Patent Publication Number: US-2023159810-A1

Title: Use of composition as refrigerant in compressor, compressor, and refrigeration cycle apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of PCT International Application No. PCT/JP2021/025498, filed on Jul. 6, 2021, which claims priority under 35 U.S.C. 119(a) to Patent Application No. JP 2020-121383, filed in Japan on Jul. 15, 2020, all of which are hereby expressly incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the use of a composition as a refrigerant in a compressor, the compressor, and a refrigeration cycle apparatus. 
     BACKGROUND ART 
     Conventionally, hydrofluoroolefins (HFO refrigerants) having lower global warming potential (hereinafter also simply referred to as GWP) than HFC refrigerants have attracted attention for refrigeration apparatuses. For example, 1,2-difluoroethylene (HFO-1132) is considered as a refrigerant with low GWP in Patent Literature 1 (Japanese Patent Laid-Open No. 2019-196312). 
     SUMMARY 
     The use of a composition as a refrigerant in a compressor according to a first aspect is the use of a composition as a refrigerant in a compressor in which the dimension of a gap of a predetermined portion in the compressor is less than or equal to 2 mm. The predetermined portion is a portion through which the refrigerant flows around an ignition energy generation portion in the compressor. The composition includes one or more compounds selected from the group consisting of ethylene-based fluoroolefins, 2,3,3,3-tetrafluoropropene (HFO-1234yf), and 1,3,3,3-tetrafluoropropene (HFO-1234ze). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic configuration diagram of a refrigeration cycle apparatus. 
         FIG.  2    is a block configuration diagram of the refrigeration cycle apparatus. 
         FIG.  3    is a side cross-sectional view illustrating a schematic configuration of a compressor. 
         FIG.  4    is a plan cross-sectional view illustrating a region around a cylinder chamber of the compressor. 
         FIG.  5    is a schematic cross-sectional view illustrating the details of a region around adjacent portions of coils. 
         FIG.  6    is a schematic cross-sectional view illustrating the details of a region around a portion where a bearing portion and a crankshaft are adjacent to each other. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a compressor, a refrigeration cycle apparatus, and the use of a composition as a refrigerant in such a compressor or an apparatus will be specifically described with reference to examples. However, the following description is not intended to limit the present disclosure. 
     (1) Refrigeration Cycle Apparatus  1   
     A refrigeration cycle apparatus  1  is an apparatus for performing vapor-compression refrigeration cycles to process a heat load of a target space. For example, the refrigeration cycle apparatus  1  is an air-conditioning apparatus for conditioning air in a target space. 
       FIG.  1    is a schematic configuration diagram of the refrigeration cycle apparatus.  FIG.  2    is a block configuration diagram of the refrigeration cycle apparatus. 
     The refrigeration cycle apparatus  1  mainly includes an outdoor unit  20 ; an indoor unit  30 ; a liquid-side refrigerant communication pipe  6  and a gas-side refrigerant communication pipe  5  each connecting the outdoor unit  20  and the indoor unit  30 ; a remote controller (not illustrated); and a controller  7  that controls the operation of the refrigeration cycle apparatus  1 . 
     In the refrigeration cycle apparatus  1 , refrigeration cycles are performed such that a refrigerant enclosed in a refrigerant circuit  10  is compressed, and is then cooled or condensed, and is then decompressed, and is then heated or evaporated, and is then compressed again. In the present embodiment, the refrigerant circuit  10  is filled with a refrigerant for performing vapor-compression refrigeration cycles. 
     (2) Refrigerant 
     Examples of the refrigerant filling the refrigerant circuit  10  include one or more compounds selected from the group consisting of ethylene-based fluoroolefins, 2,3,3,3-tetrafluoropropene (HFO-1234yf), and 1,3,3,3-tetrafluoropropene (HFO-1234ze). Note that regarding the burning velocity defined by the ISO 817, 1,3,3,3-tetrafluoropropene (HFO-1234ze) with a burning velocity of 1.2 cm/s is more preferable than 2,3,3,3-tetrafluoropropene (HFO-1234yf) with a burning velocity of 1.5 cm/s. Regarding the LFL (Lower Flammability Limit) defined by the ISO 817, 1,3,3,3-tetrafluoropropene (HFO-1234ze) with a LFL of 65000 vol.ppm or 6.5% is more preferable than 2,3,3,3-tetrafluoropropene (HFO-1234yf) with a LFL of 62000 vol.ppm or 6.2%. In particular, the refrigerant may include one or more compounds selected from the group consisting of 1,2-difluoroethylene (HFO-1132), 1,1-difluoroethylene (HFO-1132a), 1,1,2-trifluoroethylene (HFO-1123), monofluoroethylene (HFO-1141), and perhaloolefins. Above all, the refrigerant, including 1,2-difluoroethylene (HFO-1132) and/or 1,1,2-trifluoroethylene (HFO-1123), is preferable. 
