Patent Publication Number: US-2018031280-A1

Title: Hermetic refrigerant compressor and refrigeration apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a reciprocating sealed refrigerant compressor which reciprocates a piston inside a cylinder to compress a refrigerant, and a refrigeration device including this sealed refrigerant compressor. 
     2. Description of the Related Art 
     This application claims priority to and the benefit of Japanese Patent Application No. 2016-149265 filed on Jul. 29, 2016, the entire disclosure of which is incorporated herein by reference. 
     A reciprocating refrigerant compressor is configured to accommodate an electric component and a compression component in a sealed container. Lubricating oil is reserved in the sealed container. The lubricating oil is reserved in a lower portion of the interior of the sealed container. The compression component includes a cylinder and a piston. When a vertical direction of the sealed container is a longitudinal direction, the cylinder and the piston are disposed to extend in a lateral direction (direction perpendicular to the vertical direction). The compression component is configured to compress the refrigerant in such a manner that the electric component causes the piston to reciprocate inside the cylinder. 
     Conventionally, the reciprocating refrigerant compressor is required to provide a low vibration. In recent years, the reciprocating refrigerant compressor is required to provide a lower vibration and have a smaller size. As described above, in the reciprocating refrigerant compressor, the cylinder and the piston of the compression component are disposed to extend in a lateral direction. For this reason, an unbalanced load in the lateral direction tends to occur due to the reciprocating motion of the piston. The unbalanced load is a significant cause of a vibration of the refrigerant compressor. 
     As a conventional method for cancelling or relieving the unbalanced load state, it is known that a balance weight is mounted on the compression component or the electric component. The compression component includes a crankshaft having a main shaft section rotatably mounted on the cylinder block. It is known that the balance weight is mounted on the crankshaft. The electric component includes a stator and a rotor. It is also known that the balance weight is mounted on the upper surface or lower surface of the rotor. 
     However, mounting the balance weight results in an increase in the number of members of the refrigerant compressor and an increase in the number of manufacturing steps of the refrigerant compressor. This increases manufacturing cost. To avoid this, Japanese Laid-Open Patent Application Publication No. 2013-087685 discloses a configuration in which the balance weight is secured to an eccentric shaft of the crankshaft of the compression component, and the end surface of the rotor of the electric component is provided with an end plate integrated with a weight member comprising a rolled member having a portion bent at a right angle. Since the weight member is integrated with the end plate, assembling work steps can be made easier and the number of members does not increase. 
     SUMMARY OF THE INVENTION 
     In recent years, the sealed refrigerant compressor is required to provide a lower vibration and have a smaller size than the conventional sealed refrigerant compressor. In the above-described method of mounting the balance weight, it is necessary to secure a space for the balance weight in the interior of the sealed container, depending on a mounting location of the balance weight. For this reason, the size of the refrigerant compressor may not be reduced. 
     The present invention has been developed to solve the above-described problem, and an object of the present invention is to provide a reciprocating sealed refrigerant compressor which can realize a lower vibration and a smaller size. 
     To solve the above described problem, according to a first aspect of the present disclosure, a sealed refrigerant compressor comprises a sealed container in which lubricating oil is reserved in a lower portion in an interior of the sealed container; an electric component accommodated in the sealed container; and a compression component accommodated in the sealed container and configured to be driven by the electric component, wherein the compression component includes a cylinder disposed inside the sealed container to extend in a direction crossing a vertical direction, and a piston which is reciprocatable inside the cylinder, wherein the electric component includes a stator, and a rotor having a lower surface facing an oil surface of the lubricating oil, and the rotor has a shape in which a diameter of the rotor is larger than a length of the rotor in a rotational axis direction thereof, and wherein a core of the rotor is provided with at least one balance hole for adjusting a load balance during rotation of the rotor. 
     In accordance with this configuration, in the reciprocating sealed refrigerant compressor, the core of the rotor with a large diameter is provided with at least one balance hole, and thus an unbalanced load state can be cancelled or relieved as in the case of providing the balance weight. It is sufficient that at least one balance hole is provided in the core of the rotor. Therefore, depending on the unbalanced load state of the sealed refrigerant compressor, the balance hole with a simple structure can be provided more flexibly. Since the load of the rotor can be adjusted into an unbalanced state, the load balance of the whole of the sealed refrigerant compressor can be adjusted well. As a result, the sealed refrigerant compressor can realize a lower vibration and a smaller size. 
     According to another aspect of the present disclosure, a refrigeration device comprises the above sealed refrigerant compressor. 
