Patent Publication Number: US-8985978-B2

Title: Scroll compressor with bypass holes

Description:
TECHNICAL FIELD 
     The present invention relates to a scroll compressor that can be incorporated into refrigerating cycles such as, for example, room-air conditioners, car-air conditioners, refrigerators or other air conditioners in which a refrigerant containing no chlorine atoms, having a small global warming potential, and mainly comprising hydrofluoroolefin having a carbon-carbon double bond is employed as a refrigerant. 
     BACKGROUND ART 
     Conventional refrigerating appliances generally employ an HFC (hydrofluorocarbon) refrigerant having a zero-ozone depletion potential as a refrigerant, but in recent years the use of the HFC refrigerant becomes a problem because it has a very large global warming potential. In view of this, a compressor for use with a refrigerant having a small ozone depletion potential and a small global warming potential has been developed. However, the refrigerant having a small global warming potential generally shows poor stability and has a problem in stability and reliability when used in refrigerating cycles such as, for example, room-air conditioners, car-air conditioners, refrigerators or other air conditioners, all of which are predicated on long-term use. 
     On the other hand, in the refrigerating cycle, the compressor acts to inhale a gas refrigerant vaporized in an evaporator and compress it to a predetermined pressure and, hence, in order to ensure the stability and reliability of the refrigerant, a state of which greatly varies from a low pressure to a high pressure and from a low temperature to a high temperature, sufficient measures must be taken for the compressor. 
     As shown in  FIG. 7 , a conventional scroll compressor has a plurality of compression chambers  103  defined between a stationary scroll  101  and an orbiting scroll  102 , and an inhaled refrigerant is compressed, utilizing the fact that the compression chambers  103  move while reducing a volume thereof. The refrigerant compressed to a predetermined pressure is discharged to a discharge chamber through a discharge port  104  defined in an end plate of the stationary scroll  101  at a central portion thereof. 
     In the scroll compressor of the above-described construction, the pressure the compression chambers  103  always undergoes a given process based on a suction pressure and a volumetric change of the compression chambers  103 , irrespective of a discharge pressure. Because of this, an excessive pressure increase occurs depending on the timing at which the discharge port  104  communicates with the compression chambers  103  and causes unstable behaviors of the orbiting scroll  102 , in which the orbiting scroll  102  is separated from the stationary scroll  101  or conversely, an abnormal pressure acts on the orbiting scroll  102 . 
     In a scroll compressor having symmetrical compression chambers that has been developed to solve this kind of problem, communication holes are provided to respectively communicate the compression chambers in the middle of compression with a rear side of the stationary scroll and with a rear side of the orbiting scroll, and these communication holes leading to the rear sides are located on a central side relative to a communication hole leading to a discharge side, thereby always applying an appropriate pressure to the orbiting scroll (see, for example, Patent Document 1). 
     PATENT DOCUMENT(S) 
     
         
         Patent Document 1: JP 5-49830 B2 
       
    
     SUMMARY OF INVENTION 
     Problems to be solved by the Invention 
     However, in the above-described conventional refrigerating appliances, the use of a refrigerant containing no chlorine atoms, having a small global warming potential, and mainly comprising hydrofluoroolefin having a carbon-carbon double bond poses the following problems. That is, the refrigerant containing no chlorine atoms, having a small global warming potential, and mainly composed of hydrofluoroolefin having a carbon-carbon double bond is likely to decompose at high temperatures and, hence, this refrigerant decomposes with an increase in discharge temperature caused by excessive compression or re-expansion, thus resulting in a reduction in stability. In particular, in room-air conditioners, car-air conditioners, refrigerators, other air conditioners or the like, all of which are used for long periods, decomposition caused by a temperature increase is accumulated over a long period of time and, accordingly, countermeasures against the temperature increase are particularly important. 
     The present invention has been developed to solve the above-described problem and is intended to provide a scroll compressor that employs a refrigerant having a small global warming potential as a refrigerant, can curb an increase in temperature of a discharged refrigerant caused by excessive compression, and is superior in efficiency, reliability and durability. 