     Herein, examples of ethylene-based fluoroolefins include 1,2-difluoroethylene (HFO-1132), 1,1-difluoroethylene (HFO-1132a), 1,1,2-trifluoroethylene (HFO-1123), monofluoroethylene (HFO-1141), and perhaloolefins. Examples of perhaloolefins include chlorotrifluoroethylene (CFO-1113) and tetrafluoroethylene (FO-1114). 
     Note that the refrigerant circuit  10  is also filled with refrigerator oil together with the aforementioned refrigerant. 
     (3) Outdoor Unit  20   
     The outdoor unit  20  is connected to the indoor unit  30  via the liquid-side refrigerant communication pipe  6  and the gas-side refrigerant communication pipe  5 , and consists part of the refrigerant circuit  10 . The outdoor unit  20  mainly includes a compressor  21 , a four-way switching valve  22 , an outdoor heat exchanger  23 , an outdoor expansion valve  24 , an outdoor fan  25 , a receiver  41 , a gas-side shut-off valve  28 , and a liquid-side shut-off valve  29 . 
     The compressor  21  is a device that compresses a low-pressure refrigerant in a refrigeration cycle up to a high pressure. Herein, the compressor  21  may be a hermetic compressor in which a rotary-type or scroll-type positive-displacement compression element is rotationally driven by a compressor motor. In the present embodiment, a rotary compressor is used. The compressor motor is used to change the volume, and its operating frequency can be controlled with an inverter. 
     The four-way switching valve  22  switches a flow channel of the refrigerant circuit  10 . Specifically, the four-way switching valve  22  can switch between a state in which the discharge side of the compressor  21  and the outdoor heat exchanger  23  are connected and the suction side of the compressor  21  and the gas-side shut-off valve  28  are connected and a state in which the discharge side of the compressor  21  and the gas-side shut-off valve  28  are connected and the suction side of the compressor  21  and the outdoor heat exchanger  23  are connected. 
     The outdoor heat exchanger  23  is a heat exchanger that functions as a radiator or a condenser for a high-pressure refrigerant in a refrigeration cycle during the cooling operation, and functions as an evaporator for a low-pressure refrigerant in a refrigeration cycle during the heating operation. 
     The outdoor expansion valve  24  is provided between the liquid-side outlet of the outdoor heat exchanger  23  and the liquid-side shut-off valve  29  in the refrigerant circuit  10 . The outdoor expansion valve  24  is a motor-operated expansion valve with an adjustable opening degree. 
     The outdoor fan  25  produces an air flow for causing outdoor air to be sucked into the outdoor unit  20 , and causing the sucked air to exchange heat with a refrigerant in the outdoor heat exchanger  23 , and then causing the air to be discharged to the outside. The outdoor fan  25  is rotationally driven by an outdoor fan motor. 
     The receiver  41  is a refrigerant container that is provided between the suction side of the compressor  21  and one of connection ports of the four-way switching valve  22 , and that can store an excess refrigerant in the refrigerant circuit  10  as a liquid refrigerant. 
     The liquid-side shut-off valve  29  is a manual valve disposed at a portion of the outdoor unit  20  connected to the liquid-side refrigerant communication pipe  6 . 
     The gas-side shut-off valve  28  is a manual valve disposed at a portion of the outdoor unit  20  connected to the gas-side refrigerant communication pipe  5 . 
     The outdoor unit  20  includes an outdoor unit controller  27  that controls the operation of each portion forming the outdoor unit  20 . The outdoor unit controller  27  has a microcomputer including a CPU and a memory, for example. The outdoor unit controller  27  is connected to an indoor unit controller  34  of each indoor unit  30  via a communication line, and transmits and receives control signals, for example. 
     The outdoor unit  20  is provided with a discharge pressure sensor  61 , a discharge temperature sensor  62 , a suction pressure sensor  63 , a suction temperature sensor  64 , an outdoor heat exchange temperature sensor  65 , and an outdoor air temperature sensor  66 , for example. Each of such sensors is electrically connected to the outdoor unit controller  27 , and transmits a detection signal to the outdoor unit controller  27 . The discharge pressure sensor  61  detects the pressure of a refrigerant flowing through a discharge pipe that connects the discharge side of the compressor  21  and one of the connection ports of the four-way switching valve  22 . The discharge temperature sensor  62  detects the temperature of the refrigerant flowing through the discharge pipe. The suction pressure sensor  63  detects the pressure of a refrigerant flowing through a suction pipe that connects the suction side of the compressor  21  and the receiver  41 . The suction temperature sensor  64  detects the temperature of the refrigerant flowing through the suction pipe. The outdoor heat exchange temperature sensor  65  detects the temperature of a refrigerant flowing through the liquid-side outlet of the outdoor heat exchanger  23  on the side opposite to the side connecting to the four-way switching valve  22 . The outdoor air temperature sensor  66  detects the temperature of outdoor air before it passes through the outdoor heat exchanger  23 . 
     (4) Indoor Unit  30   
     The indoor unit  30  is disposed on an indoor wall surface or ceiling as a target space, for example. The indoor unit  30  is connected to the outdoor unit  20  via the liquid-side refrigerant communication pipe  6  and the gas-side refrigerant communication pipe  5 , and consists part of the refrigerant circuit  10 . 