     In accordance with the above-described configuration of the present invention, it becomes possible to obtain advantages that the sealed refrigerant compressor can realize a lower vibration and a smaller size. 
     The above and further objects, features and advantages of the present invention will more fully be apparent from the following detailed description of preferred embodiment with reference to accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing the exemplary configuration of a sealed refrigerant compressor according to Embodiment 1 of the present disclosure. 
         FIGS. 2A to 2C  are views showing the exemplary configuration of a rotor included in the sealed refrigerant compressor of  FIG. 1 . 
         FIGS. 3A to 3D  are views showing another exemplary configuration of the rotor of  FIGS. 2A to 2C . 
         FIGS. 4A to 4C  are views showing another exemplary configuration of the rotor included in the sealed refrigerant compressor of  FIG. 1 . 
         FIG. 5  is a cross-sectional view showing the exemplary configuration of a sealed refrigerant compressor according to Embodiment 2 of the present disclosure. 
         FIGS. 6A to 6C  are views showing another exemplary configuration of an electric component included in the sealed refrigerant compressor of  FIG. 4 . 
         FIG. 7  is a schematic view showing the exemplary configuration of an article storage device according to Embodiment 3 of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A sealed refrigerant compressor of the present disclosure comprises a sealed container in which lubricating oil is reserved in a lower portion in an interior of the sealed container; an electric component accommodated in the sealed container; and a compression component accommodated in the sealed container and configured to be driven by the electric component, wherein the compression component includes a cylinder disposed inside the sealed container to extend in a direction crossing a vertical direction, and a piston which is reciprocatable inside the cylinder, wherein the electric component includes a stator, and a rotor having a lower surface facing an oil surface of the lubricating oil, and the rotor has a shape in which a diameter of the rotor is larger than a length of the rotor in a rotational axis direction thereof, and wherein a core of the rotor is provided with at least one balance hole for adjusting a load balance during rotation of the rotor. 
     In accordance with this configuration, in the reciprocating sealed refrigerant compressor, the core of the rotor with a large diameter is provided with at least one balance hole, and thus the unbalanced load state can be cancelled or relieved as in the case of providing the balance weight. It is sufficient that at least one balance hole is provided in the core of the rotor. Therefore, depending on the unbalanced load state of the sealed refrigerant compressor, the balance hole with a simple structure can be provided more flexibly. Since the load of the rotor can be adjusted into an unbalanced state, the load balance of the whole of the sealed refrigerant compressor can be adjusted well. As a result, the sealed refrigerant compressor can realize a lower vibration and a smaller size. 
     In the above sealed refrigerant compressor, the rotor may include a permanent magnet and does not include a magnet protective member covering an outer periphery of the permanent magnet provided in the core, and the at least one balance hole may be located not to be line-symmetric or point-symmetric with respect to a rotational axis of the rotor. 
     In accordance with this configuration, even in the configuration in which the at least one balance hole is located not to be line-symmetric or point-symmetric with respect to the rotational axis of the rotor, it becomes possible to substantially suppress or avoid a situation in which a change in a magnetic field attributed to the balance hole virtually affects the electric component. Therefore, the size of the balance hole can be reduced, and the shape of the balance hole can be simplified. In addition, the balance hole(s) can be disposed at any location(s) which is/are other than the symmetric location. Therefore, depending on the unbalanced load state of the sealed refrigerant compressor, the balance hole with a simpler structure can be provided more flexibly. Since the load of the rotor can be adjusted into an unbalanced state, the load balance of the whole of the sealed refrigerant compressor can be adjusted well. As a result, the sealed refrigerant compressor can realize a lower vibration and a smaller size. 
     In the above sealed refrigerant compressor, the at least one balance hole may be provided in the core in such a manner that at least a part of the balance hole is located outward relative to the permanent magnet when viewed from the rotational axis direction of the rotor (in a plan view). 
     In the above sealed refrigerant compressor, the compression component may be accommodated in the sealed container in such a manner that the compression component is located above the electric component. 
     In the above sealed refrigerant compressor, the at least one balance hole may extend in the rotational axis direction of the rotor. 
     In the above sealed refrigerant compressor, the at least one balance hole may be a through-hole. 
     In the above sealed refrigerant compressor, a balance weight may be fastened to an upper surface of the rotor to adjust a load balance, and the balance hole may be provided within a portion of the core of the rotor to which the balance weight is fastened. 
     In the above sealed refrigerant compressor, the at least one balance hole may be a blind hole having a bottom surface which is set to be higher than an upper surface of the stator. 
