Patent Publication Number: US-10767905-B2

Title: Ejector

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/JP2017/002203 filed on Jan. 24, 2017 and published in Japanese as WO 2017/135092 A1 on Aug. 10, 2017. This application is based on and claims the benefit of priority from Japanese Patent Applications No. 2016-018068 filed on Feb. 2, 2016, and No. 2016-248886 filed on Dec. 22, 2016. The entire disclosures of all of the above applications are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to an ejector that reduces a pressure of a fluid, and draws the fluid due to a suction action of a jet fluid jetted at high speed. 
     BACKGROUND ART 
     Up to now, Patent Literature 1 discloses an ejector that is applied to a vapor-compression refrigeration cycle device. In the ejector disclosed in Patent Literature 1, a refrigerant that flows out of an evaporator through a refrigerant suction port provided in a body is drawn by a suction action of supersonic jet refrigerant jetted from a nozzle passage for reducing the pressure of the refrigerant. Then, in a diffuser passage, a mixture refrigerant of the jet refrigerant and a suction refrigerant (that is, the refrigerant on an evaporator outlet side) is raised in pressure and flow out to an intake side of a compressor. 
     In more detail, in the ejector disclosed in Patent Literature 1, a passage formation member, which is a substantially conical valve body portion, is disposed inside the body, and a refrigerant passage having an annular cross section is provided between an inner surface of the body and a conical lateral surface of the passage formation member. A portion of the refrigerant passage on a most upstream side in a refrigerant flow is used as a nozzle passage, and a portion of the refrigerant passage on a downstream side of the nozzle passage in the refrigerant passage is used as a diffuser passage. 
     Further, in Patent Literature 1, a swirling space is provided in the body of the ejector to swirl the refrigerant flowing into the nozzle passage around a center axis of the passage formation member. In the swirling space, a liquid-phase refrigerant flowing out of a radiator is swirled so that the refrigerant on a swirling center side is reduced in pressure and boiled. Then, the refrigerant in a two-phase separation state in which a columnar gas-phase refrigerant (hereinafter referred to as “gas column”) is generated on a swirling center side flows into the nozzle passage. 
     With the above configuration, in the ejector disclosed in Patent Literature 1, the boiling of the refrigerant in the nozzle passage is promoted and an energy conversion efficiency when converting a pressure energy of the refrigerant into a kinetic energy in the nozzle passage is to be improved. In addition, the energy conversion efficiency of the ejector as a whole (hereinafter referred to as “ejector efficiency”) is to be improved. 
     Further, the ejector disclosed in Patent Literature 1 includes a drive mechanism that displaces the passage formation member to change a passage cross-sectional area of the refrigerant passage. As a result, in the ejector disclosed in Patent Literature 1, the ejector is intended to be operated appropriately with a change in the passage cross-sectional area of the refrigerant passage according to a load variation of the applied refrigeration cycle device. 
     PRIOR ART LITERATURE 
     Patent Literature 
     Patent Literature 1: JP 2013-177879 A 
     SUMMARY 
     However, as a result of the present inventors&#39; studies on the ejector disclosed in Patent Literature 1 for the purpose of further improving the ejector efficiency, the high ejector efficiency cannot be stably exercised in some cases in the ejector of Patent Literature 1. Therefore, the present inventors have investigated causes of the above trouble, as a result of which the present inventors have found out the following causes. 
     First, in the ejector disclosed in Patent Literature 1, a portion of the passage formation member on an outer peripheral side and a drive mechanism are coupled to each other through multiple actuating bars. For that reason, when the passage formation member is displaced according to the load variation of the refrigeration cycle device, the center axis of the passage formation member is inclined from the center axis of the swirling space or the like in some cases. When the center axis of the passage formation member is inclined, the passage cross-sectional area of the refrigerant passage having the annular cross section varies in a circumferential direction. 
     For that reason, since a circumferential velocity distribution is generated in the jet refrigerant jetted from the nozzle, the energy conversion efficiency in the nozzle passage is lowered, and the suction refrigerant cannot be uniformly drawn in the circumferential direction. Furthermore, if the center axis of the passage formation member is inclined, a configuration of the gas column occurring in the swirling space meanders and becomes unstable. As a result, the ejector efficiency is lessened. 
     In addition, when the ejector of Patent Literature 1 is applied to a refrigeration cycle device that employs refrigerants different in a physical property, the amount of refrigerant or the like required for causing the refrigeration cycle device to exercise a desired refrigeration capacity changes. For that reason, even if the refrigerants different in the physical property are swirled in the swirling space having the same shape, an appropriate gas column cannot be generated stably and the energy conversion efficiency in the nozzle passage cannot be improved. 
     Further, in the ejector disclosed in Patent Literature 1, the jet refrigerant jetted from the nozzle passage at a supersonic speed has a velocity component in the swirl direction. For that reason, an oblique impact wave occurring in the jet refrigerant also occurs along a swirling flow to accelerate the velocity component in a swirl direction of the jet refrigerant. As a result, a velocity difference between a flow velocity of the jet refrigerant and a flow velocity of the suction refrigerant is increased, to thereby be likely to increase an energy loss (hereinafter referred to as “mixing loss”) at the time of mixing the jet refrigerant and the suction refrigerant together. 
     In this case, in order to reduce an increase in the mixing loss, it is conceivable to accelerate the suction refrigerant to reduce the velocity difference. However, in the ejector of Patent Literature 1, the passage formation member is provided, and a refrigerant outlet of the suction passage is opened annularly on an outer circumferential side of a refrigerant ejection port of the nozzle passage. For that reason, in the ejector disclosed in Patent Literature 1, even if the suction refrigerant is simply accelerated to reduce the velocity difference, it is difficult to sufficiently reduce the mixing loss. 
     The reason is because when the suction refrigerant is accelerated and merged from the outer peripheral side of the jet refrigerant, droplets in the jet refrigerant flowing into the mixing passage for mixing the jet refrigerant and the suction refrigerant together are unevenly distributed or attached to the passage formation member side. Therefore, in the ejector disclosed in Patent Literature 1, even if the suction refrigerant is accelerated, the droplets are less likely to be uniformly distributed in the mixing passage, and the mixing loss is less likely to be sufficiently reduced. 
     In view of the above points, the present disclosure aims to provide an ejector capable of stably exercising a high energy conversion efficiency. 
     According to an aspect of the present disclosure, an ejector applied to a vapor-compression refrigeration cycle device includes a body, a passage formation member and a drive mechanism. The body includes an inflow space configured to allow a liquid-phase refrigerant to flow thereinto, a pressure reducing space configured to reduce a pressure of the refrigerant that has flowed out of the inflow space, a suction passage communicating with a downstream side of the pressure reducing space in a refrigerant flow and allowing the refrigerant suctioned from a refrigerant suction port to flow therethrough, and a pressurizing space configured to introduce therein a jet refrigerant jetted from the pressure reducing space and a suction refrigerant drawn through the suction passage. The passage formation member is at least partially disposed inside the pressure reducing space, and the passage formation member and the body define a refrigerant passage therebetween. The drive mechanism is configured to displace the passage formation member. A refrigerant passage defined between an inner peripheral surface of the body defining the pressure reducing space and an outer peripheral surface of the passage formation member is a nozzle passage functioning as a nozzle which reduces the pressure of the refrigerant and jets the refrigerant. The passage formation member is coupled to an upstream actuating bar that extends toward the inflow space and is slidably supported by the body. A central axis of the upstream actuating bar and a central axis of the passage formation member are disposed coaxially with each other. A plurality of throat portions formed on the wall surface defining the nozzle passage and configured to gradually reduce the passage cross-sectional area of the nozzle passage in a downstream direction of the refrigerant flow and then turn the flow direction of the refrigerant. A most upstream throat portion, which is one disposed on a most upstream side in the refrigerant flow among the plurality of throat portions, is formed on the passage formation member. The most upstream throat portion is formed in a shape that causes the flow direction of the refrigerant in the nozzle passage to turn toward the central axis of the passage formation member, and disposed in a region of the nozzle passage where the refrigerant flows at subsonic speed. 
     According to the configuration described above, since the drive mechanism displaces the passage formation member, the passage cross-sectional area of the nozzle passage can be adjusted according to a load variation of the applied refrigeration cycle device. 
     In that situation, since the passage formation member is supported by the upstream actuating bar disposed coaxially, even if the drive mechanism displaces the passage formation member, the center axis of the passage formation member can be prevented from being inclined. This makes it possible to prevent the ejector efficiency from becoming unstable with the inclination of the center axis of the passage formation member. 
     Furthermore, since the upstream actuating bar extends toward the inflow space, swirling flow hardly occurs in the refrigerant in the inflow space, and no gas column occurs in the inflow space. Therefore, there is no case in which the configuration of the gas column becomes unstable, thereby making the ejector efficiency unstable. 
     Further, the most upstream throat portion is formed in a region of the nozzle passage where a refrigerant flows at subsonic speed, and the most upstream throat portion functions as an edge that enlarges the passage cross-sectional area of the nozzle passage and generates a separation vortex. Accordingly, a boiling nuclei can be generated in the liquid-phase refrigerant flowing through the nozzle passage. 
     Further, the most upstream throat portion is formed on the passage formation member side, and at least a part of the nozzle passage is formed in a shape that causes the flow direction of the refrigerant to be turned toward the center axis side of the passage formation member. 
     According to the above configuration, the boiling nucleus can be supplied from the intermediate axis side to the liquid-phase refrigerant flowing through the nozzle passage. Therefore, even if no gas column or the like is generated in the refrigerant in the inflow space, the boiling of the refrigerant flowing through the nozzle passage can be promoted, and the ejector efficiency can be improved. 
     In other words, according to the ejector of the above aspect, the high energy conversion efficiency can be stably exercised regardless of the load variation of the applied refrigeration cycle device. 
     The passage formation member may be at least partially disposed inside the pressurizing space, and a refrigerant passage defined between an inner peripheral surface of the body defining the pressurizing space and the outer peripheral surface of the passage formation member may be a diffuser passage functioning as a pressure increase portion which mixes and pressurizes the jet refrigerant and the suction refrigerant. 
     According to the configuration described above, the passage cross-sectional area of the diffuser passage can be adjusted according to the load variation of the applied refrigeration cycle device. Therefore, the high energy conversion efficiency can be more stably exercised regardless of the load variation of the applied refrigeration cycle device. 
     A downstream throat portion, which is one disposed on a downstream side of the most upstream throat portion in the refrigerant flow among the plurality of throat portions, may be formed on a portion of the body which defines the pressure reducing space. At least one part of the downstream throat portion in the nozzle passage may have a shape that causes the flow direction of the refrigerant to be turned into a direction away from the center axis of the passage formation member. 
     According to the above configuration, the boiling nucleus can be also supplied from the outer peripheral side to the liquid-phase refrigerant flowing through the nozzle passage. Therefore, the boiling of the refrigerant flowing through the nozzle passage can be further promoted. 
     In addition, the passage formation member may be coupled with a downstream actuating bar that extends to the downstream side of the diffuser passage and is slidably supported by the body. According to the above configuration, since the passage formation member can be supported at both end sides of the center axis by the upstream actuating bar and the downstream side actuating bar, the center axis of the passage formation member can be more reliably prevented from being inclined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an ejector refrigeration cycle according to a first embodiment. 
