Patent Publication Number: US-2010129244-A1

Title: Hermetic compressor

Description:
TECHNICAL FIELD 
     The present invention relates to hermetic compressors used mainly for domestic refrigerators. 
     BACKGROUND ART 
     A conventional hermetic compressor is disclosed in Japanese Patent Unexamined Publication, No. 2004-137926, which employs a shaft of such configuration that a countershaft portion and a main shaft portion are unitary formed in a coaxial manner with an eccentric shaft portion between them. 
     Description is provided hereinafter of the conventional hermetic compressor noted above with reference to the drawings. 
       FIG. 15  is a longitudinally sectioned view of the conventional hermetic compressor,  FIG. 16  is an enlarged view of a principal portion of a conventional shaft, and  FIG. 17  to  FIG. 21  are enlarged sectional views of the principal portion around the shaft for detailing the assembling steps of the shaft. 
     As shown in  FIG. 15  to  FIG. 21 , hermetically sealed container  1  houses motor element  9  included of stator  5  having winding  3  and rotor  7 , and compressor element  11  driven by motor element  9 . 
     Compressor element  11  includes shaft  19  having countershaft portion  15  and main shaft portion  17  provided in a coaxial manner at the upper side and the lower side of eccentric shaft portion  13 , cylinder block  23  having compression chamber  21  of a substantially cylindrical shape, and piston  25  for making reciprocating motion inside compression chamber  21 . 
     Compressor element  11  is also provided with connecting rod  27  having small end hole  33  and large end hole  37  formed unitary for connection with piston  25  and eccentric shaft portion  13 , and they are assembled into one body with cylinder block  23 . Compressor element  11  is further provided with countershaft bearing  29  for axially supporting countershaft portion  15 , and main shaft bearing  31  made of an aluminum-based material and fixed to cylinder block  23  for axially supporting main shaft portion  17 . A screw or the like means is used for fixing main shaft bearing  31  to cylinder block  23 . 
     The hermetic compressor constructed as above operates in a manner, which will be described hereinafter. 
     When rotor  7  of motor element  9  turns shaft  19 , rotary motion of eccentric shaft portion  13  is transferred to piston  25  through connecting rod  27  to make piston  25  move reciprocally inside compression chamber  21 . As a result, refrigerant gas is introduced into compression chamber  21  from a cooling system (not shown in the figures), compressed, and discharged again to the cooling system. 
     Description is provided next of the steps of assembling the shaft. 
     First, piston  25  and connecting rod  27  are connected with piston pin  35  in small end hole  33 , as shown in  FIG. 17 , to assemble piston con-rod assembly  43 . After that, piston  25  is installed into compression chamber  21  of cylinder block  23 . Cylinder block  23  is then placed with compression chamber  21  facing downward. Since piston con-rod assembly  43  is not fixed to cylinder block  23 , it slides down by its own weight to top side  23   a  of cylinder block  23 . 
     Next, countershaft portion  15  of shaft  19  is inserted into cylinder block  23  from the opposite side of countershaft bearing  29 . During this step, countershaft portion  15  is inserted into large end hole  37  of connecting rod  27  while lifting piston con-rod assembly  43 . 
     Next, in order to insert countershaft portion  15  into countershaft bearing  29  of cylinder block  23 , shaft  19  is shifted upward while lifting piston con-rod assembly  43  up to such a height that the center of axis of countershaft portion  15  comes into alignment with the axis of countershaft bearing  29 , as shown in  FIG. 18 . Then, countershaft portion  15  is pushed to bring it inserted in countershaft bearing  29 . 
     As the leading end of countershaft portion  15  begins to get into countershaft bearing  29 , countershaft portion  15  passes completely through large end hole  37 , as shown from  FIG. 19  to  FIG. 21 . Piston con-rod assembly  43  hence falls upon curved surface  41  of connecting section  39  by its own weight after countershaft portion  15  has cleared through large end hole  37 . 
     In order to fit eccentric shaft portion  13  to large end hole  37 , piston con-rod assembly  43  in its resting position on curved surface  41  is lifted again, and eccentric shaft portion  13  is then fitted into large end hole  37  when the axis of eccentric shaft portion  13  comes in alignment with that of large end hole  37 . 
     After completion of assembling shaft  19  in the manner as described above, main shaft bearing  31  is fitted to main-shaft portion  17  of shaft  19  and fixed to cylinder block  23  with screw  45 . 
