Abstract:
A heat pump device is provided with: a first refrigerant guide-in unit that guides in the high temperature, high pressure refrigerant discharged by the compressor from outside the housing; a water refrigerant heat exchanger that can dissipate heat from the high temperature, high pressure refrigerant guided in from the first refrigerant guide-in unit into a cooling fluid; and a housing accommodating the water refrigerant heat exchanger. The heat pump device is further provided with a cooling fluid guide-in unit that can guide the cooling fluid from outside the housing into the water refrigerant heat exchanger, a cooling fluid guide-out unit that can guide the cooling fluid out of the water refrigerant heat exchanger to the outside of the housing, and a first refrigerant guide-out unit that guides the refrigerant that has passed through the water refrigerant heat exchanger to the outside of the housing.

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle heat pump apparatus and a vehicle air-conditioning apparatus. 
     BACKGROUND ART 
     There is an automobile provided with both of an internal combustion engine and an electric motor, a so-called hybrid electric vehicle (HEV) or a plug-in hybrid vehicle (PHV). Typically, a vehicle air-conditioning apparatus mounted in such a vehicle provides heating to a vehicle interior using heat of the internal combustion engine and Joule heat generated by electrical power of a storage battery. 
     In addition, an air-conditioning apparatus configured to perform a cooling operation using a heat pump cycle is typically used. The heat pump cycle includes: a compressor disposed in an engine compartment; an outside heat exchanger disposed on a front side of a vehicle or at a position where air can be introduced to the outside heat exchanger; an evaporator disposed on an intake air path of the vehicle interior; and an expansion valve and/or the like. A high-temperature and high-pressure refrigerant compressed by the compressor is delivered to the outside heat exchanger and is cooled, and the cooled refrigerant is further brought into a low-temperature and low-pressure state by the expansion valve, and is delivered to the evaporator. The evaporator cools air supplied into the vehicle interior. The evaporator is provided in a heating, ventilation, and air conditioning system (hereinafter, referred to as an HVAC system) installed in the vehicle interior. 
     Heretofore, there have been several proposals for a vehicle air-conditioning apparatus that provides heating to the vehicle interior using a heat pump so as not to waste electrical power of the storage battery (see, e.g., Patent Literature (PTL) 1). 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     Japanese Patent Application Laid-Open No. HEI 8-197937 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the conventional vehicle air-conditioning apparatus which uses the heat pump cycle only during a cooling operation, a refrigerant pipe pattern is relatively simple as described above. 
     However, in the conventional vehicle air-conditioning apparatus which performs a heating operation using the heat pump cycle, the compressor and a cooling water-to-refrigerant heat exchanger are accommodated in the same housing (refer to FIGS. 21 to 24 in PTL 1). Hereinafter, a case will be discussed where the conventional vehicle air-conditioning apparatus configured to use the heat pump cycle only during the cooling operation is changed to perform the heating operation using the heat pump cycle as well. At this time, when the compressor and the cooling water-to-refrigerant heat exchanger are accommodated in the same housing, a refrigerant pipe pattern in the vicinity of the compressor is considerably changed, which is a problem. 
     In an automobile, various configuration elements such as an engine, a motor, a transmission, an air-conditioning compressor, and an intake air path are mounted in a small space. Accordingly, the layout flexibility of the configuration elements is low. 
     In the automotive field, a technical improvement is attempted via a so-called minor change in which a configuration is not considerably changed but is partially changed. 
     The vehicle air-conditioning apparatus may be improved as a minor change of a vehicle, and in this case, the configuration of the vehicle air-conditioning apparatus is required to be modified so that other components of the vehicle are not affected. 
     Refrigerant pipes of the vehicle air-conditioning apparatus using the heat pump cycle are installed so as to avoid interference with other configuration elements of the vehicle. For this reason, a small change in the refrigerant pipe pattern is a pre-requisite for modifying the vehicle air-conditioning apparatus without affecting other configuration elements of the vehicle. Unlike cooling water pipes, the refrigerant pipes are made of aluminum, for example, so as to bear a high pressure. For this reason, a change in the layout of the refrigerant pipes is not an easy task. The refrigerant pipes are preferably not considerably changed so as not to considerably affect the layout of other configuration elements of the vehicle. 
     An object of the present invention is to provide a vehicle heat pump apparatus and a vehicle air-conditioning apparatus which involve only few changes in a refrigerant pipe pattern compared to a conventional vehicle air-conditioning apparatus using a heat pump cycle only during a cooling operation, and which can perform a heating operation using a heat pump cycle. 
     Solution to Problem 
     A vehicle heat pump apparatus according to an aspect of the present invention is a vehicle heat pump apparatus that introduces and uses a high-temperature and high-pressure refrigerant discharged from a compressor configured to compress a suctioned refrigerant disposed outside a housing, the apparatus including: a first refrigerant introduction section through which the high-temperature and high-pressure refrigerant discharged from the compressor is introduced from outside the housing; a cooling water-to-refrigerant heat exchanger capable of releasing heat from the high-temperature and high-pressure refrigerant introduced from the first refrigerant introduction section to a cooling water; the housing that accommodates the cooling water-to-refrigerant heat exchanger; a cooling water introduction section that allows the cooling water to be introduced into the cooling water-to-refrigerant heat exchanger from outside the housing; a cooling water outlet section that allows the cooling water to flow through outside the housing from the cooling water-to-refrigerant heat exchanger; and a first refrigerant outlet section that allows the refrigerant passing through the cooling water-to-refrigerant heat exchanger to flows through outside the housing. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to easily perform not only a cooling operation but also a heating operation using a heat pump cycle by connecting a vehicle heat pump apparatus to an outside heat exchanger, a compressor, and an evaporator via pipes. In addition, it is possible to reduce changes in a refrigerant pipe pattern compared to a conventional vehicle air-conditioning apparatus using the heat pump cycle during a cooling operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram illustrating a vehicle heat pump apparatus and a vehicle air-conditioning apparatus of Embodiment 1 of the present invention; 
         FIG. 2  is a diagram illustrating a cooling operation performed by the vehicle air-conditioning apparatus of Embodiment 1; 
         FIG. 3  is a diagram illustrating a heating operation performed by the vehicle air-conditioning apparatus of Embodiment 1; 
         FIG. 4  is a diagram illustrating changes to refrigerant pipes from a conventional vehicle air-conditioning apparatus; 
         FIG. 5  is a configuration diagram illustrating a variation of the vehicle heat pump apparatus and the vehicle air-conditioning apparatus according to Embodiment 1 of the present invention; 
         FIG. 6  is a configuration diagram illustrating another variation of the vehicle heat pump apparatus and the vehicle air-conditioning apparatus according to Embodiment 1 of the present invention; 
         FIG. 7  is a configuration diagram illustrating a vehicle air-conditioning apparatus according to Embodiment 2 of the present invention; 
         FIG. 8  is a graph illustrating examples of the set values of an expansion valve; 
         FIG. 9  is a graph illustrating states of the expansion valve during the heating operation and the cooling operation; 
         FIG. 10  is a diagram illustrating a state of a cooling operation performed by the vehicle air-conditioning apparatus of Embodiment 2; and 
         FIG. 11  is a diagram illustrating a state of a heating operation performed by the vehicle air-conditioning apparatus of Embodiment 2 when outdoor temperature is very low. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     Embodiment 1 
       FIG. 1  is a configuration diagram illustrating a vehicle heat pump apparatus and a vehicle air-conditioning apparatus of Embodiment 1 of the present invention. 
