Abstract:
The disclosed operation method of a heat pump-type vehicle air conditioning system involves a step for setting a cold operating mode for raising the output air temperature of the air conditioner by means of a heater or a normal operating mode for raising the heating COP; a step for detecting the temperatures inside and outside the vehicle; and a step which, by selecting either the cold operating mode or the normal operating mode on the basis of the detected temperatures inside and outside of the vehicle, is for bypassing a condenser, controlling the opening of an electronic expansion valve contained in a bypass unit connected in series to a gas/liquid separating liquid coolant storage unit downstream of the aforementioned heater, and adjusting the pressure drop applied to the coolant.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method of operating a heat-pump type vehicular air conditioning system incorporated in a vehicle for air-conditioning the passenger cabin of the vehicle. 
       BACKGROUND ART 
       [0002]    Vehicles, e.g., engine automobiles having an internal combustion engine, hybrid automobiles having an engine and a secondary battery (or a secondary battery and a fuel cell or the like) in combination, electric automobiles, and fuel cell automobiles, incorporate various types of vehicular air conditioning systems therein. 
         [0003]    For example, as shown in  FIG. 12 , the vehicular air conditioning apparatus disclosed in Japanese Laid-Open Patent Publication No. 2009-023564 includes a compressor  1  for drawing in and discharging a refrigerant, a condenser  3  disposed in an air conditioning unit case  2  for heating air by performing heat exchange between air and the refrigerant that is discharged from the compressor  1  in a heating mode, a receiver  4  for receiving refrigerant that flows in from the condenser  3  and performing gas-liquid separation in the heating mode, a supercooler  5  for supercooling liquid refrigerant that flows in from the receiver  4  by performing heat exchange between the liquid refrigerant and ambient air in the heating mode, a depressurizer  6  for depressurizing the refrigerant that is supercooled by the supercooler  5  in the heating mode, and an outdoor heat exchanger  7  for evaporating the refrigerant that is depressurized by the depressurizer  6  in the heating mode. 
         [0004]    With the above vehicular air conditioning apparatus, (a degree of) subcooling is achieved by the receiver and further is achieved reliably by the supercooler  5 , which is disposed downstream of the receiver  4 , using ambient air in the heating mode. The vehicular air conditioning apparatus is rendered highly efficient and excellent in heating performance by means of a relatively simple cyclic arrangement. 
       SUMMARY OF INVENTION 
       [0005]    According to Japanese Laid-Open Patent Publication No. 2009-023564, the receiver  4  and the supercooler  5  are used only in the heating mode, and are not necessary in a cooling mode. Therefore, the number of components dedicated to the heating mode is increased, thereby making the vehicular air conditioning apparatus uneconomical. 
         [0006]    According to Japanese Laid-Open Patent Publication No. 2009-023564, furthermore, the vehicular air conditioning apparatus does not have a buffer for compensating for a refrigerant shortage when liquid refrigerant remains trapped in the outdoor heat exchanger  7  that is cooled in the cooling mode. Consequently, due to the refrigerant shortage, air-conditioning performance is lowered. 
         [0007]    The present invention has been made in an effort to solve the aforementioned problems. An object of the present invention is to provide a heat-pump type vehicular air conditioning system, which is capable of selecting either a heating capability priority or an operation efficiency priority depending on inside and outside temperatures of a passenger compartment, for enabling good air conditioning capability and improving economic efficiency. 
         [0008]    According to the present invention, there is provided a method of operating a heat pump type vehicular air conditioning system comprising a condenser for performing heat exchange between a refrigerant and ambient air, the condenser being connected to a heat pump circulation path for circulating the refrigerant with a compressor, a first evaporator connected to the heat pump circulation path, for performing heat exchange between the refrigerant and air-conditioning air, a heater connected to the heat pump circulation path, for performing heat exchange between the refrigerant, which has been delivered from the compressor, and the air-conditioning air, which has passed through the evaporator, a second evaporator connected to a branch path that branches from the heat pump circulation path, for performing heat exchange between the refrigerant and a heat medium that is discharged from a cabin, a gas-liquid separation refrigerant storage unit disposed downstream of the condenser, a subcondenser disposed downstream of the gas-liquid separation refrigerant storage unit, a bypass unit for connecting the gas-liquid separation refrigerant storage unit downstream of and in series with the heater in bypassing relation to the condenser in a heating mode, the bypass unit having a pressure loss device for imparting a pressure loss to the refrigerant, and temperature detectors for detecting a temperature outside of a vehicle and a temperature inside of the vehicle. 
