Patent Publication Number: US-10767651-B2

Title: Two-cylinder hermetic compressor

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a two-cylinder hermetic compressor used for an outdoor unit of an air conditioner and a freezer. 
     2. Description of the Related Art 
     Generally, a hermetic compressor used for an outdoor unit of an air conditioner and a freezer includes an electric motor unit and a compressor mechanism unit in a sealed container. The electric motor unit and the compressor mechanism unit are connected to each other by a shaft, and a piston attached to an eccentric portion of the shaft revolves with the rotation of the shaft. A main bearing and an auxiliary bearing are mounted on both end faces of a cylinder having the piston provided therein, and the shaft is supported by the main bearing and the auxiliary bearing. In most cases, the diameter of the shaft is constant except for an eccentric portion. 
     On the other hand, PTL 1(Unexamined Japanese Patent Publication No. 2008-14150) discloses a shaft having different diameters. 
     PTL 1 discloses a shaft in which the side on which the electric motor unit is provided with respect to the eccentric portion is defined as a main shaft portion, and the side opposite to the side on which the electric motor unit is provided is defined as an auxiliary shaft portion, wherein the diameter of the auxiliary shaft portion is set smaller than the diameter of the main shaft portion. 
     Note that, in PTL 1, a thrust load of the shaft is received by the lower end of the auxiliary shaft portion, except for the case in which a rolling bearing is provided on the auxiliary bearing. 
     Meanwhile, in a one-cylinder hermetic compressor that has conventionally been used most often, stress exerted from a compression chamber is received by a main shaft portion disposed on the side of an electric motor unit, so that stress received by an auxiliary shaft portion is extremely small. 
     Therefore, even if the diameter of the auxiliary shaft portion is set smaller than the diameter of the main shaft portion as disclosed in PTL 1, any problems hardly occur. 
     However, it has been shown as a result of an analysis conducted by the present inventors that, in a two-cylinder hermetic compressor, stress exerted from each of compression chambers is dispersed into the main shaft portion and the auxiliary shaft portion, so that large stress is also applied on the auxiliary shaft portion. 
     SUMMARY 
     The present disclosure provides a two-cylinder hermetic compressor that can reduce maximum stress exerted on an auxiliary shaft portion to suppress an amount of sliding frictional wear on the auxiliary shaft portion. 
     Specifically, in the two-cylinder hermetic compressor according to one example of the exemplary embodiment in the present disclosure, a diameter of the auxiliary shaft portion is set larger than a diameter of a main shaft portion. 
     According to this configuration, maximum stress exerted on the auxiliary shaft portion is reduced, whereby an amount of sliding frictional wear on the auxiliary shaft portion can be suppressed. 
     In addition, in the two-cylinder hermetic compressor according to one example of the exemplary embodiment in the present disclosure, a thrust load of the shaft is received by the surface of an auxiliary bearing on the side of a second cylinder. 
     According to the configuration in which the thrust load is received by the surface of the auxiliary bearing on the side of the second cylinder, an area of a receiving portion is easy to be designed to be large as compared to the configuration of receiving the thrust load on the auxiliary shaft portion, whereby the thrust load can be stably received. 
     In addition, in the two-cylinder hermetic compressor according to one example of the exemplary embodiment in the present disclosure, a diameter of a first eccentric portion is set smaller than a dimeter of a second eccentric portion. 
     According to this configuration, a sliding loss on the first eccentric portion can be decreased. 
     As described above, according to the present disclosure, maximum stress exerted on an auxiliary shaft portion can be reduced to suppress an amount of sliding frictional wear on the auxiliary shaft portion, in a two-cylinder hermetic compressor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a two-cylinder hermetic compressor according to an exemplary embodiment of the present disclosure; 
         FIG. 2  is a side view of a shaft used in the two-cylinder hermetic compressor according to the exemplary embodiment of the present disclosure; 
         FIG. 3  is a diagram illustrating specifications of Examples and Comparative Example used for the test of maximum stress values on an auxiliary shaft portion in the two-cylinder hermetic compressor according to the exemplary embodiment of the present disclosure; 
         FIG. 4  is a graph showing the test result of maximum stress values on auxiliary shaft portions in Examples and Comparative Example shown in  FIG. 3 ; and 
         FIG. 5  is an analysis diagram showing a stress distribution on auxiliary shaft portions in Examples and Comparative Example shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a description will be given of an exemplary embodiment of the present disclosure with reference to the drawings. 
