. Specifically, first temperature sensor 22 is provided in refrigerant supply passage 16, second pressure sensor 23 is provided in space 15a of housing 15, second temperature sensor 24 is provided in refrigerant discharge passage 17, and third temperature sensor 25 is provided in plain bearing 14. The locations where the first temperature sensor 22, the second pressure sensor 23, the second temperature sensor 24, and the third temperature sensor 25 are provided are not limited to the locations shown in FIG. 2, as long as they can detect the temperatures and pressures described above.

[0031] [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.

[0032] 4, the refrigerant circulation system 100 includes, in addition to the flow rate control valve 20, the first temperature sensor 22, the second pressure sensor 23, the second temperature sensor 24, and the third temperature sensor 25, 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), a motor rotation speed sensor 26 that detects the motor rotation speed of the motor 1 (the rotation speed of the rotor 11 and the rotating shaft 13, which is synonymous with the rotation speed), 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 by the processor 50a (including basic control programs such as an OS and application programs that are run on the OS to realize specific functions) and various data.

[0033] Specifically, the control device 50 controls the flow rate adjustment valve 20 of the motor 1 based on the detected values detected by the first pressure sensor 21, the first temperature sensor 22, the second pressure sensor 23, the second temperature sensor 24, the third temperature sensor 25, and the motor rotation speed sensor 26. In particular, in this embodiment, the control device 50 grasps (estimates) the frictional heat generated in the sliding bearing 14 of the motor 1 based on the motor rotation speed detected by the motor rotation speed sensor 26 or the sliding surface temperature detected by the third temperature sensor 25, and controls the opening of the flow rate adjustment valve 20 to adjust the flow rate of the refrigerant in order to suppress various effects caused by this frictional heat.

[0034] [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.

[0035] First, the refrigeration cycle of the refrigerant circulation system 100 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.

[0036] 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).

[0037] In 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 degree 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 liquid refrigerant from flowing into the compressor 3 (liquid backflow / liquid return). However, if the degree of superheat is too great, the cooling capacity will be reduced, i.e. the stator 12 will not be cooled effectively by the refrigerant.

[0038] Next, the basic concept of the flow rate control method according to this embodiment will be described with reference to Figure 5. Figure 5 shows the motor rotation speed on the horizontal axis and heat due to friction generated in the sliding bearing 14 of the motor 1 (this is the frictional heat described above and uniquely corresponds to the friction coefficient) on the vertical axis, and depicts a Stribeck curve for the sliding bearing 14. Specifically, solid line graph G1 shows frictional heat due to boundary lubrication in the sliding bearing 14, dashed line graph G2 shows frictional heat due to fluid lubrication in the sliding bearing 14, and dash-dot line graph G3 shows frictional heat resulting from the combination of frictional heat due to boundary lubrication and frictional heat due to fluid lubrication (frictional heat due to mixed lubrication).

[0039] As shown in Figure 5, in the low rotation speed region R1, frictional heat due to fluid lubrication does not occur, but only frictional heat due to boundary lubrication occurs. In the high rotation speed region R3, frictional heat due to boundary lubrication does not occur, but only frictional heat due to fluid lubrication occurs. In the medium rotation speed region R2 between regions R1 and R3, frictional heat due to both boundary lubrication and fluid lubrication (mixed lubrication) occurs. It can also be seen that frictional heat due to boundary lubrication rapidly decreases as the motor rotation speed increases, or in other words, rapidly increases as the motor rotation speed decreases (graph G1). In contrast, frictional heat due to fluid lubrication is generally smaller than frictional heat due to boundary lubrication, and it can also be seen that frictional heat due to fluid lubrication gradually increases as the motor rotation speed increases (graph G2).