     According to another aspect of the present disclosure, a refrigeration device comprises the above sealed refrigerant compressor. 
     Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. Throughout the drawings, the same or corresponding components are designated by the same reference symbols, and will not be described in repetition. 
     Embodiment 1 
     [Configuration of Sealed Refrigerant Compressor] 
     Referring to  FIG. 1 , a sealed refrigerant compressor  10 A according to Embodiment 1 includes an electric component  20 A and a compression component  30  which are accommodated in a sealed container  11 , and a refrigerant gas and lubricating oil  13  are reserved in the sealed container  11 . The electric component  20 A and the compression component  30  constitute a compressor body  12 . The compressor body  12  is disposed inside the sealed container  11  in a state in which the compressor body  12  is elastically supported by a suspension spring (not shown) provided on the bottom portion of the sealed container  11 . 
     The sealed container  11  is provided with a suction pipe (not shown) and a discharge pipe (not shown). The first end of the suction pipe is in communication with the inner space of the sealed container  11 , and the second end thereof is connected to a refrigeration device (not shown), thus constituting a refrigeration cycle such as a refrigerant circuit. The first end of the discharge pipe is connected to the compression component  30 , and the second end thereof is connected to the refrigeration device. As will be described later, the refrigerant gas having been compressed by the compression component  30  is led to the refrigerant circuit through the discharge pipe, while the refrigerant gas from the refrigerant circuit is led to the inner space of the sealed container  11  through the suction pipe. 
     The specific configuration of the sealed container  11  is not particularly limited. In the present embodiment, the sealed container  11  is manufactured by, for example, drawing of an iron plate. The refrigerant gas is reserved in the sealed container  11  in a relatively low temperature state and at a pressure which is substantially equal to that on a low-pressure side in the refrigerant circuit including the sealed refrigerant compressor  10 A. Lubricating oil  13  is reserved in the sealed container  11  and lubricates a crankshaft  40  (which will be described later) included in the compression component  30 . As shown in  FIG. 1 , the lubricating oil  13  is reserved in the bottom portion of the sealed container  11 . 
     The kind of the refrigerant gas is not particularly limited. The refrigerant gas known in the field of the refrigeration cycle is suitably used. In the present embodiment, for example, R600a which is a hydrocarbon based refrigerant gas is suitably used. R600a has a relatively low global warming potential (GNP). For the purpose of protection of global environments, R600a is one of refrigerant gases suitably used. The kind of the lubricating oil  13  is not particularly limited. The lubricating oil known in the field of the compressor is suitably used. 
     As shown in  FIG. 1 , the electric component  20 A includes at least a stator  21 A and a rotor  22 A. The stator  21 A is secured to the lower side of a cylinder block  31  (which will be described later) included in the compression component  30  by use of a fastener member such as a bolt (not shown). The rotor  22 A is disposed inward relative to the stator  21 A and coaxially with the stator  21 A. The rotor  22 A is configured to secure a main shaft section  41  of the crankshaft  40  (which will be described later) included in the compression component  30  by, for example, shrinkage fitting (thermal insert). 
     As shown in  FIG. 1 , the rotor  22 A rotates around a rotational axis R extending in a longitudinal direction and indicated by one-dotted line. The rotor  22 A is disposed inside the sealed container  11  in such a manner that the lower surface of the rotor  22 A faces the oil surface of the lubricating oil  13 . As shown by black block arrows of  FIG. 1 , when the length of the rotor  22 A in the direction of the rotational axis R is Lr, and the diameter of the rotor  22 A is Ld, the length Lr is smaller than the diameter Ld (Lr&lt;Ld). In brief, the rotor  22 A has a structure in which the diameter Ld is larger than the axial length Lr of the rotor  22 A. The rotor  22 A is elongated in the lateral direction. 
     The upper surface of the rotor  22 A faces a bearing unit  35  which is a part of the cylinder block  31  (which will be described later). The stator  21 A has a plurality of winding wires. The rotor  22 A has a plurality of permanent magnets  23  facing the plurality of winding wires. In the present embodiment, as shown in  FIG. 1 , the rotor  22 A has a configuration in which the plurality of permanent magnets  23  are embedded in a core (iron core) which is the body of the rotor  22 A. The electric component  20 A is an interior permanent magnet motor (IPM) motor. 