     The indoor unit  30  includes an indoor heat exchanger  31  and an indoor fan  32 . 
     The indoor heat exchanger  31  is connected on its liquid side to the liquid-side refrigerant communication pipe  6 , and is connected on its gas side to the gas-side refrigerant communication pipe  5 . The indoor heat exchanger  31  is a heat exchanger that functions as an evaporator for a low-pressure refrigerant in a refrigeration cycle during the cooling operation, and functions as a condenser for a high-pressure refrigerant in a refrigeration cycle during the heating operation. 
     The indoor fan  32  produces an air flow for causing indoor air to be sucked into the indoor unit  30 , and causing the sucked air to exchange heat with a refrigerant in the indoor heat exchanger  31 , and then causing the air to be discharged to the outside. The indoor fan  32  is rotationally driven by an indoor fan motor. 
     The indoor unit  30  includes the indoor unit controller  34  that controls the operation of each unit forming the indoor unit  30 . The indoor unit controller  34  includes a microcomputer including a CPU and a memory, for example. The indoor unit controller  34  is connected to the outdoor unit controller  27  via the communication line, and transmits and receives control signals, for example. 
     The indoor unit  30  is provided with an indoor liquid-side heat exchange temperature sensor  71  and an indoor air temperature sensor  72 , for example. Each of such sensors is electrically connected to the indoor unit controller  34 , and transmits a detection signal to the indoor unit controller  34 . The indoor liquid-side heat exchange temperature sensor  71  detects the temperature of a refrigerant flowing through the liquid-refrigerant-side outlet of the indoor heat exchanger  31 . The indoor air temperature sensor  72  detects the temperature of indoor air before it passes through the indoor heat exchanger  31 . 
     (5) Controller  7   
     In the refrigeration cycle apparatus  1 , the outdoor unit controller  27  and the indoor unit controller  34  are connected via the communication line, thus consisting the controller  7  that controls the operation of the refrigeration cycle apparatus  1 . The controller  7  mainly includes a CPU (central processing unit) and a memory, such as ROM and RAM. Note that various processes and control performed by the controller  7  are implemented as the portions, which are included in the outdoor unit controller  27  and/or the indoor unit controller  34 , function in an integrated manner. 
     (6) Operation Modes 
     The refrigeration cycle apparatus  1  can execute at least a cooling operation mode and a heating operation mode. 
     The controller  7  determines for example, whether the instruction indicates the cooling operation mode or the heating operation mode, based on an instruction received from the remote controller or the like, and executes the mode. 
     In the cooling operation mode, the operating frequency of the compressor  21  is controlled to control the volume so that the evaporating temperature of the refrigerant in the refrigerant circuit  10  reaches a target evaporating temperature, for example. 
     The gaseous refrigerant discharged from the compressor  21  is condensed in the outdoor heat exchanger  23  via the four-way switching valve  22 . The refrigerant that has flowed through the outdoor heat exchanger  23  is decompressed while passing through the outdoor expansion valve  24 . 
     The refrigerant decompressed in the outdoor expansion valve  24  flows through the liquid-side refrigerant communication pipe  6  via the liquid-side shut-off valve  29 , and is then sent to the indoor unit  30 . After that, the refrigerant evaporates in the indoor heat exchanger  31 , and then flows into the gas-side refrigerant communication pipe  5 . The refrigerant that has flowed through the gas-side refrigerant communication pipe  5  is sucked into the compressor  21  again via the gas-side shut-off valve  28 , the four-way switching valve  22 , and the receiver  41 . 
     In the heating operation mode, the operating frequency of the compressor  21  is controlled to control the volume so that the condensation temperature of the refrigerant in the refrigerant circuit  10  reaches a target condensation temperature, for example. 
     The gaseous refrigerant discharged from the compressor  21  flows through the four-way switching valve  22  and the gas-side refrigerant communication pipe  5 , and then flows into the gas-side end of the indoor heat exchanger  31  of the indoor unit  30  so that the refrigerant is condensed or is allowed to radiate heat in the indoor heat exchanger  31 . The refrigerant, which has been condensed or has been allowed to radiate heat in the indoor heat exchanger  31 , flows through the liquid-side refrigerant communication pipe  6 , and then flows into the outdoor unit  20 . 
     The refrigerant that has passed through the liquid-side shut-off valve  29  of the outdoor unit  20  is decompressed in the outdoor expansion valve  24 . The refrigerant that has been decompressed in the outdoor expansion valve  24  evaporates in the outdoor heat exchanger  23 , and is sucked into the compressor  21  again via the four-way switching valve  22  and the receiver  41 . 
     (7) Detailed Configuration of Compressor  21   
     The compressor  21  of the present embodiment is a one-cylinder rotary compressor as illustrated in  FIG.  3   , and is a rotary compressor including a casing  81  as well as a drive mechanism  82  and a compression mechanism  88  disposed in the casing  81 . In the compressor  21 , the compression mechanism  88  is disposed below the drive mechanism  82  in the casing  81 . 
