Air conditioning device for vehicle

Abstract

[Problem] To stably and effectively continue hot gas heating operation and to improve the durability of a compressor. [Solution] Provided is an air conditioning device for vehicle, which is provided with: a refrigerant circuit that includes a compressor, an indoor heat exchange unit, an external heat exchange unit, and a hot gas bypass that decompresses at least a portion of a refrigerant compressed by the compressor without passing through the indoor heat exchange unit and the external heat exchange unit, and returns the refrigerant to the compressor; and a control device that can execute a hot gas heating mode in which the refrigerant circuit is controlled, a portion of the refrigerant compressed by the compressor flows to the indoor heat exchange unit, and the rest of the refrigerant flows to the hot gas bypass. The control device calculates a first target rotation speed based on an intake refrigerant pressure and a second target rotation speed based on an intake refrigerant temperature, respectively, to the compressor when the hot gas heating mode is executed, and controls the compressor with the smaller one of the first target rotation speed or the second target rotation speed as a target rotation speed, when the intake refrigerant pressure exceeds a first threshold pressure or when the intake refrigerant temperature exceeds a first threshold temperature.

Description

Vehicle air conditioning system

[0001] The present invention relates to an air conditioning system for a vehicle.

[0002] In recent years, vehicles such as hybrid vehicles and electric vehicles, which have a traction motor powered by power supplied from an onboard battery, have become widespread. A known vehicle air conditioner for such vehicles uses a heat pump (refrigerant circuit) as a heat source.

[0003] In vehicle air conditioners that use a heat pump, an external heat exchanger functions as a heat absorber during heating operation to obtain heat from outside air. Therefore, when the outside temperature becomes extremely low, it becomes difficult to absorb heat from the outside air, resulting in a significant decrease in heating capacity. In contrast, hot gas heating, which does not absorb heat from outside air or the like, but instead uses high-temperature, high-pressure refrigerant discharged from a compressor, is known as an effective heating method in extremely low-temperature environments.

[0004] For example, in the vehicle air conditioning system of Patent Document 1, a heat pump circulates refrigerant to perform hot gas heating operation as follows: In the heat pump, a portion of the high-temperature, high-pressure refrigerant discharged from the compressor flows through a bypass flow path to be decompressed and then returned to the compressor, while the remainder exchanges heat with air blown into the vehicle cabin in an indoor heat exchanger, is decompressed, and then returned to the compressor without passing through an external heat exchanger.

[0005] Japanese Patent Application Laid-Open No. 2023-46604

[0006] In the above-described vehicle air conditioning system, in order to maintain stable and effective operation not only in endothermic heating operation in which heat is absorbed from outside air, etc., but also in the above-described hot gas heating operation, the components of the refrigerant circuit are controlled so that the pressure and temperature on the suction and discharge sides of the compressor fall within predetermined ranges including target values. In particular, when the suction refrigerant pressure drops, the compression ratio increases, the discharge refrigerant temperature rises, and the volumetric efficiency decreases. Therefore, in endothermic heating operation, the components are controlled so that the suction refrigerant pressure does not fall below a predetermined lower limit.

[0007] On the other hand, in hot gas heating operation, a portion of the high-temperature, high-pressure refrigerant discharged from the compressor flows through a bypass passage and is returned to the compressor. This means that the refrigerant suction pressure to the compressor tends to be higher than in endothermic heating operation, and the refrigerant suction pressure may exceed a predetermined upper limit. In such cases, the vehicle air conditioner adjusts the refrigerant suction pressure by controlling each component of the refrigerant circuit, such as the opening of the expansion valve or the heat dissipation amount in the indoor heat exchanger. However, even with such adjustments, the refrigerant suction pressure may still exceed the upper limit. If the refrigerant suction pressure exceeds the upper limit, problems such as difficulty in maintaining stable hot gas operation and reduced compressor durability may occur.

[0008] The present invention was made in consideration of these circumstances, and its objectives include continuing hot gas heating operation stably and effectively while improving the durability of the compressor.

[0009] The present invention provides a vehicle air conditioning system comprising: a refrigerant circuit including a compressor, an indoor heat exchange unit, an external heat exchange unit, and a hot gas bypass that decompresses and returns at least a portion of the refrigerant compressed by the compressor without passing through the indoor heat exchange unit and the external heat exchange unit; and a control device that controls the refrigerant circuit and is capable of executing a hot gas heating mode in which a portion of the refrigerant compressed by the compressor flows through the indoor heat exchange unit and the remainder flows through the hot gas bypass.In this vehicle air conditioning system, when the hot gas heating mode is executed, the control device calculates, for the compressor, a first target rotation speed based on a suction refrigerant pressure and a second target rotation speed based on a suction refrigerant temperature, and controls the compressor to use the smaller of the first target rotation speed or the second target rotation speed as the target rotation speed when the suction refrigerant pressure exceeds a first threshold pressure or when the suction refrigerant temperature exceeds the first threshold temperature.

[0010] According to the present invention, it is possible to continue hot gas heating operation stably and effectively, and to improve the durability of the compressor.

