Vehicle air conditioning system

Abstract

The present invention provides a vehicle air conditioning system that can prevent compressor malfunctions caused by liquid compression occurring during the startup control of heating using a hot gas cycle. [Solution] The control device 200 performs a startup control that flows the refrigerant only through the hot gas bypass path, and determines whether liquid compression occurs in the compressor 11 while the startup control is being performed. If it determines that liquid compression occurs in the compressor 11 while the startup control is being performed, it switches to a parallel circuit that flows the refrigerant through the hot gas bypass path and the condenser path, and circulates the heat transfer medium in the heat transfer medium circuit 20 so that heat exchange can occur between the refrigerant and the heat transfer medium in the high-temperature heat exchanger 12, which is the condenser.

Description

Technical Field

[0001] The present invention relates to a vehicle air conditioner. Background Art

[0002] Conventionally, vehicle air conditioners that perform startup control for hot gas heating operation have been known. For example, Patent Document 1 discloses a vehicle air conditioner that suppresses heat radiation of a refrigerant in an indoor condenser during a preparatory operation before hot gas heating.

[0003] Further, conventionally, techniques for preventing liquid refrigerant from overflowing an accumulator have been known. For example, Patent Document 2 discloses a technique for reducing the amount of refrigerant stored in the accumulator by causing the refrigerant to flow into a flow path through which refrigerant does not normally flow during mode switching, in order to suppress sudden boiling caused by a pressure drop of the refrigerant in the accumulator and consequent entrainment of liquid refrigerant when the mode is switched. Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2024-062473 Patent Document 2 International Publication No. WO 2023 / 199912 Summary of the Invention Problem to be Solved by the Invention

[0005] An object of the present invention is to provide a vehicle air conditioner capable of preventing malfunctions of a compressor caused by liquid compression that occurs during execution of startup control of heating by a hot gas cycle. Means for Solving the Problem

[0006] According to one aspect of the present invention, a vehicle air conditioning system comprises a refrigerant circuit having a compressor, a condenser, an expansion device, an evaporator, and an accumulator; a heat transfer medium circuit through which a heat transfer medium that exchanges heat with the refrigerant in the condenser circulates; and a control device, wherein the refrigerant circuit includes a condenser path through which the refrigerant discharged by the compressor flows upstream of the accumulator via the condenser, and a hot gas bypass path through which the refrigerant discharged by the compressor bypasses the condenser and flows upstream of the accumulator, and the control device performs a start-up control that flows the refrigerant only through the hot gas bypass path, determines whether liquid compression occurs in the compressor while the start-up control is being performed, and if it determines that liquid compression occurs in the compressor while the start-up control is being performed, switches to a parallel circuit that flows the refrigerant through the hot gas bypass path and the condenser path, and circulates the heat transfer medium in the heat transfer medium circuit so that heat exchange between the refrigerant and the heat transfer medium is possible in the condenser. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a vehicle air conditioning system that can prevent compressor malfunctions caused by liquid compression occurring during the execution of heating start-up control using a hot gas cycle. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a circuit diagram showing an example of the configuration of a vehicle air conditioning system. [Figure 2] Figure 2 is a flowchart showing an example of the startup control process. [Figure 3] Figure 3 is a flowchart showing an example of the startup control process. [Modes for carrying out the invention]

[0009] [Configuration of vehicle air conditioning system] <Overview of vehicle air conditioning systems> Figure 1 is an explanatory diagram illustrating the schematic of a vehicle air conditioning system 1. The vehicle air conditioning system 1 is mounted on a vehicle. The vehicle is preferably a vehicle equipped with a battery for driving. The vehicle may be, for example, an electric vehicle (BEV: Battery Electric Vehicle), a hybrid vehicle (HEV: Hybrid Electric Vehicle), a plug-in hybrid vehicle (PHEV: Plug-in Hybrid Electric Vehicle), or a fuel cell vehicle (FCEV: Fuel Cell Electric Vehicle).

[0010] The vehicle air conditioning system 1 includes a refrigerant circuit 10 through which a refrigerant circulates. For example, hydrofluoroolefins may be used as the refrigerant.

[0011] The vehicle air conditioning system 1 includes a heat transfer medium circuit 20 through which a heat transfer medium, such as coolant, is circulated.

[0012] The vehicle air conditioning system 1 includes an HVAC (Heating, Ventilation, and Air Conditioning) unit 100 as an air conditioning unit.

[0013] The vehicle air conditioning system 1 includes a control device 200 that controls the operation of the vehicle air conditioning system 1.

[0014] The refrigerant circuit 10 includes a compressor 11, a high-temperature side heat exchanger 12 which is a condenser, depressurizing devices 13a, 13b, and 13c which are expansion devices, a first low-temperature side heat exchanger 14 which is an evaporator, and a second low-temperature side heat exchanger 16 which is an evaporator.

[0015] The compressor 11 compresses a gaseous refrigerant into a high-temperature and high-pressure state, and then discharges the compressed refrigerant. The high-temperature side heat exchanger 12 condenses the gaseous refrigerant compressed by the compressor 11 and dissipates heat. The pressure reducing devices 13a, 13b, 13c expand the liquid refrigerant to reduce the pressure thereof. The first low-temperature side heat exchanger 14 and the second low-temperature side heat exchanger 16 evaporate the low-temperature and low-pressure liquid refrigerant and absorb heat. The refrigerant circuit 10 functions as a heat pump that circulates a refrigerant and repeatedly performs compression, condensation, expansion and evaporation.