[0040] When the vehicle 200 is traveling at low speeds or decelerating to a stop, the motor rotation speed falls within a low rotation speed region R1, resulting in relatively large amounts of frictional heat generation due to boundary lubrication. Because the motor rotation speed is low at this time, the demand for refrigerant cooling of the stator 12 is low. However, if the refrigerant flow rate is reduced in response to this demand for cooling, frictional heat generation in the sliding bearing 14 may cause wear or seizure. In contrast, when the vehicle 200 is accelerating at full throttle or accelerating from start, the motor rotation speed falls within a high rotation speed region R3, resulting in relatively large amounts of frictional heat generation due to fluid lubrication. Because the motor rotation speed is high at this time, the stator 12 reaches a relatively high temperature. However, the refrigerant in the sliding bearing 14 is heated by frictional heat (and may even vaporize), preventing the refrigerant from sufficiently cooling the stator 12, potentially resulting in a reduction in the output of the motor 1.

[0041] Here, frictional heat due to boundary lubrication is caused by solid-state contact between the sliding bearing 14 and the rotating shaft 13 (more specifically, contact between protrusions on the rough surface of the solid). This type of frictional heat due to boundary lubrication occurs mainly in the relatively low region R1 (including the low-speed side of region R2), and is transient heat generated by a flint-like flash temperature at the contact point. Because frictional heat due to boundary lubrication changes too quickly, it is difficult to grasp (track) using the detected value of a temperature sensor, but it can be grasped based on the motor rotation speed. In other words, the solid-state contact that occurs between the sliding bearing 14 and the rotating shaft 13 can be accurately grasped based on the magnitude of the motor rotation speed.

[0042] In contrast, frictional heat generated by fluid lubrication is caused by shear heat generated when the fluid (refrigerant) sandwiched between the sliding bearing 14 and the rotating shaft 13 is dragged by rotation. This type of frictional heat generated by fluid lubrication occurs mainly in the relatively high region R3 (including the high rotation side of region R2) and is cumulative heat generated by long-term shear. Therefore, if an attempt is made to determine frictional heat generated by fluid lubrication based on the motor rotation speed as described above, a discrepancy will occur, so it is preferable to determine the heat using the temperature detected by a temperature sensor, specifically the sliding surface temperature detected by the third temperature sensor 25.

[0043] In light of the above, in this embodiment, the control device 50 estimates the transient temperature rise at the sliding surface due to frictional heat based on the motor rotation speed detected by the motor rotation speed sensor 26 in a relatively low rotation speed range including at least region R1 where frictional heat due to boundary lubrication occurs, specifically, in a rotation speed range below a predetermined threshold N1 (a rotation speed predetermined within the medium rotation speed range R2), and controls the flow control valve 20 based on the estimation result. Specifically, the control device 50 controls the flow control valve 20 to increase the refrigerant flow rate because the lower the motor rotation speed, the greater the frictional heat due to boundary lubrication. Note that the threshold N1 is, for example, the motor rotation speed at which the magnitude of frictional heat due to boundary lubrication and that due to fluid lubrication switch places.

[0044] In response to this, in a relatively high rotation speed range including at least region R3 where frictional heat generation due to fluid lubrication occurs, specifically a rotation speed range equal to or greater than threshold value N1, control device 50 estimates the cumulative temperature rise at the sliding surface due to frictional heat generation based on the sliding surface temperature detected by third temperature sensor 25, rather than the motor rotation speed described above, and controls flow rate control valve 20 based on the estimation result. Specifically, because the higher the sliding surface temperature, the greater the frictional heat generation due to fluid lubrication, control device 50 controls flow rate control valve 20 to increase the refrigerant flow rate.

[0045] Furthermore, in this embodiment, the control device 50 calculates the amount of heat generated by friction in the sliding bearing 14 (frictional heat generation amount) and the amount of heat generated in the coil of the stator 12 of the motor 1 to be cooled by the refrigerant (coil heat generation amount), calculates the required cooling capacity to be achieved by the refrigerant circulation system 100 based on these frictional heat generation amount and coil heat generation amount, and controls the flow rate adjustment valve 20 based on this required cooling capacity. That is, in this embodiment, the control device 50 uses the cooling demand for the stator 12 plus the amount of frictional heat generation as the required cooling capacity for the entire refrigerant circulation system 100, and controls the flow rate of the refrigerant with the flow rate adjustment valve 20.