[0011] Fig. 1 is an explanatory diagram showing an example of the system configuration of a vehicle air conditioner according to an embodiment of the present invention; Fig. 2 is an explanatory diagram showing a control device of a vehicle air conditioner according to an embodiment of the present invention; Fig. 3 is a diagram showing the configuration of a control device, etc., in an electric vehicle (EV) according to an embodiment of the present invention; Fig. 4 is an explanatory diagram showing the operation of a refrigerant circuit during hot gas heating operation in a vehicle air conditioner according to an embodiment of the present invention; Fig. 5 is a control block diagram of a compressor by the control device of a vehicle air conditioner according to an embodiment of the present invention; Fig. 6 is a flowchart showing the flow of compressor control by the control device during hot gas heating operation in a vehicle air conditioner according to an embodiment of the present invention;

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same reference numerals in different drawings indicate parts with the same function, and duplicated explanations in each drawing will be omitted as appropriate. In the drawings, bold black lines in the refrigerant circuit 10 indicate refrigerant flow paths through which high-pressure refrigerant flows, and hollow lines indicate refrigerant flow paths through which decompressed refrigerant flows. In addition, dashed lines in the refrigerant circuit 10 indicate refrigerant flow paths through which refrigerant does not flow.

[0013] 1 shows an example of the configuration of a vehicle air conditioner 1 according to an embodiment of the present invention. The configuration shown here is merely an example, and the present invention is not limited to a specific configuration.

[0014] The vehicle air conditioner 1 includes a refrigerant circuit 10 and an air conditioning unit 20. The refrigerant circuit 10 includes a compressor 2, indoor heat exchangers 21 and 22 provided inside the air conditioning unit 20, and an external heat exchanger 11 provided outside the vehicle cabin, which are arranged along a refrigerant flow path. The indoor heat exchangers 21 and 22 are provided to exchange heat between the refrigerant and air flowing through the air conditioning unit 20, and the external heat exchanger 11 is provided to exchange heat between the refrigerant and outside air outside the vehicle cabin. The indoor heat exchanger 21 is used to heat the air, and the indoor heat exchanger 22 is used to cool the air. Immediately downstream of the indoor heat exchanger 21, a refrigerant pressure sensor 44B is provided to detect an outlet refrigerant pressure Pci (high-pressure side refrigerant pressure) and a refrigerant temperature sensor 43B is provided to detect an outlet refrigerant temperature Tc (high-pressure side refrigerant temperature) from the indoor heat exchanger 21.

[0015] The compressor 2 compresses the refrigerant and circulates it through the refrigerant circuit 10. The refrigerant compressed by the compressor 2 is reduced to a required pressure by passing through an appropriately selected refrigerant flow path, for example, through a first pressure reduction section V1, a second pressure reduction section V2, a third pressure reduction section V3, and a fourth pressure reduction section V4, which are expansion valves. The refrigerant circuit 10 is provided with flow path switching valves 12 and 13 for switching the refrigerant flow path and check valves 14 and 15 for regulating the flow direction of the refrigerant. An accumulator 16 is provided immediately upstream of the compressor 2 in the refrigerant circuit 10 to recover liquid refrigerant and separate the refrigerant into gas and liquid. A refrigerant pressure sensor 44A and a refrigerant temperature sensor 43A are provided between the accumulator 16 and the compressor 2 to detect a suction refrigerant pressure Ps (low-pressure side refrigerant pressure) and a suction refrigerant temperature Ts (low-pressure side refrigerant temperature).

[0016] As described above, the air conditioning unit 20 is equipped with the indoor heat exchangers 21, 22 inside, and air introduced from the room or the outside by the blower 23 passes through the indoor heat exchangers 21, 22 and is blown into the room. The air conditioning unit 20 is provided with an air damper 24. When the air damper 24 shown in FIG. 1 is fully open, the air introduced by the blower 23 passes through both the indoor heat exchangers 21, 22 and is blown into the room.

[0017] Furthermore, when the air damper 24 is fully closed, it blocks the inlet side of the indoor heat exchanger 21, and air introduced by the blower 23 passes only through the indoor heat exchanger 22 before being blown into the room. Another air damper 25 provided in the air conditioning unit 20 switches the air introduced into the blower 23 between indoor and outdoor. The air damper 25 can selectively close an air inlet 25A connected to the outdoors or an air inlet 25B connected to the indoors, allowing air to be introduced from either one. Furthermore, by setting the air damper 25 to an intermediate position, air can be introduced from both the air inlet 25A and the air inlet 25B.

[0018] Although the above-described external heat exchanger 11 and indoor heat exchangers 21, 22 have been described as examples in which the refrigerant directly exchanges heat with the air, the refrigerant may indirectly exchange heat with the air via a heat medium that has exchanged heat with the refrigerant. That is, the refrigerant may absorb heat from the air via the heat medium, or the refrigerant may release heat to the air via the heat medium.

[0019] As shown in Fig. 1, the vehicle air conditioner 1 includes a heat medium circuit 30. The heat medium circuit 30 circulates a heat medium using a circulation pump 31, heats the heat medium using a heater (ECH: Electric Coolant Heater) 32, and recovers waste heat from a temperature-controlled object such as a battery using a temperature-controlled object heat exchanger 33. The refrigerant circuit 10 and the heat medium circuit 30 are provided with a refrigerant-heat medium heat exchanger 34 that exchanges heat between the refrigerant and the heat medium via a flow path 34A through which the refrigerant flows and a flow path 34B through which the heat medium flows. The heat medium circuit 30 is provided as needed.