[0016] The high-temperature side heat exchanger 12 includes a refrigerant passage 12a through which the refrigerant circulating in the refrigerant circuit 10 passes, and a heat medium passage 12b through which the heat medium circulating in the heat medium circuit 20 passes. Heat exchange between the heat medium and the refrigerant in the high-temperature side heat exchanger 12 can heat the heat medium circulating in the heat medium circuit 20.

[0017] The first low-temperature side heat exchanger 14 includes a refrigerant passage 14a through which the refrigerant circulating in the refrigerant circuit 10 passes, and a heat medium passage 14b through which the heat medium circulating in a heat medium circuit (not shown) passing through the cooler core 31 passes. Heat exchange between the heat medium and the refrigerant in the first low-temperature side heat exchanger 14 can cool the heat medium circulating in the heat medium circuit passing through the cooler core 31.

[0018] The second low-temperature side heat exchanger 16 includes a refrigerant passage 16a through which the refrigerant circulating in the refrigerant circuit 10 passes, and a heat medium passage 16b through which the heat medium circulating in a heat medium circuit (not shown) passing through temperature control objects such as a motor and a battery passes. Heat exchange between the heat medium and the refrigerant in the second low-temperature side heat exchanger 16 can cool the heat medium circulating in the heat medium circuit passing through the temperature control object.

[0019] Each element of the refrigerant circuit 10 is connected by refrigerant flow paths 10a, 10b, 10c, 10d, 10e, 10f, 10g, 10h, 10i.

[0020] That is, the discharge side 11a of the compressor 11 is connected to the suction side 11b of the compressor 11 via the refrigerant flow path 10a, the branching portion a1, the refrigerant flow path 10b, the merging portion b1, and the refrigerant flow path 10c downstream therefrom connected thereto. A pressure reducing device 13a is provided on the path of the refrigerant flow path 10b. An accumulator 15 is provided on the path of the refrigerant flow path 10c.

[0021] Further, the discharge side 11a of the compressor 11 is connected to an inlet of the refrigerant passage 12a of the high temperature-side heat exchanger 12 via the refrigerant flow path 10a connected thereto, the branching portion a1, and the refrigerant flow path 10d. An outlet of the refrigerant passage 12a of the high temperature-side heat exchanger 12 is connected to an inlet of the refrigerant passage 14a of the first low temperature-side heat exchanger 14 via the refrigerant flow path 10e connected thereto, the branching portion a2, and the refrigerant flow path 10f downstream therefrom. A pressure reducing device 13b is provided on the path of the refrigerant flow path 10f. An outlet of the refrigerant passage 14a of the first low temperature-side heat exchanger 14 is connected to the suction side 11b of the compressor 11 via the refrigerant flow path 10g connected thereto, the merging portion b1, and the refrigerant flow path 10c downstream therefrom.

[0022] Further, the outlet of the refrigerant passage 12a of the high temperature-side heat exchanger 12 is connected to an inlet of the refrigerant passage 16a of the second low temperature-side heat exchanger 16 via the refrigerant flow path 10e connected thereto, the branching portion a2, and the refrigerant flow path 10h downstream therefrom. A pressure reducing device 13c is provided on the path of the refrigerant flow path 10h. An outlet of the refrigerant passage 16a of the second low temperature-side heat exchanger 16 is connected to the suction side 11b of the compressor 11 via the refrigerant flow path 10i connected thereto, the merging portion b1, and the refrigerant flow path 10c downstream therefrom.

[0023] As described above, by configuring the refrigerant flow paths as described above, the refrigerant flow path 10b functions as a bypass path through which the refrigerant discharged from the compressor 11 bypasses the high temperature-side heat exchanger 12 serving as a condenser and flows to the upstream side of the accumulator 15.

[0024] Further, the refrigerant flow paths 10d, 10e, 10f, and 10g function as a condenser path through which the refrigerant discharged from the compressor 11 flows to the upstream side of the accumulator 15 via the high temperature-side heat exchanger 12 serving as a condenser.

[0025] The heat transfer medium circuit 20 circulates the heat transfer medium that exchanges heat with the refrigerant in the high-temperature heat exchanger 12, which is a condenser. In the heat transfer medium circuit 20, the heat transfer medium circulates through the heater core 21 by being pushed by the circulation pump P20.

[0026] The heater core 21 and the cooler core 31 are housed in the HVAC unit 100. The HVAC unit 100 is equipped with a blower 140. The cooler core 31 is located downstream of the blower 140, and the heater core 21 is located downstream of the cooler core 31. Therefore, the air blown by the blower 140 passes through the cooler core 31 and then through the heater core 21.

[0027] The control device 200 includes a processor, memory, storage, and an interface. The processor is, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The memory is, for example, RAM (Random Access Memory). The storage is rewritable non-volatile memory such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or flash memory. The storage stores a system program including an OS (Operating System) and a control program including computer-readable code necessary for control calculations. The processor performs various processes by reading the system program and the control program, loading them into memory, and executing them. The interface controls communication between the control device 200 and the components of the vehicle air conditioning system 1.