     As described above, since the rotor  22 A is disposed inward relative to the stator  21 A, the electric component  20 A is an inner rotor motor. The rotor  22 A has a structure in which the core is formed with balance through-holes  24 A and a balance weight  25  is mounted on the upper surface of the core. The electric component  20 A is connected to an external inverter drive circuit (not shown), and is inverter-driven at one of a plurality of operating frequencies. The specific configuration of the rotor  22 A will be described later. 
     The compression component  30  is driven by the electric component  20 A and is configured to compress the refrigerant gas. In the present embodiment, as shown in  FIG. 1 , the compression component  30  is accommodated in the sealed container  11  in such a manner that the compression component  30  is located above the electric component  20 A. As shown in  FIG. 1 , the compression component  30  includes the cylinder block  31 , a cylinder  32 , a piston  33 , a compression chamber  34 , the bearing unit  35 , the crankshaft  40 , a valve plate  36 , a cylinder head  37 , a suction muffler  38 , etc. 
     The cylinder block  31  is provided with the cylinder  32  and the bearing unit  35 . The cylinder  32  is disposed to extend in a direction crossing a vertical direction, and fastened to the bearing unit  35 . More specifically, when the vertical direction is a longitudinal direction and a horizontal direction (direction perpendicular to the vertical direction) is a lateral direction, in a state in which the sealed refrigerant compressor  10 A is placed on a horizontal plane, the cylinder  32  is disposed to extend in the lateral direction in the interior of the sealed container  11  and fastened to the bearing unit  35 . 
     A bore having a substantially cylindrical shape and a diameter that is substantially equal to that of the piston  33  is provided inside the cylinder  32 . The piston  33  is reciprocatingly inserted into the bore. The cylinder  32  and the piston  33  define the compression chamber  34 . The refrigerant gas is compressed in the compression chamber  34 . The bearing unit  35  supports the main shaft section  41  of the crankshaft  40  in such a manner that the main shaft section  41  is rotatable. 
     The crankshaft  40  is supported inside the sealed container  11  in such a manner that the axis of the crankshaft  40  extends in the longitudinal direction. The crankshaft  40  includes the main shaft section  41 , an eccentric shaft section  42 , a connecting rod  43 , a flange portion  44 , an oil feeding mechanism (not shown), etc. As described above, the main shaft section  41  of the crankshaft  40  is secured to the rotor  22 A of the electric component  20 A. The eccentric shaft section  42  is eccentric with respect to the main shaft section  41 . The connecting rod  43  is a coupling section coupling the eccentric shaft section  42  and the piston  33  to each other. The flange portion  44  integrally connects the eccentric shaft section  42  and the main shaft section  41  to each other. The oil feeding mechanism is provided so that the lower end of the main shaft section  41  which is immersed in the lubricating oil  13  is in communication with the upper end of the eccentric shaft section  42 . The oil feeding mechanism is formed by, for example, an oil feeding pump and a spiral groove formed on the surface of the main shaft section  41 . The oil feeding mechanism feeds the lubricating oil  13  to the crankshaft  40 . 
     As described above, the piston  33  inserted into the cylinder  32  is coupled to the connecting rod  43 . The piston  33  is disposed in such a manner that the axis of the piston  33  crosses the axial direction of the crankshaft  40 . In the present embodiment, the crankshaft  40  is disposed in such a manner its center axis extends in the longitudinal direction (its axial direction). In contrast, the piston  33  is disposed in such a manner its center axis extends in the lateral direction (its axial direction). Therefore, the axial direction of the piston  33  is perpendicular to the axial direction of the crankshaft  40 . As described above, the connecting rod  43  couples the piston  33  and the eccentric shaft section  42  to each other. Therefore, the rotational motion of the crankshaft  40  rotating by the electric component  20 A is transmitted to the piston  33  via the connecting rod  43 . This causes the piston  33  to reciprocate inside the cylinder  32 . 
     As described above, the piston  33  is inserted into the first end portion (on the crankshaft  40  side) of the cylinder  32 . The second end portion (away from the crankshaft  40 ) is closed by the valve plate  36  and the cylinder head  37 . The valve plate  36  is located between the cylinder  32  and the cylinder head  37 . The valve plate  36  is provided with a suction valve (not shown) and a discharge valve (not shown). The cylinder head  37  is formed with a discharge space therein. The refrigerant gas from the compression chamber  34  is discharged into the discharge space of the cylinder head  37  when the discharge valve of the valve plate  36  is opened. The cylinder head  37  is in communication with the discharge pipe (not shown). 