     The vehicle air-conditioning apparatus of Embodiment 1 of the present invention includes vehicle heat pump apparatus  10 ; engine cooler (equivalent to an internal combustion engine cooler)  40 ; heater core  44 ; evaporator  48 ; compressor  12 ; expansion valve  52 ; outside heat exchanger  56 ; opening and closing valve  60 ; cooling water pipes, refrigerant pipes, and connection portions which connect the components; and the like. Heater core (equivalent to a heating heat exchanger)  44  and evaporator  48  are included in HVAC system  70  mounted in a vehicle interior. Here, the vehicle interior refers to a space positioned inside a fire wall. 
     Vehicle heat pump apparatus  10  includes cooling water-to-refrigerant heat exchanger  14 ; accumulator  16 ; three-way valve  18 ; check valve  20 ; orifice opening and closing valve  22 ; opening and closing valve  24 ; housing  26 ; cooling water introduction pipe  31 ; cooling water outlet pipe  32 ; two refrigerant outlet pipes  33  and  35 ; two refrigerant introduction pipes  34  and  36 ; and a control section. 
     Compressor  12  compresses the suctioned refrigerant to a high-temperature and high-pressure state, and discharges the compressed refrigerant. Compressor  12  includes a compressor mechanism therein, in which the compressor mechanism compresses the suctioned refrigerant, and discharges the compressed refrigerant. For example, the compressor mechanism is driven by an electric motor. A suction inlet for the refrigerant in compressor  12  communicates with an outlet of a refrigerant path of evaporator  48  via pipes and connection portion  19 . In addition, the suction inlet for the refrigerant in compressor  12  communicates with refrigerant outlet pipe  35  via pipes and connection portion  19 . Connection portion  19  works to simply communicate the outlet of the refrigerant path of evaporator  48 , refrigerant outlet pipe  35 , and the suction inlet for the refrigerant in compressor  12  with each other. A refrigerant discharge outlet of compressor  12  communicates with an inlet of a refrigerant path of cooling water-to-refrigerant heat exchanger  14  via refrigerant introduction pipe  36 . 
     Cooling water-to-refrigerant heat exchanger  14  has a cooling water path and the refrigerant path, and the cooling water path and the refrigerant path are configured to be in large area contact with each other so that a large amount of heat exchange can be performed therebetween. An inlet of the refrigerant path communicates with the discharge outlet of compressor  12 , and an outlet of the refrigerant path communicates with refrigerant outlet pipe  33  provided with orifice opening and closing valve  22 . An inlet of the cooling water path is connected to three-way valve  18  via a pipe, and an outlet for the cooling water is connected to check valve  20  via a pipe. 
     The high-temperature and high-pressure refrigerant flows through cooling water-to-refrigerant heat exchanger  14  while compressor  12  is driven, and in contrast, the cooling water is made to flow or not to flow through cooling water-to-refrigerant heat exchanger  14  by the switching of three-way valve  18 . When the cooling water flows through cooling water-to-refrigerant heat exchanger  14 , heat is released from the high-temperature and high-pressure refrigerant to the cooling water, and when the cooling water does not flow, the high-temperature and high-pressure refrigerant passes through cooling water-to-refrigerant heat exchanger  14  while maintaining substantially the same high temperature. 
     Three-way valve  18  is switched by electric control to allow the cooling water to flow from cooling water introduction pipe  31  to either one of cooling water-to-refrigerant heat exchanger  14  and cooling water outlet pipe  32 . 
     Check valve  20  prevents a reverse flow of the cooling water to cooling water-to-refrigerant heat exchanger  14 . 
     In the embodiment, three-way valve  18  and check valve  20  are equivalent to cooling-water switching valves that switch the flow path of the cooling water between a flow path formed to bypass cooling water-to-refrigerant heat exchanger  14  and a flow path connected to cooling water-to-refrigerant heat exchanger  14 . 
     Orifice opening and closing valve  22  is equivalent to an opening and closing valve having the function of an expansion valve. Orifice opening and closing valve  22  is an opening and closing valve configured to work as an expansion valve during a heating operation, and is electrically controlled by the control section to switch between an open state and a closed state. For example, orifice opening and closing valve  22  has a large-diameter path and an orifice made up of a small-diameter path, and the large-diameter path is configured to be openable and closeable. When the large-diameter path is opened, orifice opening and closing valve  22  allows the refrigerant to pass therethrough, and when the large-diameter path is closed and only the path of the orifice is open, a high-pressure refrigerant expands via the small-diameter path. The expanded refrigerant becomes a low-temperature and low-pressure refrigerant. 
     In a variation, it is possible to realize the same function as that of orifice opening and closing valve  22  by providing an opening and closing valve and a path configured to bypass the opening and closing valve in replacement of orifice opening and closing valve  22 , and providing an orifice on the bypass path. In another variation, an electronic expansion valve may be provided, and may work as an expansion valve which is fully opened to allow the refrigerant to pass therethrough, and adjusts the opening thereof. Each of the variations is equivalent to an opening and closing valve having the function of an expansion valve. 
     Refrigerant introduction pipe  34  communicates with an input port of accumulator  16  via opening and closing valve  24 . An output port of accumulator  16  communicates with refrigerant outlet pipe  35 . Opening and closing valve  24  is electrically controlled by the control section to open and close a path between refrigerant introduction pipe  34  and the input port of accumulator  16 . 
     Accumulator  16  separates a gaseous refrigerant from a liquefied refrigerant, and delivers only the gaseous refrigerant to compressor  12  via refrigerant outlet pipe  35 . 
     Each of three-way valve  18 , orifice opening and closing valve  22 , and opening and closing valve  24  switches between an open state and a closed state in response to an electric signal transmitted from a control section of the vehicle air-conditioning apparatus. Alternatively, each of three-way valve  18 , orifice opening and closing valve  22 , and opening and closing valve  24  may be configured to switch between an open state and a closed state in response to a signal that is output by the control section of vehicle heat pump apparatus  10  based on a command from the control section of the vehicle air-conditioning apparatus. 
     Housing  26  accommodates cooling water-to-refrigerant heat exchanger  14 , accumulator  16 , three-way valve  18 , check valve  20 , orifice opening and closing valve  22 , and opening and closing valve  24 , and integrates the components into a single package. The surrounding of housing  26  may be insulated. 
     Refrigerant outlet pipe  33  and refrigerant outlet pipe  35  are respectively equivalent to a first refrigerant outlet section and a second refrigerant outlet section of vehicle heat pump apparatus  10 . Refrigerant introduction pipe  36  and refrigerant introduction pipe  34  are respectively equivalent to a first refrigerant introduction section and a second refrigerant introduction section of vehicle heat pump apparatus  10 . An end of each of refrigerant outlet pipes  33  and  35  and refrigerant introduction pipes  34  and  36  is exposed to the outside of housing  26 , and is connected to the refrigerant pipes of the vehicle air-conditioning apparatus. A connector or a socket for pipe connection may be provided at the end of each of refrigerant outlet pipes  33  and  35  and refrigerant introduction pipes  34  and  36 . 