[0028] The control device 200 receives detection information from various sensors provided by the vehicle air conditioning system 1. Based on the detection information from the various sensors, the control device 200 controls the operation of the vehicle air conditioning system 1. For example, the control device 200 controls the rotational speed of the compressor 11, the operation of the pressure reducing devices 13a, 13b, and 13c, the operation of the circulation pump P20, and the operation of the blower 140.

[0029] [Operation of the vehicle's air conditioning system 1] The specific operation of the vehicle air conditioning system 1 will be explained below.

[0030] At extremely low temperatures, it is necessary to perform a start-up control before starting heating operation to raise the temperature of the heat transfer medium to the temperature required for heating. For example, one could consider performing a start-up control using a heat exchange cycle called a hot gas cycle, which utilizes a hot gas bypass path.

[0031] Specifically, first, gaseous refrigerant is flowed through two paths: a condenser path and a hot gas bypass path. When the refrigerant from the condenser path and the hot gas bypass path merge and flow into the accumulator 15, the liquid refrigerant in the accumulator 15 is heated and heat is stored in the liquid refrigerant. As a result, the refrigerant in the refrigerant circuit 10 is heated, and the temperature and pressure of the refrigerant drawn in by the compressor 11 increase. By repeating this cycle, when the temperature of the refrigerant rises to a temperature suitable for heating the heat transfer medium, the heat transfer medium in the heat transfer medium circuit is circulated. This causes heat exchange between the refrigerant and the heat transfer medium in the condenser, and the temperature of the heat transfer medium rises. Then, after the temperature of the heat transfer medium has risen, the operation of the blower 140 is started to perform heating. This makes it possible to raise the discharge temperature even at extremely low temperatures.

[0032] However, in the above-described startup control, when gaseous refrigerant is flowed, excess liquid refrigerant is stored in the accumulator 15, but there is a risk that the liquid refrigerant may overflow from the accumulator 15 due to its accumulation. Furthermore, there is a risk that the liquid refrigerant may overflow from the accumulator 15 due to thermal expansion of the liquid refrigerant within the accumulator 15. If the liquid refrigerant overflows from the accumulator 15, liquid compression will occur in the compressor 11, leading to a malfunction of the compressor 11. Therefore, in order to avoid overflow from the accumulator 15, it is necessary to ensure sufficient volume in the accumulator 15. For this reason, it becomes difficult to miniaturize the accumulator 15, and it becomes difficult to reduce the space, weight, and cost of the refrigerant circuit 10.

[0033] Therefore, in this embodiment, two types of startup control 1 and startup control 2 will be described, which aim to prevent malfunctions of the compressor 11 due to liquid compression by miniaturizing the accumulator 15 and preventing liquid refrigerant from overflowing from the accumulator 15.

[0034] <Startup control 1> An example of the startup control 1 performed by the control device 200 will be explained using Figure 2.

[0035] As shown in Figure 2, the control device 200 determines whether or not a startup control request has occurred (S1). A startup control request occurs when the outside temperature becomes extremely low and it becomes difficult to perform outside air intake heating.

[0036] The control device 200 terminates processing if no startup control request has been generated (S1:NO).

[0037] If a request for startup control is received (S1:YES), the control device 200 executes the first stage of startup control (S2).

[0038] In the first stage of startup control, the control device 200 starts the circulation pump P20 so that the flow rate of the heat transfer medium in the heat transfer medium circuit 20 is low. For example, the circulation pump P20 is started so that the flow rate of the heat transfer medium is 5 L / min. The control device 200 also fully opens the pressure reducing device 13a, opens the pressure reducing device 13b to a small degree, and fully closes the pressure reducing device 13c. The opening degree of the pressure reducing device 13b is, for example, 10%. The control device 200 also starts the compressor 11 at a low rotational speed.

[0039] As a result, the control device 200 flows the refrigerant through the hot gas bypass path and the condenser path, and performs startup control to circulate the heat transfer medium in the heat transfer medium circuit 20 so that heat exchange can be performed between the refrigerant and the heat transfer medium in the high-temperature side heat exchanger 12, which is the condenser.

[0040] In other words, the control device 200 flows the heat transfer medium in the heat transfer medium circuit 20 at a constant flow rate while simultaneously flowing a small amount of refrigerant through the condenser path to condense it in the high-temperature heat exchanger 12. This allows for the presence of liquid refrigerant not only in the accumulator 15 but also in the high-temperature heat exchanger 12. This allows the liquid refrigerant in the refrigerant circuit 10 to be distributed between the accumulator 15 and the high-temperature heat exchanger 12. Therefore, it becomes possible to reduce the amount of liquid refrigerant stored in the accumulator 15, thus preventing the liquid refrigerant from overflowing from the accumulator 15. This prevents malfunctions of the compressor 11 due to liquid compression.

[0041] Next, the control device 200 performs the second stage of startup control (S3).

[0042] In the second stage of startup control, the control device 200 maintains the output of the circulation pump P20 at the output level of the first stage. Therefore, the flow rate of the heat transfer medium in the heat transfer medium circuit 20 is maintained at a low flow rate. The control device 200 also maintains the fully open pressure reducing device 13a and the fully closed pressure reducing device 13c.