     (7-1) Drive Mechanism 
     The drive mechanism  82  is housed in the upper part of the internal space of the casing  81 , and drives the compression mechanism  88 . The drive mechanism  82  includes a motor  83  as a drive source, and a crankshaft  84  as a drive shaft attached to the motor  83 . 
     The motor  83  is a motor for rotationally driving the crankshaft  84 , and mainly includes a rotor  85  and a stator  86 . The rotor  85  has the crankshaft  84  fit-inserted in its internal space, and rotates together with the crankshaft  84 . The rotor  85  includes laminated electromagnetic steel plates and a magnet embedded in a rotor body. The stator  86  is disposed radially outward of the rotor  85  with a predetermined space from the rotor  85 . The stator  86  is disposed while being divided into a plurality of sections at predetermined intervals in the circumferential direction. That is, the stator  86  includes a plurality of sections provided in the circumferential direction each including laminated electromagnetic steel plates and a coil  86   a  wound around a stator body  86   c  having teeth  86   b . In the motor  83 , the rotor  85  is caused to rotate together with the crankshaft  84  with an electromagnetic force that is generated in the stator  86  as a current is passed through the coil  86   a.    
     Herein, the upper end of the casing  81  is provided with a terminal portion  98  for supplying power to the compressor  21  from outside. The coil  86   a  of the stator  86  is supplied with power via a cluster  96  as a connection member, which is connected to the terminal portion  98  from the inside of the casing  81 , and an electric wire  97  extending from the cluster  96 . 
     The terminal portion  98  includes, as terminal pins, a plurality of outer pins  98   a  extending to the outside of the casing  81 , and a plurality of inner pins  98   b  extending to the inside of the casing  81 . The cluster  96  has an approximately rectangular parallelepiped shape. The external profile of the cluster  96  is formed of resin. A face of the cluster  96  on the side of the terminal portion  98  is provided with portions for receiving the plurality of inner pins  98   b  of the terminal portion  98 . In a state where the cluster  96  is coupled to the plurality of inner pins  98   b  of the terminal portion  98 , a gap Z is produced between the face of the cluster  96  on the side of the terminal portion  98  and a root portion of the casing  81  from which the plurality of inner pins  98   b  extend. A refrigerant is present in the gap Z including a region around the plurality of inner pins  98   b  of the casing  81 . The dimension of the gap Z in the direction in which the plurality of inner pins  98   b  of the casing  81  extend is less than or equal to 2.0 mm. The dimension of the gap Z is preferably less than or equal to 1.5 mm, and more preferably less than or equal to 1.0 mm. Note that, in a region of the gap Z around the inner pins  98   b , the distance from the inner pins  98   b  in a direction perpendicular to the extension direction of the inner pins  98   b  is preferably greater than or equal to the dimension of the gap Z. In such a configuration, when the compressor  21  is supplied with power from outside while driven, a current flows through the plurality of outer pins  98   a  and the plurality of inner pins  98   b  of the terminal portion  98 ; the electric wire  97 ; and the coil  86   a.    
     Each coil  86   a  has a cylindrical cross-sectional shape with an identical diameter as illustrated in a cross-sectional view along the axial direction of  FIG.  5   . The plurality of coils  86   a  are gathered such that their outer surfaces are in contact with each other at a contact point P. As indicated by the dotted lines on the rims in  FIG.  5   , the two coils  86   a  that are in contact with each other at the contact point P have opposed faces S that are curved surfaces facing each other at a portion including the contact point P. Since the coils  86   a  each have a cylindrical cross-sectional shape, the two coils  86   a  that are in contact with each other have a gap X produced between their opposed faces S on opposite sides of the direction of the tangent to the contact point P in the cross-sectional view along the axial direction. The dimension of the gap X in the direction in which the centers of the two coils  86   a  are arranged is less than or equal to 2.0 mm. The dimension of the gap X is preferably less than or equal to 1.5 mm, and more preferably less than or equal to 1.0 mm. Specifically, it is preferable that the maximum dimension of the gap X in the direction in which the centers of the two coils  86   a  are arranged be less than or equal to 2.0 mm, the distance D between the centers of the two coils  86   a  arranged in contact with each other be less than or equal to 2.0 mm, and the diameter of each coil  86   a  be less than or equal to 2.0 mm. Note that the outer surface of each coil  86   a  preferably has an insulating film. 
     The crankshaft  84  is an approximately cylindrical member that is fit-inserted in the rotor  85 , and rotates about the rotation axis. As illustrated in  FIG.  4   , a crankpin  84   a , which is an eccentric portion of the crankshaft  84 , is inserted through a roller  89   a  (which is described below) of a piston  89  of the compression mechanism  88 , and fits in the roller  89   a  in a state where it can transmit torque from the rotor  85 . The crankshaft  84  rotates with the rotation of the rotor  85 , and eccentrically rotates the crankpin  84   a , thus causing the roller  89   a  of the piston  89  of the compression mechanism  88  to revolve. That is, the crankshaft  84  has a function of transmitting a drive force of the motor  83  to the compression mechanism  88 . 