         [0009]    The method comprises the steps of establishing a cold-climate operating mode for increasing the temperature of the air conditioning air that is heated by the heater and discharged into the cabin, and a normal operating mode for increasing heating efficiency with respect to electric power, detecting the temperature outside of the vehicle and the temperature inside of the vehicle, and selecting either the cold-climate operating mode or the normal operating mode based on the detected temperature outside of the vehicle and the detected temperature inside of the vehicle, and controlling the pressure loss device. 
         [0010]    According to the present invention, when a pressure loss is imparted to the refrigerant by the pressure loss device, the pressure of the refrigerant is increased, and in addition, the amount of work performed by the compressor is increased. Therefore, the temperature of the air-conditioning air, which is heat-exchanged by the heater, is increased when the air-conditioning air is discharged into the cabin, thereby quickly heating the cabin (cold-climate operating mode). 
         [0011]    When the pressure loss imparted to the refrigerant is reduced, the pressure of the refrigerant is lowered, and in addition, the amount of work performed by the compressor is lowered. Therefore, a heating COP (a measure of heating ability per heating electric power consumption) is increased for allowing the air conditioning system to operate economically in a heating mode (normal operating mode). 
         [0012]    Therefore, the vehicular air conditioning system is capable of selecting either a heating capability priority or an operation efficiency priority, depending on the temperatures inside and outside of the cabin, for thereby enabling good air conditioning capability and improving economic efficiency. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a schematic block diagram of a heatpump type vehicular air conditioning system to which an operating method according to a first embodiment of the present invention is applied; 
           [0014]      FIG. 2  is a schematic view showing the manner in which the vehicular air conditioning system operates in a heating mode; 
           [0015]      FIG. 3  is a flowchart of the operating method; 
           [0016]      FIG. 4  is a diagram showing a cycle on a Mollier chart plotted when the vehicular air conditioning system operates in a cold-climate operating mode; 
           [0017]      FIG. 5  is a diagram showing the relationship between the temperature outside of the vehicle, the temperature inside of the vehicle, and operating modes; 
           [0018]      FIG. 6  is a diagram illustrating a process of controlling the opening of an electronic expansion valve; 
           [0019]      FIG. 7  is a diagram showing the relationship between the opening of the electronic expansion valve, consumed electric power, and a heating COP; 
           [0020]      FIG. 8  is a diagram showing a cycle on a Mollier chart plotted when the vehicular air conditioning system operates in a normal operating mode; 
           [0021]      FIG. 9  is a schematic block diagram of a heatpump type vehicular air conditioning system to which an operating method according to a second embodiment of the present invention is applied; 
           [0022]      FIG. 10  is a diagram illustrating a control process for switching between a capillary and a bypass passage; 
           [0023]      FIG. 11  is a diagram showing the relationship between switching between the capillary and the bypass passage, consumed electric power, and a heating COP; and 
           [0024]      FIG. 12  is a diagram illustrative of the vehicular air conditioning apparatus disclosed in Japanese Laid-Open Patent Publication No. 2009-023564. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    As shown in  FIGS. 1 and 2 , a heat pump-type vehicular air conditioning system  10  to which an operating method according to a first embodiment of the present invention is applied is incorporated in an automobile (vehicle)  12  for air-conditioning a passenger cabin (vehicle compartment)  14  of the automobile  12 . 
         [0026]    The air conditioning system  10  includes a heat pump circulation path  18  for circulating a refrigerant with a compressor  16 . The heat pump circulation path  18  includes therein a condenser unit (subcooling condenser)  20  for performing heat exchange between the refrigerant and ambient air, an expansion valve  22  for depressurizing the refrigerant delivered from the condenser unit  20 , a first evaporator  24  for performing heat exchange between the refrigerant, which has passed through the expansion valve  22 , and air-conditioning air, and a heater  26  for performing heat exchange between the refrigerant, which has been delivered from the compressor  16 , and the air-conditioning air, which has passed through the first evaporator  24 . 
         [0027]    The heat pump circulation path  18  branches into a branch path  28 , which includes a second evaporator  30  for performing heat exchange between a heat medium discharged from the cabin  14  (waste heat gas from the cabin  14 ) and the refrigerant. 