     Engine cooler  40  and heater core  44  are connected in series to each other between cooling water outlet pipe  32  and cooling water introduction pipe  31 . Outside heat exchanger  56  and evaporator  48  are connected sequentially in series to each other between refrigerant outlet pipe  33  and the suction inlet of compressor  12 . 
     A refrigerant path disposed to connect evaporator  48  and the suction inlet of compressor  12  is also connected to refrigerant outlet pipe  35 . A refrigerant path between outside heat exchanger  56  and evaporator  48  branches, and the branch path is connected to refrigerant introduction pipe  34 . Hereinafter, a detailed description will be given. 
     Cooling water introduction pipe  31  and cooling water outlet pipe  32  are respectively equivalent to a cooling water introduction section and a cooling water outlet section of vehicle heat pump apparatus  10 . An end of each of cooling water introduction pipe  31  and cooling water outlet pipe  32  is exposed to the outside of housing  26 , and is connected to the cooling water pipes of the vehicle air-conditioning apparatus. The end of each of cooling water introduction pipe  31  and cooling water outlet pipe  32  may be provided with a connector or a socket for pipe connection. 
     Engine cooler  40  includes a water jacket that allows the cooling water to flow around the internal combustion engine, and a pump that makes the cooling water flow through the water jacket. Heat is released from the internal combustion engine to the cooling water flowing through the water jacket. An inlet and an outlet of a cooling water path of the water jacket communicate respectively to heater core  44  and cooling water introduction pipe  31  of vehicle heat pump apparatus  10 . 
     Heater core  44  is a device in which the cooling water exchanges heat with air, and is disposed in intake air path B of HVAC system  70 , through which air is supplied to the vehicle interior. A cooling water path of heater core  44  communicates with engine cooler  40  and cooling water outlet pipe  32  of vehicle heat pump apparatus  10 . Fan F 2  introduces outside air or the like to intake air path B of HVAC system  70 . 
     Evaporator  48  is a section in which the refrigerant expanded to a low-temperature and low-pressure state exchanges heat with air, and is disposed in intake air path B of HVAC system  70 . When the refrigerant expanded to a low-temperature and low-pressure state passes through evaporator  48 , the low-temperature and low-pressure refrigerant evaporates by absorbing heat from air. An inlet of a refrigerant path of evaporator  48  communicates with outside heat exchanger  56  via a pipe while expansion valve  52  and opening and closing valve  60  are interposed between the inlet and outside heat exchanger  56 . An outlet of the refrigerant path of evaporator  48  communicates with the suction inlet of compressor  12  via pipes and connection portion  19 . 
     Expansion valve  52  allows a high-pressure refrigerant to expand to a low-temperature and low-pressure state, and discharges the low-temperature and low-pressure refrigerant to evaporator  48 . Expansion valve  52  is disposed outside vehicle heat pump apparatus  10 , and is connected to the vicinity of evaporator  48 . 
     Outside heat exchanger  56  has a refrigerant flow path and an air flow path, and is disposed in the vicinity of the forefront of the vehicle in the engine compartment, and in outside heat exchanger  56 , heat is exchanged between the refrigerant and outside air flowing through each of the paths. An inlet of the refrigerant path of outside heat exchanger  56  communicates with refrigerant outlet pipe  33  of vehicle heat pump apparatus  10  via a pipe. An outlet of the refrigerant path branches into two pipes in the middle of the path, and the two pipes communicate respectively to evaporator  48  and one refrigerant introduction pipe  34  of vehicle heat pump apparatus  10 . 
     During a heating operation, a low-temperature and low-pressure refrigerant flows through outside heat exchanger  56  and absorbs heat from outside air, and during a cooling operation, a high-temperature and high-pressure refrigerant flows through outside heat exchanger  56 , and heat is released from a high-temperature and high-pressure refrigerant to outside air. For example, fan F 1  blows outside air against outside heat exchanger  56 . 
     Opening and closing valve  60  is provided in the middle of the pipe through which the refrigerant flows from outside heat exchanger  56  to evaporator  48 , and is electrically controlled to open and close the pipe. 
     [Cooling Operation] 
       FIG. 2  is a diagram illustrating a cooling operation performed by the vehicle air-conditioning apparatus of Embodiment 1. Hatched portions of pipes illustrated in  FIG. 2  indicate that the refrigerant or the cooling water does not flow through the hatched portions. 
     During the cooling operation, opening and closing valve  24  is switched to close, opening and closing valve  60  is switched to open, orifice opening and closing valve  22  is switched to open, and a port of three-way valve  18  connected to cooling water-to-refrigerant heat exchanger  14  is switched to close. 
     Due to switching, the cooling water circulates through engine cooler  40  and heater core  44 , and in contrast, the cooling water does not flow to cooling water-to-refrigerant heat exchanger  14 . Since an air mixture damper in intake air path B of HVAC system  70  is switched in order for air not to flow to heater core  44 , ventilation air supplied to the vehicle interior is not heated. 
     After the refrigerant is compressed to a high-temperature and high-pressure state by compressor  12 , the high-temperature and high-pressure refrigerant passes through cooling water-to-refrigerant heat exchanger  14  while maintaining a high temperature, and is delivered to outside heat exchanger  56 . Thereafter, the refrigerant is cooled in outside heat exchanger  56 , and then the cooled refrigerant expands to a low-temperature and low-pressure state while passing through expansion valve  52 , and then is delivered to evaporator  48 . In evaporator  48 , the refrigerant absorbs heat from air to be delivered to the vehicle interior, the air is cooled and the refrigerant evaporates. The evaporated refrigerant returns to compressor  12 . 
     It is possible to deliver cooled air to the vehicle interior via such a heat pump cycle. 
     [Heating Operation] 
       FIG. 3  is a diagram illustrating a heating operation performed by the vehicle air-conditioning apparatus of Embodiment 1. Hatched portions of pipes illustrated in  FIG. 3  indicate that the refrigerant or the cooling water does not flow through the hatched portions. 
     During the heating operation, opening and closing valve  24  is switched to open, opening and closing valve  60  is switched to close, orifice opening and closing valve  22  is switched to close, and a port of three-way valve  18  connected to cooling water outlet pipe  32  is switched to close. 
     Due to switching, the cooling water circulates through engine cooler  40 , cooling water-to-refrigerant heat exchanger  14 , and heater core  44 . During the circulation, the cooling water is heated in engine cooler  40  and cooling water-to-refrigerant heat exchanger  14 , and in heater core  44 , heat is released from the cooling water to air flowing through intake air path B of HVAC system  70 . 
     In vehicle heat pump apparatus  10 , heat generated by compressor  12  is transferred to the cooling water in cooling water-to-refrigerant heat exchanger  14 . 