         FIG. 2  is a cross-sectional view of an ejector according to the first embodiment. 
         FIG. 3  is a cross-sectional view taken along a line III-III of  FIG. 2 . 
         FIG. 4  is a schematic cross-sectional view of a part IV in  FIG. 2 . 
         FIG. 5  is a Mollier diagram showing a change in a state of a refrigerant in the ejector refrigeration cycle according to the first embodiment. 
         FIG. 6  is a schematic cross-sectional view of a part VI in  FIG. 4 . 
         FIG. 7  is a schematic cross-sectional view of a portion corresponding to  FIG. 6  in an ejector of a comparative example. 
         FIG. 8  is an illustrative diagram illustrating characteristics and an entropy generation amount of an impact waves generated when the refrigerant turns a corner. 
         FIG. 9  is a schematic cross-sectional view of a part of an ejector according to a second embodiment. 
         FIG. 10  is a schematic cross-sectional view showing a mixing passage of an ejector according to a third embodiment. 
         FIG. 11  is a schematic cross-sectional view of a part of an ejector according to a fourth embodiment. 
         FIG. 12  is a cross-sectional view of an ejector according to a fifth embodiment. 
         FIG. 13  is a schematic diagram of an ejector refrigeration cycle according to another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, multiple embodiments for implementing the present disclosure will be described referring to drawings. In the respective embodiments, a part that corresponds to a matter described in a preceding embodiment may be assigned the same reference numeral, and redundant explanation for the part may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. The parts may be combined even if it is not explicitly described that the parts can be combined. The embodiments may be partially combined even if it is not explicitly described that the embodiments can be combined, provided there is no harm in the combination. 
     First Embodiment 
     A first embodiment of the present disclosure will be described with reference to  FIGS. 1 to 8 . As illustrated in  FIG. 1 , an ejector  13  of the present embodiment is applied to a vapor-compression refrigeration cycle device including an ejector as a refrigerant pressure reducing device, that is, an ejector refrigeration cycle  10 . Moreover, the ejector refrigeration cycle  10  is applied to a vehicle air conditioner, and performs a function of cooling a blown air to be blown into a vehicle interior that is an air-conditioning target space. Therefore, a cooling target fluid in the ejector refrigeration cycle  10  according to the present embodiment is the blown air. 
     In addition, the ejector refrigeration cycle  10  according to the present embodiment employs an HFO based refrigerant (specifically, R1234yf) as the refrigerant, and forms a subcritical refrigeration cycle in which a high-pressure side refrigerant pressure does not exceed a critical pressure of the refrigerant. A refrigerator oil for lubricating a compressor  11  is mixed with the refrigerant, and a part of the refrigerator oil is circulated in the cycle together with the refrigerant. 
     The compressor  11  that is one configuration equipment of the ejector refrigeration cycle  10  draws the refrigerant, raises a pressure of the refrigerant to a high-pressure refrigerant, and discharges the refrigerant. The compressor  11  is disposed in an engine compartment together with an engine (internal combustion engine) which outputs a vehicle traveling driving force. Furthermore, the compressor  11  is an engine-driven-type compressor that is driven by a rotational drive power output from the engine through a pulley, a belt, and the like. 
     In more detail, in the present embodiment, the compressor  11  employs a swash plate type variable capacity type compressor that is configured so that a refrigerant discharge capacity can be adjusted by changing a discharge volume. The compressor  11  has a discharge capacity control valve not shown for changing the discharge capacity. The operation of the discharge capacity control valve is controlled according to a control current output from a control device to be described later. 
     A refrigerant inlet side of a condensing portion  12   a  of a radiator  12  is connected to a discharge port of the compressor  11 . The radiator  12  is a radiation heat exchanger that performs a heat exchange between the high-pressure refrigerant discharged from the compressor  11  and a vehicle exterior air (outside air) blown by a cooling fan  12   d  to radiate the heat from the high-pressure refrigerant and cool the high-pressure refrigerant. The radiator  12  is disposed on a front side of the vehicle in the engine compartment. 
     More specifically, the radiator  12  is a so-called subcooling condenser which includes a condensing portion  12   a , a receiver portion  12   b , and a subcooling portion  12   c.    
     The condensing portion  12   a  is a condensation heat exchanging unit that performs the heat exchange between the high pressure gas-phase refrigerant discharged from the compressor  11  and the outside air blown from the cooling fan  12   d  and radiates and condenses the high-pressure gas-phase refrigerant. The receiver portion  12   b  is a refrigerant container that separates the refrigerant that has flowed out of the condensing portion  12   a  into gas and liquid, and accumulates an excess liquid-phase refrigerant. The subcooling portion  12   c  is a heat exchanging unit that performs the heat exchange between a liquid-phase refrigerant that has flowed out of the receiver portion  12   b  and the outside air blown from the cooling fan  12   d , and super-cools the liquid-phase refrigerant. 
     The cooling fan  12   d  is an electric blower, a rotating speed (that is, blown air amount) of which is controlled according to a control voltage output from the control device. A refrigerant inflow port  31   a  of the ejector  13  is connected to a refrigerant outlet side of the subcooling portion  12   c  of the radiator  12 . 
     The ejector  13  has a function of a refrigerant pressure reducing device that reduces a pressure of a high-pressure refrigerant in a subcooling state which has flowed out of the radiator  12  and allows the refrigerant to flow to the downstream side. Further, the ejector  13  has a function of a refrigerant transport device that draws and transports a refrigerant (that is, an evaporator  14  outlet side refrigerant) that has flowed out of an evaporator  14  to be described later by a suction action of a jet refrigerant jetted at a high speed. 
     In addition, the ejector  13  according to the present embodiment functions as a gas-liquid separator for separating the pressure reduced refrigerant into gas and liquid. In other words, the ejector  13  according to the present embodiment is configured as an ejector integrated with a gas-liquid separation function in which the ejector and the gas-liquid separator are integrated with each other (that is, modularized). 
     The ejector  13  is disposed in the engine compartment together with the compressor  11  and the radiator  12 . Incidentally, respective up and down arrows in  FIG. 1  indicate up and down directions in a state where the ejector  13  is mounted in the vehicle, and the respective up and down directions in a state where other equipment of the ejector refrigeration cycle  10  is mounted in the vehicle are not limited to the above arrows. 
     A specific configuration of the ejector  13  will be described with reference to  FIGS. 2 to 4 . The respective up and down arrows in  FIG. 2  indicate up and down directions in a state where the ejector refrigeration cycle  10  is mounted on a vehicle air conditioner.  FIGS. 2 and 3  are axial cross-sectional views of the ejector  13 ,  FIG. 2  is a cross-sectional view taken along a line II-II in  FIG. 3 , and  FIG. 3  is a cross-sectional view taken along a line III-III in  FIG. 2 . 
       FIG. 4  is a partially enlarged schematic cross-sectional views illustrating the refrigerant passage provided inside the ejector  13 , and the same parts as those in  FIGS. 2 and 3  are denoted by identical symbols. 
     As illustrated in  FIGS. 2 and 3 , the ejector  13  according to the present embodiment includes a body  30  configured by combining the multiple components together. 
     More specifically, the body  30  includes an upper body  311 , a lower body  312 , a gas-liquid separation body  313 , and the like. The respective bodies  311  to  313  form an outer shell of the ejector  13  and also functions as a housing for internally accommodating other components. The housing bodies  311  to  313  are formed of a hollow member made of metal (in the present embodiment, made of aluminum alloy). It should be noted that the housing bodies  311  to  313  may be made of resin. 
     In an internal space defined by combining the upper body  311  and the lower body  312  together, the components of the body  30  such as a nozzle  32  and a diffuser body  33  which will be described later are fixed. 
     The upper body  311  is provided with multiple refrigerant inflow ports such as the refrigerant inflow port  31   a  and a refrigerant suction port  31   b . The refrigerant inflow port  31   a  is a refrigerant inflow port through which the refrigerant that has flowed out of the radiator  12  flows. The refrigerant suction port  31   b  is a refrigerant inflow port for drawing the refrigerant that has flowed out of the evaporator  14 . 
     The gas-liquid separation body  313  is provided with multiple refrigerant inflow and outflow ports such as a liquid-phase refrigerant outflow port  31   c  and a gas-phase refrigerant outflow port  31   d . The liquid-phase refrigerant outflow port  31   c  is a refrigerant outflow port through which the liquid-phase refrigerant separated in the gas-liquid separation space  30   f  defined in the gas-liquid separation body  313  flows out to a refrigerant inlet side of the evaporator  14 . The gas-phase refrigerant outflow port  31   d  is a refrigerant outflow port through which the gas-phase refrigerant separated in the gas-liquid separation space  30   f  flows out to an intake port side of the compressor  11 . 
     The nozzle  32  is formed of a cylindrical member made of metal (in the present embodiment, made of stainless steel). As shown in  FIGS. 2 and 3 , the nozzle  32  is disposed on a bottom surface of the upper body  311  on an axial one end side of the upper body  311  (opposite side to the lower body  312 ). The nozzle  32  is fixed into a hole provided in the upper body  311  by press fitting so that no refrigerant leaks through a gap between the upper body  311  and the nozzle  32 . 
     An inside of the nozzle  32  is provided with an inflow space  30   a  into which the refrigerant flowing through the refrigerant inflow port  31   a  flows. The inflow space  30   a  is formed in a shape of a substantially columnar rotating body. A center axis of the inflow space  30   a  is disposed coaxially with a center axis CL of a passage formation member  35  which will be described later. As is apparent from  FIGS. 2 and 3 , the center axis CL of the present embodiment extends in a substantially horizontal direction. Incidentally, the shape of the rotating body is a cubic shape formed when a plane figure is rotated around one straight line (center axis) on the same plane. 
     The upper body  311  is provided with a refrigerant inflow passage  31   e  that guides the refrigerant flowing from the refrigerant inflow port  31   a  to the inflow space  30   a  side. The refrigerant inflow passage  31   e  is formed in a shape extending in a radial direction when viewed from a direction of the center axis of the inflow space  30   a  and is formed so as to allow the refrigerant flowing into the inflow space  30   a  to flow toward the center axis of the inflow space  30   a.    
     A pressure reducing space  30   b  is defined in an interior of the nozzle  32  and on the downstream side of the inflow space  30   a  in the refrigerant flow to reduce the pressure of the refrigerant that has flowed out of the inflow space  30   a  and allow the refrigerant to flow out to the downstream side. The pressure reducing space  30   b  is formed in a shape of a rotating body in which top sides of two truncated cone shaped spaces are coupled to each other. The center axis of the pressure reducing space  30   b  is also disposed coaxially with the center axis CL of the passage formation member  35 . 
     A top side of a conical passage formation member  35  is disposed in the interior of the pressure reducing space  30   b . The passage formation member  35  is a valve body portion that is disposed in a refrigerant passage provided inside the body  30 . The passage formation member  35  performs a function of changing the passage cross-sectional area of the refrigerant passage by displacement in the center axis CL direction. 
     More specifically, the passage formation member  35  is formed of a conical member made of a resin (made of nylon 6 or nylon 66 in the present embodiment) having resistance to refrigerant. The passage formation member  35  is formed in a conical shape with an outer diameter enlarged more as the passage formation member  35  moves more away from the pressure reducing space  30   b  (that is, toward the downstream side in the refrigerant flow). 