     The suction muffler  38  is located on a lower side in the interior of the sealed container  11 , from the perspective of the cylinder  32  and the cylinder head  37 . The suction muffler  38  has a muffling space therein. The suction muffler  38  is in communication with the compression chamber  34  via the valve plate  36 . When the suction valve of the valve plate  36  is opened, the refrigerant gas in the interior of the suction muffler  38  is suctioned into the compression chamber  34 . 
     [Operation of Sealed Refrigerant Compressor] 
     Next, the operation of the sealed refrigerant compressor  10 A having the above-described configuration will be specifically described in conjunction with advantages thereof. Although not shown in  FIG. 1 , the suction pipe and the discharge pipe of the sealed refrigerant compressor  10 A are connected to the refrigeration device having a well-known configuration, and constitute the refrigerant circuit. 
     When electric power is supplied from an external power supply to the electric component  20 A, a current flows through the stator  21 A and a magnetic field is generated, which causes the rotor  22 A to rotate. According to the rotation of the rotor  22 A, the main shaft section  41  of the crankshaft  40  rotates. The rotation of the main shaft section  41  of the crankshaft  40  is transmitted to the piston  33  via the flange portion  44 , the eccentric shaft section  42 , and the connecting rod  43 , and thereby the piston  33  reciprocates inside the cylinder  32 . Correspondingly, the refrigerant gas is suctioned, compressed, and discharged inside the compression chamber  34 . 
     Hereinafter, of directions in which the piston  33  moves inside the cylinder  32 , a direction in which the volume of the compression chamber  34  increases will be referred to “increase direction”, and a direction in which the volume of the compression chamber  34  decreases will be referred to “decrease direction.” When the piston  33  moves in the increase direction, the refrigerant gas in the interior of the compression chamber  34  is expanded. Then, when a pressure in the compression chamber  34  falls below a suction pressure, the suction valve of the valve plate  36  starts to be opened due to a difference between the pressure in the compression chamber  34  and a pressure in the suction muffler  38 . 
     According to this operation, the refrigerant gas with a low temperature, which has been returned from the refrigeration device, is released to the inner space of the sealed container  11  through the suction pipe. Then, the refrigerant gas is introduced into the muffling space of the suction muffler  38 . At this time, as described above, the suction valve of the valve plate  36  starts to be opened. Therefore, the refrigerant gas having been introduced into the muffling space of the suction muffler  38  flows into the compression chamber  34 . Then, when the piston  33  moves in the decrease direction from a bottom dead center inside the cylinder  32 , the refrigerant gas in the interior of the compression chamber  34  is compressed, and the pressure in the compression chamber  34  increases. Also, due to the difference between the pressure in the compression chamber  34  and the pressure in the suction muffler  38 , the suction valve of the valve plate  36  is closed. 
     Then, when the pressure in the compression chamber  34  exceeds a pressure in the cylinder head  37 , the discharge valve (not shown) starts to be opened, due to the difference between the pressure in the compression chamber  34  and the pressure in the cylinder head  37 . According to this operation, the compressed refrigerant gas is discharged into the cylinder head  37 , until the piston  33  reaches a top dead center inside the cylinder  32 . Then, the refrigerant gas having been discharged into the cylinder head  37  is sent out to the refrigeration device through the discharge pipe. 
     Then, when the piston  33  moves in the increase direction again from the top dead center inside the cylinder  32 , the refrigerant gas in the interior of the compression chamber  34  is expanded, which decreases the pressure in the compression chamber  34 . When the pressure in the compression chamber  34  falls below the pressure in the cylinder head  37 , the discharge valve of the valve plate  36  is closed. 
     The above-described suction, compression, and discharge strokes are performed in repetition in every rotation of the crankshaft  40 , and thus the refrigerant gas is circulated within the refrigeration cycle. 
     [Configuration of Rotor] 
     In the sealed refrigerant compressor  10 A according to the present embodiment, as shown in  FIGS. 1 and 2A to 2C , the rotor  22 A of the electric component  20 A is provided with the balance through-holes  24 A. As described above, the rotor  22 A according to the present embodiment is the IPM rotor, and therefore, the permanent magnets  23  are embedded in the core which is the body of the rotor  22 A. As shown in  FIG. 2C , the balance through-holes  24 A are provided in the core at locations that are other than the locations at which the permanent magnets  23  are embedded in the core. In the present embodiment, as indicated by broken lines of  FIG. 2C , the permanent magnets  23  are entirely embedded in the core. In this structure, the rotor  22 A does not include magnet protective members covering the outer peripheral surfaces of the permanent magnets  23 . In other words, the rotor  22 A does not require the magnet protective members for covering the permanent magnets  23 . 