     The air mixture damper in intake air path B is switched to allow air to flow to heater core  44 , and air to be delivered to the vehicle interior is warmed. 
     After the refrigerant is compressed to a high-temperature and high-pressure state by compressor  12 , the high-temperature and high-pressure refrigerant releases heat to the cooling water while passing through cooling water-to-refrigerant heat exchanger  14 . After heat is released, the high-pressure refrigerant expands to a low-temperature and low-pressure state while passing through orifice opening and closing valve  22 , and is delivered to outside heat exchanger  56 . In outside heat exchanger  56 , the refrigerant absorbs heat from outside air, and the refrigerant evaporates. The evaporated refrigerant returns to compressor  12  via accumulator  16 . The refrigerant does not flow through evaporator  48 , and heat exchange is not performed in evaporator  48 . 
     It is possible to deliver warm air to the vehicle interior via such an operation. Heat from the engine is effectively used so as to warm air, and a shortage of the engine heat is supplemented by using the heat pump cycle. In addition, heat discharged from compressor  12  is effectively used to warm air. Since the heat pump cycle is used for air heating, it is possible to reduce power consumption per the amount of heating. 
     [Comparison Between Pipe Paths] 
       FIG. 4  is a diagram illustrating changes to the refrigerant pipes from the conventional vehicle air-conditioning apparatus. In  FIG. 4 , solid lines indicate pipes of the conventional vehicle air-conditioning apparatus. 
     [Regarding Conventional Vehicle Air-Conditioning Apparatus] 
     In the conventional vehicle air-conditioning apparatus which uses the heat pump cycle only during the cooling operation, outside heat exchanger  56  is disposed in the vicinity of the forefront of the vehicle in the engine compartment, and intake air path B, heater core  44 , and evaporator  48  are disposed in HVAC system  70  provided in the vehicle interior. Compressor  12  is disposed in the engine compartment. 
     In this configuration, refrigerant pipes are illustrated by solid lines in  FIG. 4 . The refrigerant pipes are made up of only three pipes: pipe P 1  running via expansion valve  52  from outside heat exchanger  56  at the forefront of the vehicle in the engine compartment to evaporator  48  in the vehicle interior; pipe P 2  running from compressor  12  to outside heat exchanger  56 ; and pipe P 3  running from evaporator  48  in the vehicle interior to compressor  12 . 
     While avoiding collision with other components of the vehicle, each of pipes P 1  to P 3  is routed on a straight path as much as possible in order for the refrigerant not to undergo a large pressure loss. In particular, the layout of pipe P 1  to be installed over a long range is preferentially designed to be a straight path. 
     Cooling water pipes W 1  and W 2  are installed between engine cooler  40  in the engine compartment and heater core  44  in HVAC system  70 . 
     A description to be given hereinbelow relates to a case in which the conventional vehicle air-conditioning apparatus configured to use the heat pump cycle only during the cooling operation is changed to perform the heating operation using the heat pump cycle by adopting vehicle heat pump apparatus  10 . 
     A change from the conventional pipes is the addition of two refrigerant pipes P 21  and P 22 . Refrigerant pipe P 21  is connected to refrigerant outlet pipe  35  of vehicle heat pump apparatus  10 , and refrigerant pipe P 22  is connected to refrigerant introduction pipe  34  of vehicle heat pump apparatus  10 . 
     Partial pipe P 2   b  of long pipe P 2  provided over the engine compartment is removed, which is another change. In a state where pipe P 2   b  is removed, a part of pipe P 2  connected to the refrigerant discharge outlet of compressor  12  is referred to as pipe P 2   a , and another part of pipe P 2  connected to outside heat exchanger  56  is referred to as pipe P 2   c.    
     Refrigerant pipe P 2   a  is connected to refrigerant introduction pipe  36  of vehicle heat pump apparatus  10 , and refrigerant pipe P 2   c  is connected to refrigerant outlet pipe  33  of vehicle heat pump apparatus  10 . 
     Pipes W 21  and W 22  are provided between vehicle heat pump apparatus  10  and heater core  44 , and the heated cooling water circulates through pipes W 21  and W 22 . Partial pipe W 1   a  of pipe W 1  communicating with engine cooler  40  is decoupled, and pipes W 21  and W 22  are connected to vehicle heat pump apparatus  10  so as to bypass partial pipe W 1   a . Pipe W 21  is connected to cooling water introduction pipe  31 , and pipe W 22  is connected to cooling water outlet pipe  32 . 
     In cooling water-to-refrigerant heat exchanger  14  of vehicle heat pump apparatus  10 , the high-temperature and high-pressure refrigerant compressed by compressor  12  releases heat to the cooling water. The heat is transferred to heater core  44  that warms air in intake air path B of HVAC system  70 . 
     Hereinafter, a case will be discussed where a configuration (refer to  FIGS. 21 to 24  in PTL 1) in which the same housing accommodates the compressor and the cooling water-to-refrigerant heat exchanger disclosed in PTL 1 is adopted. In addition, a case will be discussed where the conventional vehicle air-conditioning apparatus configured to use the heat pump cycle only during the cooling operation is changed to perform the heating operation using the heat pump cycle by adopting this configuration. 
     In this case, it is necessary to replace the compressor of the conventional vehicle air-conditioning apparatus with an apparatus that accommodates the compressor and the cooling water-to-refrigerant heat exchanger in the same housing. For this reason, it is necessary to considerably change a pipe pattern in the vicinity of the compressor. 
     In Embodiment 1 
     In contrast, as known from the comparison between  FIG. 1  and  FIG. 4 , the configuration of the embodiment is obtained only by making the following changes to the refrigerant pipes of the conventional vehicle air-conditioning apparatus: refrigerant pipes P 21  and P 22  are added, and vehicle heat pump apparatus  10  is disposed at a position of partial pipe P 2   b  removed from pipe P 2 . 
     Since the disposition of the compressor is not changed, it is possible to easily perform the heating operation using the heat pump cycle while reducing changes in the refrigerant pipe pattern. 
     In vehicle heat pump apparatus  10  and the vehicle air-conditioning apparatus of the embodiment, the following effects are obtained. That is, it is possible to perform the heating operation using the heat pump cycle by only adding the two pipes to, and removing the partial pipe from the conventional pipes of the vehicle air-conditioning apparatus which uses the heat pump cycle only during the cooling operation. 
     Accordingly, the embodiment is particularly effective for a case in which the conventional vehicle air-conditioning apparatus originally mounted in a vehicle is replaced with the vehicle air-conditioning apparatus capable of performing the heating operation using the heat pump cycle via a minor change or an optional change. That is, when vehicle heat pump apparatus  10  and spaces for additional refrigerant pipes P 21  and P 22  are provided, it is possible to apply the vehicle air-conditioning apparatus of the embodiment without affecting the layout of other components of the vehicle. It is possible to configure vehicle heat pump apparatus  10  as a relatively small apparatus, which will be described later, and to easily dispose vehicle heat pump apparatus  10  between configuration elements of the conventional vehicle air-conditioning apparatus. 
     [Variation 1] 
       FIG. 5  is a configuration diagram illustrating a variation of the vehicle heat pump apparatus and the vehicle air-conditioning apparatus according to the embodiment of the present invention. 