[0043] On the other hand, the control device 200 controls the opening of the pressure reducing device 13b to an opening such that the discharge superheat of the compressor 11 is equal to or greater than a desired value (for example, 5K), and the intake superheat of the compressor 11 does not occur, thereby satisfying the conditions under which an appropriate amount of liquid refrigerant is present in the high-temperature heat exchanger 12 and the accumulator 15.

[0044] In other words, by managing the discharge superheat, it is possible to prevent liquid refrigerant from overflowing from the accumulator 15, while by managing the intake superheat, it is possible to prevent a shortage of liquid refrigerant in the accumulator 15. This prevents the occurrence of liquid compression and provides the effect of startup control that warms the refrigerant by accumulating heat in the liquid refrigerant. In other words, by accumulating heat in the liquid refrigerant secured in the accumulator 15, it is possible to suppress the extension of the startup control execution time and reduce the amount of liquid refrigerant remaining in the accumulator 15, thereby preventing the occurrence of liquid compression.

[0045] Therefore, in the second stage of startup control, the control device 200 determines whether the discharge superheat is above a predetermined value (S4). This increases the amount of liquid refrigerant returning from the condenser path, causing the liquid refrigerant to overflow from the accumulator 15, and it is possible to determine whether liquid compression occurs in the compressor 11. Alternatively, a sensor installed in the accumulator 15 may be used to detect whether liquid compression occurs.

[0046] If the discharge superheat is not above a predetermined value (S4:NO), the control device 200 reduces the opening of the pressure reducing device 13b located in the condenser path (S9). In other words, if it is determined that liquid compression is occurring in the compressor 11, the opening of the pressure reducing device 13b, which is an expansion device located in the condenser path, is reduced. Then, the process returns to S4.

[0047] In other words, if it is determined that liquid compression is occurring in the compressor 11, the opening of the pressure reducing device 13b located in the condenser path is reduced, and the amount of refrigerant flowing through the hot gas bypass path is increased. This makes it possible to reduce the amount of liquid refrigerant returning from the condenser path, thereby preventing liquid refrigerant from overflowing from the accumulator 15. In addition, the refrigerant flowing into the suction side 11b of the compressor 11 can be superheated. Therefore, the occurrence of liquid compression in the compressor 11 can be suppressed.

[0048] Furthermore, in the second stage of startup control, the control device 200 detects that if the discharge superheat is above a predetermined value (S4: YES), then liquid compression has not occurred and there is no risk of liquid compression occurring. In this case, the control device 200 determines whether or not the intake superheat is above a predetermined value (S5). This allows it to determine whether or not the amount of liquid refrigerant in the accumulator 15 is below a predetermined amount by reducing the amount of liquid refrigerant returning from the condenser path. Alternatively, the amount of liquid refrigerant may be detected by a sensor installed in the accumulator 15.

[0049] Then, if the intake superheat is above a predetermined value (S5: YES), the control device 200 increases the opening of the pressure reducing device 13b located in the condenser path (S10). In other words, if it is determined that the amount of liquid refrigerant in the accumulator 15 is below a predetermined amount, the opening of the pressure reducing device 13b, which is an expansion device located in the condenser path, is increased. After that, the process returns to S4.

[0050] In other words, if the liquid refrigerant in the accumulator 15 is insufficient, the amount of liquid refrigerant returning from the condenser path is increased to store liquid refrigerant in the accumulator 15. By ensuring a certain amount of liquid refrigerant in the accumulator 15, the heat from the high-temperature refrigerant flowing through the hot gas bypass path can be stored, allowing the suction temperature of the compressor 11 (i.e., the temperature of the refrigerant circulating in the refrigerant circuit 10) to rise stably and quickly, thus shortening the time required for startup control.

[0051] Next, in the second stage of startup control, if the intake superheat is below a predetermined value (S5:NO), the control device 200 increases the rotational speed of the compressor 11 (S6). At this time, if the rotational speed of the compressor 11 is at its maximum rotational speed, the rotational speed of the compressor 11 is maintained.

[0052] Next, in the second stage of startup control, the control device 200 determines whether the temperature of the heat transfer medium in the heat transfer medium circuit 20 is at a temperature that can achieve the target discharge temperature (S7). That is, it determines whether the temperature of the heat transfer medium in the heat transfer medium circuit 20 is at a temperature that can blow air at the target discharge temperature into the vehicle interior.

[0053] If the temperature of the heat transfer medium in the heat transfer medium circuit 20 is not at a temperature that can achieve the target discharge temperature (S7:NO), the control device 200 returns to S4.

[0054] Through the above process, in the second stage of startup control, the control device 200 increases the rotational speed of the compressor 11 while ensuring that an appropriate amount of liquid refrigerant is present in the high-temperature heat exchanger 12 and the accumulator 15. The control device 200 then increases the rotational speed of the compressor 11 or maintains the maximum rotational speed until the temperature of the heat transfer medium in the heat transfer medium circuit 20 becomes equivalent to the temperature at which air at the target discharge temperature can be blown into the vehicle interior.

[0055] If the temperature of the heat transfer medium in the heat transfer medium circuit 20 is at a temperature at which the target discharge temperature can be achieved (S7:YES), the control device 200 executes the third stage of startup control (S8).

[0056] In the third stage of startup control, the control device 200 starts the blower 140 and controls the rotation speed of the compressor 11 so that the outlet temperature of the air blown into the vehicle cabin reaches the target outlet temperature. The control device 200 also controls the opening of the pressure reducing device 13b so that the discharge superheat of the compressor 11 is above a desired value, while controlling the opening of the pressure reducing device 13a so that the temperature and pressure of the refrigerant drawn in by the compressor 11 remain constant.