     Further, an annular member  35   a  having an annular shape is disposed on the top side of the passage formation member  35 . The annular member  35   a  is made of the same material as that of the passage formation member  35 . An outer shape of the annular member  35   a  is formed in a shape of a rotating body in which bottom surfaces of two truncated cones are coupled to each other. 
     The annular member  35   a  is shaped to have a largest outer diameter portion  30   n  at a substantially central portion in the center axis direction and have a smallest outer diameter portion  30   p  at a most downstream portion in the refrigerant flow. In the present embodiment, the annular member  35   a  and the passage formation member  35  are formed as separate members. However, if the passage formation member  35  and the like can be assembled in the body  30 , the annular member  35   a  and the passage formation member  35  may be formed integrally with each other. 
     In addition, a substantially truncated conical space is provided from the bottom surface side of the passage formation member  35  inside the passage formation member  35 . In other words, the passage formation member  35  is formed in a cup shape (that is, a cup shape). Further, a shaft  351  is coupled to the passage formation member  35 . The shaft  351  is formed of a cylindrical rod member made of metal (in the present embodiment, made of stainless steel). A center axis of the shaft  351  is disposed coaxially with the center axis CL of the passage formation member  35 . 
     The shaft  351  is insert-molded in the passage formation member  35 . As a result, the passage formation member  35  and the shaft  351  are integrated together. Further, the shaft  351  includes an upstream actuating bar  351   a  and a downstream actuating bar  351   b . Therefore, a center axis of the upstream actuating bar  351   a  and a center axis of the downstream actuating bar  351   b  are also disposed coaxially with each other. 
     The upstream actuating bar  351   a  extends from the top of the passage formation member  35  so as to penetrate through the inflow space  30   a  and is slidably supported in a bearing hole of the upper body  311 . The downstream actuating bar  351   b  extends from the top of the passage formation member  35  toward the downstream side of the diffuser passage  13   c  to be described later and is slidably supported in a bearing hole of the support member  36  provided in the lower body  312 . In other words, the shaft  351  is slidably supported by the body  30  at both axial end sides. 
     The support member  36  is formed of a cylindrical member made of a metal (in the present embodiment, an aluminum alloy), and is fixed to the lower body  312  through a fixing member not shown. Further, a coil spring  36   a  for applying a load directed at the inflow space  30   a  side to the downstream actuating bar  351   b  is accommodated inside the support member  36 . The load of the coil spring  36   a  can be adjusted by an adjustment screw  36   b  provided on the support member  36 . 
     A leading end portion of the upstream actuating bar  351   a  on the inflow space  30   a  side is coupled to the drive mechanism  37 . The drive mechanism  37  outputs a driving force for displacing the shaft  351  and the passage formation member  35  in the axial direction. Details of the drive mechanism  37  will be described later. 
     Next, a description will be given of the refrigerant passage that is defined between an outer peripheral surface of the passage formation member  35  on the top side (that is, the inflow space  30   a  side) and an inner peripheral surface of a portion defining the pressure reducing space  30   b  of the nozzle  32 , and through which the refrigerant that has flowed out of the inflow space  30   a  flows. The refrigerant passage is a nozzle passage  13   a  that functions as a nozzle which reduces the pressure of the refrigerant and jets the refrigerant. An axial vertical cross-section of the nozzle passage  13   a  is formed into an annular shape (a shape excluding a small diameter circular shape disposed coaxially from a circular shape). 
     As described above, the annular member  35   a  is disposed on the top side of the passage formation member  35 . For that reason, as shown in  FIG. 4 , a wall surface of the nozzle passage  13   a  on a side of the center axis CL (that is, the passage formation member  35  and the annular member  35   a  side) has a shape on an axial cross-sectional plane to be separated from the center axis CL toward the downstream side in the refrigerant flow in a range extending from the upstream side of the annular member  35   a  toward the largest outer diameter portion  30   n.    
     Further, the shape comes closer to the center axis CL toward the downstream side in the refrigerant flow in a range extending from the largest outer diameter portion  30   n  toward the smallest outer diameter portion  30   p . The shape is separated from the center axis CL from the smallest outer diameter portion  30   p  toward the downstream side in the refrigerant flow. 
     On the other hand, as shown in  FIG. 4 , a wall surface of the nozzle passage  13   a  on a side opposite to the center axis CL (that is, a side of a portion providing the pressure reducing space  30   b  in the nozzle  32 ) has a shape on the axial cross-sectional plane to come closer to the center axis CL toward the downstream side in the refrigerant flow in a range extending from the inflow space  30   a  side toward the smallest inner diameter portion  30   m . Further, the shape is separated from the center axis CL from the smallest inner diameter portion  30   m  toward the downstream side in the refrigerant flow. 
     For that reason, as shown in  FIG. 4 , the nozzle passage  13   a  according to the present embodiment is roughly divided into a first passage  131 , a second passage  132 , and a third passage  133 . 
     The first passage  131  is a refrigerant passage that is provided in a range from the upstream side of the annular member  35   a  in the refrigerant flow to the largest outer diameter portion  30   n , in which the passage cross-sectional area gradually decreases. The second passage  132  is a refrigerant passage that is provided in a range from the largest outer diameter portion  30   n  of the annular member  35   a  to the smallest inner diameter portion  30   m  of the nozzle  32 , and is reduced after the passage cross-sectional area immediately after the first passage  131  has been enlarged. The third passage  133  is a refrigerant passage that is provided on a downstream side in the refrigerant flow from the smallest inner diameter portion  30   m  of the nozzle  32 , in which the passage cross-sectional area is gradually enlarged. 
     In other words, the present embodiment forms a throat portion in which the passage cross-sectional area of the nozzle passage  13   a  is gradually reduced toward the downstream side in the refrigerant flow by the largest outer diameter portion  30   n  of the annular member  35   a  and the smallest inner diameter portion  30   m  of the nozzle  32 , and then a flow direction of at least a part of the refrigerant is suddenly turned. 
     Further, the largest outer diameter portion  30   n  of the annular member  35   a  is a most upstream throat portion that is disposed on the most upstream side in the refrigerant flow. With the formation of the largest outer diameter portion  30   n , the nozzle passage  13   a  is shaped to enlarge the passage cross-sectional area toward the center axis CL side. Further, the largest outer diameter portion  30   n  is disposed in a region of the nozzle passage  13   a  through which the refrigerant in the subsonic speed state flows. 
     On the other hand, the smallest inner diameter portion  30   m  of the nozzle  32  is a downstream throat portion that is disposed on the downstream side of the most upstream throat portion in the refrigerant flow. The smallest inner diameter portion  30   m  is formed in a shape enlarging the passage cross-sectional area of the nozzle passage  13   a  toward a side away from the center axis CL of the passage formation member  35 . 
     In other words, the nozzle passage  13   a  of the present embodiment changes the passage cross-sectional area so as to function as a two-stage throttle type Laval nozzle having multiple (two in the present embodiment) throat portions (throat portions). Further, in the nozzle passage  13   a , the refrigerant is reduced in pressure, accelerated so that a flow rate of the refrigerant reaches a supersonic speed, and jetted. 
     Further, in the nozzle passage  13   a  of the present embodiment, the dimensions of the annular member  35   a  and the nozzle  32  are set so that the smallest passage cross-sectional area of the refrigerant passage provided by the most upstream throat portion (that is, the largest outer diameter portion  30   n  of the annular member  35   a ) is smaller than the smallest passage cross-sectional area of the refrigerant passage provided by the downstream throat portion (in other words, the smallest inner diameter portion  30   m  of the nozzle  32 ). 
     For that reason, when the drive mechanism  37  displaces the passage formation member  35  to close the nozzle passage  13   a , the largest outer diameter portion  30   n  of the annular member  35   a  comes into contact with the nozzle  32 . 
     Next, as shown in  FIGS. 2 and 3 , the diffuser body  33  is disposed on the downstream side of the nozzle  32  inside the upper body  311  in the refrigerant flow. The diffuser body  33  is formed of a cylindrical member made of metal (in the present embodiment, an aluminum alloy). The diffuser body  33  may be divided into multiple members so that a refrigerant ejection port  13   e  side of the nozzle  32  can be accommodated in the through hole  33   a  provided inside the diffuser body  33 . 
     An outer peripheral side of the diffuser body  33  is press-fitted into an inner peripheral side surface of the upper body  311  so that the diffuser body  33  is fixed to the upper body  311 . Incidentally, an O-ring is disposed as a sealing member not shown between the diffuser body  33  and the upper body  311  so that no refrigerant leaks from a gap between those members. 
     A through hole  33   a  penetrating in the axial direction is provided in a central portion of the diffuser body  33 . The through hole  33   a  is formed in a shape of a substantially truncated conical rotating body, and a center axis of the through hole  33   a  is disposed coaxially with the center axis CL of the passage formation member  35 . Furthermore, in the present embodiment, a leading end portion of the nozzle  32  on the side of the refrigerant ejection port  13   e  extends to an inside of the through hole  33   a  of the diffuser body  33 . 
     A suction passage  13   b  is provided between an inner peripheral surface of the through hole  33   a  of the diffuser body  33  and an outer peripheral surface of the leading end portion of the nozzle  32 . The suction passage  13   b  guides the refrigerant drawn from the refrigerant suction port  31   b  to the refrigerant flow downstream side of the pressure reducing space  30   b  (that is, the nozzle passage  13   a ). For that reason, when viewed from the direction of the center axis CL, a suction refrigerant outlet  13   f , which is the most downstream portion of the suction passage  13   b , opens annularly on an outer peripheral side of the refrigerant ejection port  13   e.    
     A pressurizing space  30   e  is formed in the through hole  33   a  of the diffuser body  33  on the downstream side of the suction passage  13   b  in the refrigerant flow. The pressurizing space  30   e  is formed into a substantially truncated conical shape that gradually spreads in the refrigerant flow direction. The pressurizing space  30   e  is a space into which the jet refrigerant jetted from the nozzle passage  13   a  described above and the suction refrigerant drawn from the suction passage  13   b  flow. 
     The lower side of the passage formation member  35  is located inside the pressurizing space  30   e . A mixing passage  13   d  and a diffuser passage  13   c  are provided between an inner peripheral surface of a portion defining the pressurizing space  30   e  of the diffuser body  33  and an outer peripheral surface of a lower side of the passage formation member  35 . The mixing passage  13   d  is a refrigerant passage in which the jet refrigerant and the suction refrigerant are mixed together. The diffuser passage  13   c  is a refrigerant passage in which the mixture refrigerant of the jet refrigerant and the suction refrigerant is increased in pressure. 
     The mixing passage  13   d  is disposed on the upstream side of the diffuser passage  13   c  in the refrigerant flow. The mixing passage  13   d  is formed into a shape gradually reduced in the passage cross-sectional area toward the downstream side in the refrigerant flow. More specifically, as shown in  FIG. 4 , an outline of a wall surface defining the mixing passage  13   d  in the diffuser body  33  on a cross-sectional plane including the center axis CL is inclined to come closer to the passage formation member  35  in a downstream direction of the refrigerant flow. As a result, the passage cross-sectional area of the mixing passage  13   d  is reduced toward the downstream side in the refrigerant flow. 