     (7-2) Compression Mechanism 
     The compression mechanism  88  is housed in the lower part of the casing  81 . The compression mechanism  88  compresses a refrigerant sucked thereinto via a suction pipe  99 . The compression mechanism  88  is a rotary compression mechanism, and mainly includes a front head  91 , a cylinder  92 , the piston  89 , and a rear head  93 . A refrigerant compressed in a compression chamber S 1  of the compression mechanism  88  is discharged to a space in which the motor  83  is disposed and the lower end of a discharge pipe  95  is located from a front-head discharge hole  91   c  formed in the front head  91  via a muffler space S 2  surrounded by the front head  91  and a muffler  94 . 
     (7-2-1) Cylinder 
     The cylinder  92  is a metal cast member. The cylinder  92  includes a cylindrical central portion  92   a , a first extension portion  92   b  extending radially outward from the central portion  92   a  to one side, and a second extension portion  92   c  extending from the central portion  92   a  to a side opposite to the first extension portion  92   b . The first extension portion  92   b  has formed therein a suction hole  92   e  for sucking a low-pressure refrigerant in a refrigeration cycle. A cylindrical space on the inner side of an inner peripheral face  92   a   1  of the central portion  92   a  corresponds to a cylinder chamber  92   d  into which a refrigerant sucked through the suction hole  92   e  flows. The suction hole  92   e  extends from the cylinder chamber  92   d  to an outer peripheral face of the first extension portion  92   b , and is open at the outer peripheral face of the first extension portion  92   b . The suction hole  92   e  has inserted therein the tip end portion of the suction pipe  99 . In addition, the cylinder chamber  92   d  houses the piston  89  for compressing a refrigerant that has flowed into the cylinder chamber  92   d , for example. 
     The cylinder chamber  92   d , which is formed by the cylindrical central portion  92   a  of the cylinder  92 , has at its lower end a first end that is open, and has at its upper end a second end that is open. The first end that is the lower end of the central portion  92   a  is closed by the rear head  93  described below. The second end that is the upper end of the central portion  92   a  is closed by the front head  91  described below. 
     The cylinder  92  has formed therein a blade oscillation space  92   f  in which a bushing  89   c  and a blade  89   b  described below are disposed. The blade oscillation space  92   f  is formed across a region from the central portion  92   a  to the first extension portion  92   b , and the blade  89   b  of the piston  89  is oscillatably supported on the cylinder  92  via the bushing  89   c . The blade oscillation space  92   f  is formed to extend toward the outer periphery side from the cylinder chamber  92   d  around the suction hole  92   e  as seen in plan view. 
     (7-2-2) Front Head 
     As illustrated in  FIG.  3   , the front head  91  includes a front-head disc portion  91   b  that closes the opening at the second end, which is the upper end, of the cylinder  92 , and an upper bearing portion  91   a  extending upward from the peripheral edge of the front-head opening in the center of the front-head disc portion  91   b . The upper bearing portion  91   a  is cylindrical and functions as a bearing for the crankshaft  84 . 
     The inner peripheral face of the upper bearing portion  91   a  and the outer peripheral face of the crankshaft  84  have a slight gap formed therebetween so as to allow the crankshaft  84  to rotate as illustrated in a side cross-sectional view of  FIG.  6   . The gap has lubricity as refrigerator oil is present in the gap. Herein, a portion around the upper end of the inner peripheral face of the upper bearing portion  91   a  has formed thereon a curved surface R 1  that expands radially outward more at positions closer to the upper end and is gently curved so as to protrude upward and inward as illustrated in  FIG.  6   . In this manner, providing the curved surface R 1  can suppress the concentrated generation of frictional heat at the upper end of the inner peripheral face of the upper bearing portion  91   a  while the crankshaft  84  is rotating. In addition, as the curved surface R 1  is provided around the upper end of the inner peripheral face of the upper bearing portion  91   a  in this manner, a gap Y 1  is produced between the curved surface R 1  and the outer peripheral face of the crankshaft  84  in the radial direction of the crankshaft  84 . The dimension of the gap Y 1  in the radial dimension of the crankshaft  84  from the outer peripheral face of the crankshaft  84  is designed to be less than or equal to 2.0 mm at maximum. The dimension of the gap Y 1  is preferably less than or equal to 1.5 mm, and is more preferably less than or equal to 1.0 mm. Note that the dimension of the curved surface R 1  in the longitudinal direction of the crankshaft  84  is preferably greater than or equal to the dimension of the gap Y 1 , for example. 
     The front-head disc portion  91   b  has formed therein the front-head discharge hole  91   c  at a plane position illustrated in  FIG.  4   . A refrigerant, which has been compressed in the compression chamber S 1  having a variable volume in the cylinder chamber  92   d  of the cylinder  92 , is intermittently discharged through the front-head discharge hole  91   c . The front-head disc portion  91   b  is provided with a discharge valve that opens or closes the outlet of the front-head discharge hole  91   c . When pressure in the compression chamber S 1  has become higher than pressure in the muffler space S 2 , the discharge valve is opened due to the pressure difference, thereby causing the refrigerant to be discharged to the muffler space S 2  through the front-head discharge hole  91   c.    