         [0028]    The condenser unit  20  includes a condenser (condensing device)  32 , a gas-liquid separation refrigerant storage unit (subcooling tank)  34 , and a subcondenser (supercooling device)  36 , which are connected mutually in series downstream of the heater  26 , and through which the refrigerant flows in a cooling mode. A solenoid-operated valve  38   a  is disposed upstream of the condenser  32 . 
         [0029]    A bypass unit  40  is connected to the heat pump circulation path  18 , for connecting the heater  26  and the gas-liquid separation refrigerant storage unit  34  to each other in bypassing relation to the condenser  32  in a heating mode. The bypass unit  40  includes a first bypass passage  42   a  that branches from the heat pump circulation path  18  and is connected to the gas-liquid separation refrigerant storage unit  34  of the condenser unit  20 . The first bypass passage  42   a  includes an electronic expansion valve  43  the opening of which is adjustable by an electric signal, and which functions as a pressure loss device for causing the refrigerant to undergo a pressure loss. The electronic expansion valve  43  may be replaced with an automatic restriction valve, an automatic flow regulating valve, a fixed restriction valve, or the like. 
         [0030]    The expansion valve  22  includes a means (not shown) for detecting the temperature of the refrigerant, which is delivered from the first evaporator  24  and cools the air-conditioning air. An opening of the expansion valve  22  is automatically variable depending on the temperature and pressure of the refrigerant delivered from the first evaporator  24 , for thereby varying the flow rate of the refrigerant. 
         [0031]    The heat pump circulation path  18  also includes a three-way valve  44   a  disposed at a junction between a path portion near the expansion valve  22  and an inlet of the branch path  28 . The heat pump circulation path  18  further includes a three-way valve  44   b  disposed at a junction between an outlet of a second bypass passage  42   b,  which bypasses the first evaporator  24 , and the heat pump circulation path  18 . The second evaporator  30  is disposed in a rear portion of the automobile  12  (see  FIG. 2 ). 
         [0032]    Between the first evaporator  24  and the heater  26 , an air mixing damper  46  is disposed for introducing air-conditioning air cooled by the first evaporator  24  into the cabin  14  in bypassing relation to the heater  26 . 
         [0033]    The automobile  12  has an ambient air inlet  48  for introducing ambient air as air-conditioning air. The first evaporator  24  and the heater  26  are successively disposed in this order downstream of the ambient air inlet  48 . 
         [0034]    The air conditioning system  10  includes a controller (ECU)  50 , which functions as a flow path switching means for controlling the solenoid-operated valve  38   a  and the three-way valves  44   a,    44   b  to switch between the heating mode and the cooling mode. The controller  50  also controls the air conditioning system  10  in its entirety (see  FIG. 1 ). A first temperature sensor  52   a  for detecting the temperature outside of the vehicle, and a second temperature sensor  52   b  for detecting the temperature inside of the vehicle (the temperature inside of the cabin) are connected respectively to the controller  50 . 
         [0035]    A method of operating the air conditioning system  10  will be described below with reference to the flowchart shown in  FIG. 3  and the cycle diagram shown in  FIG. 4 . 
         [0036]    When the air conditioning system  10  is operated in a heating mode, as shown in  FIG. 5 , a cold-climate operating mode and a normal operating mode are established. The cold-climate operating mode and the normal operating mode, which are stored as a map in the controller  50 , are preset based on the temperature outside of the vehicle and the temperature inside of the vehicle. 
         [0037]    The cold-climate operating mode is an operating mode for quickly heating the cabin with higher emphasis placed on heating ability by increasing the electric power consumed by the compressor  16 . The normal operating mode is an operating mode with higher emphasis placed on the heating COP (a measure of heating efficiency with respect to electric power). A heating efficiency index is given by the heating COP=heating ability/heating electric power consumption. 
         [0038]    In the cold-climate operating mode, the opening of the electronic expansion valve  43  is reduced to impart a pressure loss to the refrigerant in the heat pump circulation path  18 . The degree of opening and the temperature of the electronic expansion valve  43  are set so as to follow the relationship shown in  FIG. 6 . The relationship between the electric power consumed depending on the opening of the electronic expansion valve  43  and the heating COP is illustrated in  FIG. 7 . 
         [0039]    When the air conditioning system  10  starts to operate in the heating mode, the first temperature sensor  52   a  detects the temperature outside of the vehicle, and the second temperature sensor  52   b  detects the temperature inside of the vehicle (step S 1  in  FIG. 3 ). Then, control proceeds to step S 2 , whereupon a decision is made concerning the map, based on the detected temperature outside of the vehicle and the detected temperature inside of the vehicle, for judging whether or not the vehicle is in a cold climate (step S 3 ). 