     As illustrated in  FIG. 5 , vehicle heat pump apparatus  10  according to the embodiment of the present invention may have the entirety or any one of the following valves provided outside housing  26 : opening and closing valve  24 , orifice opening and closing valve  22 , three-way valve  18 , and check valve  20 . 
     Two opening and closing valves  24  and  60  can be replaced with a three-way valve that is provided at branch locations d 1  and d 2  of the refrigerant pipe. 
     The configuration in which the cooling water is allowed to flow while bypassing cooling water-to-refrigerant heat exchanger  14  or via cooling water-to-refrigerant heat exchanger  14  is not limited to the configuration in which three-way valve  18  and check valve  20  are used, and a plurality of opening and closing valves can be configured. 
     [Variation 2] 
       FIG. 6  is a configuration diagram illustrating another variation of the vehicle heat pump apparatus and the vehicle air-conditioning apparatus according to Embodiment 1 of the present invention. A configuration is different from that illustrated in  FIG. 5  in that two opening and closing valves  24  and  60  are replaced with one three-way valve  21 . 
     Three-way valve  21  is electrically controlled. During the cooling operation, three-way valve  21  allows the refrigerant passing through outside heat exchanger  56  to be delivered to only evaporator  48 . During the heating operation, three-way valve  21  allows the refrigerant passing through outside heat exchanger  56  to be delivered to only refrigerant introduction pipe  34  of vehicle heat pump apparatus  10 . 
     Embodiment 1 of the present invention has been described thus far. 
     Compressor  12  of the embodiment may include an electric motor configured to drive the compressor mechanism which compresses the suctioned refrigerant and discharges the compressed refrigerant. Compressor  12  of the embodiment may drive the compressor mechanism by transmitting driving force from the outside of compressor  12 , for example, driving force of the internal combustion engine, to the compressor mechanism via a belt or the like. 
     In the embodiment, a pipe is configured as a refrigerant introduction section or a refrigerant outlet section of vehicle heat pump apparatus  10 ; however, the refrigerant introduction section or the refrigerant outlet section may be configured as a connector or a socket for pipe connection embedded in a wall of housing  26 . Similarly, the cooling water introduction section or the cooling water outlet section may be configured as a connector or a socket for pipe connection embedded in a wall of housing  26 . 
     In the description of the embodiment, the cooling water absorbing heat from the internal combustion engine is supplied to the heater core; however, a configuration in which the cooling water flows from only vehicle heat pump apparatus  10  to heater core  44  may be adopted. 
     A new vehicle air-conditioning apparatus and a new vehicle heat pump apparatus of the embodiment may be mounted in a vehicle. The vehicle heat pump of the embodiment may replace a part of the conventional vehicle air-conditioning apparatus which uses the heat pump cycle only during the cooling operation illustrated in  FIG. 4 . By virtue of the replacement, it is possible to realize the vehicle air-conditioning apparatus of the embodiment, and to perform the heating operation using the heat pump cycle. 
     Embodiment 2 
     Background and Problem Related to Embodiment 2 
     There is an automobile provided with both of an internal combustion engine and an electric motor, a so-called hybrid electric vehicle (HEV) or a plug-in hybrid vehicle (PHV). In these vehicles, since it is not possible to obtain heat from the internal combustion engine during motor drive mode, a vehicle air-conditioning apparatus configured to perform a heating operation using a heat pump cycle is adopted. The same situation applies to an electric vehicle (EV) in which an internal combustion engine is not mounted. 
     A vehicle air-conditioning apparatus disclosed in PTL 1 (Japanese Patent Application Laid-Open No. HEI 8-197937) includes a compressor that compresses a refrigerant; an evaporator for cooling disposed in a duct through which air is guided to a vehicle interior; an expansion valve that supplies a low-temperature and low-pressure refrigerant to the evaporator; and a plurality of heat exchangers that heat air in the duct using a refrigerant&#39;s heat transferred by a secondary refrigerant (for example, cooling water). 
     In the vehicle air-conditioning apparatus, during the heating operation, a considerable amount of heat exchange cannot be performed in the evaporator for cooling. The reason for this is that unnecessary cooling is provided to the vehicle interior. Accordingly, the vehicle air-conditioning apparatus may be provided with a branch circuit for heating which allows the refrigerant to flow therethrough without the intervention of the evaporator for cooling and the expansion valve. Here, the circuit refers to one turn of a refrigerant path through which the refrigerant circulates. 
     In the vehicle air-conditioning apparatus, during the heating operation, the heat pump cycle is realized by using a heat exchanger (outside heat exchanger) and an expansion valve provided separately in the branch circuit without allowing the refrigerant to flow through the evaporator. Accordingly, the refrigerant absorbs heat from outside air, and heating is provided to the vehicle interior using the heat (for example, refer to FIG. 1 in PTL 1). 
     In a state where the vehicle air-conditioning apparatus adopts the branch circuit for heating which allows the refrigerant to flow therethrough without the intervention of the evaporator and the expansion valve, and when there is no implementation of any specific scheme, opening and closing valves are respectively provided in the branch circuit for heating and a refrigerant circuit for cooling, and the flow of the refrigerant is switched between the heating operation and the cooling operation. However, there is a problem in that this configuration causes an increase in the number of components of the air-conditioning apparatus. 
     In contrast, in an air-conditioning apparatus illustrated in FIG. 1 in PTL 1, an opening and closing valve is not provided on a refrigerant path of evaporator ( 25 ) and expansion valve ( 24 ), and opening and closing valve ( 28 ) is provided on bypass path ( 42 ) that bypasses the path. 
     However, this configuration has a problem in that even during the heating operation in which the opening and closing valve for opening and closing the bypass path is opened, a relatively considerable amount of the refrigerant flows through evaporator ( 25 ) and expansion valve ( 24 ). The unnecessary flow of the refrigerant leads to a decrease in air-conditioning performance. 
     In addition, during the heating operation, when the refrigerant passes through the expansion valve, and flows to the evaporator at a low outdoor temperature, the evaporator may become frozen, which is a problem. 
     An object of this embodiment is to reduce the number of components and to prevent a refrigerant from unnecessarily flowing during a heating operation in a vehicle air-conditioning apparatus having the branch circuit for heating that allows the refrigerant to flow therethrough without the intervention of an evaporator and an expansion valve. 
     Description of Embodiment 2 
       FIG. 7  is a configuration diagram illustrating a vehicle heat pump apparatus and a vehicle air-conditioning apparatus according to Embodiment 2 of the present invention. 
     The vehicle air-conditioning apparatus of Embodiment 2 of the present invention includes vehicle heat pump apparatus  110 ; engine cooler  140 ; heater core  144 ; evaporator  148 ; expansion valve  152 ; outside heat exchanger  156 ; refrigerant pipes and cooling water pipes which connect the configuration elements; and the like. 