     In the conventional assembling steps described above, however, the axis of eccentric shaft portion  13  cannot be aligned easily with the axis of large end hole  37  when shaft  19  is fitted while lifting piston con-rod assembly  43  upward from curved surface  41  whereon large end hole  37  is resting. It thus has a drawback of poor workability and low productivity because sliding surfaces can be damaged when eccentric shaft portion  13  and large end hole  37  are forcibly rubbed with each other, and the assembling requires a considerable time. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above problem of the prior art, and it aims to provide a hermetic compressor featuring good workability and high productivity in assembling while preventing damages to sliding surfaces during insertion of an eccentric shaft portion of a shaft into a large end hole. 
     The hermetic compressor of the present invention includes a compressor element enclosed in a hermetically sealed container. The compressor element includes a cylinder block constituting a compression chamber of a substantially cylindrical shape, and a shaft having an eccentric shaft portion, a countershaft portion and a main shaft portion integrally-formed, the countershaft portion and the main shaft portion being formed in a coaxial manner with the eccentric shaft portion between them. The compressor element also includes a countershaft bearing formed at the cylinder block for axially supporting the countershaft portion, a main shaft bearing also formed at the cylinder block for axially supporting the main shaft portion, a piston for making a reciprocating motion inside the compression chamber, and a connecting rod for connecting the piston and the eccentric shaft portion, the connecting rod provided with a large end hole which is fitted to the eccentric shaft portion. Connecting section is formed between the eccentric shaft portion and the countershaft portion of the shaft, the connecting section has an axial length sufficient to allow the large end hole to move into a position coaxial with the eccentric shaft portion, and an extended surface of the eccentric shaft portion is formed at a side, which is opposite to an eccentric axis, of the connecting section. 
     According to this structure, the eccentric shaft portion of the shaft can be inserted easily into the large end hole by taking advantage of the extended surface of the connecting section after making the countershaft portion clear through the large end hole. This structure can thus has advantages of preventing damages to the sliding surfaces of the large end hole and the eccentric shaft portion of the shaft, and improving workability and productivity in the assembling process. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinally sectioned view of a hermetic compressor according to a first exemplary embodiment of the present invention; 
         FIG. 2  is an enlarged view of a principal portion of a shaft according to this exemplary embodiment; 
         FIG. 3  is an enlarged sectional view of the principal portion around the shaft for detailing assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 4  is another enlarged sectional view of the principal portion around the shaft for detailing the assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 5  is another enlarged sectional view of the principal portion around the shaft for detailing the assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 6  is still another enlarged sectional view of the principal portion around the shaft for detailing the assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 7  is a perspective view of a main portion of the shaft according to this exemplary embodiment; 
         FIG. 8  is yet another enlarged sectional view of the principal portion around the shaft for detailing the assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 9  is a longitudinally sectioned view of a hermetic compressor according to a second exemplary embodiment of the present invention; 
         FIG. 10  is an enlarged view of a principal portion of a shaft according to this exemplary embodiment; 
         FIG. 11  is an enlarged sectional view of the principal portion around the shaft for detailing assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 12  is another enlarged sectional view of the principal portion around the shaft for detailing the assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 13  is still another enlarged sectional view of the principal portion around the shaft for detailing the assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 14  is yet another enlarged sectional view of the principal portion around the shaft for detailing the assembling steps of the shaft according to this exemplary embodiment; 
         FIG. 15  is a longitudinally sectioned view of a conventional hermetic compressor; 
         FIG. 16  is an enlarged view of a principal portion of a conventional shaft; 
         FIG. 17  is an enlarged sectional view of the principal portion around the conventional shaft for detailing assembling steps of the shaft; 
         FIG. 18  is another enlarged sectional view of the principal portion around the conventional shaft for detailing the assembling steps of the shaft; 
         FIG. 19  is another enlarged sectional view of the principal portion around the conventional shaft for detailing the assembling steps of the shaft; 
         FIG. 20  is still another enlarged sectional view of the principal portion around the conventional shaft for detailing the assembling steps of the shaft; and 
         FIG. 21  is yet another enlarged sectional view of the principal portion around the conventional shaft for detailing the assembling steps of the shaft. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Description will be provided hereinafter of exemplary embodiments of the present invention by referring to the drawings. 