[0020] The vehicle air conditioner 1 includes a control device 100 shown in Fig. 2. The control device 100 controls the refrigerant circuit 10, the air conditioning unit 20, and the heat medium circuit 30 based on various input signals (such as an air conditioning instruction signal and a charger connection signal) and detection signals from the sensor unit 40.

[0021] The sensor unit 40 that inputs detection signals to the control device 100 includes, for example, an outside air sensor 41 that detects outside air conditions such as outside air temperature and outside air humidity, a compressor current sensor 42 that detects the power consumption (energy consumption) of the compressor 2, a refrigerant temperature sensor 43 and a refrigerant pressure sensor 44 that detect the state of the refrigerant, an occupant sensor 45 that detects the presence or absence of an occupant in the vehicle cabin, and an air temperature sensor 46 that detects the air temperature of the air conditioning unit 20.

[0022] In particular, the refrigerant temperature sensor 43 includes a refrigerant temperature sensor 43A that detects the intake refrigerant temperature Ts (low-pressure side refrigerant temperature) sucked into the compressor 2, and a refrigerant temperature sensor 43B that detects the outlet refrigerant temperature Tc (high-pressure side refrigerant temperature) of the indoor heat exchanger 21 (see Figure 1).

[0023] The refrigerant pressure sensor 44 also includes a refrigerant pressure sensor 44A that detects a suction refrigerant pressure Ps (low-pressure side refrigerant pressure) sucked into the compressor 2, and a refrigerant pressure sensor 44B that detects an outlet refrigerant pressure Pci (high-pressure side refrigerant pressure) of the indoor heat exchanger 21 (see FIG. 1). These sensors are just examples, and the sensor unit 40 is provided with various sensors that detect information required for the control device 100 to perform various controls.

[0024] The control devices of the control device 100 are the compressor 2, the first pressure reduction section V1, the second pressure reduction section V2, the third pressure reduction section V3, the fourth pressure reduction section V4, and the flow path switching valves 12 and 13 in the refrigerant circuit 10, the blower 23, the air dampers 24 and 25 in the air conditioning unit 20, and the circulation pump 31 in the heat medium circuit 30. The control device 100 also controls the vehicle air conditioner 1 according to the processing results of the control device 100. The vehicle air conditioner 1 can be switched by the control device 100 between an endothermic heating operation in which the refrigerant is caused to absorb heat in the external heat exchanger 11, and a hot gas heating operation in which the refrigerant compressed by the compressor 2 is caused to release heat in the indoor heat exchanger 21 without absorbing heat in the external heat exchanger 11, thereby heating the vehicle cabin.

[0025] [Configuration of Control Device in Electric Vehicle (EV)] As shown in Fig. 3 , the control device 100 provided in the vehicle air conditioner 1 is configured as a single ECU connected to various ECUs (Electronic Control Units) that control the electric vehicle EV via an in-vehicle network L. The control device 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, an I / F (Interface) 104 for input / output, an I / F (Interface) 105 for in-vehicle communication, and the like, and each piece of hardware is connected to one another via a bus 106.

[0026] The CPU 101 controls the control device 100 by executing various programs stored in the ROM 102. The ROM 102 is a non-volatile memory. For example, the ROM 102 stores programs executed by the CPU 101, data necessary for the CPU 101 to execute the programs, etc. The RAM 103 is a main storage device such as a dynamic random access memory (DRAM) or a static random access memory (SRAM).

[0027] For example, RAM 103 functions as a work area used by CPU 101 when executing a program. Input / output I / F 104 is connected to various sensors and monitors installed in the EV, and inputs data to CPU 101 and outputs data processed by CPU 101. In-vehicle communication I / F 105 is connected to an in-vehicle network L, and controls data transmission and reception with other ECUs set in the EV.

[0028] The control device 100 controls the above-mentioned vehicle air conditioning device 1 by a program executed by the CPU 101 when data related to the surrounding environment or data related to the driving status of the EV is input via the input / output I / F 104 and the in-vehicle I / F 105.

[0029] The EV is equipped with a battery B. The battery B is charged by connecting a charger plug PS to a battery plug BP, and power is supplied to the vehicle air conditioner 1 via the battery B. The state in which the plug PS is connected to the battery plug BP is transmitted to the control device 100 via the in-vehicle network L as a charger connection signal.

[0030] [Hot gas heating operation] At extremely low temperatures, hot gas heating is used because it is difficult for the external heat exchanger 11 to absorb heat. In hot gas heating operation, the refrigerant compressed by the compressor 2 is not allowed to absorb heat in the external heat exchanger 11, but some or all of the refrigerant is dissipated in the indoor heat exchanger 21 to heat the vehicle interior.

[0031] The operation of the refrigerant circuit 10 during hot gas heating operation will be described with reference to Figure 4. In this operation, a portion of the high-temperature, high-pressure refrigerant discharged from the compressor 2 passes through the indoor heat exchanger 21 and the flow switching valve 12, is decompressed in the third pressure reduction section V3 to become a low-pressure refrigerant, passes through the refrigerant heat medium heat exchanger 34, undergoes gas-liquid separation in the accumulator 16, and returns to the compressor 2. At this time, in the refrigerant circuit 10, the first pressure reduction section V1 is fully closed, so that refrigerant does not flow to the external heat exchanger 11. In addition, the fourth pressure reduction section V4 is fully closed, so that refrigerant does not flow to the indoor heat exchanger 22.