         [0040]    If the vehicle is judged to be in a cold climate (YES in step S 3 ), then control proceeds to step S 4  in which the air conditioning system  10  enters the cold-climate operating mode. In the cold-climate operating mode, the controller  50  adjusts the opening of the electronic expansion valve  43 . 
         [0041]    When the air conditioning system  10  operates in the heating mode, as shown in  FIG. 2 , the compressor  16  is actuated to deliver refrigerant into the heat pump circulation path  18 . The refrigerant is supplied to the heater  26 , which performs heat exchange between the refrigerant and the air-conditioning air (radiates heat into the air-conditioning air), to thereby increase the temperature of the air-conditioning air. 
         [0042]    The solenoid-operated valve  38   a  is closed to allow the refrigerant, which has been discharged from the heater  26 , to pass through the first bypass passage  42   a  directly into the gas-liquid separation refrigerant storage unit  34  in bypassing relation to the main condenser  32 , while a pressure loss is imparted to the refrigerant by the electronic expansion valve  43 . The refrigerant flows from the gas-liquid separation refrigerant storage unit  34  and through the subcondenser  36 , which cools the refrigerant and delivers the cooled refrigerant to the expansion valve  22 . 
         [0043]    The refrigerant is depressurized by the expansion valve  22  and flows in a branching manner through the three-way valve  44   a  and into the branch path  28 , from which the refrigerant is introduced into the second evaporator  30 . The second evaporator  30  performs heat exchange between the refrigerant and a heat source in the cabin  14 . The refrigerant then bypasses the first evaporator  24  and flows through the second bypass passage  42   b  and the expansion valve  22  back into the compressor  16 . 
         [0044]    If the vehicle is judged to not be in a cold climate (NO in step S 3 ), then control proceeds to step S 5 , in which the air conditioning system  10  enters the normal operating mode. In the normal operating mode, the opening of the electronic expansion valve  43  is controlled to be at 100% (fully open state) (see −t5° C. or higher) in order to operate the air conditioning system  10  with higher emphasis placed on the heating COP. The cold-climate operating mode and the normal operating mode are selectively carried out until the heating mode is stopped (step S 6 ). 
         [0045]    According to the first embodiment, the condenser  32 , the gas-liquid separation refrigerant storage unit  34 , and the subcondenser  36  are connected mutually in series downstream of the heater  26 . The heat pump circulation path  18  includes the bypass unit  40 , which connects the heater  26  to the gas-liquid separation refrigerant storage unit  34  in bypassing relation to the condenser  32  in the heating mode. The bypass unit  40  includes the electronic expansion valve  43 . 
         [0046]    When the air conditioning system  10  operates in the heating mode, as shown in  FIG. 2 , a portion of the heat pump circulation path  18  downstream of the heater  26  is connected through the electronic expansion valve  43  to the gas-liquid separation refrigerant storage unit  34  in bypassing relation to the condenser  32 . The gas-liquid separation refrigerant storage unit  34  thus functions as a subcooling tank, while the subcondenser  36  is capable of functioning as a subcooling device (refer to the gas-liquid separation refrigerant storage unit  34  and the subcondenser  36  in  FIG. 4 ). 
         [0047]    In the cold-climate operating mode, the opening of the electronic expansion valve  43  is controlled to be in a closed state (n% in  FIG. 6 ), thereby imparting a pressure loss to the refrigerant circulated in the heat pump circulation path  18 . The pressure of the refrigerant is thus increased to provide a large subcooling region. Therefore, the amount of work performed (electric power consumed) by the compressor  16  is increased. 
         [0048]    Consequently, the power of the compressor  16  can be positively extracted as heat for enabling an increased heating ability. The temperature of the air-conditioning air, which is heat-exchanged by the heater  26 , is increased when the air-conditioning air is discharged into the cabin  14   a,  thereby quickly heating the cabin  14 . Such an effect follows from the fact that the enthalpy difference in the heater  26  can be increased. 
         [0049]    The subcooling region in the heating mode can be increased by reducing the opening of the electronic expansion valve  43  (see  FIG. 4 ). Consequently, the inlet temperature of the gas-liquid separation refrigerant storage unit  34  and the subcondenser  36 , which serves as a subcooling heat exchanger, can be lowered to a temperature equivalent to that of ambient air temperature, which is very low. Therefore, heat radiated from the subcooling heat exchanger into the ambient air is minimized. 