     Means to Solve the Problems 
     In order to solve the above-described problem inherent in the prior art, the scroll compressor according to the present invention employs therein a refrigerant containing no chlorine atoms, having a small global warming potential, and mainly comprising hydrofluoroolefin having a carbon-carbon double bond as a refrigerant. The scroll compressor according to the present invention has a bypass hole defined in an end plate of a stationary scroll to allow a plurality of compression chambers to communicate with a discharge chamber before the compression chambers communicate with a discharge port. A check valve is provided on the bypass hole to allow the refrigerant to flow from the compression chambers to the discharge chamber. 
     This construction can restrain a temperature increase that may be caused by excessive compression of the refrigerant immediately before the refrigerant is discharged from the discharge port, thereby making it possible to restrain decomposition of the refrigerant. 
     Effects of the Invention 
     The scroll compressor according to the present invention employs therein a refrigerant having a small global warming potential and a small ozone depletion potential and can restrain a temperature increase of the refrigerant leading to promotion of decomposition of the refrigerant. Accordingly, an improved scroll compressor can be provided that is superior in efficiency, reliability and durability while attending to the global environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above construction and features of the present invention will become apparent from the following description of preferred embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1  is a sectional view of a scroll compressor according to a first embodiment of the present invention, 
         FIG. 2  is an enlarged sectional view of an essential portion of a compression mechanism mounted in the scroll compressor according to the first embodiment, 
         FIG. 3  is a top plan view of an orbiting scroll mounted in the scroll compressor according to the first embodiment, 
         FIG. 4  is a comparative graph indicating pressures in compression chambers in the first embodiment of the present invention and in a comparative example, 
         FIG. 5  is a top plan view of an orbiting scroll mounted in a scroll compressor according to a second embodiment of the present invention, 
         FIG. 6  is a graph indicating details of losses in bypass holes in the first embodiment and in the second embodiment of the present invention, and 
         FIG. 7  is a sectional view of a conventional scroll compressor. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A first invention is directed to a scroll compressor that employs therein a single-component refrigerant mainly comprising hydrofluoroolefin having a carbon-carbon double bond or a mixture refrigerant containing this refrigerant. This scroll compressor includes a stationary scroll having a stationary end plate and a stationary scroll wrap rising up from the stationary end plate. The stationary end plate has a discharge port defined therein at a central portion thereof so as to open into a discharge chamber. The scroll compressor also includes an orbiting scroll having an orbiting end plate and an orbiting scroll wrap rising up from the orbiting end plate. The orbiting scroll is held in engagement with the stationary scroll to define a plurality of compression chambers therebetween. The stationary end plate also has a bypass hole defined therein to allow the compression chambers to communicate with the discharge chamber before the compression chambers communicate with the discharge port. A check valve is provided on the bypass hole to allow the refrigerant to flow from the compression chambers to the discharge chamber. According to this construction, the use of a refrigerant having a small global warming potential and a small ozone depletion potential as a refrigerant restrains a baneful influence on the global environment and, also, although the refrigerant is likely to decompose at high temperatures, the provision of the bypass hole can restrain a temperature increase caused by excessive compression and minimize decomposition of the refrigerant even in long-term use. 
     In the scroll compressor according to the first invention, a second invention is such that a plurality of bypass holes are provided to communicate with the compression chambers over a wide range. Also, an increase in total effective flow passage area can reduce a resistance to flow of each bypass hole, this making it possible to assuredly restrain a temperature increase caused by excessive compression. 
     In the scroll compressor according to the first or second invention, a third invention is such that at least one of the bypass holes is a circular communication hole. The circular shape minimizes a ratio of the resistance to flow to the area of the bypass holes, thereby further reducing a temperature increase caused by excessive compression. 
     In the scroll compressor according to any one of the first to third inventions, a fourth invention is such that at least one of the bypass holes is formed at a position that allows the at least one bypass hole to open into only one of a first compression chamber formed on an outer side of the orbiting scroll wrap and a second compression chamber formed on an inner side of the orbiting scroll wrap. Such a position is an optimum position where the refrigerant in each compression chamber opens the check valve on the bypass hole when the refrigerant has reached a discharge pressure, thus making it possible to minimize a temperature increase caused by excessive compression. 