[0032] The refrigerant circuit 10 has a hot gas bypass 10V that reduces the pressure of at least a portion of the refrigerant compressed by the compressor 2 and returns it to the compressor 2 without passing through the indoor heat exchanger 21 and the external heat exchanger 11. In the hot gas bypass 10V, a portion of the high-temperature, high-pressure refrigerant is branched off at a branch point P1 immediately downstream of the compressor 2, reduced in pressure at a second pressure reduction section V2, and merged with the low-pressure refrigerant reduced in pressure at a third pressure reduction section V3 at a junction point P2 immediately upstream of the accumulator 16.

[0033] By providing such a hot gas bypass 10V, the liquid refrigerant condensed by heat radiation in the indoor heat exchanger 21 is mixed with the gas refrigerant that has passed through the hot gas bypass 10V to produce a gas-rich refrigerant that can be returned to the compressor 2. Furthermore, by increasing the flow rate of refrigerant flowing through the hot gas bypass 10V, the amount of heat radiation in the indoor heat exchanger 21 can be suppressed, and by adjusting the flow rate of refrigerant flowing through the hot gas bypass 10V by opening or closing the second pressure reduction section V2, it is possible to maintain a balance between the amount of heat radiation from the refrigerant circuit 10 and the amount of heat input to the compressor 2. In other words, the second pressure reduction section V2 functions as a flow rate adjustment section that adjusts the flow rate of refrigerant flowing through the hot gas bypass 10V.

[0034] During hot gas heating operation, the refrigerant flow in the flow path passing through the indoor heat exchanger 21 is decompressed in the third decompression section V3, so that the refrigerant becomes high-pressure refrigerant upstream and low-pressure refrigerant downstream. In this case, it is important to maintain heating capacity that heat exchange does not occur in the refrigerant / heat medium heat exchanger 34 in the low-pressure flow path. In the air conditioning unit 20, air introduced by the blower 23 is heated by heat released from the indoor heat exchanger 21 and then blown into the vehicle cabin.

[0035] Although the flow of refrigerant in the refrigerant circuit 10 during endothermic heating operation is not shown, in the refrigerant circuit 10 during endothermic heating operation, the second pressure reduction section V2, the third pressure reduction section V3, the fourth pressure reduction section V4, and the flow path switching valve 12 are fully closed, while the flow path switching valve 13 is fully open and the first pressure reduction section V1 is open.

[0036] In the endothermic heating operation, the high-temperature, high-pressure refrigerant discharged from the compressor 2 passes through the indoor heat exchanger 21 in the air conditioning unit 20 and is depressurized in the first depressurization section V1, and the low-pressure refrigerant passes through the external heat exchanger 11 and passes through the flow path switching valve 13, the check valve 14, and the accumulator 16 before being returned to the compressor 2. At this time, the high-pressure refrigerant discharged from the compressor 2 condenses and releases heat in the indoor heat exchanger 21, is depressurized in the first depressurization section V1 to become low-pressure refrigerant, absorbs heat and evaporates in the external heat exchanger 11, and returns to the compressor 2. In the air conditioning unit 20, air introduced by the blower 23 is heated by the heat released in the indoor heat exchanger 21 and is blown into the vehicle cabin.

[0037] [Control of Compressor by Control Device] Hereinafter, control of the compressor in the vehicle air conditioner according to this embodiment will be described. Fig. 5 is a block diagram showing control of the compressor 2 by the control device 100. The control device 100 periodically acquires the outlet refrigerant pressure Pci of the indoor heat exchanger 21 as the high-pressure side refrigerant pressure, the suction refrigerant pressure Ps of the compressor 2 as the low-pressure side refrigerant pressure, and the suction refrigerant temperature Ts of the compressor 2, and controls the compressor 2 based on these.

[0038] That is, in the control device 100, the restriction determination unit 200 determines whether the target rotation speed of the compressor 2 needs to be restricted based on the outlet refrigerant pressure Pci, the suction refrigerant pressure Ps, and the suction refrigerant temperature Ts (lower part of Figure 5), and the protection determination unit 300 determines whether protection of the compressor 2 is needed (upper part of Figure 5).

[0039] The results of the determinations made by the limit determination unit 200 and the protection determination unit 300 are input to the selector 400, and the compressor 2 is controlled in accordance with the output from the selector 400. The limit determination unit 200, the protection determination unit 300, and the selector 400 are realized by the CPU 101 provided in the control device 100 reading a program stored in the ROM 102 into the RAM 103 and executing it.

[0040] The restriction determination unit 200 includes a Pci restriction determination unit 201, a Ps restriction determination unit 202, a Psu restriction determination unit 203, a Ts restriction determination unit 204, and a minimum value selection unit 205. The current target rotation speed TGNC_BASE of the compressor 2, the outlet refrigerant pressure Pci, the suction refrigerant pressure Ps, and the suction refrigerant temperature Ts are input to the restriction determination unit 200, and based on these, it is determined whether or not the target rotation speed of the compressor 2 needs to be restricted, and the target rotation speed TGNC is calculated.