[0057] As a result, in the third stage of startup control, when the temperature of the heat transfer medium in the heat transfer medium circuit 20 becomes equivalent to the temperature at which air at the target discharge temperature can be blown into the vehicle cabin, the blower 140 can be started and heating operation can be performed. In addition, stable control can be performed by maintaining the discharge temperature at the target discharge temperature.

[0058] Furthermore, when executing the startup control 1, it is preferable that, under cryogenic conditions, the capacity of the accumulator 15 is less than or equal to the amount of liquid refrigerant stored when the refrigerant circuit 10, including the first low-temperature heat exchanger 14 and the second low-temperature heat exchanger 16, is filled with gaseous refrigerant. This ensures that even if the capacity of the accumulator 15, which is normally designed to prevent liquid refrigerant from overflowing, is reduced, a region for liquid refrigerant to exist in the high-temperature heat exchanger 12 can be secured, thereby preventing liquid compression.

[0059] <Startup control 2> An example of the startup control 2 performed by the control device 200 will be explained using Figure 3.

[0060] As shown in Figure 3, the control device 200 determines whether or not a startup control request has occurred (S20). A startup control request occurs when the outside temperature becomes extremely low and it becomes difficult to perform outside air intake heating.

[0061] The control device 200 terminates processing if no startup control request has been generated (S20: NO).

[0062] If a request for startup control is received (S20:YES), the control device 200 executes the first stage of startup control (S21).

[0063] In the first stage of startup control, the control device 200 fully opens the pressure reducing device 13a, fully closes the pressure reducing device 13b, and fully closes the pressure reducing device 13c. As a result, refrigerant does not flow through the condenser path, and refrigerant flows through the hot gas bypass path.

[0064] Then, if the discharge superheat is above a certain value (e.g., 5K) and there is no risk of liquid compression, the rotational speed of the compressor 11 is increased. On the other hand, if it is detected that the refrigerant heat storage is complete because the suction temperature (e.g., 0°C) and pressure (e.g., 0.3 MPa) of the compressor 11 are above a certain value, or if it is detected that liquid compression will occur because the discharge superheat of the compressor 11 falls below a certain value, the system moves to the second stage of startup control.

[0065] Therefore, in the first stage of startup control, the control device 200 determines whether the discharge superheat is above a predetermined value (S22). This allows it to determine whether the temperature of the refrigerant in the accumulator 15 rises, causing the volume of the liquid refrigerant in the accumulator 15 to expand, and whether liquid compression occurs due to the liquid refrigerant overflowing from the accumulator 15.

[0066] Then, if the discharge superheat is not above a predetermined value (S22:NO), the control device 200 proceeds to S27. In other words, if liquid compression occurs, it proceeds to the second stage of startup control.

[0067] In the second stage of the startup control, the circuit is switched to a parallel circuit that flows the refrigerant through the hot gas bypass path and the condenser path, and the heat transfer medium in the heat transfer medium circuit 20 is circulated so that heat exchange can occur between the refrigerant and the heat transfer medium in the high-temperature side heat exchanger 12, which is the condenser. As a result, condensation in the high-temperature side heat exchanger 12 allows liquid refrigerant to be present not only in the accumulator 15 but also in the high-temperature side heat exchanger 12. This allows the liquid refrigerant in the refrigerant circuit 10 to be distributed between the accumulator 15 and the high-temperature side heat exchanger 12. Therefore, the amount of liquid refrigerant stored in the accumulator 15 can be reduced. This prevents malfunctions in the compressor 11 caused by liquid compression due to the volume of liquid refrigerant in the accumulator 15 expanding as the temperature of the refrigerant in the accumulator 15 rises, causing the liquid refrigerant to overflow from the accumulator 15.

[0068] Furthermore, the control device 200 detects that if the discharge superheat is above a predetermined value (S22: YES), liquid compression has not occurred and there is no risk of liquid compression occurring. In this case, the control device 200 determines whether the refrigerant suction temperature and pressure of the compressor 11 are below a predetermined value (S23). This allows it to determine whether or not the heat storage of the refrigerant has been completed.

[0069] Then, if the refrigerant intake temperature and pressure of the compressor 11 are below a predetermined value (S23: YES), the control device 200 increases the rotational speed of the compressor 11 (S24). After that, it returns to S22. In other words, if the heat storage of the refrigerant is not complete and the refrigerant is not sufficiently heated, the rotational speed of the compressor 11 is increased to heat the refrigerant.

[0070] The control device 200 detects that the refrigerant heat storage is complete if the refrigerant suction temperature and pressure of the compressor 11 are not below a predetermined value (S23:NO). In this case, the process proceeds to S27. That is, if the refrigerant heat storage is complete, the process proceeds to the second stage of startup control.

[0071] Next, the control device 200 executes the second stage of startup control (S27). In the second stage of startup control, the control device 200 maintains the fully open pressure reducing device 13a and the fully closed pressure reducing device 13c. The control device 200 also opens the pressure reducing device 13b to a small degree and starts the circulation pump P20 so that the flow rate of the heat transfer medium in the heat transfer medium circuit 20 becomes low. For example, the pressure reducing device 13b is opened to 10%, and the circulation pump P20 is started so that the flow rate of the heat transfer medium becomes 5 L / min.