       FIG. 1  is a sectional view of a two-cylinder hermetic compressor according to one example of the exemplary embodiment of the present disclosure. 
     Two-cylinder hermetic compressor  1  according to one example of the present exemplary embodiment in the present disclosure includes electric motor unit  20  and compression mechanism unit  30  in sealed container  10 . Electric motor unit  20  and compression mechanism unit  30  are connected to each other by shaft  40 . 
     Electric motor unit  20  includes stator  21  fixed on an inner surface of sealed container  10  and rotor  22  rotating in stator  21 . 
     Two-cylinder hermetic compressor  1  according to the present exemplary embodiment includes first compression mechanism unit  30 A and second compression mechanism unit  30 B as compression mechanism unit  30 . 
     First compression mechanism unit  30 A includes first cylinder  31 A, first piston  32 A disposed in first cylinder  31 A, and a vane (not illustrated) that partitions the interior of first cylinder  31 A. First compression mechanism unit  30 A suctions a low-pressure refrigerant gas and compresses this refrigerant gas due to the revolution of first piston  32 A in first cylinder  31 A. 
     Similar to first compression mechanism unit  30 A, second compression mechanism unit  30 B includes second cylinder  31 B, second piston  32 B disposed in second cylinder  31 B, and a vane (not illustrated) that partitions the interior of second cylinder  31 B. Second compression mechanism unit  30 B suctions a low-pressure refrigerant gas and compresses this refrigerant gas due to the revolution of second piston  32 B in second cylinder  31 B. 
     Main bearing  51  is disposed on one surface of first cylinder  31 A, and intermediate plate  52  is disposed on another surface of first cylinder  31 A. 
     In addition, intermediate plate  52  is disposed on one surface of second cylinder  31 B, and auxiliary bearing  53  is disposed on another surface of second cylinder  31 B. 
     That is to say, intermediate plate  52  partitions first cylinder  31 A and second cylinder  31 B. Intermediate plate  52  has an opening larger than the diameter of shaft  40 . 
     Shaft  40  is constituted by main shaft portion  41  which has rotor  22  attached thereto and is supported by main bearing  51 , first eccentric portion  42  having first piston  32 A attached thereto, second eccentric portion  43  having second piston  32 B attached thereto, and auxiliary shaft portion  44  supported by auxiliary bearing  53 . 
     First eccentric portion  42  and second eccentric portion  43  are formed to have a phase difference of 180 degrees, and connection shaft portion  45  is formed between first eccentric portion  42  and second eccentric portion  43 . 
     First compression chamber  33 A is formed between main bearing  51  and intermediate plate  52  and between the inner peripheral surface of first cylinder  31 A and the outer peripheral surface of first piston  32 A. In addition, second compression chamber  33 B is formed between intermediate plate  52  and auxiliary bearing  53  and between the inner peripheral surface of second cylinder  31 B and the outer peripheral surface of second piston  32 B. 
     The volume of first compression chamber  33 A and the volume of second compression chamber  33 B are the same. Specifically, the inner diameter of first cylinder  31 A and the inner diameter of second cylinder  31 B are the same, and the outer diameter of first piston  32 A and the outer diameter of second piston  32 B are the same. In addition, the height of first cylinder  31 A on the inner periphery thereof and the height of second cylinder  31 B on the inner periphery thereof are the same, and the height of first piston  32 A and the height of second piston  32 B are the same. 
     Oil reservoir  11  is formed at the bottom of sealed container  10 , and oil pickup  12  is provided at the lower end of shaft  40 . 
     In addition, oil feed path  47  is formed inside shaft  40  in the axial direction, and a communication path for feeding oil to a sliding surface of compression mechanism unit  30  is formed in oil feed path  47 . 