[0041] When the input outlet refrigerant pressure Pci exceeds a predetermined upper limit, the Pci restriction determination unit 201 outputs a target rotation speed TGNC_LPci calculated based on the outlet refrigerant pressure Pci to the minimum value selection unit 205. When the outlet refrigerant pressure Pci does not exceed the predetermined upper limit, the Pci restriction determination unit 201 outputs the current target rotation speed TGNC_BASE of the compressor 2 to the minimum value selection unit 205 as the target rotation speed TGNC_LPci.

[0042] When the input suction refrigerant pressure Ps falls below a predetermined lower limit, the Ps limitation determination unit 202 outputs a target rotation speed TGNC_LPs calculated based on the suction refrigerant pressure Ps to the minimum value selection unit 205. When the suction refrigerant pressure Ps does not fall below the predetermined value, the Ps limitation determination unit 202 outputs the current target rotation speed TGNC_BASE of the compressor 2 to the minimum value selection unit 205 as the target rotation speed TGNC_LPs.

[0043] When the input suction refrigerant pressure Ps exceeds a predetermined upper limit, the Psu limitation determination unit 203 outputs a target rotation speed TGNC_LPsu calculated based on the suction refrigerant pressure Ps to the minimum value selection unit 205. When the suction refrigerant pressure Ps does not exceed the predetermined upper limit, the Psu limitation determination unit 203 outputs the current target rotation speed TGNC_BASE of the compressor 2 to the minimum value selection unit 205 as the target rotation speed TGNC_LPsu.

[0044] Similarly, when the input suction refrigerant temperature Ts exceeds a predetermined upper limit, the Ts limit determination unit 204 outputs the target rotation speed TGNC_LTs calculated based on the suction refrigerant temperature Ts to the minimum value selection unit 205. When the suction refrigerant temperature Ts does not exceed the predetermined upper limit, the Ts limit determination unit 204 outputs the current target rotation speed TGNC_BASE of the compressor 2 to the minimum value selection unit 205 as the target rotation speed TGNC_LTs.

[0045] The current target rotation speed TGNC_BASE, target rotation speed TGNC_LPci, target rotation speed TGNC_LPs, target rotation speed TGNC_LPsu, and target rotation speed TGNC_LTs of the compressor 2 are input to the minimum value selection unit 205, and the minimum value among these is output as the target rotation speed TGNC.

[0046] The protection determination unit 300 includes a Pci protection determination unit 301, a Ps protection determination unit 302, a Psu protection determination unit 303, a Ts protection determination unit 304, and an OR circuit 305. The protection determination unit 300 receives the outlet refrigerant pressure Pci, the suction refrigerant pressure Ps, and the suction refrigerant temperature Ts as input, and determines whether or not protection of the compressor 2 is required based on these.

[0047] If the input outlet refrigerant pressure Pci is greater than the upper limit value and exceeds a predetermined protection value for protecting the compressor 2, the Pci protection determination unit 301 outputs a protection signal to the OR circuit 305. If the outlet refrigerant pressure Pci does not exceed the protection value, no signal is output to the OR circuit 305.

[0048] When the input suction refrigerant pressure Ps is smaller than the aforementioned lower limit value and falls below a predetermined protection value for protecting the compressor 2, the Ps protection determination unit 302 outputs a protection signal to the OR circuit 305. When the suction refrigerant pressure Ps does not fall below the protection value, no signal is output to the OR circuit 305.

[0049] If the input suction refrigerant pressure Ps is greater than the upper limit value and exceeds a predetermined protection value to protect the compressor 2, the Psu protection determination unit 303 outputs a protection signal to the OR circuit 305. If the suction refrigerant pressure Ps does not exceed the protection value, no signal is output to the OR circuit 305.

[0050] Similarly, when the input suction refrigerant temperature Ts is greater than the upper limit value and exceeds a predetermined protection value to protect the compressor 2, the Ts limit determination unit 204 outputs a protection signal to the OR circuit 305. When the suction refrigerant temperature Ts does not exceed the protection value, no signal is output to the OR circuit 305.

[0051] The OR circuit 305 receives protection signals from the Pci protection determination unit 301, the Ps protection determination unit 302, the Psu protection determination unit 303, and the Ts protection determination unit 304, and when one or more protection signals are input, determines that protection of the compressor 2 is required, and outputs the protection signal to the selector 400. When no protection signal is input from any of the Pci protection determination unit 301, the Ps protection determination unit 302, the Psu protection determination unit 303, and the Ts protection determination unit 304, the OR circuit 305 determines that protection of the compressor 2 is not required, and does not output a protection signal to the selector 400.

[0052] The selector 400 receives the target rotation speed from the restriction determination unit 200, and also receives a protection signal only when the protection determination unit 300 requires protection of the compressor 2. If the selector 400 does not receive a protection signal from the protection determination unit 300, it controls the compressor 2 in accordance with the target rotation speed TGNC calculated by the restriction determination unit 200, and if the protection determination unit 300 outputs a protection signal for the compressor 2, it protects the compressor 2, i.e., stops driving the compressor 2.

[0053] During heating operation of the vehicle air conditioner 1, if the intake refrigerant pressure Ps of the refrigerant circuit 10 decreases, the compression ratio increases, the discharge refrigerant temperature rises, and volumetric efficiency decreases. Therefore, the control device 100 normally controls each component device, including the compressor 2, so that the intake refrigerant pressure does not fall below a predetermined lower limit value.