     First Exemplary Embodiment 
       FIG. 1  is a longitudinally sectioned view of a hermetic compressor according to the first exemplary embodiment of the present invention,  FIG. 2  is an enlarged view of a principal portion of a shaft, and  FIG. 3  through  FIG. 6  are sectional views of the principal portion around the shaft for detailing assembling steps of the shaft.  FIG. 7  is a perspective view of a principal portion of the shaft, and  FIG. 8  is another enlarged sectional view of the principal portion around the shaft for detailing the assembling steps. 
     Referring now to  FIG. 1  through  FIG. 8 , description is provided hereinafter of the hermetic compressor according to this exemplary embodiment of the invention. 
     In  FIG. 1  to  FIG. 8 , hermetically sealed container  101  is filled with a refrigerant (not shown), and it also stores refrigerating machine oil (not shown). In one instance here, the refrigerant is a hydrocarbon group refrigerant of R600a, and the refrigerating machine oil is a mineral oil having good compatibility with the refrigerant. 
     Motor element  103  includes stator  105  connected to an external power supply (not shown), and rotor  107  disposed inside stator  105  with a predetermined space. 
     Compressor element  109  includes shaft  117  having countershaft portion  113  and main shaft portion  115  formed in a coaxial manner at the upper side and the lower side of eccentric shaft portion  111 , cylinder block  121  made of a material such as iron-based cast material and having compression chamber  119  of a substantially cylindrical shape formed therein, and piston  127  for making reciprocating motion inside compression chamber  119 . 
     Compressor element  109  also includes connecting rod  129  provided with small end hole  130  and large end hole  131  formed therein for connecting piston  127  and eccentric shaft portion  111 . Compressor element  109  further includes countershaft bearing  123  provided in cylinder block  121  for axially supporting countershaft portion  113  of shaft  117 . Furthermore, compressor element  109  includes main shaft bearing  125  made of an aluminum-based material, which is fixed to cylinder block  121  for axially supporting main shaft portion  115  of shaft  117 . Screw  132  is used for fixing main shaft bearing  125  to cylinder block  121 . 
     An outer diameter of countershaft portion  113  of shaft  117  is smaller than an outer diameter of eccentric shaft portion  111 . Connecting section  133  is formed between eccentric shaft portion  111  and countershaft portion  113  of shaft  117 , and connecting section  133  has an axial length sufficient to allow large end hole  131  of connecting rod  129  inserted from eccentric shaft portion  111  to move into a position coaxial with eccentric shaft portion  111 . Extended surface  135  of eccentric shaft portion  111  is formed at a side, which is opposite to an eccentric axis, of connecting section  133 . Extended surface  135  is processed simultaneously with a finishing process of eccentric shaft portion  111 . 
     In other words, extended surface  135  formed on connecting section  133  is coaxial with eccentric shaft portion  111 , and they both have same curvature with a high precision. Eccentric shaft portion  111  is provided with chamfered edge  136  on end surface  137  nearer to countershaft portion  113 . 
     In addition, curved configuration  139  is formed between the eccentric axis side of connecting section  133  and end surface  137 , which is a side of countershaft portion  113 , of eccentric shaft portion  111  of shaft  117 . Curved configuration  143  is formed between one side of connecting section  133  opposite the eccentric axis side and end surface  141 , which is a side of the eccentric shaft portion  111 , of the countershaft portion  113  of shaft  117 . 
     Rotor  105  is fitted to main shaft portion  115  of shaft  117 . Stator  105  is fixed in a position underneath cylinder block  121 . 
     The hermetic compressor constructed as above operates in a manner, which will be described hereinafter. 
     Rotor  107  of motor element  103  rotates shaft  117 . When this occurs, the rotary motion of eccentric shaft portion  111  is transferred to piston  127  through connecting rod  129 . This makes piston  127  moves reciprocally in compression chamber  119 . As a result, the refrigerant gas is introduced into compression chamber  119  from a cooling system (not shown), compressed, and discharged again to the cooling system. 
     Description is provided next of the steps of assembling shaft  117 . 