     As shown in  FIGS. 2A to 2C , the rotor  22 A has a rotor shaft hole  29   a  at a center thereof. The main shaft section  41  of the crankshaft  40  and the lower end of the bearing unit  35  of the cylinder block  31  are insertable into the rotor shaft hole  29   a . Therefore, the center line in the extending direction of the rotor shaft hole  29   a  conforms to the rotational axis R of the rotor  22 A.  FIG. 2A  which is the plan view and  FIG. 2C  which is the bottom view indicate the rotational axis R by a cross mark, while  FIG. 2B  which is the longitudinal sectional view indicates the rotational axis R by one-dotted line. 
     As can be seen from  FIG. 2B , the rotor shaft hole  29   a  has a shape in which its upper part and its lower part are different from each other in inner diameter (its upper part and its lower part have different inner diameters). The rotor shaft hole  29   a  has a stepped part so that a portion of the bearing unit  35  into which the main shaft section  41  is inserted is inserted into the upper part of the rotor shaft hole  29   a , and only the main shaft section  41  is inserted into the lower part of the rotor shaft hole  29   a . As shown in  FIG. 1 , the bearing unit  35  constitutes the lower part of the cylinder block  31 . In the present embodiment, the bearing unit  35  extends in the lateral direction over the entire sealed container  11 . The center part of the bearing unit  35  has a cylindrical shape protruding in a downward direction. The upper part of the main shaft section  41  is inserted into the center part of the bearing unit  35 . Therefore, the rotor shaft hole  29   a  has a shape in which the diameter of the upper part is greater than that of the lower part. In this structure, the upper part of the rotor shaft hole  29   a  supports the cylindrical portion of the bearing unit  35  (and the main shaft section  41  inserted into the cylindrical portion of the bearing unit  35 ) in a state in which the cylindrical portion of the bearing unit  35  is inserted into the rotor shaft hole  29   a , and the lower part supports only the main shaft section  41  inserted into the rotor shaft hole  29   a.    
     The core constituting the body of the rotor  22 A has a configuration in which a plurality of electromagnetic steel plates (thin iron plates) of a disc shape are stacked together (laminated). To integrate the plurality of electromagnetic steel plates to construct the core, fastener members are provided to penetrate the plurality of electromagnetic steel plates in the direction of the rotational axis R, as shown in  FIGS. 1 and 2B . In the present embodiment, as shown in  FIGS. 2A and 2B , the plurality of electromagnetic steel plates are integrated together by use of caulking pins  26 . The plurality of electromagnetic steel plates are formed with caulking holes, respectively, into which the caulking pins  26  are inserted. 
     As shown in  FIG. 2B , end plates  27  are provided on the upper surface and lower surface of the rotor  22 A, respectively. Therefore, the upper ends and lower ends of the balance through-holes  24 A are closed by the end plates  27 . As shown in  FIGS. 1 and 2B , a balance weight  25  (which will be described later) is fastened to the upper surface of the rotor  22 A. Therefore, the balance weight  25  is located on the upper side of the end plate  27 . In the example of  FIG. 2A , the balance through-holes  24 A are indicated by broken lines, while in the example of  FIG. 2C , the permanent magnets  23  and the balance through-holes  24 A are indicated by broken lines. 
     The balance through-holes  24 A are balance holes for adjusting a load balance during the rotation of the rotor  22 A. In the present embodiment, two balance through-holes  24 A are provided. As shown in  FIGS. 1 and 2B , the balance through-holes  24 A extend in the direction of the rotational axis R of the rotor  22 A. As shown in  FIGS. 2A and 2C , when viewed from the lower surface of the rotor  22 A, the two balance through-holes  24 A are eccentrically located in a portion of the rotor  22 A which is in the vicinity of the outer periphery of the rotor  22 A. In other words, in the present embodiment, the plurality of balance through-holes  24 A of the rotor  22 A are provided for the eccentric location in the core which is the body of the rotor  22 A in such a manner that the balance through-holes  24 A are not point-symmetric or line-symmetric with respect to the rotational axis R. 
     A sealed refrigerant compressor of a rotary type as well as the sealed refrigerant compressor of a reciprocating type is known. In the sealed refrigerant compressor of a rotary type, the rotor is typically elongated in the longitudinal direction. Specifically, the length Lr of the rotor in the rotational axis direction is set to be larger than the diameter Ld (Lr&gt;Ld) of the rotor. Conventionally, in the sealed refrigerant compressor of a rotary type, it is known that the core of the rotor is formed with a plurality of balance blind holes which are line-symmetric or point-symmetric with respect to the rotational axis of the rotor. 