[0046] Next, the flow rate control method according to this embodiment will be described in more detail with reference to Fig. 6. Fig. 6 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.

[0047] First, in step S10, the control device 50 acquires various information such as the detection values detected by the first pressure sensor 21, the first temperature sensor 22, the second pressure sensor 23, the second temperature sensor 24, the third temperature sensor 25, and the motor rotation speed sensor 26. Then, in step S11, the control device 50 determines whether the motor rotation speed acquired in step S10 is less than the threshold value N1 described above.

[0048] If, as a result of step S11, it is determined that the motor rotation speed is less than threshold value N1 (step S11: Yes), the control device 50 proceeds to step S12. In step S12, the control device 50 calculates the amount of frictional heat generated in the sliding bearing 14 based on the motor rotation speed acquired in step S10, that is, it estimates the transient temperature rise on the sliding surface caused by frictional heat due to boundary lubrication. In this case, the control device 50 calculates a larger amount of frictional heat as the motor rotation speed decreases. For example, the control device 50 calculates the amount of frictional heat from the friction coefficient, solid contact pressure, motor rotation speed (rotational speed), and specific frictional heat. This solid contact pressure can be found from the Hertzian contact area, microprotrusion density, microprotrusion curvature, standard deviation of microprotrusion height, etc.

[0049] On the other hand, if the result of step S11 shows that the control device 50 does not determine that the motor rotation speed is less than threshold value N1 (step S11: No), that is, if the motor rotation speed is equal to or greater than threshold value N1, the control device 50 proceeds to step S13. In step S13, the control device 50 calculates the amount of frictional heat generated in the sliding bearing 14 based on the sliding surface temperature (detected by the third temperature sensor 25) acquired in step S10, that is, estimates the cumulative temperature rise at the sliding surface caused by frictional heat due to fluid lubrication. In this case, the control device 50 calculates a larger amount of frictional heat as the sliding surface temperature increases. For example, the control device 50 calculates the amount of frictional heat from factors such as the viscosity of the refrigerant and the speed gradient of the motor rotation speed (rotational speed) between the sliding bearing 14 and the rotating shaft 13. The amount of frictional heat calculated in this manner increases as the sliding surface temperature increases.

[0050] After steps S12 and S13, the control device 50 proceeds to step S14. In step S14, the control device 50 calculates the coil heat generation amount according 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.

[0051] Next, in step S15, the control device 50 determines the required cooling capacity to be realized by the refrigeration cycle of the refrigerant circulation system 100 based on the frictional heat generation amount calculated in step S12 or S13 and the coil heat generation amount calculated in step S14. Specifically, the control device 50 adds the frictional heat generation amount and the coil heat generation amount, and determines the required cooling capacity (a value that uniquely corresponds to the heat generation amount) according to the heat generation amount obtained by this addition.

[0052] Next, in step S16, the control device 50 calculates the target expansion pressure to be set after the refrigerant expands, based on the required cooling capacity determined in step S15. 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 required cooling capacity (the 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.

[0053] Next, in step S17, 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 S16. For example, the target valve opening is a value (opening) that should be applied according to the target expansion pressure, which is determined in advance. Then, in step S18, 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 determined in step S17.