     First suction pipe  13 A and second suction pipe  13 B are connected to the side surface of sealed container  10 , and discharge pipe  14  is connected to the top of sealed container  10 . 
     First suction pipe  13 A is connected to first compression chamber  33 A, and second suction pipe  13 B is connected to second compression chamber  33 B, respectively. Accumulator  15  is provided at the upstream side of first suction pipe  13 A and second suction pipe  13 B. Accumulator  15  separates the refrigerant returning from a freezing cycle into a liquid refrigerant and a gas refrigerant. The gas refrigerant flows through first suction pipe  13 A and second suction pipe  13 B. 
     Due to the rotation of shaft  40 , first piston  32 A and second piston  32 B revolve in first compression chamber  33 A and second compression chamber  33 B, respectively. 
     The gas refrigerant suctioned from first suction pipe  13 A and second suction pipe  13 B into first compression chamber  33 A and second compression chamber  33 B is compressed in first compression chamber  33 A and second compression chamber  33 B due to the revolution of first piston  32 A and second piston  32 B, and then, discharged into sealed container  10 . While the gas refrigerant discharged into sealed container  10  rises through electric motor unit  20 , oil is separated therefrom, and then, the resultant gas refrigerant is discharged outside of sealed container  10  from discharge pipe  14 . 
     The oil sucked from oil reservoir  11  due to the rotation of shaft  40  is fed into compression mechanism unit  30  from the communication path to allow the sliding surface of compression mechanism unit  30  to be smooth. 
       FIG. 2  is a side view of a shaft used in the two-cylinder hermetic compressor according to one example of the exemplary embodiment of the present disclosure. 
     Shaft  40  is constituted by main shaft portion  41 , first eccentric portion  42 , second eccentric portion  43 , auxiliary shaft portion  44 , and connection shaft portion  45 . 
     If the diameter of main shaft portion  41  is defined as d1, the diameter of first eccentric portion  42  is defined as d2, the diameter of second eccentric portion  43  is defined as d3, the diameter of auxiliary shaft portion  44  is defined as d4, and the diameter of connection shaft portion  45  is defined as d5, diameter d4 of auxiliary shaft portion  44  is set larger than diameter d1 of main shaft portion  41 . 
     Two-cylinder hermetic compressor according to the present exemplary embodiment is configured such that diameter d4 of auxiliary shaft portion  44  is set larger than diameter d1 of main shaft portion  41 , thereby being capable of reducing maximum stress exerted on auxiliary shaft portion  44  to suppress an amount of sliding frictional wear on auxiliary shaft portion  44 . 
     Note that, since second piston  32 B is inserted into second eccentric portion  43  from auxiliary shaft portion  44 , the inner diameter of second piston  32 B is required to be set larger as compared to the case in which diameter d4 of auxiliary shaft portion  44  is set to be the same as diameter d1 of main shaft portion  41 . 
     Conventionally, first piston  32 A and second piston  32 B are generally configured to have the same shape so as to use the same element. However, in the present exemplary embodiment, the inner diameter of second piston  32 B is set larger than the inner diameter of first piston  32 A. Specifically, by setting the inner diameter of first piston  32 A to be smaller than the inner diameter of second piston  32 B, diameter d2 of first eccentric portion  42  is made smaller than diameter d3 of second eccentric portion  43 . Accordingly, a sliding loss on first eccentric portion  42  can be reduced. 
     First communication path  12 A which is in communication with oil feed path  47  formed inside shaft  40  is open at the end of main shaft portion  41  on the side of first eccentric portion  42 , and second communication path  12 B which is in communication with oil feed path  47  formed inside shaft  40  is open at the end of auxiliary shaft portion  44  on the side of second eccentric portion  43 . 
     The diameter is set to be smaller than diameter d1 of main shaft portion  41  on the position where first communication path  12 A is open, and the diameter is set to be smaller than diameter d4 of auxiliary shaft portion  44  on the position where second communication path  12 B is open, whereby oil can be reliably fed to compression mechanism unit  30 . 