     In the scroll compressor according to any one of the first to fourth inventions, a fifth invention is such that at least one of the bypass holes is formed at a position that allows the at least one bypass hole to open into both of a first compression chamber formed on an outer side of the orbiting scroll wrap and a second compression chamber formed on an inner side of the orbiting scroll wrap, the at least one bypass hole having a shape and a size that do not allow the at least one bypass hole to simultaneously open into the first compression chamber and the second compression chamber. If the first and second compression chambers communicate with each other via the bypass holes, a pressure difference between them causes re-expansion of the refrigerant to thereby cause a temperature increase in the compression chambers, but the-above described configuration can avoid such a phenomenon. 
     In the scroll compressor according to any one of the first to fifth inventions, a sixth invention is such that the check valve is made up of a reed valve mounted on a surface of the stationary end plate. Compared with a check valve having, for example, a spring within a bypass hole, the reed valve acts to restrain a resistance to flow to thereby reduce a temperature increase caused by excessive compression. 
     In the first to sixth inventions, a seventh invention is characterized in that a refrigerant mainly comprising hydrofluoroolefin having a carbon-carbon double bond or a mixture refrigerant containing this refrigerant and mixed with hydrofluorocarbon having no double bonds is used. The use of such a refrigerant can effectively provide a highly-reliable and highly-efficient scroll compressor. 
     In the first to sixth inventions, an eighth invention is characterized in that a mixture refrigerant comprising tetrafluoropropene or trifluoropropene as a hydrofluoroolefin and difluoromethane as a hydrofluorocarbon is used. This feature can reduce a circulation volume of the refrigerant in a refrigerating cycle to thereby restrain excessive compression caused by a pressure loss, thus making it possible to effectively provide a highly-reliable and highly-efficient scroll compressor. 
     In the scroll compressor according to any one of the first to sixth inventions, a ninth invention is characterized in that a mixture refrigerant comprising tetrafluoropropene or trifluoropropene as a hydrofluoroolefin and, pentafluoroethane as a hydrofluorocarbon is used. This feature can reduce a discharge temperature of the compressor in a refrigerating cycle, thus making it possible to effectively provide a highly-reliable and highly efficient scroll compressor. 
     In the scroll compressor according to any one of the first to ninth inventions, a tenth invention is characterized in that at least one of the bypass holes has a diameter D, the stationary end plate has a length L in a thickness direction, and a ratio D/L ranges from 2.4 to 7.2. This feature can optimize a ratio of a pressure loss of the refrigerant passing thorough the bypass holes to a loss caused by re-expansion of the refrigerant within the bypass holes, thus making it possible to provide a highly-efficient scroll compressor that can restrain a temperature increase within the compression chambers. 
     Embodiments of the present invention are described hereinafter with reference to the drawings, but the present invention is not limited to the embodiments. 
     Embodiment 1 
     In the present invention, a single-component refrigerant mainly comprising hydrofluoroolefin having a carbon-carbon double bond or a mixture refrigerant containing this refrigerant is used as a refrigerant 
       FIG. 1  is a vertical sectional view of a scroll compressor according to a first embodiment of the present invention.  FIG. 2  is an enlarged sectional view of an essential portion of a compression mechanism mounted in the scroll compressor of  FIG. 1 , and  FIG. 3  is a top plan view of the compression mechanism. Operation and function of the scroll compressor are explained hereinafter. 