     Vehicle heat pump apparatus  110  includes electric compressor  112 ; cooling water-to-refrigerant heat exchanger  114 ; accumulator  116 ; three-way valve  118 ; check valve  120 ; orifice opening and closing valve  122 ; opening and closing valve  124 ; housing  126 ; cooling water introduction pipe  131 ; cooling water outlet pipe  132 ; one refrigerant outlet pipe  133 ; and two refrigerant introduction pipes  134  and  135 . 
     Electric compressor  112  is electrically driven to compress the suctioned refrigerant to a high-temperature and high-pressure state, and to discharge the compressed refrigerant. A suction inlet for the refrigerant in electric compressor  112  communicates with two refrigerant introduction pipes  134  and  135  via accumulator  116 , and a refrigerant discharge outlet of electric compressor  112  communicates with an inlet of a refrigerant path of cooling water-to-refrigerant heat exchanger  114 . 
     Cooling water-to-refrigerant heat exchanger  114  has a cooling water path and a refrigerant path, and the cooling water path and the refrigerant path are configured to be in large area contact with each other so that a large amount of heat exchange can be performed therebetween. An inlet of the refrigerant path communicates with the discharge outlet of electric compressor  112 , and an outlet of the refrigerant path communicates with refrigerant outlet pipe  133  provided with orifice opening and closing valve  122 . An inlet of the cooling water path is connected to three-way valve  118  via a pipe, and an outlet for the cooling water is connected to check valve  120  via a pipe. 
     The high-temperature and high-pressure refrigerant flows through cooling water-to-refrigerant heat exchanger  114  while electric compressor  112  is driven, and in contrast, the cooling water is made to flow or not to flow through cooling water-to-refrigerant heat exchanger  114  by the switching of the three-way valve. When the cooling water flows through cooling water-to-refrigerant heat exchanger  114 , heat is released from the high-temperature and high-pressure refrigerant to the cooling water, and when the cooling water does not flow therethrough, the high-temperature and high-pressure refrigerant passes through cooling water-to-refrigerant heat exchanger  114  while maintaining substantially the same high temperature. 
     Three-way valve  118  is switched by electric control to allow the cooling water introduced from cooling water introduction pipe  131  to flow to either one of cooling water-to-refrigerant heat exchanger  114  and cooling water outlet pipe  132 . 
     Check valve  120  prevents a reverse flow of the cooling water to cooling water-to-refrigerant heat exchanger  114 . 
     Orifice opening and closing valve  122  is an opening and closing valve having the function of an expansion valve, and is switched to open or closed by electric control. For example, orifice opening and closing valve  122  has a large-diameter path and an orifice made up of a small-diameter path, and the large-diameter path is configured to be openable and closeable. When the large-diameter path is opened, orifice opening and closing valve  122  allows the refrigerant to pass therethrough, and when the large-diameter path is closed, a high-pressure refrigerant expands via the path of the orifice. The expanded refrigerant becomes a low-temperature and low-pressure refrigerant. 
     Opening and closing valve  124  is provided between an inlet of refrigerant introduction pipe  134  and a junction of two refrigerant introduction pipes  134  and  135 , and opens and closes a path between the inlet and the junction by electric control. 
     Accumulator  116  separates a gaseous refrigerant from a liquefied refrigerant, and delivers only the gaseous refrigerant to electric compressor  112 . 
     Each of three-way valve  118 , orifice opening and closing valve  122 , and opening and closing valve  124  switches between an open state and a closed state in response to an electric signal transmitted from a control section of the vehicle air-conditioning apparatus. Alternatively, each of three-way valve  118 , orifice opening and closing valve  122 , and opening and closing valve  124  may be configured to switch between an open state and a closed state in response to a signal that is output by a control section of vehicle heat pump apparatus  110  based on a command from the control section of the vehicle air-conditioning apparatus. 
     Housing  126  accommodates electric compressor  112 , cooling water-to-refrigerant heat exchanger  114 , accumulator  116 , three-way valve  118 , check valve  120 , orifice opening and closing valve  122 , and opening and closing valve  124 , and integrates these configuration elements into a single package. The surrounding of housing  126  may be insulated, and electric compressor  112  and cooling water-to-refrigerant heat exchanger  114  may be disposed close together in housing  126  so that heat exchange can be made therebetween. 
     An end of each of refrigerant outlet pipe  133  and refrigerant introduction pipes  134  and  135  is exposed to the outside of housing  126 , and is connected to the refrigerant pipes of the vehicle air-conditioning apparatus. A connector or a socket for pipe connection may be provided at the end of each of refrigerant outlet pipe  133  and refrigerant introduction pipes  134  and  135 . 
     An end of each of cooling water introduction pipe  131  and cooling water outlet pipe  132  is exposed to the outside of housing  126 , and is connected to the cooling water pipes of the vehicle air-conditioning apparatus. A connector or a socket for pipe connection may be provided at the end of each of cooling water introduction pipe  131  and cooling water outlet pipe  132 . 
     Engine cooler  140  includes a water jacket that allows the cooling water to flow around the internal combustion engine, and a pump that makes the cooling water flow through the water jacket. Heat is released from the internal combustion engine to the cooling water flowing through the water jacket. The cooling water absorbing heat from the internal combustion engine passes through heater core  144 , and heat can be released from the cooling water via a radiator (not illustrated). For example, the radiator is disposed at a front face of a vehicle. When the temperature of the cooling water is lower than a predetermined temperature, an opening and closing valve (not illustrated) provided in a cooling water circuit is closed, and the cooling water circulates through the internal combustion engine and heater core  144 , or the internal combustion engine and vehicle heat pump apparatus  110 . For example, the opening and closing valve (not illustrated) may be a thermostat. An outlet and an inlet of a cooling water path of the water jacket are connected respectively to heater core  144  and cooling water introduction pipe  131  of vehicle heat pump apparatus  110 . 
     Heater core  144  is a section in which the cooling water exchanges heat with air, and is disposed in intake air path B 100  of HVAC system  170 , through which air is supplied to a vehicle interior. A cooling water path of heater core  144  communicates with engine cooler  140  and cooling water outlet pipe  132  of vehicle heat pump apparatus  110 . Intake air path B 100  is disposed in the vicinity of the vehicle interior, and fan F 102  introduces outside air or the like to intake air path B 100 . 
     Evaporator  148  is a section in which the refrigerant expanded to a low-temperature and low-pressure state exchanges heat with air, and is disposed in intake air path B 100  of HVAC system  170 . When the refrigerant expanded to a low-temperature and low-pressure state passes through evaporator  148 , the low-temperature and low-pressure refrigerant evaporates by absorbing heat from air. An inlet of a refrigerant path of evaporator  148  communicates with outside heat exchanger  156  via expansion valve  152 . An outlet of the refrigerant path of evaporator  148  communicates with refrigerant introduction pipe  135  of the vehicle heat pump apparatus via the pipe. 
     In intake air path B 100  of HVAC system  170 , evaporator  148  is disposed at a position in which outside air is introduced, and heater core  144  is disposed in the vicinity of a ventilation air port connected to the vehicle interior. 
     Expansion valve  152  allows a high-pressure refrigerant to expand to a low-temperature and low-pressure state, and delivers the low-temperature and low-pressure refrigerant to evaporator  148 . Expansion valve  152  is disposed in the vicinity of evaporator  148 . Expansion valve  152  will be described in detail later. 