     Furthermore, a smallest passage cross-sectional area of the mixing passage  13   d  is set to be smaller than a total of a passage cross-sectional area of the refrigerant ejection port  13   e  and a passage cross-sectional area of the suction refrigerant outlet  13   f . As a result, a mixing performance of the jet refrigerant and the suction refrigerant is improved in the mixing passage  13   d.    
     The diffuser passage  13   c  is formed into a shape gradually reduced in the passage cross-sectional area toward the downstream side in the refrigerant flow. As a result, in the diffuser passage  13   c , a velocity energy of the mixture refrigerant can be converted into a pressure energy. Therefore, the diffuser passage  13   c  functions as a diffuser portion (pressure increase portion). Both of the mixing passage  13   d  and the diffuser passage  13   c  have an annular cross-sectional shape perpendicular to the center axis. 
     In this example, as shown in  FIG. 4 , the nozzle passage  13   a  may be defined as a refrigerant passage provided in a range where a line segment extending in a normal direction from the outer peripheral surface of the passage formation member  35  intersects with a portion of the nozzle  32  which defines the pressure reducing space  30   b . The diffuser passage  13   c  may be defined as a refrigerant passage provided in a range where a line segment extending in the normal direction from the outer peripheral surface of the passage formation member  35  intersects with a portion of the diffuser body  33  which defines the pressurizing space  30   e.    
     The suction refrigerant outlet  13   f  of the suction passage  13   b  in the cross-sectional view of  FIG. 4  may be defined by a line segment extending in a direction normal to the outer peripheral surface of the passage formation member  35 , which is a line segment extending a leading end portion of the refrigerant ejection port  13   e  of the nozzle  32  to the diffuser body  33 . 
     The mixing passage  13   d  may be defined as a refrigerant passage that connects the nozzle passage  13   a , the suction passage  13   b , and the diffuser passage  13   c . Further, the smallest passage cross-sectional area of the mixing passage  13   d  is a passage cross-sectional area at the most downstream portion of the mixing passage  13   d  in the refrigerant flow (that is, the most upstream portion of the diffuser passage  13   c  in the refrigerant flow). 
     Further, the nozzle passage  13   a , the suction passage  13   b , the diffuser passage  13   c , and the mixing passage  13   d  are defined between the outer peripheral surface of the passage formation member  35  and the inner peripheral surface of the body  30  (specifically, the nozzle  32  and the diffuser body  33 ). 
     For that reason, with the adjustment of an angle between the center axis CL and the outer peripheral surface of the passage formation member  35  and an angle between the center axis CL and the inner peripheral surface of the body  30 , even if the passage cross-sectional area is kept constant toward the downstream side in the refrigerant flow, a width in the radial direction (flow channel width) of each passage can be increased or decreased toward the downstream side in the refrigerant flow. 
     Next, the drive mechanism  37  will be described. The drive mechanism  37  displaces the passage formation member  35 , to thereby change the passage cross-sectional areas of the nozzle passage  13   a  and the diffuser passage  13   c . As shown in  FIGS. 2 and 3 , the drive mechanism  37  is disposed outside the upper body  311  and on an axial extension line of the upstream actuating bar  351   a . The drive mechanism  37  includes a diaphragm  371 , an upper cover  372 , a lower cover  373 , and the like. 
     The upper cover  372  forms an enclosure space formation member that forms a part of an enclosure space  37   a  in cooperation with the diaphragm  371 . The upper cover  372  forms a cup-shaped member formed of metal (stainless steel in the present embodiment). 
     The enclosure space  37   a  is a space filled with a temperature sensitive medium whose pressure varies with a change in temperature. In more detail, the enclosure space  37   a  is a space in which the temperature sensitive medium having a composition comparable to that of the refrigerant circulating through the ejector refrigeration cycle  10  is enclosed with a predetermined enclosure density. 
     Therefore, as the temperature sensitive medium of the present embodiment, a medium containing R1234yf as a main component (for example, a mixed medium of R1234yf and helium) can be adopted. Further, the enclosure density of the temperature sensitive medium is set so as to appropriately displace the passage formation member  35  during normal operation of the cycle as will be described later. 
     The lower cover  373  forms an introduction space formation member that defines an introduction space  37   b  in cooperation with the diaphragm  371 . The lower cover  373  is formed of the same metal member as that of the upper cover  372 . The introduction space  37   b  is a space into which the suction refrigerant drawn from the refrigerant suction port  31   b  is introduced through a communication passage not shown. 
     The outer peripheral edge portions of the upper cover  372  and the lower cover  373  are fixed to each other by swaging or the like. Further, the outer peripheral side edge of the diaphragm  371  is sandwiched between the upper cover  372  and the lower cover  373 . As a result, the diaphragm  371  partitions a space provided between the upper cover  372  and the lower cover  373  into the enclosure space  37   a  and the introduction space  37   b.    
     The diaphragm  371  is a pressure responsive member that displaces according to a pressure difference between an internal pressure of the enclosure space  37   a  and a pressure of the suction refrigerant flowing through the suction passage  13   b . Therefore, it is preferable that the diaphragm  371  is made of a material which is rich in elasticity and excellent in pressure resistance and airtightness. 
     Therefore, in the present embodiment, the diaphragm  371  is formed of a metal thin plate made of stainless steel (SUS 304). In addition, the diaphragm  371  may be made of a rubber base material such as an EPDM (ethylene propylene diene rubber) containing a base fabric (polyester) or an HNBR (hydrogenated nitrile rubber). 
     A disk-shaped plate member  374  made of metal (aluminum alloy in the present embodiment) is disposed on the introduction space  37   b  side of the diaphragm  371 . The plate member  374  is disposed so as to come in contact with the diaphragm  371 . Further, a leading end portion of the upstream actuating bar  351   a  is coupled to the plate member  374 . Therefore, the shaft  351  and the passage formation member  35  according to the present embodiment are displaced so that a total load of a load received from the drive mechanism  37  (specifically, the diaphragm  371 ) and a load received from the coil spring  36   a  is balanced. 
     More specifically, when a temperature (degree of superheat SH) of the refrigerant on the outlet side of the evaporator  14  rises, a saturation pressure of the temperature sensitive medium sealed in the enclosure space  37   a  rises and a pressure difference obtained by subtracting an internal pressure in the introduction space  37   b  from an internal pressure in the enclosure space  37   a  is increased. As a result, the diaphragm  371  is displaced to the introduction space  37   b  side, and the load received by the upstream actuating bar  351   a  from the drive mechanism  37  increases. 
     Therefore, when the temperature (degree of superheat SH) of the refrigerant on the outlet side of the evaporator  14  rises, the passage formation member  35  is displaced in a direction of enlarging the passage cross-sectional area in the nozzle passage  13   a  or the like. 
     On the other hand, when a temperature (degree of superheat SH) of the refrigerant on the outlet side of the evaporator  14  decreases, the saturation pressure of the temperature sensitive medium sealed in the enclosure space  37   a  decreases and a pressure difference obtained by subtracting the internal pressure in the introduction space  37   b  from the internal pressure in the enclosure space  37   a  is reduced. As a result, the diaphragm  371  is displaced to the side of the enclosure space  37   a , and the load applied to the upstream actuating bar  351   a  from the drive mechanism  37  is reduced. 
     Therefore, when the temperature (degree of superheat SH) of the refrigerant on the outlet side of the evaporator  14  drops, the passage formation member  35  is displaced in a direction of reducing the passage cross-sectional area in the nozzle passage  13   a  or the like. 
     In other words, the drive mechanism  37  of the present embodiment is configured by a mechanical mechanism, and the diaphragm  371  displaces the passage formation member  35  according to the degree of superheat SH of the refrigerant on the outlet side of the evaporator  14 . The passage cross-sectional area of the nozzle passage  13   a  or the like is adjusted so that the degree of superheat SH of the refrigerant on the outlet side of the evaporator  14  comes closer to a predetermined reference degree of superheat KSH. It should be noted that the reference degree of superheat KSH can be changed by adjusting the load of the coil spring  36   a  described above. 
     Furthermore, in the present embodiment, a cover member  375  that covers the drive mechanism  37  is disposed on an outer peripheral side of the drive mechanism  37 . This prevents the temperature sensitive medium in the enclosure space  37   a  from being influenced by an outside air temperature in an engine compartment. 
     Next, as shown in  FIGS. 2 and 3 , the lower body  312  is provided with a mixture refrigerant outflow port  31   g . The mixture refrigerant outflow port  31   g  is a refrigerant outflow port through which a gas-liquid mixed state refrigerant flowing out of the diffuser passage  13   c  flows out to the side of the gas-liquid separation space  31   f  provided in the gas-liquid separation body  313 . A passage cross-sectional area of the mixture refrigerant outflow port  31   g  is set to be smaller than a passage cross-sectional area of the most downstream portion of the diffuser passage  13   c.    
     The gas-liquid separation body  313  is formed in a cylindrical shape. A gas-liquid separation space  30   f  is defined inside the gas-liquid separation body  313 . The gas-liquid separation space  30   f  is defined as a space having a substantially cylindrical rotating body shape. The center axes of the gas-liquid separation body  313  and the gas-liquid separation space  30   f  extend in the vertical direction. For that reason, the center axes of the gas-liquid separation body  313  and the gas-liquid separation space  30   f  are orthogonal to the center axis of the passage formation member  35  and the like. 
     Further, the gas-liquid separation body  313  is disposed so that the refrigerant flowing into the gas-liquid separation space  30   f  from the mixture refrigerant outflow port  31   g  of the lower body  312  flows along a wall surface of the gas-liquid separation space  30   f  on the outer peripheral side. As a result, in the gas-liquid separation space  30   f , the gas-liquid of the refrigerant is separated by the action of a centrifugal force generated when the refrigerant is swirled around the center axis. 
     A cylindrical pipe  313   a  is disposed at an axial center portion of the gas-liquid separation body  313 . The cylindrical pipe  313   a  is disposed coaxially with the gas-liquid separation space  30   f  and extends in the vertical direction. A liquid-phase refrigerant outflow port  31   c  is provided in a cylindrical side surface of the gas-liquid separation body  313  on the bottom surface side. The liquid-phase refrigerant outflow port  31   c  allows the liquid-phase refrigerant separated in the gas-liquid separation space  30   f  to flow out along an outer peripheral side wall surface of the gas-liquid separation space  30   f . Further, a gas-phase refrigerant outflow port  31   d  is provided in a lower side end portion of the pipe  313   a . The gas-phase refrigerant outflow port  31   d  allows the gas-phase refrigerant separated in the gas-liquid separation space  30   f  to flow out. 
     Further, an oil return hole  313   b  is provided in a root portion of the pipe  313   a  in the gas-liquid separation space  30   f  (that is, the lowermost portion in the gas-liquid separation space  30   f ). The oil return hole  313   b  communicates the gas-liquid separation space  30   f  with a gas-phase refrigerant passage defined in the pipe  313   a . The oil return hole  313   b  is a communication passage for returning a refrigerator oil dissolved in the liquid-phase refrigerant to the compressor  11  through the gas-phase refrigerant outflow passage  34   b  together with the liquid-phase refrigerant. 