     As shown in  FIG. 1 , the scroll compressor according to the first embodiment of the present invention includes a dosed container  1 , in which a compression mechanism  2 , an electric motor  3  and an oil sump  20  are accommodated. Details of the compression mechanism  2  are explained with reference to  FIG. 2 . The closed container  1  accommodates a main bearing  11  secured thereto by welding or shrink fitting, a shaft  4  journaled in the main bearing  11 , a stationary scroll  12  bolted to the main bearing  11 , and an orbiting scroll  13  interposed between the main bearing  11  and the stationary scroll  12  and held in engagement with the stationary scroll  12 . A rotation constraint mechanism  14  including, for example, an Oldham&#39;s ring for preventing rotation of the orbiting scroll  13  about its own axis, but allowing the orbiting scroll  13  to travel on a circular orbit is provided between the orbiting scroll  13  and the main bearing  11 . The shaft  4  has an eccentric shaft  4   a  formed therewith at an upper portion thereof, eccentric rotation of which drives the orbiting scroll  13  to travel on the circular orbit. Each of the stationary scroll  12  and the orbiting scroll  13  is of a construction having an end plate and a scroll wrap rising up (protruding) from the end plate. 
     A plurality of compression chambers  15  are formed between the stationary scroll  12  and the orbiting scroll  13  and move from an outer peripheral side toward a central portion while reducing a volume thereof to inhale a refrigerant therein through a suction pipe  16  leading to the outside of the closed container  1  and through a suction port  17  defined in the stationary scroll  12  at an outer periphery thereof. The refrigerant so inhaled is trapped within the compression chambers  15  for compression. When the refrigerant reaches a predetermined pressure, the refrigerant passes through a through-hole or discharge port  18  defined in the stationary scroll  12  at a central portion thereof (central position of the end plate) and through a plurality of through-holes or circular bypass holes  68  defined in the end plate of the stationary scroll  12  at positions different from the discharge port  18  and opens a reed valve (check valve)  19  before the refrigerant is discharged into the closed container  1 . A valve stopper  69  for controlling a lift of the reed valve  19  is provided to avoid damage of the reed valve  19  that may be caused by excessive deformation thereof. The reed valve  19  is mounted on, for example, a surface of the end plate of the stationary scroll  12  at a position where the bypass holes  68  are formed. 
     A pump  25  is mounted on a lower end of the shaft  4  and has a suction opening positioned inside the oil sump  20 . Because the pump  25  is driven in synchronization with the scroll compressor, the pump  25  can assuredly suck up oil  6  in the oil sump  20  formed at a bottom portion of the closed container  1 , irrespective of pressure conditions or a running speed, thereby eliminating lack of oil. The oil  6  sucked up by the pump  25  is supplied to the compression mechanism  2  through an oil supply hole  26  defined in the shaft  4  so as to extend therethrough. If foreign substances in the oil  6  are removed by, for example, an oil filter before the oil  6  is sucked up by the pump  6  or after the former has been sucked up by the latter, entry of the foreign substances into the compression mechanism  2  can be prevented, thus making it possible to further enhance the reliability. 
     The oil  6  introduced into the compression mechanism  2  has a pressure substantially equal to that of a refrigerant discharged from the scroll compressor and becomes a source of back pressure with respect to the orbiting scroll  13 . Accordingly, the orbiting scroll  13  is prevented from moving away from the stationary scroll  12  or from being disproportionately held in partial contact with the stationary scroll  12  and stably fulfills a predetermined compression function. Further, part of the oil  6  is supplied to or escapes to a mating portion between the eccentric shaft  4   a  and the orbiting scroll  13  and to a bearing bush  66  between the shat  4  and the main bearing  11  by a supply pressure or under its own weight to lubricate respective portions. After lubrication, the oil  6  drops and returns to the oil sump  20 . 
     A sealing member  78  is disposed on a rear surface  13   e  of the end plate of the orbiting scroll  13  to partition a rear side of the end plate into a high-pressure region  30  located inside the sealing member  78  and a back pressure chamber  29  located outside the sealing member  78 . Because the sealing member  78  acts to completely separate between a pressure in the high-pressure region  30  and a pressure in the back pressure chamber  29 , it becomes possible to stably control a pressure load on the rear surface  13   e  of the orbiting scroll  13 . 