[0054] Next, FIG. 7 is a time chart illustrating a flow rate control method according to this embodiment. FIG. 7 shows the time variations of the output demand of the motor 1 (corresponding to the accelerator pedal depression of the vehicle 200), the motor rotation speed, the amount of frictional heat generated, the amount of coil heat generated, and the valve opening of the flow rate control valve 20 of the motor 1. As shown in FIG. 7, from time t1, the output demand of the vehicle 200 increases, and the vehicle 200 accelerates, for example, from 0 km / h (stopped state) to 40 km / h. Then, from time t2 after time t1, the output demand becomes constant, and the vehicle 200 begins steady-state driving. In this case, while the motor rotation speed is below the threshold N1 (from time t1 to time t4, described below), the control device 50 calculates the amount of transient frictional heat generated by boundary lubrication in the sliding bearing 14 based on the motor rotation speed, and controls the valve opening of the flow rate control valve 20 based on this amount of frictional heat generated and the amount of coil heat generated.

[0055] Subsequently, at time t3 after time t2, the output demand of the vehicle 200 increases again, and the vehicle 200 accelerates, for example, from 40 km / h to 100 km / h. Then, from time t5 after time t3, the output demand becomes constant, and the vehicle 200 begins steady driving. In this case, at time t4 immediately after time t3, the motor rotation speed becomes equal to or greater than threshold value N1, so the control device 50 calculates the cumulative amount of frictional heat generated by fluid lubrication in the sliding bearing 14 based on the sliding surface temperature detected by the third temperature sensor 25 instead of the motor rotation speed, and controls the valve aperture of the flow control valve 20 based on this amount of frictional heat and the amount of coil heat generation. While the motor rotation speed is equal to or greater than threshold value N1 (from time t4 onwards), the control device 50 controls the valve aperture of the flow control valve 20 using the amount of frictional heat calculated in this way based on the sliding surface temperature.

[0056] [Action and effect] Next, the operation and effects of the refrigerant circulation system 100 according to this embodiment will be described.

[0057] In this embodiment, a refrigerant circulation system 100 that circulates a refrigerant containing CO2 includes a motor 1 that includes 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 sliding bearing 14 that supports the rotating shaft 13 and is lubricated using the refrigerant compressed by the compressor 3, wherein the motor 1 is configured so that the refrigerant passing through the motor 1 flows out of the sliding bearing 14 and is expanded to be used to cool the stator 12, a third temperature sensor 25 that detects the sliding surface temperature of the sliding bearing 14, and a control device 50 that is 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 flow rate of the refrigerant in accordance with the sliding surface temperature detected by the third temperature sensor 25.

[0058] According to this embodiment, in a refrigerant circulation system 100 that lubricates the sliding bearing 14 of the motor 1 with a refrigerant, the cumulative frictional heat generated by fluid lubrication in the sliding bearing 14 can be determined based on the sliding surface temperature of the sliding bearing 14. Therefore, according to this embodiment, the flow rate adjustment valve 20 of the motor 1 can be accurately controlled by taking into account the frictional heat generated by fluid lubrication in the sliding bearing 14. Specifically, when frictional heat is high, the flow rate of the refrigerant can be increased by the flow rate adjustment valve 20, and as a result, it is possible to ensure the cooling performance of the refrigerant for the motor 1 (stator 12).

[0059] Furthermore, according to this embodiment, the control device 50 controls the flow rate adjustment valve 20 so that the flow rate of the refrigerant increases as the sliding surface temperature increases. This effectively prevents insufficient cooling of the motor 1 (stator 12) caused by heating of the refrigerant due to frictional heat generation.

[0060] Furthermore, according to this embodiment, the control device 50 controls the flow control valve 20 based on the sliding surface temperature only when the motor rotation speed is equal to or greater than a predetermined threshold value N1. As a result, in the high rotation speed range where cumulative frictional heat due to fluid lubrication occurs, this frictional heat can be accurately determined based on the sliding surface temperature, and the flow control valve 20 can be controlled.