     Piston con-rod assembly  147  is assembled beforehand, as shown in  FIG. 3 , in which piston  127  and small end hole  130  in connecting rod  129  are connected with piston pin  145 . After piston  127  of piston con-rod assembly  147  is built into compression chamber  119  of cylinder block  121 , cylinder block  121  is placed with compression chamber  119  facing downward. Since piston con-rod assembly  147  is not fixed, it slides down by its own weight to top side  121   a  of cylinder block  121 . 
     Next, countershaft portion  113  of shaft  117  is inserted into cylinder block  121  from the opposite side of countershaft bearing  123 . During this step, countershaft portion  113  is inserted into large end hole  131  of connecting rod  129  while lifting piston con-rod assembly  147 . 
     Next, in order to insert countershaft portion  113  into countershaft bearing  123  of cylinder block  121 , shaft  117  is shifted upward while lifting piston con-rod assembly  147  up to such a height that the axis of countershaft portion  113  comes into alignment with the axis of countershaft bearing  123 , as shown in  FIG. 4 . Then, countershaft portion  113  is pushed in a manner to be inserted in countershaft bearing  123 . 
     As the leading end of countershaft portion  113  begins to get into countershaft bearing  123 , countershaft portion  113  clears completely through large end hole  131  at about the same time, as shown in  FIG. 5 . Piston con-rod assembly  147  then falls by its own weight upon connecting section  133  provided with extended surface  135  having the same curvature as that of the inner wall of large end hole  131  at the opposite side of the eccentric axis. 
     In this instance, curved configuration  143  is formed between one side of connecting section  133  opposite the eccentric axis and end surface  141 , which is a side of eccentric shaft portion  111 , of countershaft portion  113 , as shown in  FIG. 6 . Therefore, piston con-rod assembly  147  can slide along curved configuration  143  to extended surface  135  while keeping an inner sliding surface of large end hole  131  in contact with curved configuration  143 . This structure prevents damages to the inner sliding surface of large end hole  131  of connecting rod  129  since it can alleviate an impact, which occurs when large end hole  131  falls upon connecting section  133 . 
     As shown in  FIG. 6  and  FIG. 7 , there is also curved configuration  139  formed between the eccentric axis side of connecting section  133  and end surface  137  of eccentric shaft portion  111 . It is therefore possible to increase a circumferential dimension of extended surface  135  at the side closer to eccentric shaft portion  111 . It can hence reduce the possibility of large end hole  131  to become tilted with respect to extended surface  135 . Additionally, it helps ease the alignment of the center of axes before fitting eccentric shaft portion  111 , which substantially improves the workability of inserting eccentric shaft portion  111  into large end hole  131 . 
     Afterwards, shaft  117  can be pushed further by taking advantage of extended surface  135 , as shown in  FIG. 8 , since the center of axis of eccentric shaft portion  111  is already in alignment to the axis of large end hole  131 . As a result, large end hole  131  slides over extended surface  135  to easily fit to eccentric shaft portion  111 , and to thereby complete the process of fitting countershaft portion  113  to countershaft bearing  123  of cylinder block  121 . 
     Although the combination of refrigerant and refrigerating machine oil described here is an example using R600a and mineral oil, this invention can be embodied with any type of refrigerant selected from the group of R290, a mixture containing this and other refrigerants, R134a, R152, R407C, R404A and R410, and any kind of refrigerating machine oil compatible with the above refrigerants. 
     The hermetic compressor of this exemplary embodiment includes compressor element  109  enclosed inside hermetically sealed container  101 , as described above. Compressor element  109  is provided with cylinder block  121  constituting compression chamber  119  of a substantially cylindrical shape, and shaft  117  having eccentric shaft portion  111 , countershaft portion  113  and main shaft portion  115  integrally-formed, countershaft portion  113  and main shaft portion  115  being formed in the coaxial manner with eccentric shaft portion  111  between them. Compressor element  109  also includes countershaft bearing  123  formed at cylinder block  121  for axially supporting countershaft portion  113 , main shaft bearing  125  also formed at cylinder block  121  for axially supporting main shaft portion  115 , piston  127  for making reciprocating motion inside compression chamber  119 , and connecting rod  129  for connecting piston  127  and eccentric shaft portion  111 , connecting rod  129  provided with large end hole  131  which is fitted to eccentric shaft portion  111 . Connecting section  133  is formed between eccentric shaft portion  111  and countershaft portion  113  of shaft  117 , and connecting section  133  has an axial length sufficient to allow large end hole  131  to move into a position coaxial with eccentric shaft portion  111 . Extended surface  135  of eccentric shaft portion  111  is formed on at a side, which is opposite the eccentric axis, of connecting section  133 . In the assembling step for fitting eccentric shaft portion  111  of shaft  117  to large end hole  131  in connecting rod  129 , all what is required is to slide the sliding surface of large end hole  131  over the extended surface of eccentric shaft portion  111  after inserting countershaft portion  113  of shaft  117  into large end hole  131  of connecting rod  129 , to easily complete the alignment of the center of axes of eccentric shaft portion  111  and large end hole  131 , and insertion of eccentric shaft portion  111  into large end hole  131 . Accordingly, this structure can prevent the sliding surfaces of eccentric shaft portion  111  of shaft  117  and large end hole  131  of connecting rod  129  from being damaged. The structure can thus improve workability and productivity of the assembling process, thereby providing the hermetic compressor of high reliability and high productivity. 