     In one example, in the sealed refrigerant compressor of a rotary type, each of the upper end surface and lower end surface of the rotor is formed with two balance blind holes which are adjacent to each other and occupy almost one fourth of each of the end surfaces. The balance blind holes of each of the upper end surface and lower end surface of the rotor are point-symmetric with respect to the rotational axis of the rotor. The balance blind holes having such a configuration can adjust a load balance by adjusting their depths rather than their positions. 
     In another example, the core of the rotor is formed with a first balance through-hole and a second balance through-hole which are line-symmetric with respect to the rotational axis of the rotor. In this configuration, if the balance through-holes have the same shape, they function to cancel (counteract) effects of adjusting the load balance. To avoid this, a portion of one of the first and second balance through-holes is set to have a smaller diameter, the depth of the blind hole is adjusted instead of the use of the through-hole, or one of the first and second balance through-holes is composed of a plurality of balance through-holes, in order to minimize cancellation of the load balance. 
     As described the above, in the conventional sealed refrigerant compressor of a rotary type, in a case where the core of the rotor elongated in the longitudinal direction is formed with the plurality of balance holes which are point-symmetric or line-symmetric with respect to the rotational axis of the rotor. The balance holes have a large size and occupy about the half of the circumference of the rotor, or have a complicated structure in which the balance holes are different from each other in diameter, depth, or the number. 
     It is also conventionally known that the core of the rotor of the electric component is formed with a slit hole in order to mitigate an unbalanced magnetic flux density or a magnetic salient-pole property. In view of this, if the core of the rotor is improperly formed with a hole, an undesired change in a magnetic field (disorder of the magnetic field) may occur. It is known that a surface permanent magnet motor (SPM) comprises, for example, a magnet protective member (cover) made of stainless steel, to protect the permanent magnets. Depending on the configuration of the rotor or the stator, the magnet protective member cause an undesired change in a magnetic field (disorder of the magnetic field). To prevent or avoid the problem associated with the magnet protective member, the IPM motor is configured in such a manner that the permanent magnets are embedded in the core. 
     In the above-described sealed refrigerant compressor of a rotary type, in which the core of the rotor is formed with the balance holes, the rotor is required to have the magnet protective members. In this case, if the balance holes are provided to be non-symmetric with respect to the rotational axis of the rotor, the degree of the disorder of the magnetic field may be increased due to the presence of magnet protective members. For this reason, it is presumed that the balance holes are required to be point-symmetric or line-symmetric with respect to the rotational axis of the rotor, as described above. 
     Regarding the above-described problem, the present inventors intensively studied. In the reciprocating sealed refrigerant compressor, to reduce the size of the compressor, the rotor is elongated in the lateral direction (see  FIG. 1  or the like), and the diameter Ld of the rotor is set to be larger than the length Lr of the rotor in the rotational axis direction (Ld&gt;Lr). Also, in the reciprocating sealed refrigerant compressor, the IPM motor which does not require the magnet protective members or the SPM motor which does not include the magnet protective members is used. 
     In the electric component  20 A which does not require the magnet protective members, it can be revealed that by forming in the core of the rotor, the plurality of balance holes which are non-symmetric with respect to the rotational axis R, it becomes possible to well adjust the load balance of the rotor  22 A without providing the large balance holes or the balance holes with a complicated shape, like the sealed refrigerant compressor of a rotary type. 
     As described above, the rotor  22 A of the present embodiment is formed with the plurality of balance through-holes  24 A which are non-symmetric with respect to the rotational axis R without providing the magnet protective members. This configuration can substantially suppress or avoid a situation in which the disorder of the magnetic field attributed to the balance through-holes  24 A virtually affects the electric component  20 A. Therefore, the size of the balance through-holes  24 A can be reduced, and the shape of the balance through-holes  24 A can be simplified. In addition, the balance through-holes  24 A can be disposed at any locations which are other than the symmetric locations. Thus, the balance through-holes  24 A with a simpler configuration can be disposed more flexibly, depending on the unbalanced load state of the sealed refrigerant compressor  10 A. As a result, the load balance of the rotor  22 A can be adjusted well, and the sealed refrigerant compressor  10 A can realize a lower vibration and a smaller size. 