[0054] Therefore, during heating operation of the vehicle air conditioner 1, particularly during endothermic heating operation, the Pci restriction determination unit 201 and the Ps restriction determination unit 202 mainly calculate whether or not restriction of the compressor 2 is necessary and the target rotation speed TGNC when the restriction is necessary, and the Pci protection determination unit 301 and the Ps protection determination unit 302 determine whether or not protection of the compressor 2 is necessary.

[0055] On the other hand, as described above, in hot gas heating operation, a portion of the high-temperature, high-pressure refrigerant discharged from the compressor 2 returns to the compressor 2 via the hot gas bypass 10V, so the suction refrigerant pressure to the compressor 2 is likely to be higher than in endothermic heating operation. If the suction refrigerant pressure exceeds an upper limit (a threshold pressure, described later), problems such as difficulty in stably and effectively continuing the hot gas heating operation and a decrease in the durability of the compressor 2 may occur.

[0056] Therefore, during hot gas heating operation, the control device 100 mainly calculates whether compressor restriction is necessary and the target rotation speed TGNC when restriction is required using the Psu restriction judgment unit 203 and the Ts restriction judgment unit 204, and determines whether compressor 2 needs to be protected using the Psu protection judgment unit 303 and the Ts protection judgment unit 304.

[0057] In other words, during hot gas heating operation, when the input suction refrigerant pressure Ps exceeds the first threshold pressure Ps_th1, which is a predetermined upper limit value, the Psu limitation judgment unit 203 outputs the target rotation speed TGNC_LPsu calculated based on the suction refrigerant pressure Ps to the minimum value selection unit 205.

[0058] In addition, when the input suction refrigerant temperature Ts exceeds a first threshold temperature Ts_th1, which is a predetermined upper limit value, the Ts limit judgment unit 204 outputs the target rotation speed TGNC_LTs calculated based on the suction refrigerant temperature Ts to the minimum value selection unit 205.

[0059] The minimum value selection unit 205 receives the current target rotation speed TGNC_BASE, target rotation speed TGNC_LPci, target rotation speed TGNC_LPs, target rotation speed TGNC_LPsu, and target rotation speed TGNC_LTs of the compressor 2, and outputs the minimum value among these as the target rotation speed TGNC.

[0060] Here, the first threshold pressure Ps_th1 can be determined, for example, by the following equation (1) based on the maximum suction refrigerant pressure UL_Psu determined by the specifications of the compressor 2 and a value LON_Psu determined based on the outside air temperature: Ps_th1=UL_Psu−LON_Psu (1)

[0061] Then, in the Psu restriction judgment unit 203, when the suction refrigerant pressure Ps exceeds the first threshold pressure Ps_th1, the target rotation speed TGNC_LPsu is calculated based on the current target rotation speed TGNC_BASE of the compressor 2, the first threshold pressure Ps_th1, the suction refrigerant pressure Ps, and the gain for the compressor 2, that is, according to the following equation (2).

[0062] TGNC_LPsu=TGNC_BASE+((UL_Psu-LON_Psu)-Ps)*GUL_Psu...(2)

[0063] In addition, in the Psu restriction determination unit 203, when the suction refrigerant pressure Ps does not exceed the first threshold pressure Ps_th1, the target rotation speed TGNC_LPsu is set to the current target rotation speed TGNC_BASE of the compressor 2.

[0064] Similarly, the first threshold temperature Ts_th1 can be determined, for example, by the following equation (3) based on the maximum suction refrigerant temperature UL_Ts determined by the specifications of the compressor 2 and the value LON_Tsu determined based on the outside air temperature: Ts_th1=UL_Ts−LON_Ts (3)

[0065] In other words, the first threshold pressure Ps_th1 and the first threshold temperature Ts_th1 can be changed based on the outside air temperature, and it is preferable to lower the first threshold pressure Ps_th1 and the first threshold temperature Ts_th1 as the outside air temperature decreases, and to raise the first threshold pressure Ps_th1 and the first threshold temperature Ts_th1 as the outside air temperature increases.

[0066] The amount of heat dissipated in the indoor heat exchanger 21 fluctuates as the outside air temperature fluctuates, and the intake refrigerant pressure Ps also fluctuates. However, by changing the first threshold pressure Ps_th1 and the first threshold temperature Ts_th1 based on the outside air temperature, it is possible to determine a more appropriate first threshold pressure Ps_th1 and first threshold temperature Ts_th1 that correspond to the fluctuations in the intake refrigerant pressure Ps caused by fluctuations in the outside air temperature.

[0067] Then, in the Ts limit determination unit 204, when the intake refrigerant temperature Ts exceeds the first threshold temperature Ts_th1, the target rotation speed TGNC_LTs is calculated based on the current target rotation speed TGNC_BASE of the compressor 2, the first threshold temperature Ts_th1, the intake refrigerant temperature Ts, and the gain for the compressor 2, that is, according to the following equation (4).

[0068] TGNC_LTs=TGNC_BASE+((UL_Ts-LON_Ts)-Ts)*GUL_Ts...(4)

[0069] When the intake refrigerant temperature Ts does not exceed the first threshold temperature Ts_th1, the Ts limit determination unit 204 sets the target rotation speed TGNC_LTs to the current target rotation speed TGNC_BASE of the compressor 2.