     Outside heat exchanger  156  has a refrigerant flow path and an air flow path, and is disposed in the vicinity of the forefront of the vehicle, and in outside heat exchanger  156 , heat is exchanged between the refrigerant and outside air flowing through each of the paths. An inlet of the refrigerant path of outside heat exchanger  156  communicates with refrigerant outlet pipe  133  of vehicle heat pump apparatus  110  via a pipe. An outlet of the refrigerant path of outside heat exchanger  156  branches into two pipes in the middle of the path, and the two pipes communicate respectively to evaporator  148  and refrigerant introduction pipe  134  of vehicle heat pump apparatus  110 . 
     During a heating operation, a low-temperature and low-pressure refrigerant flows through outside heat exchanger  156  and absorbs heat from outside air, and during a cooling operation, a high-temperature and high-pressure refrigerant flows through outside heat exchanger  156 , and releases heat to outside air. For example, fan F 101  blows outside air against outside heat exchanger  156 . 
     [Details of Expansion Valve] 
       FIG. 8  is a graph illustrating examples of the set values of the expansion valve, and  FIG. 9  is a graph illustrating states of the expansion valve during the heating operation and the cooling operation. 
     Expansion valve  152  is provided with a temperature detection section that detects temperature, and a valve that is opened and closed by the operation of the temperature detection section and is opened to allow the refrigerant to pass therethrough and to expand. For example, expansion valve  152  of the embodiment is a gas sealed expansion valve that has a refrigerant sealed therein, the type of the refrigerant being the same as that of the temperature detection section in use, and expansion valve  152  has a mechanism of being opened and closed mechanically. Specifically, expansion valve  152  has a structure in which a pressure differential between the pressure of the sealed gas in the temperature detection section and the pressure of a low-pressure refrigerant works against a spring pressure that closes the valve. The temperature detection section detects a refrigerant outlet temperature while being in contact with a refrigerant outlet section of evaporator  148 . When the pressure differential exceeds the spring pressure, the valve is opened, and the refrigerant passes through the valve and expands. 
     When Hydro-Fluoro-Olefin (HFO)-1234yf is used as a refrigerant of a heat pump cycle, the set value of expansion valve  152  is determined as follows. 
     When the detected temperature is 0° C., the set value is included in 0.10 MPa (G: gauge pressure) to 0.14 MPa (G). 
     When the detected temperature is 10° C., the set value is included in 0.21 MPa (G) to 0.26 MPa (G). 
     More preferably, when HFO-1234yf is used as a refrigerant, the set value of expansion valve  152  may be determined as follows. 
     When the detected temperature is 0° C., the set value is included in 0.12 MPa (G) to 0.14 MPa (G). 
     When the detected temperature is 10° C., the set value is included in 0.23 MPa (G) to 0.26 MPa (G). 
     Here, the set value indicates the pressure ((G) in the pressure unit indicates atmospheric reference pressure, that is, gauge pressure) of a low-pressure refrigerant, at which expansion valve  152  is closed from an open state, and is dependent on the refrigerant outlet temperature (temperature detected by the temperature detection section) of evaporator  148 . 
     In each of the graphs in  FIGS. 8 and 9 , the set values of expansion valve  152  are illustrated. 
     When R134a is used as a refrigerant of the heat pump cycle, the set value of expansion valve  152  is determined as follows. R134a is also referred to as Hydro-Fluoro-Carbon (HFC)-134a. 
     When the detected temperature is 0° C., the set value is included in 0.08 MPa (G) to 0.12 MPa (G). 
     When the detected temperature is 10° C., the set value is included in 0.19 MPa (G) to 0.24 MPa (G). 
     More preferably, when R134a is used as a refrigerant, the set value of expansion valve  152  may be determined as follows. 
     When the detected temperature is 0° C., the set value is included in 0.10 MPa (G) to 0.12 MPa (G). 
     When the detected temperature is 10° C., the set value is included in 0.21 MPa (G) to 0.24 MPa (G). 
     As illustrated in  FIG. 9 , when the set value is set as described above, during a stable cooling operation, the pressure of the low-pressure refrigerant and the refrigerant outlet temperature of evaporator  148  are approximately included in range W 101 . Accordingly, during the stable cooling operation, expansion valve  152  is stably opened. 
     In contrast, during a stable heating operation, the pressure of the low-pressure refrigerant and the refrigerant outlet temperature of evaporator  148  are approximately included in range W 102 . Since air blowing against evaporator  148  in intake air path B 100  is mainly outside air, when the refrigerant does not flow through evaporator  148 , the temperature (refrigerant outlet temperature of evaporator  148 ) detected by expansion valve  152  is substantially the same as the outdoor temperature. 
     As a result, when the detected temperature is lower than a range of −3° C. to −7° C., expansion valve  152  operates to close. As described above, the detected temperature of expansion valve  152  when expansion valve  152  is closed becomes substantially the same as the outdoor temperature. Accordingly, at the outdoor temperature (temperature greater than “−7° C. to −3° C.”) at which a dehumidification operation is required to be performed, it is possible to perform the dehumidification operation by less frequently opening expansion valve  152  via the aforementioned opening and closing operation. 
     For example, when the outdoor temperature is −5° C., the saturation pressure of the refrigerant is 0.15 MPa (G), and the saturation pressure is 0.06 MPa (G) or less, expansion valve  152  is opened. 
     In contrast, at a low outdoor temperature (temperature lower than “−7° C. to −3° C.”) at which the dehumidification operation is not required to be performed, expansion valve  152  is closed, and the refrigerant does not flow to evaporator  148  by the aforementioned opening and closing operation. Accordingly, an unnecessary flow of the refrigerant is prevented, and a decrease in air-conditioning performance is prevented. In addition, evaporator  148  is prevented from being frozen, which would otherwise occur due to an excessive decrease in the temperature of evaporator  148 . 
     In the vehicle air-conditioning apparatus of the embodiment, an opening and closing valve is not provided on a path of expansion valve  152  and evaporator  148 . In the vehicle air-conditioning apparatus of the embodiment, since expansion valve  152  is automatically opened and closed, it is possible to realize an appropriate flow of the refrigerant during the heating operation and the cooling operation. For this reason, it is not necessary to provide the opening and closing valve on a path of expansion valve  152  and evaporator  148 , and to control the opening and closing of the path. 
     A description to be given hereinbelow relates to an operation of the vehicle air-conditioning apparatus of the embodiment during the cooling operation, and during the heating operation when the outdoor temperature is very low. 
     [Cooling Operation] 
       FIG. 10  is a diagram illustrating a cooling operation performed by the vehicle air-conditioning apparatus of Embodiment 2. Hatched portions of pipes illustrated in  FIG. 10  indicate that the refrigerant or the cooling water does not flow through the hatched portions. 
     During the cooling operation, opening and closing valve  124  is switched to close, orifice opening and closing valve  122  is switched to open, and a port of three-way valve  118  connected to cooling water-to-refrigerant heat exchanger  114  is switched to close. 