     As shown in  FIG. 1 , the refrigerant inlet side of the evaporator  14  is connected to the liquid-phase refrigerant outflow port  31   c  of the ejector  13 . The evaporator  14  is a heat-absorbing heat exchanger that exchanges a heat between a low-pressure refrigerant whose pressure is reduced by the ejector  13  and a blown air which is blown from a blower fan  14   a  into the vehicle interior, thereby evaporating the low-pressure refrigerant and exerting a heat absorbing action. 
     The blower fan  14   a  is an electric blower of which the rotation speed (blown air amount) is controlled by a control voltage output from the control device. The refrigerant suction port  31   b  of the ejector  13  is connected to an outlet side of the evaporator  14 . Further, the gas-phase refrigerant outflow port  31   d  of the ejector  13  is connected with the intake port side of the compressor  11 . 
     The control device not shown includes a well-known microcomputer including a CPU, a ROM and a RAM, and peripheral circuits of the microcomputer. The control device performs various calculations and processes based on a control program stored in the ROM. The control device controls the operation of the various electric actuators  11 ,  12   d ,  14   a , and so on 
     In addition, the control device is connected with multiple air conditioning control sensor groups such as an inside air temperature sensor, an outside air temperature sensor, an insolation sensor, an evaporator temperature sensor, and a discharge pressure sensor, and the control device receives detection values from those sensor groups. 
     In more detail, the inside air temperature sensor is an inside air temperature detection unit that detects a vehicle interior temperature. The outside air temperature sensor is an outside air temperature detection unit that detects an outside air temperature. The insolation sensor is a detection unit that detects the amount of insolation in the vehicle interior. The evaporator temperature sensor is an evaporator temperature detection unit that detects a blowing air temperature (evaporator temperature) from the evaporator  14 . The discharge pressure sensor is an outlet side pressure detection unit that detects a pressure of the refrigerant on the outlet side of the radiator  12 . 
     Furthermore, an operation panel not shown is connected to an input side of the control device. The operation panel is disposed in the vicinity of an instrument panel positioned at a front part in the vehicle interior. Operation signals output from various operation switches disposed on the operation panel are input to the control device. An air conditioning operation switch for requesting the execution of air conditioning in the vehicle interior, a vehicle interior temperature setting switch for setting the temperature of the vehicle interior, and the like are provided as the various operation switches that are mounted on the operation panel. 
     Meanwhile, the control device of the present embodiment is integrated with a control unit for controlling the operations of various control target devices connected to the output side of the control device, but a configuration of the control device (hardware and software), which controls the operations of the respective control target devices forms the control unit of the respective control target devices. 
     For example, in the present embodiment, a configuration which controls the operation of a discharge capacity control valve of the compressor  11  to control the refrigerant discharge capacity of the compressor  11  configures a discharge capacity control unit. It is needless to say that the discharge capacity control unit may be configured as another control device different from the control device. 
     Next, the operation of the present embodiment configured as described above will be described with reference to a Mollier diagram of  FIG. 5 . First, when the operation switch of the operation panel is turned on, the control device actuates the discharge capacity control valve, the cooling fan  12   d , and the blower fan  14   a , and so on of the compressor  11 . With the above configuration, the compressor  11  draws, compresses, and discharges the refrigerant. 
     A high-temperature high-pressure refrigerant (a point a in  FIG. 5 ) discharged from the compressor  11  flows into the condensing portion  12   a  of the radiator  12 , exchanges a heat with an outside air blown from the cooling fan  12   d , and radiates the heat and is condensed. The refrigerant condensed by the condensing portion  12   a  is separated into gas and liquid by the receiver portion  12   b . The liquid-phase refrigerant, which has been subjected to gas-liquid separation by the receiver portion  12   b , exchanges a heat with an outside air blown from the cooling fan  12   d  by the subcooling portion  12   c . The liquid-phase refrigerant further radiates the heat to provide a subcooled liquid-phase refrigerant (from a point a to a point b in  FIG. 5 ). 
     The subcooled liquid-phase refrigerant that has flowed out of the subcooling portion  12   c  of the radiator  12  is isentropically depressurized by the nozzle passage  13   a , and jetted. The nozzle passage  13   a  is defined between an inner peripheral surface of the pressure reducing space  30   b  of the ejector  13  and an outer peripheral surface of the passage formation member  35 . 
     In more detail, in the nozzle passage  13   a  of the present embodiment, the passage cross-sectional area is reduced in the first passage  131 , to thereby reduce a pressure of the liquid-phase refrigerant in the subsonic speed state and accelerate a speed of the liquid-phase refrigerant (from a point b to a point c 1  in  FIG. 5 ). The pressure of the refrigerant that has flowed into the second passage  132  is recovered by enlargement of the passage area (from a point c 1  to a point c 2  in  FIG. 5 ). 
     The largest outer diameter portion  30   n  of the annular member  35   a  forming the most upstream portion of the second passage serves as an edge so that a separation vortex occurs in the refrigerant flowing into the second passage  132 , and a boiling nucleus is generated in the refrigerant on the center axis CL side. The smallest inner diameter portion  30   m  of the nozzle  32  forming the most upstream portion of the third passage  133  serves as an edge so that a separation vortex occurs in the refrigerant flowing into the third passage  133 , and a boiling nucleus is generated in the refrigerant on the outer peripheral side. 
     Choking (choking) occurs in the boil promoted refrigerant in the vicinity of the smallest inner diameter portion  30   m  of the nozzle  32 . As a result of the choking, the refrigerant reaches the sound speed, is accelerated to a supersonic speed in the third passage  133 , and is jetted from the refrigerant ejection port  13   e  (from a point c 2  to a point c 3  in  FIG. 5 ). 
     In this situation, the passage cross-sectional area of the refrigerant passage defined by the largest outer diameter portion  30   n  of the annular member  35   a  (that is, the smallest passage cross-sectional area of the nozzle passage  13   a ) is adjusted such that the degree of superheat of the refrigerant on the outlet side of the evaporator  14  (a point h in  FIG. 5 ) comes closer to a reference degree of superheat KSH. 
     Further, the refrigerant that has flowed out of the evaporator  14  (the point h in  FIG. 5 ) is drawn through the refrigerant suction port  31   b  and the suction passage  13   b  due to the suctioning action of the jet refrigerant which has been jetted from the nozzle passage  13   a . The jet refrigerant jetted from the nozzle passage  13   a  and the suction refrigerant drawn through the suction passage  13   b  flow into the diffuser passage  13   c  and join together (from the point c to point d, and from point h 1  to point d in  FIG. 5 ). 
     In this example, the most downstream portion of the suction passage  13   b  of the present embodiment is formed in a shape whose passage cross-sectional area is gradually reduced toward a refrigerant flowing direction. For that reason, the suction refrigerant to pass through the suction passage  13   b  increases a flow velocity while reducing the pressure of the suction refrigerant (from the point h to the point h 1  in  FIG. 5 ). 
     In the diffuser passage  13   c , a kinetic energy of the refrigerant is converted into a pressure energy by an increase in the refrigerant passage cross-sectional area. As a result, a pressure of the mixture refrigerant rises while the jet refrigerant and the suction refrigerant are mixed together (from the point d to the point e in  FIG. 5 ). The refrigerant that has flowed out of the diffuser passage  13   c  is separated into gas and liquid in the gas-liquid separation space  30   f  (from the point e to a point f, and from the point e to point g in  FIG. 5 ). 
     The liquid-phase refrigerant separated in the gas-liquid separation space  30   f  flows into the evaporator  14  with a pressure loss when flowing through the refrigerant flow channel extending from the ejector  13  to the evaporator  14  (from a point g to a point g 1  in  FIG. 5 ). The refrigerant that has flowed into the evaporator  14  absorbs the heat from the blown air blown by the blower fan  14   a , and evaporates (from the point g 1  to the point h in  FIG. 5 ). Accordingly, the blown air is cooled. 
     On the other hand, the gas-phase refrigerant that has been separated in the gas-liquid separation space  30   f  flows out of the gas-phase refrigerant outflow port  31   d , and is drawn into the compressor  11  and compressed again (from the point f to the point a in  FIG. 5 ). 
     The ejector refrigeration cycle  10  of the present embodiment operates as described above, and can cool the blown air to be blown into the vehicle interior. 
     In the ejector refrigeration cycle  10  of the present embodiment, the refrigerant that has been increased in pressure by the diffuser passage  13   c  is drawn into the compressor  11 . Therefore, according to the ejector refrigeration cycle  10 , a power consumption of the compressor  11  is reduced, and a coefficient of performance (COP) of the cycle can be improved in comparison with a general refrigeration cycle device in which refrigerant evaporation pressure in an evaporator is substantially equal to a pressure of the refrigerant drawn in the compressor. 
     According to the ejector  13  of the present embodiment, since the drive mechanism  37  is provided, the passage formation member  35  can be displaced according to a load variation of the ejector refrigeration cycle  10  to regulate the passage cross-sectional areas of the nozzle passage  13   a  and the diffuser passage  13   c.    
     Therefore, the ejector  13  can appropriately operate by changing the passage cross-sectional area of the refrigerant passage (specifically, the nozzle passage  13   a  and the diffuser passage  13   c ) internally formed according to the load variation of the ejector refrigeration cycle  10 . 
     As in the ejector  13  of the present embodiment, in the configuration in which the passage formation member  35  is displaced according to the load variation of the ejector refrigeration cycle  10 , the center axis CL of the passage formation member  35  may be inclined with respect to the center axes of the inflow space  30   a , the pressure reducing space  30   b , the pressurizing space  30   e , and the like. 
     If the center axis CL of the passage formation member  35  is inclined, because the passage cross-sectional area of the refrigerant passage having the annular cross section changes in the circumferential direction, there is a risk that a high ejector efficiency cannot be stably exercised. 
     On the other hand, in the ejector  13  of the present embodiment, the passage formation member  35  and the upstream actuating bar  351   a  of the shaft  351  are integrated together in such a manner that the center axis CL of the passage formation member  35  and the center axis of the upstream actuating bar  351   a  are disposed coaxially. As a result, even when the drive mechanism  37  displaces the passage formation member  35  together with the shaft  351 , the center axis CL of the passage formation member  35  can be prevented from being inclined. 
     Further, in the ejector  13  of the present embodiment, since the downstream actuating bar  351   b  is provided, the passage formation member  35  can be supported at both end sides of the center axis CL. Therefore, the center axis CL of the passage formation member  35  can be more reliably prevented from being inclined. As a result, the ejector efficiency can be prevented from becoming unstable. 
     Further, in the ejector  13  of the present embodiment, the upstream actuating bar  351   a  penetrates through the inflow space  30   a , and the center axis of the upstream actuating bar  351   a  and the center axis of the inflow space  30   a  are disposed coaxially. This makes it difficult for the refrigerant in the inflow space  30   a  to being swirled around the center axis, and also prevents a gas column from occurring at a center of the inflow space  30   a  even if the refrigerant is swirled temporarily. 
     Therefore, there is no case in which the center axis CL of the passage formation member  35  is inclined, and the configuration of the gas column becomes unstable. As a result, the ejector efficiency can be prevented from becoming unstable. Furthermore, since the swirling flow around the center axis is less likely to occur in the refrigerant in the inflow space  30   a , when the jet refrigerant and the suction refrigerant are mixed together in the mixing passage  13   d , an increase in the mixing loss caused by a difference in the flow direction between the jet refrigerant and the suction refrigerant can be reduced when the injected refrigerant and the suction refrigerant are mixed together. 