[0070] On the other hand, when the input suction refrigerant pressure Ps exceeds a second threshold pressure Ps_th2 that is greater than the first threshold pressure Ps_th1, the Psu protection determination unit 303 outputs a protection signal to the OR circuit 305. Similarly, when the input suction refrigerant temperature Ts exceeds a second threshold temperature Ts_th2 that is greater than the first threshold temperature Ts_th1, the Ts protection determination unit 304 outputs a protection signal to the OR circuit 305.

[0071] The OR circuit 305 receives protection signals from the Psu protection determination unit 303 and the Ts protection determination unit 304, and determines that protection of the compressor 2 is required if a protection signal is input from either unit, and determines that protection of the compressor 2 is not required if a protection signal is not input from either the Psu protection determination unit 303 or the Ts protection determination unit 304.

[0072] Here, the second threshold pressure Ps_th2 is a value greater than the first threshold pressure Ps_th1 and is a protection value that is predetermined to protect the compressor 2. For example, the second threshold pressure Ps_th2 can be determined by the following equation (5) based on the maximum suction refrigerant pressure UL_Psu determined according to the specifications of the compressor 2 and a value HYS_Psu that takes hysteresis into consideration: Ps_th2=UL_Psu-HYS_Psu (5)

[0073] Similarly, the second threshold temperature Ts_th2 is a value greater than the first threshold temperature Ts_th1 and is a protection value determined in advance to protect the compressor 2. For example, the second threshold temperature Ts_th2 can be determined by the following equation (6) based on the maximum suction refrigerant temperature UL_Ts determined by the specifications of the compressor 2 and a value HYS_Ts that takes hysteresis into consideration: Ts_th2=UL_Ts−HYS_Ts (6)

[0074] The control of the compressor 2 by the control device 100 during the hot gas heating operation in the vehicle air conditioner configured as above will be described with reference to the flowchart of FIG.

[0075] As shown in Figure 6, when hot gas heating operation is performed in the vehicle air conditioning system 1 (step S11), the control device 100 acquires the intake refrigerant pressure Ps from the refrigerant pressure sensor 44A provided on the intake side of the compressor 2, and acquires the intake refrigerant temperature Ts from the refrigerant temperature sensor 43A at a predetermined interval (step S12).

[0076] In the control device 100, if the input suction refrigerant pressure Ps is equal to or lower than the first threshold pressure Ps_th1 (No in step S13) and the suction refrigerant temperature Ts is also equal to or lower than the first threshold temperature Ts_th1 (No in step S14), the compressor 2 is controlled based on the current target rotation speed TGNC_BASE (step S15).

[0077] On the other hand, if the suction refrigerant pressure Ps is equal to or lower than the first threshold pressure Ps_th1 (No in step S13) but the suction refrigerant temperature Ts is greater than the first threshold temperature Ts_th1 (Yes in step S14), proceed to step S17, and determine whether to limit the target rotation speed of compressor 2 (proceed to step S18) or protect compressor 2 (proceed to step S21) based on the suction refrigerant temperature Ts.

[0078] This is because even if the intake refrigerant pressure Ps is below the first threshold pressure Ps_th1 (No in step S13), the intake refrigerant temperature Ts may become overheated and rise above the saturation temperature, and therefore, in order to ensure safety, it is preferable to control the compressor 2 taking into account the relationship between the intake refrigerant temperature Ts and the first threshold temperature Ts_th1 or the second threshold temperature Ts_th2.

[0079] Furthermore, if the suction refrigerant pressure Ps is greater than the first threshold pressure Ps_th1 (Yes in step S13) and is equal to or less than the second threshold pressure Ps_th2 (No in step S16), the process proceeds to step S17, where it is determined based on the suction refrigerant temperature Ts whether to limit the target rotation speed of the compressor 2 (proceed to step S18) or protect the compressor 2 (proceed to step S21).

[0080] In step S17, if the intake refrigerant temperature Ts is greater than the first threshold temperature Ts_th1 (Yes in step S14) and is less than or equal to the second threshold temperature Ts_th2 (No in step S17), the target rotation speed TGNC_LPsu and the target rotation speed TGNC_LTs are obtained (steps S18, S19), and the smaller of the two is set as the target rotation speed TGNC to control the compressor 2 (step S20).

[0081] If the intake refrigerant pressure Ps exceeds the second threshold pressure Ps_th2 (Yes in step S16), and if the intake refrigerant temperature Ts exceeds the second threshold temperature Ts_th2 (Yes in step S17), the compressor 2 is protected, i.e., the operation of the compressor 2 is stopped (step S21).

[0082] After stopping the compressor 2, the control device 100 monitors whether the suction refrigerant pressure Ps falls below the second threshold pressure Ps_th2 (step S22) and whether the suction refrigerant temperature Ts falls below the second threshold temperature Ts_th2 (step S23). If the suction refrigerant pressure Ps and the suction refrigerant temperature Ts fall below the second threshold pressure Ps_th2 (Yes in step S22) and the second threshold temperature Ts_th2 (Yes in step S23), the control device 100 restarts the compressor 2 (step S24) and repeats the above process until the hot gas heating operation ends (step S25).