[0072] As a result, in the second stage of the startup control, the circuit switches to a parallel circuit that flows the refrigerant through the hot gas bypass path and the condenser path, and the heat transfer medium in the heat transfer medium circuit 20 is circulated so that heat exchange can be performed between the refrigerant and the heat transfer medium in the high-temperature heat exchanger 12, which is the condenser.

[0073] In the second stage of startup control, when transitioning from the first stage to the second stage of startup control and switching to a parallel circuit, the discharge superheat increases as the liquid refrigerant in the accumulator 15 decreases. On the other hand, if this condition continues and the liquid refrigerant in the accumulator 15 becomes insufficient, the effect of startup control by the hot gas cycle that stores heat in the liquid refrigerant in the accumulator 15 will diminish. Furthermore, if the liquid refrigerant in the accumulator 15 becomes insufficient, the intake superheat will be activated.

[0074] Therefore, in the second stage of startup control, the control device 200 controls the opening of the pressure reducing device 13b to an opening such that the discharge superheat is above a certain value and no suction superheat occurs, thereby creating the conditions for an appropriate amount of liquid refrigerant to be present in the high-temperature heat exchanger 12 and the accumulator 15. In other words, by managing the discharge superheat, it prevents liquid refrigerant from overflowing from the accumulator 15, and by managing the suction superheat, it prevents a shortage of liquid refrigerant in the accumulator 15. This prevents the occurrence of liquid compression and provides the effect of startup control that warms the refrigerant by storing heat in the liquid refrigerant. In other words, by storing heat in the liquid refrigerant secured in the accumulator 15, it is possible to suppress the extension of the startup control execution time and reduce the amount of liquid refrigerant remaining in the accumulator 15, thereby preventing the occurrence of liquid compression.

[0075] Therefore, in the second stage of startup control, the control device 200 determines whether the discharge superheat is above a predetermined value (S28). This increases the amount of liquid refrigerant returning from the condenser path, causing the liquid refrigerant to overflow from the accumulator 15, and it is possible to determine whether liquid compression occurs in the compressor 11. Alternatively, a sensor installed in the accumulator 15 may be used to detect whether liquid compression occurs.

[0076] If the discharge superheat is not above a predetermined value (S28:NO), the control device 200 reduces the opening of the pressure reducing device 13b located in the condenser path (S33). In other words, if it is determined that liquid compression occurs in the compressor 11 after switching to the parallel circuit, the opening of the pressure reducing device 13b, which is an expansion device located in the condenser path, is reduced. Then, the process returns to S28.

[0077] In other words, if it is determined that liquid compression is occurring in the compressor 11, the opening of the pressure reducing device 13b located in the condenser path is reduced, and the amount of refrigerant flowing through the hot gas bypass path is increased. This makes it possible to reduce the amount of liquid refrigerant returning from the condenser path, thereby preventing liquid refrigerant from overflowing from the accumulator 15. In addition, the refrigerant flowing into the suction side 11b of the compressor 11 can be superheated. Therefore, the occurrence of liquid compression in the compressor 11 can be suppressed.

[0078] Furthermore, in the second stage of startup control, the control device 200 detects that if the discharge superheat is above a predetermined value (S28: YES), liquid compression has not occurred and there is no risk of liquid compression occurring. In this case, the control device 200 determines whether or not the intake superheat is above a predetermined value (S29). This allows the control device to determine whether or not the amount of liquid refrigerant in the accumulator 15 is below a predetermined amount by reducing the amount of liquid refrigerant returning from the condenser path. Alternatively, the amount of liquid refrigerant may be detected by a sensor installed in the accumulator 15.

[0079] Then, if the intake superheat is above a predetermined value (S29: YES), the control device 200 increases the opening of the pressure reducing device 13b located in the condenser path (S34). In other words, if it is determined that the amount of refrigerant in the accumulator 15 is below a predetermined amount after switching to the parallel circuit, the opening of the pressure reducing device 13b, which is an expansion device located in the condenser path, is increased. After that, the process returns to S28.

[0080] In other words, if the liquid refrigerant in the accumulator 15 is insufficient, the amount of liquid refrigerant returning from the condenser path is increased to store liquid refrigerant in the accumulator 15. By ensuring a certain amount of liquid refrigerant in the accumulator 15, the heat from the high-temperature refrigerant flowing through the hot gas bypass path can be stored, allowing the suction temperature of the compressor 11 (i.e., the temperature of the refrigerant circulating in the refrigerant circuit 10) to rise quickly, thus shortening the time required for startup control.

[0081] Furthermore, in the second stage of the startup control, the control device 200 intermittently opens and closes the pressure reducing device 13b located in the condenser path, thereby storing heat in the liquid refrigerant secured in the accumulator 15. This suppresses an extension of the startup control execution time, while also reducing the amount of liquid refrigerant remaining in the accumulator 15 and preventing liquid compression.

[0082] Next, in the second stage of startup control, if the intake superheat is below a predetermined value (S29:NO), the control device 200 increases the rotational speed of the compressor 11 (S30). At this time, if the rotational speed of the compressor 11 is at its maximum rotational speed, the rotational speed of the compressor 11 is maintained.