     (7-2-3) Muffler 
     As illustrated in  FIG.  3   , the muffler  94  is attached to the top face of the peripheral edge portion of the front-head disc portion  91   b  of the front head  91 . The muffler  94  forms the muffler space S 2  together with the top face of the front-head disc portion  91   b  and the outer peripheral face of the upper bearing portion  91   a , and attempts to reduce noise generated along with the discharge of a refrigerant. The muffler space S 2  and the compression chamber Si communicate with each other via the front-head discharge hole  91   c  when the discharge valve is open as described above. 
     The muffler  94  has formed therein a central muffler opening (not illustrated) for passing the upper bearing portion  91   a , and a muffler discharge hole (not illustrated) through which a refrigerant is flowed from the muffler space S 2  to a housing space for the motor  83  above the muffler space S 2 . 
     Note that the muffler space S 2 , the housing space for the motor  83 , the space where the discharge pipe  95  is located above the motor  83 , and a space where lubricating oil accumulates below the compression mechanism  88 , for example, are all continuous, and form a high-pressure space with equal pressure. 
     (7-2-4) Rear Head 
     The rear head  93  includes a rear-head disc portion  93   b  that closes the opening at the first end, which is the lower end, of the cylinder  92 , and a lower bearing portion  93   a  as a bearing extending downward from the peripheral edge portion of the opening in the center of the rear-head disc portion  93   b . The front-head disc portion  91   b , the rear-head disc portion  93   b , and the central portion  92   a  of the cylinder  92  form the cylinder chamber  92   d  as illustrated in  FIG.  4   . The lower bearing portion  93   a  axially supports the crankshaft  84  together with the aforementioned upper bearing portion  91   a.    
     The inner peripheral face of the lower bearing portion  93   a  and the outer peripheral face of the crankshaft  84  have a slight gap formed therebetween so as to allow the crankshaft  84  to rotate as illustrated in the side cross-sectional view of  FIG.  6   . The gap has lubricity as refrigerator oil is present in the gap. Herein, a portion around the lower end of the inner peripheral face of the lower bearing portion  93   a  has formed thereon a curved surface R 2  that expands radially outward more at positions closer to the lower end and is gently curved so as to protrude downward and inward as illustrated in  FIG.  6   . In this manner, providing the curved surface R 2  can suppress the concentrated generation of frictional heat at the lower end of the inner peripheral face of the lower bearing portion  93   a  while the crankshaft  84  is rotating. In addition, as the curved surface R 2  is provided around the lower end of the inner peripheral face of the lower bearing portion  93   a  in this manner, a gap Y 2  is produced between the curved surface R 2  and the outer peripheral face of the crankshaft  84  in the radial direction of the crankshaft  84 . The dimension of the gap Y 2  in the radial dimension of the crankshaft  84  from the outer peripheral face of the crankshaft  84  is designed to be less than or equal to 2.0 mm at maximum. The dimension of the gap Y 2  is preferably less than or equal to 1.5 mm, and is more preferably less than or equal to 1.0 mm. Note that the dimension of the curved surface R 2  in the longitudinal direction of the crankshaft  84  is preferably greater than or equal to the dimension of the gap Y 2 , for example. 
     (7-2-5) Piston 
     The piston  89  is disposed in the cylinder chamber  92   d , and is attached to the crankpin  84   a  that is the eccentric portion of the crankshaft  84 . The piston  89  is a member integrating the roller  89   a  and the blade  89   b . The blade  89   b  of the piston  89  is disposed in the blade oscillation space  92   f  formed in the cylinder  92 , and is oscillatably supported on the cylinder  92  via the bushing  89   c  as described above. The blade  89   b  is slidable on the bushing  89   c , and oscillates and also repeatedly moves away from the crankshaft  84  and closer to the crankshaft  84  during operation. 
     As illustrated in  FIG.  4   , the roller  89   a  and the blade  89   b  of the piston  89  form the compression chamber S 1 , which has a volume variable with the revolution of the piston  89 , such that the roller  89   a  and the blade  89   b  of the piston  89  partition the cylinder chamber  92   d.    
     The compression chamber S 1  is a space surrounded by the inner peripheral face  92   a   1  of the central portion  92   a  of the cylinder  92 , the top face of the rear-head disc portion  93   b , the bottom face of the front-head disc portion  91   b , and the piston  89 . The volume of the compression chamber S 1  changes with the revolution of the piston  89  so that a low-pressure refrigerant sucked thereinto through the suction hole  92   e  is compressed to become a high-pressure refrigerant, and is then discharged to the muffler space S 2  through the front-head discharge hole  91   c.    