     A pressure increase in the compression chambers  15  formed by the stationary scroll  12  and the orbiting scroll  13  is explained hereinafter with reference to  FIG. 3 . The compression chambers  15  formed by the stationary scroll  12  and the orbiting scroll  13  include a plurality of first compression chambers  15   a - 1 ,  15   a - 2  formed on an outer side of the scroll wrap of the orbiting scroll  13  and a plurality of second compression chambers  15   b - 1 ,  15   b - 2  formed on an inner side of the scroll wrap of the orbiting scroll  13 . The respective compression chambers  15  move toward a center while reducing a volume thereof with an orbital movement of the orbiting scroll  13 . When the compression chambers  15  reach a discharge pressure and communicate with the discharge port  18  or the bypass holes  68   a - 1 ,  68   a - 2 ,  68   b - 1 ,  68   b - 2 , a refrigerant in the compression chambers opens the reed valve  19  and is discharged into a discharge chamber  31 .  FIG. 4  depicts a comparison of the pressure in the compression chambers between a case where the bypass holes  68   a - 1 ,  68   a - 2 ,  68   b - 1 ,  68   b - 2  are provided (first embodiment) and a case where no bypass holes are provided (comparative example). If the bypass holes  68   a - 1 ,  68   a - 2 ,  68   b - 1 ,  68   b - 2  are not provided, the pressure in the compression chambers  15  continues to increase until the compression chambers  15  communicate with the discharge port  18  and, hence, the pressure in the compression chambers  15  increases over the discharge pressure in the discharge chamber  31 , which may increase a discharge temperature more than necessary. 
     In view of the foregoing, in the first embodiment, the bypass holes  68   a - 1 ,  68   a - 2 ,  68   b - 1 ,  68   b - 2  are provided at positions where they communicate respectively with the compression chambers  15  earlier (at the earlier timing) than the discharge port  18  does. Thereby, when the pressure inside the compression chambers  15  reaches the discharge pressure, discharge of the refrigerant into the discharge chamber  31  is initiated through the bypass holes  68   a - 1 ,  68   a - 2 ,  68   b - 1 ,  68   b - 2 , thereby avoiding an increase in discharge temperature caused by an excessive pressure increase. Because the bypass holes  68   a - 1 ,  68   a - 2 ,  68   b - 1 ,  68   b - 2  are all formed into a circular communication hole, a resistance to flow is minimized compared with other shapes having the same area as that of the bypass holes  68   a - 1 ,  68   a - 2 ,  68   b - 1 ,  68   b - 2 . Further, as shown in  FIG. 4 , crank angles at which the first compression chambers  15   a - 1 ,  15   a - 2  and the second compression chambers  15   b - 1 ,  15   b - 2  reach the discharge pressure differ and, hence, in the present invention the bypass holes  68   a - 1 ,  68   a - 2 ,  68   b - 1 ,  68   b - 2  are appropriately positioned such that the bypass holes  68   a - 1 ,  68   a - 2  communicate with only the first compression chambers  15   a - 1 ,  15   a - 2  and the bypass holes  68   b - 1 ,  68   b - 2  communicate with only the second compression chambers  15   b - 1 ,  15   b - 2 , thus making it possible to control an increase in discharge temperature of the refrigerant employed in the present invention that is likely decompose with an increase in temperature. 
     Embodiment 2 
       FIG. 5  is a top plan view of a compression mechanism mounted in a scroll compressor according to a second embodiment of the present invention. Because the configuration other than bypass holes  68   ab  is the same as that in the first embodiment, the same component parts as those shown in  FIG. 3  are designated by the same signs in  FIG. 5 , only the bypass holes  68   ab  are explained and explanation of the rest is omitted. 