[0083] Next, in the second stage of startup control, the control device 200 determines whether the temperature of the heat transfer medium in the heat transfer medium circuit 20 is at a temperature that can achieve the target blow-out temperature (S31). That is, it determines whether the temperature of the heat transfer medium in the heat transfer medium circuit 20 is at a temperature that can blow air at the target blow-out temperature into the vehicle interior.

[0084] If the temperature of the heat transfer medium in the heat transfer medium circuit 20 is not at a temperature that can achieve the target discharge temperature (S31:NO), the control device 200 returns to S28.

[0085] Through the above process, in the second stage of startup control, the control device 200 increases the rotational speed of the compressor 11 if the condition that liquid refrigerant is present in the high-temperature heat exchanger 12 and the accumulator 15 is met. The control device 200 then increases the rotational speed of the compressor 11 or maintains the maximum rotational speed until the temperature of the heat transfer medium in the heat transfer medium circuit 20 becomes equivalent to the temperature at which air at the target discharge temperature can be blown into the vehicle interior.

[0086] If the temperature of the heat transfer medium in the heat transfer medium circuit 20 is at a temperature at which the target discharge temperature can be achieved (S31: YES), the control device 200 executes the third stage of startup control (S32).

[0087] In the third stage of startup control, the control device 200 starts the blower 140 and controls the rotation speed of the compressor 11 so that the outlet temperature of the air blown into the vehicle cabin reaches the target outlet temperature. The control device 200 also controls the opening of the pressure reducing device 13b so that the discharge superheat of the compressor 11 is above a desired value, while controlling the opening of the pressure reducing device 13a so that the temperature and pressure of the refrigerant drawn in by the compressor 11 remain constant.

[0088] As a result, in the third stage of startup control, when the temperature of the heat transfer medium in the heat transfer medium circuit 20 becomes equivalent to the temperature at which air at the target discharge temperature can be blown into the vehicle cabin, the blower 140 can be started and heating operation can be performed. In addition, stable control can be performed by maintaining the discharge temperature at the target discharge temperature.

[0089] Furthermore, when executing the startup control 2, it is preferable that the capacity of the accumulator 15 is less than or equal to the capacity when the refrigerant circuit 10, including the first low-temperature heat exchanger 14 and the second low-temperature heat exchanger 16, is filled with gaseous refrigerant, and the stored liquid refrigerant reaches the refrigerant temperature in the accumulator 15 at the end of the startup control. This ensures that even if an accumulator 15 with a capacity that cannot absorb the expansion of the liquid refrigerant heated by the startup control is used, a region for liquid refrigerant can be secured in the condenser, thereby preventing liquid compression in the compressor 11.

[0090] [Effects of this embodiment] (1) A refrigerant circuit having a compressor, condenser, expansion device, evaporator and accumulator, A heat transfer medium circuit through which a heat transfer medium circulates to exchange heat with the refrigerant in the aforementioned condenser, Control device and A vehicle air conditioning system equipped with, The aforementioned refrigerant circuit is A condenser path through which the refrigerant discharged by the compressor flows upstream of the accumulator via the condenser, The compressor includes a hot gas bypass path through which the refrigerant discharged by the compressor bypasses the condenser and flows upstream of the accumulator, The control device flows refrigerant through the hot gas bypass path and the condenser path, and performs startup control to circulate the heat transfer medium in the heat transfer medium circuit so that heat exchange can be performed between the refrigerant and the heat transfer medium in the condenser. Therefore, in the startup control of heating using a hot gas cycle, by releasing the heat from the refrigerant in the condenser and condensing the refrigerant, it is possible to reduce the amount of liquid refrigerant stored in the accumulator, thereby preventing the liquid refrigerant from overflowing from the accumulator.

[0091] (2) In the vehicle air conditioning system of (1), The control device is When the aforementioned startup control is being performed, it is determined whether or not liquid compression occurs in the compressor. If it is determined that liquid compression is occurring in the compressor, the opening of the expansion device located in the condenser path is reduced. Therefore, it becomes possible to increase the amount of refrigerant flowing through the hot gas bypass path, which allows for increased refrigerant superheating on the compressor's suction side and prevents liquid compression from occurring in the compressor.

[0092] (3)(2) In the vehicle air conditioning system, The control device is When the aforementioned startup control is being performed, it is determined whether or not the amount of refrigerant in the accumulator is below a predetermined amount. If it is determined that the amount of refrigerant in the accumulator is below a predetermined amount, the opening of the expansion device located in the condenser path is increased. Therefore, by ensuring a certain amount of liquid refrigerant in the accumulator, it becomes possible to store the heat from the high-temperature refrigerant flowing through the hot gas bypass path in the liquid refrigerant within the accumulator. This allows the temperature of the refrigerant drawn in by the compressor to be raised stably and quickly, thus shortening the time required for startup control.

[0093] (4)(1) In the vehicle air conditioning system, The accumulator's capacity is less than or equal to the amount of liquid refrigerant stored when the refrigerant circuit is filled with gaseous refrigerant. Therefore, even if the capacity of the accumulator, which is normally designed to prevent liquid refrigerant from overflowing, is reduced, it is still possible to secure a region in the condenser where liquid refrigerant can exist, thus preventing liquid compression.