     In addition, in the ejector  13  of the present embodiment, the largest outer diameter portion  30   n  of the annular member  35   a  configuring the most upstream throat portion is formed in the region of the nozzle passage  13   a  through which the subsonic refrigerant flows, and the largest outer diameter portion  30   n  functions as an edge that rapidly enlarges the passage cross-sectional area of the nozzle passage  13   a  to generate a separation vortex. Accordingly, boiling nuclei can be generated in the liquid-phase refrigerant flowing through the nozzle passage  13   a.    
     Further, the largest outer diameter portion  30   n  of the annular member  35   a  configuring the most upstream throat portion is formed on the passage formation member  35  side (that is, on the center axis CL) side. At least a part of the nozzle passage  13   a  is formed in a shape that allows the flow direction of the refrigerant to be turned toward the center axis CL of the passage formation member  35 . 
     According to the above configuration, the boiling nucleus can be supplied from the center axis CL side to the liquid-phase refrigerant flowing through the nozzle passage  13   a . Therefore, even if no gas column or the like is generated in the refrigerant in the inflow space  30   a , the boiling of the refrigerant flowing through the nozzle passage  13   a  can be promoted, and the ejector efficiency can be improved. 
     In addition, in the ejector  13  of the present embodiment, the smallest inner diameter portion  30   m  of the nozzle  32  configuring the downstream throat portion is formed in a portion forming the pressure reducing space  30   b  of the nozzle  32 . At least a part of the nozzle passage  13   a  is formed in a shape so as to turn the flow direction of the refrigerant to a side separated from the center axis CL of the passage formation member  35 . 
     According to the above configuration, the boiling nucleus can be also supplied from the outer peripheral side to the liquid-phase refrigerant flowing through the nozzle passage  13   a . Therefore, the boiling of the refrigerant flowing through the nozzle passage  13   a  can be further promoted. 
     Further, in the ejector  13  of the present embodiment, as shown in  FIG. 4 , the passage cross-sectional area of the mixing passage  13   d  is reduced toward the downstream side in the refrigerant flow. According to the configuration described above, the losses occurring in the mixing passage  13   d  and the diffuser passage  13   c  can be reduced. 
     The above configuration will be described in more detail. In the ejector  13 , the jet refrigerant jetted from the nozzle passage  13   a  to the mixing passage  13   d  tends to have a smaller liquid proportion in the vicinity of the wall due to and inertial force of the droplet, and a flow velocity larger than that in the center of the flow channel. In other words, a flow velocity of the droplet of the jet refrigerant immediately after being jetted from the nozzle passage  13   a  is larger than a two-phase sound speed, and a flow velocity of the gas (that is, the gas-phase refrigerant of the jetted refrigerant) may be larger than a gas sound speed. On the other hand, a flow velocity of the suction refrigerant drawn from the suction passage  13   b  into the mixing passage  13   d  is smaller than the sound speed. That is, the suction refrigerant immediately after being drawn into the mixing passage  13   d  is in a subsonic speed state. 
     In that case, a velocity boundary layer is formed between the refrigerant in the supersonic speed state and the refrigerant in the subsonic speed state in the refrigerant in the mixing passage  13   d , as indicated by a thick broken line in  FIG. 6 . The flow channel cross-sectional area decreases in the flow direction (that is, a convergent flow) in the mixing passage  13   d , and the Mach number of the supersonic gas refrigerant decreases. Therefore, an oblique impact wave occurs as indicated a double thin line in  FIG. 6 . When the Mach number in the wake of the impact wave exceeds 1, an expansion wave as shown by a thin line in  FIG. 6  is generated and an impact wave is generated further in the wake of the expansion wave. However, the impact wave is changed into a convergent flow, thereby being capable of shortening an interval between the impact waves, and also capable of reducing the number of occurrences (the impact wave occurs twice in  FIG. 6 ). 
     On the other hand, as shown in  FIG. 7 , in an ejector of a comparative example in which a refrigerant flow in the mixing passage  13   d  does not become the convergent flow where the passage formation member  35  does not cross an edge line of the outlet side of the nozzle passage  13   a  indicated by a thin broken line, when the number of occurrences of the impact wave is likely to increase (three times in  FIG. 7 ), and the impact wave occurs in an area enlargement section (that is, the diffuser passage  13   c ), the Mach number upstream of the impact wave is equal to or more than 1. As a result, the refrigerant is reduced in pressure and expanded due to an area enlargement, and a pressure rise amount of the ejector is reduced. 
     The loss (entropy generation amount) of the impact wave will be described with the use of Formula (F1) of the general impact wave entropy generation amount. 
     
       
         
           
             
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     In Formula (F1), s is an entropy, γ is a specific heat ratio, R is a gas constant, β is an impact wave angle, and M is a Mach number. Subscript 1 indicates a physical quantity before the impact wave before and subscript 2 is a physical quantity after the impact wave. 
     In this way, the entropy generation amount as a loss against a pressure rise tends to increase as an impact wave angle and the Mach number increase. In addition, the entropy generation amount is increased by the number of occurrences of the impact wave. 
     In the mixing passage  18   d  of the present embodiment, as indicated by a solid arrow in an upper part of  FIG. 8 , the jet refrigerant transitions to a subsonic speed state while generating impact waves twice in the stated order of N 1  and N 2 . On the other hand, in the comparative example, as indicated by a dashed line arrow in the upper part of  FIG. 8 , the jet refrigerant transitions to the subsonic speed state while generating the impact waves three times with the Mach number higher than that of the present embodiment in the stated order of n 1 , n 2 , and n 3 . 
     Therefore, as indicated in a lower part of  FIG. 8 , the refrigerant flow in the mixing passage  13   d  is converged so as to decrease the Mach number of the flow as in the present embodiment. As a result, as indicated by the lower part of  FIG. 8 , the entropy generation amount by the impact waves (an energy loss integrated by repeating the collision) can be reduced, thereby being capable of improving the energy conversion efficiency. 
     As a result, according to the ejector  13  of the present embodiment, the high energy conversion efficiency can be stably exercised irrespective of a load variation of the applied ejector refrigeration cycle  10 . As described above, the fact that an increase in mixing loss can be reduced is extremely effective in the ejector  13  in which the suction refrigerant outlet  13   f  of the suction passage  13   b  opens annularly on the outer peripheral side of the refrigerant ejection port  13   e  of the nozzle passage  13   a.    
     In the ejector  13  of the present embodiment, the smallest passage cross-sectional area of the refrigerant passage provided by the largest outer diameter portion  30   n  of the annular member  35   a  is smaller than the smallest passage cross-sectional area of the refrigerant passage provided by the smallest inner diameter portion  30   m  of the nozzle  32 . 
     Accordingly, the flow rate of the refrigerant flowing through the nozzle passage  13   a  can be adjusted by changing the passage cross-sectional area of the refrigerant passage provided by the largest outer diameter portion  30   n . Further, a subsonic refrigerant flows through the refrigerant passage provided by the largest outer diameter portion  30   n , and the refrigerant puts into a supersonic critical state on the downstream side of the largest outer diameter portion  30   n . Therefore, the refrigerant flow rate can be adjusted with high precision in the refrigerant passage provided by the largest outer diameter portion  30   n.    
     Further, in the ejector  13  of the present embodiment, since the center axis of the upstream actuating bar  351   a  and the center axis of the downstream actuating bar  351   b  are disposed coaxially with each other, an assembling property when the passage formation member  35  and the shaft  351  are assembled inside the ejector  13  can be improved. 
     Further, since the leading end portion of the upstream actuating bar  351   a  is coupled to the plate member  374  of the drive mechanism  37 , the coupling can be easily performed as compared with a case in which the passage formation member  35  and the drive mechanism  37  are coupled to each other through the multiple actuating bars. 
     In the ejector  13  of the present embodiment, when viewed from the direction of the center axis of the inflow space  30   a , the refrigerant inflow passage  31   e  is provided so that the refrigerant flowing into the inflow space  30   a  flows toward the center axis of the inflow space  30   a . According to the above configuration, the swirling flow around the center axis can be still more prevented from occurring in the refrigerant in the inflow space  30   a.    
     Furthermore, according to the present embodiment, rigid bodies such as the upstream actuating bar  351   a  and the passage formation member  35  are disposed in the central portions of the inflow space  30   a , the pressure reducing space  30   b , and the pressurizing space  30   e . Accordingly, the axial vertical cross-sectional shapes of all the refrigerant passages defined by the inflow space  30   a , the pressure reducing space  30   b , and the pressurizing space  30   e  are annular. 
     For that reason, since both of a friction with a wall surface of an outer peripheral side wall surface and a friction with the wall surface on the inner peripheral side occur in the refrigerant flowing through those refrigerant passages, the swirling flow is not promoted. 
     Further, in the ejector  13  of the present embodiment, the smallest passage cross-sectional area of the mixing passage  13   d  is set to be smaller than a total of the passage cross-sectional area of the refrigerant ejection port  13   e  and the passage cross-sectional area of the suction refrigerant outlet  13   f . According to the above configuration, a mixing property between the jet refrigerant and the mixture refrigerant in the mixing passage  13   d  can be improved. 
     In addition, in the ejector  13  of the present embodiment, the passage cross-sectional area of the mixture refrigerant outflow port  31   g  is set to be smaller than the passage cross-sectional area of the most downstream portion of the diffuser passage  13   c . Further, the gas-liquid mixed refrigerant flowing out of the diffuser passage  13   c  flows along the wall surface of the gas-liquid separation space  30   f  on the outer peripheral side. According to the above configuration, the pressure loss of the refrigerant generated in the gas-liquid separation space  30   f  can be reduced. 
     In more detail, at the mixture refrigerant outflow port  31   g , although a static pressure drop of the refrigerant is caused by a reduction in the passage cross-sectional area, the refrigerant flowing into the gas-liquid separation space  30   f  from the mixture refrigerant outflow port  31   g  flows along the inner peripheral wall surface of the gas-liquid separation body  313  (in other words, the wall surface of the gas-liquid separation space  30   f  on the outer peripheral side). 
     For that reason, since the gas-phase refrigerant flowing into the gas-liquid separation space  30   f  from the mixture refrigerant outflow port  31   g  is prevented from being suddenly expanded in volume when flowing into the gas-liquid separation space  30   f , the energy loss caused by the volume expansion can be prevented. On the other hand, in the liquid-phase refrigerant flowing into the gas-liquid separation space  30   f  from the mixture refrigerant outflow port  31   g , the energy loss occurs by only the wall surface friction which is relatively little influenced. 
     Therefore, the kinetic energy of the refrigerant flowing into the gas-liquid separation space  30   f  having a relatively large volume from the mixture refrigerant outflow port  31   g  is converted into a pressure energy without being largely lost, and the static pressure of the refrigerant is recovered. As a result, the pressure loss of the refrigerant generated in the gas-liquid separation space  30   f  can be reduced. 