     (7-3) Operation 
     In the foregoing compressor  21 , the volume of the compression chamber S 1  changes with the movement of the piston  89  of the compression mechanism  88  that revolves with the eccentric rotation of the crankpin  84   a . Specifically, first, while the piston  89  starts revolving, a low-pressure refrigerant is sucked into the compression chamber S 1  through the suction hole  92   e . The volume of the compression chamber S 1  facing the suction hole  92   e  gradually increases while it sucks the refrigerant. When the piston  89  further revolves, the communication state between the compression chamber S 1  and the suction hole  92   e  is canceled so that the refrigerant starts to be compressed in the compression chamber S 1 . After that, the volume of the compression chamber S 1  that communicates with the front-head discharge hole  91   c  becomes significantly small, and the pressure of the refrigerant therein increases. After that, as the piston  89  further revolves, the refrigerant with the increased pressure pushes and opens the discharge valve through the front-head discharge hole  91   c , and thus is discharged to the muffler space S 2 . The refrigerant introduced into the muffler space S 2  is discharged to a space above the muffler space S 2  through the muffler discharge hole of the muffler  94 . The refrigerant discharged to the outside of the muffler space S 2  passes through a space between the rotor  85  and the stator  86  of the motor  83  to cool the motor  83 , and is then discharged from the discharge pipe  95 . 
     (8) Feature of Embodiment 
     In the refrigeration cycle apparatus  1  of the present embodiment, a refrigerant that may undergo a disproportionation reaction is used. Such a disproportionation reaction of the refrigerant occurs with a certain probability under an environment where predetermined high-temperature conditions, high-pressure conditions, and ignition energy conditions are satisfied. Then, the disproportionation reaction may propagate to surrounding regions from the portion where the disproportionation reaction has occurred. 
     In response, the inventors conducted a test of causing ignition by filling a pressure-resistant container with 1,2-difluoroethylene (HFO-1132) as a refrigerant, setting the refrigerant pressure in the pressure-resistant container to 1.0 MPa and the refrigerant temperature therein to 150° C., connecting two copper plates with a platinum wire in the pressure-resistant container, and applying a voltage across the plates to pass a current through the platinum wire. During the test, changes in the propagation of a disproportionation reaction were observed while changing the dimension of the gap between the plates. The test results demonstrate that the propagation of a disproportionation reaction occurs when the dimension of the gap between the plates is greater than or equal to 5.0 mm. The test results also demonstrate that the propagation of a disproportionation reaction does not occur when the dimension of the gap between the plates is less than or equal to 2.0 mm, and thus that the propagation of the disproportionation reaction is suppressed. 
     The compressor  21  for which the refrigerant of the present embodiment is used, and the refrigeration cycle apparatus  1  including such a compressor  21  are configured such that the dimension of the gap X between the coils  86   a  is less than or equal to 2.0 mm. Accordingly, even when a disproportionation reaction has occurred due to ignition energy generated as electric energy between the adjacent coils  86   a  during the operation of the compressor  21 , the propagation of the disproportionation reaction to portions other than the coils  86   a  can be suppressed. In particular, in an operating state where the pressure of a refrigerant flowing through the discharge pipe  95  of the compressor  21  is greater than or equal to 1 MPa, the amount of current flowing through the coils  86   a  is large, which is likely to cause generation and propagation of a disproportionation reaction. However, the propagation of the disproportionation reaction can be suppressed even under such an operation condition. Note that even when the outer surface of each coil  86   a  is covered with an insulating film, ignition energy can be generated due to a current flow therethrough if the insulating film has a production defect or if the insulating film has peeled off due to friction between the adjacent coils  86   a . However, the propagation of the disproportionation reaction is suppressed even in such a case. 
     In addition, the compressor  21  for which the refrigerant of the present embodiment is used, and the refrigeration cycle apparatus  1  including such a compressor  21  are configured such that the dimension of the gap Y 1  between the crankshaft  84  and the curved surface R 1  around the upper end of the upper bearing portion  91   a  is less than or equal to 2.0 mm. Accordingly, even when a disproportionation reaction has occurred due to ignition energy generated with frictional heat generated on the sliding surface between the crankshaft  84  and the upper bearing portion  91   a  during the operation of the compressor  21 , the propagation of the disproportionation reaction to a region around the upper portion of the upper bearing portion  91   a  can be suppressed. This is also true of the gap Y 2  between the crankshaft  84  and the curved surface R 2  around the lower end of the lower bearing portion  93   a . Specifically, even when a disproportionation reaction has occurred due to ignition energy generated with frictional heat generated on the sliding surface between the crankshaft  84  and the lower bearing portion  93   a  during the operation of the compressor  21 , the propagation of the disproportionation reaction to a region around the lower portion of the lower bearing portion  93   a  can be suppressed. In particular, in an operating state where the pressure of a refrigerant flowing through the discharge pipe  95  of the compressor  21  is greater than or equal to 1 MPa, the number of revolutions of the crankshaft  84  is large, which is likely to cause generation and propagation of a disproportionation reaction. However, the propagation of the disproportionation reaction can be suppressed even under such an operation condition. 