[0061] Furthermore, according to this embodiment, the control device 50 calculates the amount of frictional heat generated in the sliding bearing 14 according to the sliding surface temperature and the amount of heat generated by the coil of the stator 12 to be cooled, calculates the required cooling capacity to be achieved by the refrigerant circulation system 100 based on the amount of frictional heat generated and the amount of heat generated by the coil, and controls the flow rate adjustment valve 20 based on the required cooling capacity. In this way, the required cooling capacity of the entire refrigerant circulation system 100 is set taking into account the amount of frictional heat generated in the sliding bearing 14, thereby ensuring accurate cooling of the motor 1 (stator 12) by the refrigerant.

[0062] Furthermore, according to this embodiment, the refrigerant circulation system 100 further includes a first pressure sensor 21 that detects the pressure of the refrigerant after it has been compressed 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 calculates a target expansion pressure after the refrigerant expands based on the required cooling capacity, the pressure detected by the first pressure sensor 21, and the temperature detected by the first temperature sensor 22, determines a target flow rate of the refrigerant to be controlled by the flow control valve 20 to achieve the target expansion pressure, and controls the flow control valve 20 so that the refrigerant flows at the target flow rate. This allows the target expansion pressure to be accurately calculated from the required cooling capacity, and the flow control valve 20 to be controlled based on the target flow rate corresponding to this target expansion pressure, thereby accurately achieving the required cooling capacity.

[0063] [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. 8 . FIG. 8 is an enlarged cross-sectional view of the plain bearing 14 and guide portion 19 of the motor 1. As shown in FIG. 8 , 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).

[0064] Furthermore, in the embodiment described above, the sliding surface temperature of the sliding bearing 14 is detected by the third temperature sensor 25, but in a modified example, the sliding surface temperature may be estimated. For example, the frictional heat generated at the sliding surface may be calculated sequentially based on the motor rotation speed or the like, and the sliding surface temperature may be estimated from this frictional heat. [Explanation of symbols]

[0065] 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 acquire a sliding surface temperature of the sliding bearing of the motor, and to control the flow rate adjustment mechanism of the motor so as to adjust the flow rate of the refrigerant in accordance with the sliding surface temperature. A refrigerant circulation system.

2. The refrigerant circulation system according to claim 1 , wherein the control device is configured to control the flow rate adjustment mechanism so that the flow rate of the refrigerant increases as the sliding surface temperature increases.

3. The refrigerant circulation system further includes a motor rotation speed sensor that detects the rotation speed of the motor, 3. The refrigerant circulation system according to claim 1, wherein the control device is configured to control the flow rate adjustment mechanism based on the sliding surface temperature only when the rotation speed detected by the motor rotation speed sensor is equal to or greater than a predetermined threshold value.

4. The control device calculating the amount of frictional heat generated in the sliding bearing according to the sliding surface temperature and the amount of heat generated in a coil applied to the rotor or the stator to be cooled; calculating a required cooling capacity to be realized by the refrigerant circulation system based on the frictional heat generation amount and the heat generation amount of the coil; controlling the flow rate adjusting mechanism based on the required cooling capacity; The refrigerant circulation system according to claim 1 or 2, configured as follows:

5. the refrigerant circulation system further includes a pressure sensor that detects the pressure of the refrigerant after being compressed by the compressor, and a temperature sensor that detects the temperature of the refrigerant before being supplied to the sliding bearing of the motor, The control device calculating a target expansion pressure after the refrigerant expands based on the required cooling capacity, the pressure detected by the pressure sensor, and the temperature detected by the temperature sensor; determining a target flow rate of the refrigerant by the flow rate adjustment mechanism to achieve the target expansion pressure; controlling the flow rate adjustment mechanism so that the refrigerant flows at the target flow rate; The refrigerant circulation system according to claim 4, wherein the refrigerant circulation system 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 claim 1 or 2.

7. The refrigerant circulation system further includes a temperature sensor for detecting the temperature of the sliding surface, the control device is configured to acquire the sliding surface temperature detected by the temperature sensor and control the flow rate adjustment mechanism based on the sliding surface temperature. The refrigerant circulation system according to claim 1 or 2.

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