     Further, a pressure difference between the pressure in the gas-liquid separation space  30   f  and the pressure in the compressor  11  on the intake port side can be secured due to the pressure recovery. As a result, a refrigerator oil dissolved in the liquid-phase refrigerant can be surely returned to the intake port side of the compressor  11  through the oil return hole  313   b.    
     Second Embodiment 
     In the present embodiment, an example in which as shown in an enlarged cross-sectional view of  FIG. 9 , as compared with the ejector  13  of the first embodiment, a shape of an annular member  35   b  of a passage formation member  35  on a top side and a shape of a portion forming a pressure reducing space  30   b  of a nozzle  32  are changed will be described.  FIG. 9  is a diagram corresponding to  FIG. 4  in the first embodiment. In  FIG. 9 , identical portions with or equivalent portions to those in the first embodiment are denoted by the same reference numerals. The same is applied to the following drawings. 
     In more detail, an outer shape of the annular member  35   b  according to the present embodiment is formed in a shape of a rotating body in which top sides of two truncated cones are coupled to each other. Therefore, the annular member  35   b  according to the present embodiment is shaped to have a largest outer diameter portion  30   n  at a most upstream side in a refrigerant flow, and have a smallest outer diameter portion  30   p  at a substantially central portion in the center axis direction. Further, an outer diameter of an upstream actuating bar  351   a  of a shaft  351  according to the present embodiment is equal to that of the largest outer diameter portion  30   n.    
     Therefore, as shown in  FIG. 9 , an axial cross-sectional shape of a nozzle passage  13   a  by a wall surface of the nozzle passage  13   a  on a side of a center axis CL (the passage formation member  35  and the annular member  35   b  side) comes closer to the center axis CL toward the downstream side in the refrigerant flow in a range extending from the largest outer diameter portion  30   n  of the annular member  35   b  on the most upstream side toward the smallest outer diameter portion  30   p . The shape is separated from the center axis CL from the smallest outer diameter portion  30   p  toward the downstream side in the refrigerant flow. 
     On the other hand, a portion of the nozzle  32  for providing the pressure reducing space  30   b  according to the present embodiment has two diameter reduction portions of an upstream side smallest inner diameter portion  30   m  and a downstream side smallest inner diameter portion  30   q . An inner diameter of the upstream side smallest inner diameter portion  30   m  is smaller than an inner diameter of the downstream side smallest inner diameter portion  30   q.    
     Therefore, as shown in  FIG. 9 , an axial cross-sectional shape of the nozzle passage  13   a  on an opposite side of the center axis CL (a side of a portion of the nozzle  32  for providing pressure reducing space  30   b ) comes closer to the center axis CL toward the downstream side in the refrigerant flow in a range extending from the inflow space  30   a  side toward the upstream side smallest inner diameter portion  30   m . In the range from the upstream side smallest inner diameter portion  30   m  to the downstream side smallest inner diameter portion  30   q , the shape comes closer to the downstream side in the refrigerant flow after having been separated from the center axis CL. The shape is separated from the center axis CL from the downstream side smallest inner diameter portion  30   q  toward the downstream side in the refrigerant flow. 
     In addition, the second passage  132  according to the present embodiment is formed in a shape gradually reduced in the passage cross-sectional area toward the downstream side in the refrigerant flow. Furthermore, the third passage  133  according to the present embodiment is formed with two throat portions are formed, that is, an upstream side smallest inner diameter portion  30   m  and a downstream side smallest inner diameter portion  30   q . In other words, according to the present embodiment, two downstream throat portions are disposed on the downstream side of the most upstream throat portion in the refrigerant flow. 
     In other words, the nozzle passage  13   a  of the present embodiment changes the passage cross-sectional area so as to function as a multistage throttle type nozzle having multiple throat portions (throat portions). The other configurations of the ejector  13  and the ejector refrigeration cycle  10  are identical with those in the first embodiment. 
     Also, in the nozzle passage  13   a  of the ejector  13  according to the present embodiment, a pressure of the refrigerant is reduced in multiple stages. That is, in the first passage  131  of the present embodiment, the liquid-phase refrigerant in a subsonic speed state is reduced in pressure. The second passage  132  according to the present embodiment is formed into a convergent shape gradually reduced in the passage cross-sectional area toward the downstream side in the refrigerant flow. For that reason, in the second passage  132 , the refrigerant is reduced in pressure and accelerated while being kept in the subsonic state. 
     The largest outer diameter portion  30   n  of the annular member  35   a  forming the most upstream portion of the second passage serves as an edge so that a separation vortex occurs in the refrigerant flowing into the second passage  132 , and a boiling nucleus is generated in the refrigerant on the center axis CL side. The upstream side smallest inner diameter portion  30   m  of the nozzle  32  forming the most upstream portion of the third passage  133  serves as an edge so that a separation vortex occurs in the refrigerant flowing into the third passage  133 , and a boiling nucleus is generated in the refrigerant on the outer peripheral side. 
     Choking (choking) occurs in the boil promoted refrigerant in the vicinity of the upstream side smallest inner diameter portion  30   m . The refrigerant reaches sound speed by the choking. Furthermore, since the downstream side smallest inner diameter portion  30   q  serves as an edge and the boiling nucleus is generated, the boiling of the refrigerant is further promoted and the refrigerant is jetted from the refrigerant ejection port  13   e.    
     The other configuration and operation of the ejector  13  and the ejector refrigeration cycle  10  are the same as those of the first embodiment. Therefore, the ejector  13  and the ejector refrigeration cycle  10  of the present embodiment can obtain the same advantages as those in the first embodiment. In other words, the number of throat portions is not limited to two as in the first embodiment, and three or more throat portions may be provided as in the present embodiment. 
     Third Embodiment 
     In the present embodiment, as illustrated in  FIG. 10 , an example in which a shape of a mixing passage  13   d  is changed as compared with the ejector  13  in the first embodiment will be described. 
     More specifically, as shown in  FIG. 4 , an outline of a wall surface defining the mixing passage  13   d  in the passage formation member  35  according to the present embodiment on a cross-sectional plane including the center axis CL is inclined to come closer to the diffuser body  33  in a downstream direction of the refrigerant flow. As a result, the passage cross-sectional area of the mixing passage  13   d  is reduced toward the downstream side in the refrigerant flow. 
       FIG. 10  is a schematically enlarged cross-sectional view corresponding to  FIG. 6  described in the first embodiment. In addition, in  FIG. 10 , for clarification of the description, the passage formation member  35  of the first embodiment is indicated by a thin broken line. 
     The other configurations and operation of the ejector  13  and an ejector refrigeration cycle  10  are the same as those of the first embodiment. Therefore, the ejector  13  and the ejector refrigeration cycle  10  of the present embodiment can obtain the same advantages as those in the first embodiment. 
     In other words, in the present embodiment, the conical lateral surface of the passage formation member  35  is inclined so that the passage cross-sectional area of the mixing passage  13   d  is reduced toward the downstream side of the mixing passage  13   d  in the refrigerant flow. Even if the mixing passage  13   d  is provided in the above manner, as in the first embodiment, the pressure increase performance of the diffuser passage  13   c  is stabilized so that the ejector efficiency can be prevented from becoming unstable, and also the mixing loss occurring when the jet refrigerant and the suction refrigerant are mixed together can be reduced. 
     Fourth Embodiment 
     In the present embodiment, an example in which as shown in an enlarged cross-sectional view of  FIG. 11 , as compared with the ejector  13  of the first embodiment, a recess portion is provided on a top side of the passage formation member  35 , and the dent portion is dented toward a side where a passage cross-sectional area of a nozzle passage  13   a  will be described.  FIG. 11  is a diagram corresponding to  FIG. 4  described in the first embodiment. 
     Specifically, the recess portion of the present embodiment is configured by a through hole  352  provided on the top side of the passage formation member  35  and penetrates through a conical lateral surface of the passage formation member  35  in a direction perpendicular to a center axis CL. The through hole  352  is provided so as to be positioned on an upstream side of a smallest inner diameter portion  30   m  of a nozzle passage  13   a  in a refrigerant flow. 
     The other configurations and operation of the ejector  13  and an ejector refrigeration cycle  10  are the same as those of the first embodiment. Therefore, the ejector  13  and the ejector refrigeration cycle  10  of the present embodiment can obtain the same advantages as those in the first embodiment. 
     Furthermore, since the passage formation member  35  of the ejector  13  according to the present embodiment is provided with the through hole  352 , boiling nucleus can be generated by rapidly enlarging a refrigerant passage cross-sectional area of the nozzle passage  13   a . Accordingly, the boiling of the refrigerant in the nozzle passage  13   a  is promoted, thereby being capable of improving an energy conversion efficiency in the nozzle passage  13   a.    
     Further, in the ejector  13  of the present embodiment, since the through hole  352  is provided, a pressure distribution of the nozzle passage  13   a  formed in an annular sectional shape in a circumferential direction can be reduced. Therefore, even if the center axis CL of the passage formation member  35  is inclined, the ejector efficiency can be prevented from being significantly lowered. Further, the number of through hole  352  is not limited to one, but multiple through holes  352  may be provided in the circumferential direction and may be disposed at regular angular intervals. 
     Fifth Embodiment 
     In the present embodiment, as illustrated in  FIG. 12 , an example in which a configuration of an ejector  13  is simplified as compared with the ejector  13  in the first embodiment will be described.  FIG. 12  is an axial cross-sectional view corresponding to  FIG. 2  described in the first embodiment. 
     In the ejector  13  of the present embodiment, a shape of a passage formation member  35  is changed as compared with the first embodiment. The passage formation member  35  according to the present embodiment is shaped such that a cross-sectional area perpendicular to a center axis is enlarged from an upstream side in a refrigerant flow toward a downstream side, and thereafter reduced. In more detail, an outer shape of the passage formation member  35  according to the present embodiment is formed in a shape of a rotating body in which bottom surfaces of a truncated conical member and a conical member are coupled to each other. 
     For that reason, a largest outer diameter portion  30   n  is formed in a substantially central portion of the passage formation member  35  in the center axis direction. The largest outer diameter portion  30   n  functions as a most upstream throat portion described in the sixth embodiment. At least a part of the passage formation member  35  is disposed inside a pressure reducing space  30   b  defined in a nozzle  32 . 
     The nozzle  32  of the present embodiment is formed integrally with an upper body  311 . The nozzle  32  is formed with a smallest inner diameter portion  30   m  that minimizes a passage cross-sectional area of a nozzle passage  13   a . The smallest inner diameter portion  30   m  functions as the downstream throat portion described in the sixth embodiment. 
     The largest outer diameter portion  30   n  of the passage formation member  35  is positioned on the upstream side of the smallest inner diameter portion  30   m  in the refrigerant flow. The nozzle passage  13   a  defined between an outer peripheral surface of the passage formation member  35  and an inner peripheral surface of a portion of the nozzle  32  for providing the pressure reducing space  30   b  is changed in the passage cross-sectional area in the same manner as that of the Laval nozzle as in the first embodiment. 
     In other words, a portion of the nozzle passage  13   a  which is formed on the refrigerant flow upstream side of the smallest inner diameter portion  30   m  where the passage cross-sectional area is most reduced is a convergent portion whose passage cross-sectional area is gradually reduced toward the downstream side in the refrigerant flow. A portion of the nozzle passage  13   a  which is formed on the refrigerant flow downstream side of the smallest inner diameter portion  30   m  becomes a divergent portion whose passage cross-sectional area gradually increases toward the downstream side in the refrigerant flow. 