     In the hermetic compressor according to this exemplary embodiment, extended surface  135  next to eccentric shaft portion  111  is processed simultaneously with the finishing process of eccentric shaft portion  111 , and in a shape of circular arc in cross section having the same curvature as that of the inner wall of large end hole  131 , as described above. Accordingly, the center of axis of eccentric shaft portion  111  can be aligned easily with that of extended surface  135  conjoining eccentric shaft portion  111 , since extended surface  135  and eccentric shaft portion  111  are processed at the same time into shapes of the same curvature with that of the inner wall of large end hole  131 . As a result, the above structure can further improve the workability and productivity in assembling of shaft  117 , and provide the hermetic compressor of high reliability and high productivity. 
     Moreover, the hermetic compressor of this exemplary embodiment is provided with curved configuration  139  formed between the eccentric axis side of connecting section  133  and end surface  137 , which is a side of countershaft portion  113 , of eccentric shaft portion  111 , as described above. This structure can therefore prevent connecting section  133  at the side of eccentric shaft portion  111  from damaging the inner sliding surface of large end hole  131  during insertion of shaft  117  into large end hole  131  of connecting rod  129 . It can also reduce the possibility of large end hole  131  to become tilted with respect to extended surface  135  so as to help ease the alignment of the center of axes since extended surface  135  has a larger circumferential dimension at the side closer to eccentric shaft portion  111 . Accordingly, it can further prevent the sliding surface of large end hole  131  in connecting rod  129  from being damaged. As a result, it can improve the workability and productivity in assembling the shaft, and provide the hermetic compressor of high reliability and high productivity. 
     Additionally, the hermetic compressor of this exemplary embodiment is provided with curved configuration  143  formed between one side of connecting section  133  opposite the eccentric axis and end surfaces  141 , which is a side of eccentric shaft portion  111 , of countershaft portion  113 , as described above. This structure can alleviate an impact when large end hole  131  falls upon connecting section  133  since large end hole  131  slides along curved configuration  143  of connecting section  133  when it falls upon connecting section  133  after clearing through countershaft portion  113 . It can thus positively prevent the sliding surfaces of eccentric shaft portion  111  of shaft  117  and large end hole  131  of connecting rod  129  from being damaged. Accordingly, it can further improve the workability and productivity in assembling the shaft, and provide the hermetic compressor of even higher reliability and productivity. 
     Second Exemplary Embodiment 
       FIG. 9  is a longitudinally sectioned view of a hermetic compressor according to a second exemplary embodiment of the present invention,  FIG. 10  is an enlarged view of a principal portion of a shaft, and  FIG. 11  through  FIG. 14  are sectional views of the principal portion around the shaft for detailing assembling steps of the shaft. 
     With reference to  FIG. 9  through  FIG. 14 , description is provided hereinafter of the hermetic compressor according to this exemplary embodiment of the invention. 
     In  FIG. 9  to  FIG. 14 , hermetically sealed container  201  is filled with a refrigerant (not shown), and it also stores refrigerating machine oil (not shown). In this instance, the refrigerant is a hydrocarbon group refrigerant of R600a, and the refrigerating machine oil is a mineral oil having good compatibility with the refrigerant. 
     Motor element  203  includes stator  205  connected to an external power supply (not shown), and rotor  207  disposed inside stator  205  with a predetermined space. 