     Due to switching, the cooling water circulates through engine cooler  140  and heater core  144 , and in contrast, the cooling water does not flow to cooling water-to-refrigerant heat exchanger  114 . Since a louver or the like in intake air path B 100  is switched in order for air not to flow to heater core  144 , ventilation air supplied to the vehicle interior is not heated. 
     After the refrigerant is compressed to a high-temperature and high-pressure state by electric compressor  112 , the high-temperature and high-pressure refrigerant passes through cooling water-to-refrigerant heat exchanger  114  while maintaining a high temperature, and is delivered to outside heat exchanger  156 . Thereafter, the refrigerant is cooled in outside heat exchanger  156 , and then the cooled refrigerant expands to a low-temperature and low-pressure state while passing through expansion valve  152 , and then is delivered to evaporator  148 . In evaporator  148 , the refrigerant absorbs heat from air to be delivered to the vehicle interior, the air is cooled and the refrigerant evaporates. The evaporated refrigerant returns to electric compressor  112  via accumulator  116 . 
     It is possible to deliver cooled air to the vehicle interior via such a heat pump cycle. 
     [Heating Operation] 
       FIG. 11  is a diagram illustrating a heating operation performed by the vehicle air-conditioning apparatus of Embodiment 2 when the outdoor temperature is very low. Hatched portions of pipes illustrated in  FIG. 11  indicate that the refrigerant or the cooling water does not flow through the hatched portions. 
     During the heating operation, opening and closing valve  124  is switched to open, orifice opening and closing valve  122  is switched to close, and a port of three-way valve  118  connected to cooling water outlet pipe  132  is switched to close. 
     Due to switching, the cooling water circulates through engine cooler  140 , cooling water-to-refrigerant heat exchanger  114 , and heater core  144 . During the circulation, the cooling water is heated in engine cooler  140  and cooling water-to-refrigerant heat exchanger  114 , and in heater core  144 , heat is released from the cooling water to air flowing through intake air path B 100 . 
     In addition, in vehicle heat pump apparatus  110 , heat generated by electric compressor  112  is transferred to the cooling water in cooling water-to-refrigerant heat exchanger  114 , and the heat discharged from electric compressor  112  is also used as a heat source. 
     The louver or the like in intake air path B 100  is switched to allow air to flow to heater core  144 , and air to be delivered to the vehicle interior is warmed. 
     After the refrigerant is compressed to a high-temperature and high-pressure state by electric compressor  112 , the high-temperature and high-pressure refrigerant releases heat to the cooling water while passing through cooling water-to-refrigerant heat exchanger  114 . After heat is released, the high-pressure refrigerant expands to a low-temperature and low-pressure state while passing through orifice opening and closing valve  122 , and is delivered to outside heat exchanger  156 . In outside heat exchanger  156 , the refrigerant absorbs heat from outside air, and the refrigerant evaporates. The evaporated refrigerant returns to electric compressor  112  via accumulator  116 . 
     When the outdoor temperature is low (for example, −3° C. to −7° C. or less), expansion valve  152  is automatically closed. At this time, the refrigerant does not flow through evaporator  148 , and heat exchange is not performed in evaporator  148 . 
     It is possible to deliver warm air to the vehicle interior via such an operation. Heat from the engine is effectively used so as to warm air, and a shortage of the engine heat is supplemented by using the heat pump cycle. In addition, heat discharged from electric compressor  112  is effectively used to warm air. Since the heat pump cycle is used for air heating, it is possible to reduce power consumption per the amount of heating. When outdoor temperature is low, expansion valve  152  is closed, and the refrigerant does not unnecessarily flow through expansion valve  152  and evaporator  148 , and thereby there is no decrease in air-conditioning performance associated with an unnecessary flow of the refrigerant. 
     As described above, in the vehicle air-conditioning apparatus of the embodiment, during a stable cooling operation, the opening of expansion valve  152  is stable via the setting of the set value of expansion valve  152 , and allows the refrigerant to pass therethrough and to expand. In contrast, when there is a low outdoor temperature at which the dehumidification operation is not required to be performed, during a stable heating operation, expansion valve  152  is automatically closed, and the refrigerant is not allowed to flow therethrough and to expand. 
     Accordingly, even though an opening and closing valve is not provided on a path of expansion valve  152  and evaporator  148 , and the opening and closing of the path is not controlled, since expansion valve  152  is automatically opened and closed, it is possible to control an appropriate flow of the refrigerant during the heating operation and the cooling operation. 
     Since expansion valve  152  is automatically opened and closed, when there is a low outdoor temperature at which the dehumidification operation is not required to be performed, the refrigerant is prevented from unnecessarily flowing through expansion valve  152  and evaporator  148 , and a decrease in air-conditioning performance is prevented. In addition, evaporator  148  is prevented from being frozen, which would otherwise occur due to an excessive decrease in the temperature of evaporator  148 . 
     Embodiment 2 of the present invention has been described thus far. 
     The description of the embodiment has been given with the exemplary configuration in which heating is provided to the vehicle interior, the cooling water, that is, a secondary refrigerant, is heated by the heat pump cycle, and heat is released from the cooling water to air via heater core  144 . However, the configuration in which heating is provided to the vehicle interior is not limited to the one that is described in the embodiment, and various modifications can be made. 
     The disclosures of Japanese Patent Applications No. 2012-267085, filed on Dec. 6, 2012, and No. 2012-276498, filed on Dec. 19, 2012, including the specifications, drawings and abstracts are incorporated herein by reference in their entireties. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a vehicle heat pump apparatus and a vehicle air-conditioning apparatus which are mounted in a vehicle. 
     REFERENCE SIGNS LIST 
     
         
           10  Vehicle heat pump apparatus (Embodiment 1) 
           12  Compressor 
           14  Cooling water-to-refrigerant heat exchanger 
           16  accumulator 
           18  Three-way valve 
           19  Connection portion 
           20  Check valve 
           21  Three-way valve 
           22  Orifice opening and closing valve 
           24  Opening and closing valve 
           26  housing 
           31  Cooling water introduction pipe 
           32  Cooling water outlet pipe 
           33 ,  35  Refrigerant outlet pipe 
           34 ,  36  Refrigerant introduction pipe 
           40  Engine cooler 
           44  Heater core 
           48  Evaporator 
           52  expansion valve 
           56  Outside heat exchanger 
           60  Opening and closing valve 
           70  HVAC system 
         B Intake air path 
         F 1 , F 2  Fan 
           110  Vehicle heat pump apparatus (Embodiment 2) 
           112  Electric compressor 
           114  Cooling water-to-refrigerant heat exchanger 
           116  Accumulator 
           118  Three-way valve 
           120  Check valve 
           122  Orifice opening and closing valve 
           124  Opening and closing valve 
           126  Housing 
           131  Cooling water introduction pipe 
           132  Cooling water outlet pipe 
           133  Refrigerant outlet pipe 
           134 ,  135  Refrigerant introduction pipe 
           140  Engine cooler 
           144  Heater core 
           148  Evaporator 
           152  Expansion valve 
           156  Outside heat exchanger 
           170  HVAC system 
         B 100  Intake air path 
         F 101 , F 102  Fan