     As shown in  FIG. 5 , in the scroll compressor according to the second embodiment, the bypass holes  68   ab  are provided at positions where they communicate with the first compression chamber  15   a  and the second compression chamber  15   b , but any one of them does not simultaneously open into the first compression chamber  15   a  and the second compression chamber  15   b  with an orbital movement of the orbiting scroll  13 . To this end, the bypass holes  68   ab  have a diameter smaller than a thickness of an orbiting scroll wrap  13   c . At a crank angle shown in  FIG. 5 , the bypass hole  68   ab - 1  communicates with the second compression chamber  15   b - 1  and the bypass hole  68   ab - 3  communicates with the first compression chamber  15   a - 1  to avoid excessive compression, and when the orbiting scroll wrap  13   c  is located on one of the bypass holes as with the bypass hole  68   ab - 2 , the one of the bypass holes  68   ab  communicates with neither the first compression chamber  15   a - 1  nor the second compression chamber  15   b - 1 . This configuration does not cause any leakage of the refrigerant between the compression chambers and controls an increase in discharge temperature of the refrigerant employed in the present invention that is likely decompose with an increase in temperature. 
     It is to be noted here that although in the first and second embodiments a single-component refrigerant mainly comprising hydrofluoroolefin having a carbon-carbon double bond or a mixture refrigerant containing this refrigerant is used as a refrigerant, a refrigerant mainly comprising hydrofluoroolefin having a carbon-carbon double bond and mixed with hydrofluorocarbon having no double bonds may be used as the refrigerant. 
     Also, a mixture refrigerant comprising tetrafluoropropene (HFO1234yf or HFO1234ze) or trifluoropropene (HFO1243zf) as a hydrofluoroolefin and difluoromethane (HFC32) as a hydrofluorocarbon may be used as the refrigerant. 
     Further, a mixture refrigerant comprising tetrafluoropropene (HFO1234yf or HFO1234ze) or trifluoropropene (HFO1243zf) as a hydrofluoroolefin and pentafluoroethane (HFC125) as a hydrofluorocarbon may be used as the refrigerant. 
     In addition, a three-component mixture refrigerant comprising tetrafluoropropene (HFO1234yf or HFO1234ze) or trifluoropropene (HFO1243zf) as a hydrofluoroolefin and of pentafluoroethane (HFC125) and difluoromethane (HFC32) as hydrofluorocarbons may be used as the refrigerant. 
     In each case, the use of a two- or three-component refrigerant is preferable in which two or three components are mixed so as to make the global warming potential greater than or equal to 5 and less than or equal to 750, preferably less than or equal to 350. 
     As a refrigerant oil for use with the above-described refrigerants, the use of a synthetic of mainly comprising an oxygenated compound such as, for example, polyoxyalkylene glycols, polyvinyl ethers, copolymers of poly(oxy)alkylene glycol or mono ether thereof and polyvinyl ether, polyol esthers, and polycarbonates is preferred. The use of a synthetic oil mainly comprising one of alkyl benzenes and alpha olefins is also preferred. 
     If the bypass holes  68  are small in diameter D or large in length L, a pressure loss of the refrigerant passing through the bypass holes  68  becomes large and, hence, a ratio D/L of the diameter D to the length L must be greater than a certain value in terms of the pressure loss. On the other hand, a volume V of the bypass holes  68  is proportional to the length L and if the bypass holes  68  are circular, the volume V is proportional to a square of the diameter D. However, a re-expansion loss caused by re-expansion of the refrigerant within the bypass holes  68  becomes large with an increase in volume V. Accordingly, it is preferred that a product of the square of the diameter D and the length L be as small as possible. From the foregoing, an optimum range is determined based on a relationship between the pressure loss and the re-expansion loss. 
     On the other hand, the length L of the bypass holes  68  is associated with a thickness of the end plate of the stationary scroll  12 . The end plate of the stationary scroll  12  must have a thickness that can maintain a sufficient rigidity to keep deformation of the stationary scroll  12  within an allowable range in the presence of a pressure difference between a high pressure and a low pressure of the refrigerant to be compressed. An amount of deformation caused by the pressure difference is proportional to the pressure difference and inversely proportional to a cube of the thickness of the end plate. 
     When the refrigerant employed in the present invention is compared with an R410A refrigerant, the pressure of the former is reduced to about 40% and, accordingly, the thickness of the end plate can be reduced to about 75% of that of a conventional compressor designed for the R410A refrigerant. That is, the length L of the bypass holes  68  can be similarly reduced to about 75%. 