     Compressor element  209  includes shaft  217  having countershaft portion  213  and main shaft portion  215  formed in a coaxial manner at the upper side and the lower side of eccentric shaft portion  211 , cylinder block  221  made of a material such as iron-based cast material and having compression chamber  219  of a substantially cylindrical shape formed therein, and piston  227  for making reciprocating motion inside compression chamber  219 . 
     Compressor element  209  also includes connecting rod  229  provided with small end hole  230  and large end hole  231  formed therein for connecting piston  227  and eccentric shaft portion  211 . Compressor element  209  further includes countershaft bearing  223  provided in cylinder block  221  for axially supporting countershaft portion  213  of shaft  217 . Furthermore, compressor element  209  includes main shaft bearing  225  made of an aluminum-based material, which is fixed to cylinder block  221  for axially supporting main shaft portion  215  of shaft  217 . Screw  232  is used for fixing main shaft bearing  225  to cylinder block  221 . 
     An outer diameter of countershaft portion  213  of shaft  217  is of same size as that of eccentric shaft portion  211 . Connecting section  233  is formed between eccentric shaft portion  211  and countershaft portion  213  of shaft  217 , and connecting section  233  has an axial length sufficient to allow large end hole  231  of connecting rod  229  inserted from eccentric shaft portion  211  to move into a position coaxial with eccentric shaft portion  211 . Extended surface  235  of eccentric shaft portion  211  is formed on at a side, which is opposite the eccentric axis, of connecting section  233 . Extended surface  235  is processed simultaneously with the finishing process of eccentric shaft portion  211 . 
     In other words, extended surface  235  formed on connecting section  233  is coaxial with eccentric shaft portion  211 , and they both have same curvature with a high precision. Eccentric shaft portion  211  is provided with chamfered edge  236  on end surface  237  nearer to countershaft portion  213 . 
     Moreover, extended surface  238  of countershaft portion  213  is formed on connecting section  233  at the side of eccentric shaft portion  211  of shaft  217 , and extended surface  238  is processed simultaneously with the finishing process of countershaft portion  213 . 
     In other words, extended surface  238  formed on connecting section  233  is coaxial with countershaft portion  213 , and they both have same curvature with a high precision. 
     In addition, curved configuration  239  is formed between the eccentric axis side of connecting section  233  and end surface  237  of eccentric shaft portion  211  at the side nearer to countershaft portion  213  of shaft  217 . Curved configuration  243  is formed between one side of connecting section  233  opposite the eccentric axis and end surface  241 , which is a side of eccentric shaft portion  211 , of countershaft portion  213  of shaft  217 . 
     Rotor  207  is fitted to main shaft portion  215  of shaft  217 . Stator  205  is fixed in a position underneath cylinder block  221 . 
     The hermetic compressor constructed as above operates in a manner, which will be described hereinafter. 
     Rotor  207  of motor element  203  rotates shaft  217 . When this occurs, the rotary motion of eccentric shaft portion  211  is transferred to piston  227  through connecting rod  229 . This makes piston  227  move reciprocally inside compression chamber  219 . As a result, the refrigerant gas is introduced into compression chamber  219  from a cooling system (not shown), compressed, and discharged again to the cooling system. 
     Description is provided next of the steps of assembling shaft  217 . 
     Piston con-rod assembly  247  is assembled beforehand, as shown in  FIG. 11 , in which piston  227  and small end hole  230  in connecting rod  229  are connected with piston pin  245 . After piston  227  of piston con-rod assembly  247  is built into compression chamber  219  of cylinder block  221 , cylinder block  221  is placed with compression chamber  219  facing downward. Piston con-rod assembly  247  receives a force of shifting toward top side  221   a  of cylinder block  221  by its own weight. However, accessory device  248  is used in this case to hold connecting rod  229  in the vicinity of large end hole  231 , so as to keep piston con-rod assembly  247  lifted. In this way, the position of connecting rod  229  is maintained at a height where the center of axis of large end hole  231  is in alignment to that of countershaft bearing  223 . 
     Next, countershaft portion  213  of shaft  217  is inserted into cylinder block  221  from the opposite side of countershaft bearing  223 . Countershaft portion  213  is thus inserted into large end hole  231  of connecting rod  229 . During this step, countershaft portion  213  can fit to large end hole  231  with a small gap since the outer diameter of countershaft portion  213  is made to be same size as that of eccentric shaft portion  211  where large end hole  231  is fitted, and this can prevent countershaft portion  213  and large end hole  231  from hitting against each other to avoid damages to their sliding surfaces during insertion. As a result, this structure can positively prevent damages to the sliding surfaces of countershaft portion  213  of shaft  217  and large end hole  231  of connecting rod  229 . 