[0083] As described above, in the vehicle air conditioner 1 according to this embodiment, during hot gas heating operation, the first target rotation speed TGNC_LPsu based on the suction refrigerant pressure Ps and the second target rotation speed TGNC_LTs based on the suction refrigerant temperature are calculated for the compressor 2. Then, when the suction refrigerant pressure Ps exceeds the first threshold pressure Ps_th1 or when the suction refrigerant temperature Ts exceeds the first threshold temperature Ts_th1, the compressor 2 is controlled with the smaller of the first target rotation speed TGNC_LPsu or the second target rotation speed TGNC_LTs as the target rotation speed TGNC.

[0084] Furthermore, in the control device 100, the first threshold pressure Ps_th1 and the first threshold temperature Ts_th1 are changed in response to fluctuations in the outside air temperature, so that the first threshold pressure Ps_th1 and the first threshold temperature Ts_th1 can be set in accordance with fluctuations in the intake refrigerant pressure Ps caused by fluctuations in the outside air temperature, and the compressor 2 can be controlled at the optimal target rotation speed TGNC regardless of fluctuations in the outside air temperature.

[0085] In particular, when the outside air temperature drops, the intake refrigerant pressure Ps also drops, but by lowering the first threshold pressure Ps_th1 and the first threshold temperature Ts_th1 accordingly, the compressor 2 can be controlled at the optimal target rotation speed TGNC according to the outside air temperature, and operation can be continued more stably and effectively even in harsh environments at extremely low temperatures where hot gas heating operation is used.

[0086] In this way, by controlling the suction refrigerant pressure Ps and suction refrigerant temperature Ts to fall within a predetermined range including their target values, hot gas heating operation can be continued stably and effectively, and the durability of the compressor can be improved.

[0087] Furthermore, even when the control device 100 performs the above-described control, if the suction refrigerant pressure Ps exceeds the second threshold pressure Ps_th2 which is greater than the first threshold pressure Ps_th1, or if the suction refrigerant temperature Ts exceeds the second threshold temperature Ts_th2 which is greater than the first threshold temperature Ts_th1, the control device 100 stops driving the compressor 2, thereby ensuring the durability of the compressor 2 and guaranteeing safety.

[0088] Thereafter, the control device 100 drives the compressor 2 again when the suction refrigerant pressure Ps falls below the second threshold pressure Ps_th2 and the suction refrigerant temperature Ts falls below the second threshold temperature Ts_th2, thereby ensuring the durability of the compressor 2 and enabling the interrupted hot gas heating operation to be resumed under conditions that allow it to be continued stably and effectively.

[0089] As described above, according to this embodiment, in the hot gas heating operation, the hot gas heating operation can be continued stably and effectively, and the durability of the compressor can be improved.

[0090] The embodiments of the present invention have been described above in detail with reference to the drawings, but the specific configurations are not limited to these embodiments, and the present invention also includes design changes and the like that do not deviate from the gist of the present invention.

[0091] 1: Vehicle air conditioning device, 2: Compressor, 10: Refrigerant circuit, 10V: Hot gas bypass, 11: External heat exchanger, 12, 13: Flow path switching valve, 14, 15: Check valve, 16: Accumulator, 20: Air conditioning unit, 21, 22: Indoor heat exchanger, 23: Blower, 24, 25: Air damper, 25A, 25B: Air inlet, 30: Heat medium circuit, 31: Circulation pump, 33: Temperature-controlled heat exchanger, 34: Refrigerant heat medium heat exchanger, 34A, 34B: Flow path, 40: Sensor unit, 41: Outside air sensor, 42: Compressor current sensor, 43, 43A: Refrigerant temperature sensor, 44, 44A, 44B: Refrigerant pressure sensor, 45: Occupant sensor, 46: Air supply temperature sensor, 100: Control device

Claims

1. A vehicle air conditioning system comprising: a refrigerant circuit including a compressor, an indoor heat exchange unit, an external heat exchange unit, and a hot gas bypass that reduces the pressure of at least a portion of the refrigerant compressed by the compressor and returns it to the compressor without passing through the indoor heat exchange unit and the external heat exchange unit; and a control device that controls the refrigerant circuit and is capable of executing a hot gas heating mode in which a portion of the refrigerant compressed by the compressor flows through the indoor heat exchange unit and the remainder flows through the hot gas bypass, wherein, when the hot gas heating mode is executed, the control device calculates, for the compressor, a first target rotation speed based on an intake refrigerant pressure and a second target rotation speed based on an intake refrigerant temperature, and controls the compressor to set the smaller of the first target rotation speed or the second target rotation speed as the target rotation speed when the intake refrigerant pressure exceeds a first threshold pressure or when the intake refrigerant temperature exceeds the first threshold temperature.

2. The vehicle air conditioning system according to claim 1, wherein the control device is capable of changing the first threshold pressure and the first threshold temperature based on an outside air temperature, and adjusts the first threshold pressure and the first threshold temperature to be lower as the outside air temperature decreases.

3. A vehicle air conditioning system as described in claim 1 or claim 2, wherein the control device stops driving the compressor when the suction refrigerant pressure exceeds a second threshold pressure that is greater than the first threshold pressure, or when the suction refrigerant temperature exceeds a second threshold temperature that is greater than the first threshold temperature.

4. The vehicle air conditioning system according to claim 3, wherein the control device drives the compressor again when the intake refrigerant pressure falls below the second threshold pressure and the intake refrigerant temperature falls below the second threshold temperature.

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