     Third communication path  12 C which is in communication with oil feed path  47  formed inside shaft  40  is open at the side surface of first eccentric portion  42 , and fourth communication path  12 D which is in communication with oil feed path  47  formed inside shaft  40  is open at the side surface of second eccentric portion  43 . 
     Thrust receiving portion  46  is provided to second eccentric portion  43  on the side of auxiliary shaft portion  44 . Diameter d6 of thrust receiving portion  46  is smaller than diameter d3 of second eccentric portion  43  and larger than diameter d4 of auxiliary shaft portion  44 . 
     The end face of thrust receiving portion  46  is in contact with the surface of auxiliary bearing  53  on the side of second cylinder  31 B illustrated in  FIG. 1 . 
     The two-cylinder hermetic compressor according to the present exemplary embodiment receives the thrust load of shaft  40  on the surface of auxiliary bearing  53  on the side of second cylinder  31 B through the end face of thrust receiving portion  46 , thereby being capable of stably receiving the thrust load as compared to the configuration of receiving the thrust load on auxiliary shaft portion  44 . 
     Specifically, in the configuration in which the thrust load of shaft  40  is received by auxiliary shaft portion  44 , the thrust load of shaft  40  is received by the area of auxiliary shaft portion  44  excluding the area of oil feed path  47 , because oil feed path  47  is formed inside shaft  40 . Thrust receiving portion  46  has the diameter larger than the diameter of auxiliary shaft portion  44  and is eccentric relative to auxiliary shaft portion  44 . Therefore, according to the configuration in which the thrust load of shaft  40  is received by the end face of thrust receiving portion  46 , the area of the receiving portion is easily designed to be large as compared to the configuration in which the thrust load is received by auxiliary shaft portion  44 , whereby the thrust load can stably be received. 
       FIGS. 3 to 5  illustrate test results of maximum stress values on the auxiliary shaft portion in the two-cylinder hermetic compressor according to the exemplary embodiment of the present disclosure. 
       FIG. 3  shows specifications of Comparative Example in which diameter d1 of main shaft portion  41  and diameter d4 of auxiliary shaft portion  44  are the same, and Examples 1 to 4 in which diameter d4 of auxiliary shaft portion  44  is set larger than diameter d1 of main shaft portion  41 . 
     Example 1 is configured such that diameter d4 of auxiliary shaft portion  44  is 104% with respect to diameter d1 of main shaft portion  41 , Example 2 is configured such that diameter d4 of auxiliary shaft portion  44  is 108% with respect to diameter d1 of main shaft portion  41 , Example 3 is configured such that diameter d4 of auxiliary shaft portion  44  is 113% with respect to diameter d1 of main shaft portion  41 , and Example 4 is configured such that diameter d4 of auxiliary shaft portion  44  is 117% with respect to diameter d1 of main shaft portion  41 . 
       FIG. 4  is a graph showing the test result of maximum stress values on auxiliary shaft portions  44  in Comparative Example and Examples 1 to 4, and  FIG. 5  is an analysis diagram showing a stress distribution on auxiliary shaft portions  44  in Comparative Example and Examples 1 to 4. 
     As shown in  FIG. 4 , as compared to Comparative Example in which diameter d1 of main shaft portion  41  is the same as diameter d4 of auxiliary shaft portion  44 , the maximum stress value is lower by 11% in Example 1, the maximum stress value is lower by 19% in Example 2, the maximum stress value is lower by 22% in Example 3, and the maximum stress value is lower by 24% in Example 4. 
     Therefore, the test result shows that remarkable effect is obtained within the range in which the proportion of diameter d4 of auxiliary shaft portion  44  relative to diameter d1 of main shaft portion  41  exceeds 100% and not more than 117%, as compared to Comparative Example. Note that, as apparent from  FIG. 4 , the proportion is preferably not more than 117%, and more preferably not more than 108%, since the decrease rate of the maximum stress value remains the same level after the proportion exceeds 117%. 
     While the present disclosure describes a two-cylinder hermetic compressor, it is also applicable to a compressor provided with a plurality of, such as three or more, cylinders.