     When the refrigerant employed in the present invention is again compared with the R410A refrigerant, a density of the refrigerant employed in the present invention reduces to about 40% in the same performance. That is, if a suction volume of the compressor is determined to fulfill the same performance, the volume V of the bypass holes  68  can be increased to equalize the influence of the re-expansion loss thereof. Accordingly, even if the volume V is increased to 250% in the case of the refrigerant of the present invention, the re-expansion loss is the same in the same performance. 
     From the above, when the length L of the bypass holes  68  is reduced to 75% and the volume V of the bypass holes  68  is increased to 250%, even if the diameter D of the bypass holes  68  is increased to 180%, the re-expansion loss becomes the same. 
       FIG. 6  is a graph indicating details of the losses in the bypass holes  68  in the first embodiment and in the second embodiment of the present invention. A horizontal axis indicates D/L and a vertical axis indicates a ratio of the losses to a theoretical power loss. A solid line indicates a total loss in the bypass holes  68 , a single-dotted chain line indicates the re-expansion loss, a dotted line indicates a pressure loss, a thin line indicates the R410A refrigerant, and a thick line indicates the refrigerant employed in the scroll compressor according to the present invention (hereinafter referred to as the “refrigerant of the present invention”). As shown in  FIG. 6 , an aspect ratio D/L of the bypass holes  68  of the conventional compressor designed for the R410A refrigerant ranges from about 1 to about 3 and, in this range, a balance between the efficiency and the reliability of the compressor is ensured. 
     On the other hand, in the case of the refrigerant of the present invention, if the volume V of the bypass holes  68  is increased to 250% to thereby make a ratio of the re-expansion loss to a theoretical power equal to that of the R410A refrigerant, a ratio of the pressure loss to the theoretical power as indicated by the dotted line can be reduced, considering the fact that the re-expansion loss can be maintained the same even if the length L of the bypass holes  68  is reduced to 75% and the diameter D of the bypass holes  68  is increased to 180%. Specifically, if a mass flow of the refrigerant of the present invention passing through the bypass holes  68  is the same as that of the R410A refrigerant, a volumetric flow obtained by dividing the mass flow by a density increases to 250% because the density of the refrigerant of the present invention is about 40% of that of the R410A refrigerant. On the other hand, a sectional area of the bypass holes  68  increases to about 330% because the diameter D of the bypass holes  68  can be increased to 180%. Accordingly, the pressure loss can be reduced by reducing a speed of the refrigerant passing through the bypass holes  68 , which speed is obtained by dividing the volumetric volume by the sectional area. 
     As shown in  FIG. 6 , the aspect ratio D/L of the bypass holes  68  of the conventional compressor designed for the R410A refrigerant ranges from about 1 to about 3 in view of the reliability when an increased load is applied and, accordingly, when the refrigerant of the present invention is used, the aspect ratio D/L of the bypass holes  68  is increased to about 240% so as to be in the range of 2.4-7.2, thereby making it possible to enhance the efficiency due to minimization of the pressure loss and the re-compression loss in the bypass holes  68  and maintain the rigidity to keep deformation of the stationary scroll  12  within an allowable range. As a result, a balance between the efficiency and the reliability of the compressor can be achieved. 
     It is to be noted that of the various embodiments referred to above, any combination of them can produce effects of respective embodiments. 
     Although the present invention has been fully described by way of preferred embodiments with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications otherwise depart from the scope of the present invention as set forth in the appended claims, they should be construed as being included therein. 
     The contents of a specification, drawings and claims of a Japanese patent application No. 2010-155638 filed Jul. 8, 2010 are herein expressly incorporated by reference in their entirety. 
     INDUSTRIAL APPLICABILITY 
     As described above, even if a single-component refrigerant mainly comprising hydrofluoroolefin having a carbon-carbon double bond or a mixture refrigerant containing this refrigerant is used as a refrigerant, the scroll compressor according to the present invention can enhance the efficiency and the reliability. Accordingly, the rotary compressor according to the present invention is applicable to air conditioners, heat pump water heaters, refrigerator-freezers, dehumidifiers or the like.