     Further, the compressor  21  for which the refrigerant of the present embodiment is used, and the refrigeration cycle apparatus  1  including such a compressor  21  are configured such that the dimension of the gap Z between the terminal portion  98  and the cluster  96  is less than or equal to 2.0 mm. Accordingly, even when a disproportionation reaction has occurred due to ignition energy generated as electric energy from the inner pins  98   b  of the terminal portion  98  or from the connection portion between the inner pins  98   b  and the cluster  96 , for example, during the operation of the compressor  21 , the propagation of the disproportionation reaction to a region around the portion between the terminal portion  98  and the cluster  96  can be suppressed. In particular, in an operating state where the pressure of a refrigerant flowing through the discharge pipe  95  of the compressor  21  is greater than or equal to 1 MPa, the amount of power supplied to the terminal portion  98  is large, which is likely to cause generation and propagation of a disproportionation reaction. However, the propagation of the disproportionation reaction can be suppressed even under such an operation condition. 
     (9) Other Embodiments 
     (9-1) Another Embodiment A 
     The foregoing embodiment has exemplarily illustrated a case where the propagation of a disproportionation reaction that has occurred in the gap X, the gap Y 1 , the gap Y 2 , or the gap Z in the compressor  21  is suppressed. 
     In contrast, a portion where a disproportionation reaction may occur in the compressor  21  is not limited thereto, and a disproportionation reaction can occur in any portion in the compressor  21  where predetermined high-temperature conditions, high-pressure conditions, and ignition energy conditions are satisfied during the operation of the compressor  21 . Therefore, it is possible to, by setting the dimension of a gap of a portion through which a refrigerant flows around the portion where a disproportionation reaction can occur other than the aforementioned gap X, gap Y 1 , gap Y 2 , and gap Z to less than or equal to 2.0 mm, suppress the propagation of the disproportionation reaction from that portion. 
     (9-2) Another Embodiment B 
     The foregoing embodiment has exemplarily illustrated a case where the curved surface R 1  is formed around the upper end of the inner peripheral face of the upper bearing portion  91   a , and the curved surface R 2  is formed around the lower end of the inner peripheral face of the lower bearing portion  93   a.    
     In contrast, the specific shapes of the portion around the upper end of the inner peripheral face of the upper bearing portion  91   a  and the portion around the lower end of the inner peripheral face of the lower bearing portion  93   a  are not limited thereto. For example, the portion around the upper end of the inner peripheral face of the upper bearing portion  91   a  may have a structure obtained by chamfering the portion around the upper end of the inner peripheral face of the upper bearing portion  91   a  by forming an inclined surface that is inclined so as to be located radially outward of the crankshaft  84  more at positions closer to the upper end. Similarly, the portion around the lower end of the inner peripheral face of the lower bearing portion  93   a  may have a structure obtained by chamfering the portion around the lower end of the inner peripheral face of the lower bearing portion  93   a  by forming an inclined surface that is inclined so as to be located radially outward of the crankshaft  84  more at positions closer to the lower end. 
     (9-3) Another Embodiment C 
     The foregoing embodiment has exemplarily illustrated a case where a rotary compressor is used as the compressor  21 . 
     In contrast, the compressor for suppressing the propagation of a disproportionation reaction by having a small gap of a predetermined portion through which a refrigerant flows around the ignition energy generation portion is not limited to a rotary compressor, and may be a known scroll compressor or swing compressor. 
     Others 
     Note that the dimension of the gap is more preferably less than or equal to 1 mm from the perspective of more efficiently suppressing the propagation of a disproportionation reaction. 
     Note also that the ignition energy generation portion in the compressor is not limited. For example, when the compressor includes a teeth and a coil wound around the teeth, the ignition energy generation portion may include the coil in the compressor. The gap in such a case may be a gap between opposed faces of adjacent wires of the coil. 
     In addition, when the compressor includes a crankshaft and a bearing portion that rotatably supports the crankshaft, for example, the ignition energy generation portion may include a portion where the crankshaft and the bearing portion are in contact with each other. The gap in such a case may be a gap between the crankshaft and the bearing portion. 
     Further, when the compressor includes a terminal pin and a connection member connected to the terminal pin in the compressor, for example, the ignition energy generation portion may include a portion where the inner face of the terminal pin and the connection member are in contact with each other, or a gap between them. The gap in such a case may be a gap between the inner face of the terminal pin and a face of the connection member facing the inner face of the terminal pin. 
     Note that 1,2-difluoroethylene may be trans-1,2-difluoroethylene [(E)-HFO-1132], cis-1,2-difluoroethylene [(Z)-HFO-1132], or a mixture of them. 
     Supplement 
     Although the embodiments of the present disclosure have been described above, it is to be understood that various changes to the forms or details are possible without departing from the spirit or scope of the present disclosure recited in the claims. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Refrigeration cycle apparatus 
               10  Refrigerant circuit 
               21  Compressor 
               84  Crankshaft (ignition energy generation portion) 
               86   a  Coil (ignition energy generation portion) 
               91   a  Upper bearing portion (ignition energy generation portion) 
               93   a  Lower bearing portion (ignition energy generation portion) 
               95  Discharge pipe 
               96  Cluster (ignition energy generation portion) 
               97  Electric wire 
               98  Terminal portion (ignition energy generation portion) 
               98   b  Inner pins (ignition energy generation portion) 
             X Gap 
             Y 1 , Y 2  Gaps 
             Z Gap 
           
         
       
    
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Patent Laid-Open No. 2019-196312