[0094] (5) A refrigerant circuit having a compressor, condenser, expansion device, evaporator and accumulator, A heat transfer medium circuit through which a heat transfer medium circulates to exchange heat with the refrigerant in the aforementioned condenser, Control device and A vehicle air conditioning system equipped with, The aforementioned refrigerant circuit is A condenser path through which the refrigerant discharged by the compressor flows upstream of the accumulator via the condenser, The compressor includes a hot gas bypass path through which the refrigerant discharged by the compressor bypasses the condenser and flows upstream of the accumulator, The control device is A startup control is performed that flows the refrigerant only through the hot gas bypass path. When the aforementioned startup control is being performed, it is determined whether or not liquid compression occurs in the compressor. If it is determined that liquid compression occurs in the compressor while the start-up control is being performed, the system switches to a parallel circuit that flows the refrigerant through the hot gas bypass path and the condenser path, and circulates the heat transfer medium in the heat transfer medium circuit so that heat exchange can occur between the refrigerant and the heat transfer medium in the condenser. Therefore, by releasing heat in the condenser, a liquid refrigerant region is created on the condenser side, reducing the amount of liquid refrigerant in the accumulator. As a result, during the startup control of heating using the hot gas cycle, the refrigerant temperature in the accumulator rises, causing the volume of liquid refrigerant in the accumulator to expand, thus preventing the liquid refrigerant from overflowing from the accumulator. This prevents compressor malfunctions caused by liquid compression.

[0095] (6)(5) In the vehicle air conditioning system, The control device is If it is determined that liquid compression occurs in the compressor after switching to the parallel circuit, the opening of the expansion device located in the condenser path is reduced. Therefore, it becomes possible to reduce the amount of liquid refrigerant returning from the condenser path and increase the flow rate of refrigerant in the hot gas bypass path, thereby suppressing the occurrence of liquid compression in the compressor.

[0096] (7)(6) In the vehicle air conditioning system, The control device is After switching to the parallel circuit, it is determined whether the amount of refrigerant in the accumulator is below a predetermined amount. If it is determined that the amount of refrigerant in the accumulator is below a predetermined amount, the opening of the expansion device located in the condenser path is increased. Therefore, the amount of liquid refrigerant returning from the condenser path can be increased, allowing liquid refrigerant to be stored in the accumulator. As a result, the heat from the high-temperature refrigerant flowing through the hot gas bypass path can warm the liquid refrigerant in the accumulator, and the temperature of the circulating refrigerant can be raised more quickly.

[0097] (8)(5) In the vehicle air conditioning system, The control device intermittently opens and closes the expansion device located in the condenser path. Therefore, by storing heat in the liquid refrigerant secured in the accumulator, it is possible to suppress the extension of the startup control execution time while reducing the amount of liquid refrigerant remaining in the accumulator and preventing liquid compression.

[0098] (9)(5) In the vehicle air conditioning system, The accumulator's capacity is less than or equal to the capacity of the accumulator when the refrigerant circuit is filled with gaseous refrigerant and the stored liquid refrigerant reaches the refrigerant temperature at the end of the startup control. Therefore, even when using an accumulator with a capacity that cannot absorb the expansion of the liquid refrigerant heated by the startup control, it is possible to secure a region in the condenser where liquid refrigerant is present, thereby preventing liquid compression from occurring in the compressor.

[0099] Although the present invention has been described above with reference to preferred embodiments, it goes without saying that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the present invention. [Explanation of Symbols]

[0100] 1: Vehicle air conditioning system 10: Refrigerant Circuit 12: High temperature side heat exchanger 13a, 13b, 13c: Pressure reducing device 20: Heat medium circuit 21: Heater core 31: Coola Core P20: Circulation pump 200: Control device

Claims

1. A refrigerant circuit having a compressor, condenser, expansion device, evaporator and accumulator, A heat transfer medium circuit through which a heat transfer medium circulates to exchange heat with the refrigerant in the aforementioned condenser, Control device and A vehicle air conditioning system equipped with, The aforementioned refrigerant circuit is A condenser path through which the refrigerant discharged by the compressor flows upstream of the accumulator via the condenser, The compressor includes a hot gas bypass path through which the refrigerant discharged by the compressor bypasses the condenser and flows upstream of the accumulator, The control device is A startup control is performed that flows the refrigerant only through the hot gas bypass path. When the aforementioned startup control is being performed, it is determined whether or not liquid compression occurs in the compressor. If it is determined that liquid compression occurs in the compressor while the aforementioned startup control is being performed, the system switches to a parallel circuit that flows refrigerant through the hot gas bypass path and the condenser path, and circulates the heat transfer medium in the heat transfer medium circuit so that heat exchange can occur between the refrigerant and the heat transfer medium in the condenser. A vehicle air conditioning system characterized by the following features.

2. The control device is If it is determined that liquid compression occurs in the compressor after switching to the parallel circuit, the opening of the expansion device located in the condenser path is reduced. The vehicle air conditioning system according to feature 1.

3. The control device is After switching to the parallel circuit, it is determined whether the amount of refrigerant in the accumulator is below a predetermined amount. If it is determined that the amount of refrigerant in the accumulator is below a predetermined amount, the opening of the expansion device located in the condenser path is increased. The vehicle air conditioning system according to feature 2.

4. The control device intermittently opens and closes the expansion device located in the condenser path. The vehicle air conditioning system according to feature 1.

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