     Next, shaft  217  is pushed further in a manner to insert countershaft portion  213  into countershaft bearing  223  while still maintaining the position of piston con-rod assembly  247  with accessory device  248 , as shown in  FIG. 12 . During this step, extended surface  238  formed on connecting section  233  can continue to move on the sliding surface of large end hole  231  even after countershaft portion  213  has cleared therethrough because extended surface  238  of connecting section  233  is coaxial with countershaft portion  213  and they both have the same curvature with a high precision. This structure can make the position of shaft  217  stable, which help ease the process of insertion. 
     When shaft  217  is pushed by sliding it on the sliding surface of large end hole  231 , large end hole  231  comes in contact to curved configuration  239  formed between the eccentric axis side of connecting section  233  and end surface  237  of eccentric shaft portion  211  at the side nearer to countershaft portion  213 , as shown in  FIG. 13 . Piston con-rod assembly  247  is then depressed with accessory device  248  along curved configuration  239  while pushing shaft  217  further. This causes connecting rod  229  to steadily and gradually move over curved configuration  239  up to end surface  237  of eccentric shaft portion  211 . When connecting rod  229  is depressed further downward along end surface  237 , the sliding surface of large end hole  231  can be brought into contact steadily upon extended surface  235 . 
     In addition, curved configuration  239  between the eccentric axis side of connecting section  233  and end surface  237  of eccentric shaft portion  211  can increase a circumferential dimension of extended surface  235  at the side closer to eccentric shaft portion  211 , as shown in  FIG. 14 . It can hence reduce the possibility of large end hole  231  to become tilted with respect to extended surface  235 . As a result, it further helps ease the alignment of the center of axes before fitting eccentric shaft portion  211 , which substantially improves the workability of inserting eccentric shaft portion  211  into large end hole  231 . 
     Afterwards, large end hole  231  can slide on extended surface  235  when shaft  217  is pushed further since the axis of large end hole  231  is already in alignment to the axis of eccentric shaft portion  211  by making use of extended surface  235 . Accordingly, large end hole  231  can be brought easily to fit to eccentric shaft portion  211 , to thereby complete the process of fitting countershaft portion  213  to countershaft bearing  223  of cylinder block  221 . 
     Although the combination of refrigerant and refrigerating machine oil described here is an example using R600a and mineral oil, this invention can be embodied with any type of refrigerant selected from the group of R290, a mixture containing this and other refrigerants, R134a, R152, R407C, R404A and R410, and any kind of refrigerating machine oil compatible with the above refrigerants. 
     As described above, the hermetic compressor of this exemplary embodiment includes countershaft portion  213  provided with the same outer diameter as that of eccentric shaft portion  211 , which fits to large end hole  231 . This structure can therefore prevent damages to the sliding surfaces of eccentric shaft portion  211  of shaft  217  and large end hole  231  of connecting rod  229  during the assembling step of fitting eccentric shaft portion  211  of shaft  217  to large end hole  231  of connecting rod  229 , since countershaft portion  213  can fit to large end hole  231  with a small gap. The structure can also improve the workability and productivity of the assembling process, and provide the hermetic compressor of high reliability and high productivity. 
     INDUSTRIAL APPLICABILITY 
     Hermetic compressors of the present invention are suitable for many applications such as vending machines and air conditioning equipment, besides refrigerators. 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           101 ,  201  hermetically sealed container 
           109 ,  209  compressor element 
           111 ,  211  eccentric shaft portion 
           113 ,  213  countershaft portion 
           115 ,  215  main shaft portion 
           117 ,  217  shaft 
           119 ,  219  compression chamber 
           121 ,  221  cylinder block 
           123 ,  223  countershaft bearing 
           125 ,  225  main shaft bearing 
           127 ,  227  piston 
           129 ,  229  connecting rod 
           131 ,  231  large end hole 
           133 ,  233  connecting section 
           135 ,  235  extended surface 
           137 ,  237  end surface 
           139 ,  239  curved configuration 
           141 ,  241  end surface 
           143 ,  243  curved configuration