         [0050]    In the normal operating mode, the electronic expansion valve  43  is kept fully open (see  FIG. 6 ). Therefore, in the cold-climate operating mode, as shown in  FIG. 8 , the pressure of the refrigerant in the heater  26  drops from a pressure a 1  to a pressure a 2 . Therefore, the amount of work performed (electric power consumed) by the compressor  16  is reduced, and the heating COP is increased, thereby enabling the air conditioning system  10  to operate economically in the heating mode. 
         [0051]    The refrigerant can thus be introduced as a perfect liquid medium into the expansion valve  22 , and gas is effectively prevented from becoming trapped in the expansion valve  22 . Therefore, the heat pump circulation path  18  is capable of stably circulating the refrigerant, thereby easily increasing heat exchange efficiency. 
         [0052]    The gas-liquid separation refrigerant storage unit  34  is used as a subcooling tank. Consequently, the gas-liquid separation refrigerant storage unit  34  can provide a sufficient amount of refrigerant, thereby making it possible to prevent air-conditioning performance from being lowered due to a refrigerant shortage when the air conditioning system  10  operates in a transient mode. 
         [0053]    Since the heater  26  carries out heat exchange sufficiently between the refrigerant and ambient air until the refrigerant enters into the subcooling region, it is possible to reduce the amount of heat that radiates from the subcondenser  36  into the ambient air. 
         [0054]      FIG. 9  is a schematic block diagram of a heatpump type vehicular air conditioning system  70  to which an operating method according to a second embodiment of the present invention is applied. 
         [0055]    Parts of the air conditioning system  70  according to the second embodiment, which are identical to those of the air conditioning system  10  according to the first embodiment, are denoted by identical reference characters, and such features will not be described in detail below. 
         [0056]    The air conditioning system  70  includes a bypass unit  72 , which connects the heater  26  and the gas-liquid separation refrigerant storage unit  34  to each other in bypassing relation to the condenser  32  in the heating mode. The bypass unit  72  includes a first bypass passage  42   a  and a third bypass passage  42   c,  together with a capillary  74 , which is connected to the first bypass passage  42   a  and functions as a pressure loss device for imparting a pressure loss to the refrigerant. A solenoid-operated valve  38   b  is connected upstream of the capillary  74 , and another solenoid-operated valve  38   c  is connected to the third bypass passage  42   c.    
         [0057]    Similar to the first embodiment, the air conditioning system  70  switches selectively between the cold-climate operating mode and the normal operating mode according to the flowchart shown in  FIG. 3 . 
         [0058]    In the cold-climate operating mode (−t5° C. or lower in  FIG. 10 ), the solenoid-operated valve  38   b  is opened and the solenoid-operated valves  38   a,    38   c  are closed. Therefore, the refrigerant is supplied to the capillary  74 , which imparts a pressure loss to the refrigerant. 
         [0059]    In the normal operating mode (−t5° C. or higher in  FIG. 10 ), the solenoid-operated valves  38   b,    38   a  are opened and the solenoid-operated valve  38   c  is opened. The refrigerant is supplied directly to the gas-liquid separation refrigerant storage unit  34  in bypassing relation to the condenser  32  and the capillary  74 . 
         [0060]    Therefore, as shown in  FIG. 11 , the consumed electric power and the heating COP are controlled when the solenoid-operated valves  38   b,    38   c  are opened and closed to switch between the cold-climate operating mode, in which the refrigerant flows through the capillary  74 , and the normal operating mode, in which the refrigerant flows through the third bypass passage  42   c.    
         [0061]    According to the second embodiment, in the cold-climate operating mode, the temperature of the air-conditioning air, which is heat-exchanged by the heater  26  and discharged into the cabin, is increased. Thus, in the normal operating mode, the amount of work performed by the compressor  16  is reduced to thereby increase the heating COP. Therefore, the second embodiment offers the same advantages as those of the first embodiment. 
         [0062]    In  FIG. 6 , etc., relatively large temperature change intervals such as −t2° C., −t1° C. have been illustrated. However, smaller temperature change intervals may be introduced in order to provide more control temperature points, such as −8° C., −7° C., −6° C., −5° C., . . . , (not shown), for achieving the same advantages. While two operating modes, i.e., a “cold-climate operating mode” and a “normal operating mode”, have been described above, other operating modes such as an “energy saver operating mode” may be added.