     An upstream actuating bar  351   a  of a shaft  351  is integrally and coaxially coupled to a top side of the truncated conical portion disposed on the upstream side of the largest outer diameter portion  30   n  in the refrigerant flow. The upstream actuating bar  351   a  is coupled with a stepping motor  370 . The stepping motor  370  is a drive mechanism for displacing the passage formation member  35 . The operation of the stepping motor  370  is controlled according to a control signal (control pulse) output from a control device. 
     An outer diameter of the largest outer diameter portion  30   n  of the passage formation member  35  is set to be larger than an inner diameter of the smallest inner diameter portion  30   m  of the nozzle  32 . For that reason, when the stepping motor  370  displaces the passage formation member  35  to close the nozzle passage  13   a , the largest outer diameter portion  30   n  of the passage formation member  35  comes into contact with the nozzle  32 . 
     The passage cross-sectional area of a mixing passage  13   d  disposed on the downstream side of the nozzle passage  13   a  in the refrigerant flow is reduced toward the downstream side in the refrigerant flow. Furthermore, a smallest passage cross-sectional area of the mixing passage  13   d  is set to be smaller than a total of a passage cross-sectional area of the refrigerant ejection port  13   e  and a passage cross-sectional area of the suction refrigerant outlet  13   f.    
     In addition, although at least a part of the passage formation member  35  according to the present embodiment is disposed in the pressure reducing space  30   b , the passage formation member  35  is not disposed in the pressurizing space  30   e . Therefore, in the ejector  13  of the present embodiment, as shown in  FIG. 12 , the pressurizing space  30   e  is shaped such that the passage cross-sectional area is gradually reduced toward the downstream side in the refrigerant flow. The pressurizing space  30   e  functions as the diffuser passage  13   c.    
     The other configurations and operation of the ejector  13  and an ejector refrigeration cycle  10  are the same as those of the first embodiment. Therefore, the ejector  13  and the ejector refrigeration cycle  10  of the present embodiment can obtain the same advantages as those in the first embodiment. 
     Furthermore, according to the present embodiment, the passage formation member  35  is disposed in the pressure reducing space  30   b  without being disposed in the pressurizing space  30   e . This makes it possible to reduce a size of the passage formation member  35  in comparison with the case where the passage formation member  35  is disposed in both of the pressure reducing space  30   b  and the pressurizing space  30   e . As a result, the entire ejector  13  can be reduced in size and the configuration can be simplified. 
     In the ejector  13  of the present embodiment, although the downstream actuating bar  351   b  is eliminated, the upstream actuating bar  351   a  is integrally and coaxially coupled to the passage formation member  35 . Therefore, as in the first embodiment, the center axis CL of the passage formation member  35  can be prevented from being inclined with respect to the center axes of the pressure reducing space  30   b , the pressurizing space  30   e , and the like. 
     Furthermore, in the ejector  13  according to the present embodiment, the size of the passage formation member  35  can be reduced. As a result, since a load (that is, the action of a dynamic pressure) applied to the passage formation member  35  from the refrigerant is reduced, the center axis CL of the passage formation member  35  can be further prevented from being inclined. 
     Further, in the ejector of the present embodiment, the passage cross-sectional area of the mixing passage  13   d  is reduced toward the downstream side in the refrigerant flow. Therefore, as in the first embodiment, the pressure increase performance of the diffuser passage  13   c  is stabilized so that the ejector efficiency can be prevented from becoming unstable, and also the mixing loss occurring when the jet refrigerant and the suction refrigerant are mixed together can be reduced. 
     More specifically, even if the passage formation member  35  and so on are not present, a compression wave that is reflected by a velocity boundary layer and travels toward the center axis CL side collides with a compression wave traveling from an opposite side on a center axis of the mixing passage  13   d  (so-called sliding surface), reflects, and turns to the outer peripheral side. Therefore, even if the passage formation member  35  is not disposed in the mixing passage  13   d , the same advantages as those in the first embodiment can be obtained. 
     In the present embodiment, the largest outer diameter portion  30   n  serving as the most upstream throat portion is formed in the passage formation member  35 . Therefore, the boiling nucleus can be supplied from the center axis CL side to the liquid-phase refrigerant flowing through the nozzle passage  13   a . Further, the smallest inner diameter portion  30   m  serving as the downstream throat portion is formed in the nozzle  32 . Therefore, the smallest inner diameter portion  30   m  can also supply the boiling nucleus from the outer peripheral side to the liquid-phase refrigerant flowing through the nozzle passage  13   a.    
     As a result, even if no gas column or the like is generated in the refrigerant in the inflow space  30   a , the boiling of the refrigerant flowing through the nozzle passage  13   a  can be promoted, and the ejector efficiency can be improved. 
     Other Embodiments 
     The present disclosure is not limited to the above-described embodiments, but various modifications can be made thereto as follows without departing from the spirit of the present disclosure. 
     (1) In each of the embodiments described above, the example in which the center axis CL of the passage formation member  35  of the ejector  13  is disposed in the horizontal direction has been described, but the placement of the ejector  13  is not limited to the above example. For example, as shown in the overall configuration diagram of  FIG. 13 , the center axis of the passage formation member  35  may be disposed in the vertical direction. In this case, it is desirable that the liquid-phase refrigerant outflow port  31   c  is disposed on the lowermost side of the gas-liquid separation body. 
     (2) The ejector  13  is not limited to that disclosed in the embodiments described above. 
     For example, in the embodiments described above, the example in which the annular members  35   a  and  35   b  are made of the resin of the material of the passage formation member  35  for the sake of weight saving has been described. It is needless to say that the annular members  35   a  and  35   b  may be made of a metal shaft  351  and formed integrally with the shaft  351  (in more detail, the upstream actuating bar  351   a ). 
     In addition, in the embodiments described above, the example in which the upstream actuating bar  351   a  and the downstream actuating bar  351   b  are formed by the shaft  351  that is a common columnar member has been described. Alternatively, the upstream actuating bar  351   a  and the downstream actuating bar  351   b  may be formed as separate members. 
     Further, in the embodiments described above, one downstream actuating bar  351   b  is provided similarly to the upstream actuating bar  351   a . Alternatively, multiple downstream actuating bars  351   b  may be provided. The outer diameter of the upstream actuating bar  351   a  and the outer diameter of the downstream actuating bar  351   b  may be set to the same value or may be set to different values. 
     In order to reduce abrasion of a bearing hole of the upper body  311  and a bearing hole of the lower body  312  in the ejector  13 , a bearing member made of a cylindrical metal may be disposed in each bearing hole. 
     In the embodiments described above, the example in which the plate member  374  of the drive mechanism  37  is coupled to the upstream actuating bar  351   a  has been described. Alternatively, the drive mechanism may be coupled to the downstream actuating bar  351   b.    
     In the embodiments described above, the drive mechanism  37  displaces the passage formation member  35  according to the temperature and pressure of the refrigerant on the outlet side of the evaporator  14 , to thereby adjust the passage cross-sectional area of the nozzle passage  13   a  so that the degree of superheat SH of the refrigerant on the outlet side of the evaporator  14  comes closer to the reference degree of superheat KSH. However, the adjustment of the passage cross-sectional area by the drive mechanism  37  is not limited to the above example. 
     For example, the passage formation member  35  may be displaced according to the temperature and pressure of the refrigerant on the outlet side of the radiator  12 , to thereby adjust the passage cross-sectional area of the nozzle passage  13   a  so that the degree of subcooling of the refrigerant on the outlet side of the radiator  12  comes closer to a predetermined reference degree of subcooling. 
     Further, the drive mechanism  37  is not limited to that described in the embodiments described above. For example, as a temperature sensitive medium adopted in the drive mechanism according to the first to seventh embodiments, a thermowax whose volume varies depending on the temperature may be adopted. Further, as the drive mechanism, a drive mechanism having an elastic member of a shape memory alloy property may be adopted. 
     Further, in the fifth embodiment, the example in which the electrically operating stepping motor  370  is adopted as the drive mechanism has been described. Needless to say, as the drive mechanism of the ejector  13  described in the fifth embodiment, the drive mechanism  37  configured by the mechanical mechanism described in the first to fourth embodiments may be employed. 
     (3) The respective configuration equipment configuring the ejector refrigeration cycle  10  are not limited to those disclosed in the embodiments described above. 
     For example, in the embodiments described above, as the compressor  11 , an engine driven type variable capacity type compressor has been employed. Alternatively, as the compressor  11 , a fixed capacity type compressor that adjusts the refrigerant discharge capacity while changing an operation rate of the compressor through connection and disconnection of an electromagnetic clutch can be employed. Furthermore, an electric compressor equipped with a fixed capacity type compression mechanism and an electric motor and operated by receiving an electric power may be employed. In the electric compressor, the refrigerant discharge capacity can be controlled by adjusting the rotational speed of the electric motor. 
     In addition, in the above-described embodiments, examples in which a subcooling heat exchanger is employed as the radiator  12  have been described, but, it is needless to say that a normal radiator formed of only the condensing portion  12   a  may be employed as the radiator  12 . Furthermore, with a usual radiator, a receiver integrated type condenser may be adopted which is integrated with a liquid receiver (receiver) that separates a gas-liquid of a refrigerant that has been thermally radiated by a normal radiator and stores an excess liquid-phase refrigerant, together with the radiator. 
     In addition, in the embodiments described above, the example in which R1234y is adopted as the refrigerant has been described. However, the refrigerant is not limited to the above example. For example, R134a, R600a, R410A, R404A, R32, R407C, or the like may be adopted as the refrigerant. Alternatively, a mixture refrigerant in which plural types of those refrigerants are mixed together or the like may be adopted. Furthermore, carbon dioxide may be adopted as the refrigerant to configure a supercritical refrigeration cycle in which the high-pressure side refrigerant pressure is equal to or higher than the critical pressure of the refrigerant. 
     (4) In the embodiments described above, the example in which the ejector refrigeration cycle  10  according to the present disclosure is applied to the vehicle air conditioner has been described, but the application of the ejector refrigeration cycle  10  is not limited to the above configuration. For example, the ejector refrigeration cycle  10  may be applied to a stationary air conditioner, a cold storage warehouse, a vending machine for cooling heating device, and the like. 
     In the embodiments described above, the radiator  12  of the ejector refrigeration cycle  10  having the ejector  13  according to the present disclosure is used as a vehicle exterior heat exchanger by which heat exchange between the refrigerant and an outside air is performed, and the evaporator  14  is used as a usage side heat exchanger which cools a blown air. On the other hand, the evaporator  14  may be used as a vehicle exterior heat exchanger for absorbing a heat from a heat source such as outside air, and the radiator  12  may be used as a usage side heat exchanger for heating a heating target fluid such as air or water. 
     (5) In addition, the elements disclosed in the respective embodiments may be appropriately combined together in an implementable range. For example, the passage formation member  35  of the third embodiment may be applied to the second and fourth embodiments. Further, the recess portion (through hole  352 ) described in the fourth embodiment may be defined in the passage formation member  35  of the second and fifth embodiments. 
     While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. To the contrary, the present disclosure is intended to cover various modification and equivalent arrangements. In addition, while the various elements are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.