     As shown in  FIGS. 1, 2A, and 2B , in the rotor  22 A of the present embodiment, the balance weight  25  is fastened to the upper surface of the rotor  22 A. This balance weight  25  is similar to that used to adjust the load balance of the rotor  22 A in the conventional configuration. In the present embodiment, the balance weight  25  is fastened to the upper surface of the rotor  22 A rather than the lower surface of the rotor  22 A. The plurality of balance through-holes  24 A are provided within a portion of the core of the rotor  22 A to which the balance weight  25  is fastened. In other words, it is sufficient that when viewed from the upper surface or lower surface of the rotor  22 A, the plurality of balance through-holes  24 A are provided in the core at locations on a projection plane of the balance weight  25 . 
     Since the balance weight  25  are positioned in the core of the rotor  22 A, at the locations on the projection plane of the balance holes, the balance of the rotor  22 A can be improved more flexibly. For example, by providing the balance holes in the core of the rotor  22 A, the load balance can be roughly adjusted. In addition to this, by mounting the balance weight  25  on the core, the load balance can be finely adjusted. 
     The balance holes which can adjust the load balance can be formed without increasing the number of members or manufacturing steps, in manufacturing the sealed refrigerant compressor  10 A. However, the formation of the balance holes in the core of the rotor  22 A is less flexible in the manufacturing steps than mounting the balance weight  25  on the core of the rotor  22 A is. In contrast, mounting the balance weight  25  on the core of the rotor  22 A causes an increase in the number of members or the manufacturing steps. However, the balance weight  25  can be mounted on the core of the rotor  22 A at a later time. Therefore, the mounting the balance weight  25  on the core of the rotor  22 A is more flexible in the manufacturing steps than the formation of the balance holes in the core of the rotor  22 A. 
     In light of the above, by forming the balance holes in the core of the rotor  22 A, the load balance of the rotor  22 A can be roughly adjusted. Then, by mounting the balance weight  25  with a suitable number on the core of the rotor  22 A at a later time, the load balance of the rotor  22 A can be finely adjusted. Although the mounting the balance weight  25  on the core of the rotor  22 A causes an increase in the number of members or the manufacturing steps, the load balance of the rotor  22 A can be finely adjusted more suitably, by use of the balance weight  25  and the balance through-holes  24 A. 
     The balance weight  25  used in the present embodiment may be similar to that of the conventional example. For the purpose of fine adjustment of the load balance, a plurality of lighter balance weights may be prepared. By doing so, the load balance of the rotor  22 A can be finely adjusted more flexibly, and the members (fastener members, securing members, mounting members, etc.) used to mount the balance weight  25  on the core of the rotor  22 A can be simplified. The plurality of balance weights  25  with the same shape, or different shapes may be prepared. 
     Since the balance weight  25  is not provided on the lower surface of the rotor  22 A which faces the oil surface of the lubricating oil  13 , a smallest gap can be secured between the rotor  22 A and the oil surface of the lubricating oil  13 . Since the gap between the rotor  22 A and the oil surface of the lubricating oil  13  is secured, it becomes possible to prevent a situation in which the lubricating oil  13  is agitated by the rotation of the rotor  22 A. This makes it possible to substantially prevent breakage of the suction valve and the discharge valve, which is caused by an event in which the lubricating oil  13  in a bubble state is suctioned from the suction muffler  38  into the compression chamber  34 . In addition, a lower vibration of the sealed refrigerant compressor  10 A can be realized by fine adjustment of the load balance, an increase in the height of the sealed refrigerant compressor  10 A can be suppressed, and compact configuration (smaller size) of the sealed refrigerant compressor  10 A can be realized. 
     Modified Example 
     In the present embodiment, as shown in  FIGS. 1 and 2B , the balance holes are configured as the through-holes (balance through-holes  24 A) extending in the direction of the rotational axis R of the rotor  22 A. This configuration is merely exemplary. For example, the balance holes may not be the through-holes, and may be, for example, balance blind holes  24 C,  24 D (blind holes having bottoms) of  FIGS. 3A and 3B . In a case where the balance holes are the blind holes, the blind holes may be provided only in the upper surface of the rotor  22 A as shown in  FIG. 3A , may be provided only in the lower surface of the rotor  22 A, or may be provided in both of the upper and lower surfaces of the rotor  22 A. 
     In a case where the balance holes are the blind holes, the depths of the balance holes are not particularly limited. The depths of the plurality of blind holes may be equal to each other or different from each other. At this time, for example, as shown in  FIG. 3B , it is preferable that the bottom surface of the balance blind hole  24 D be set to be higher than the upper surface of the stator  21 A. This makes it possible to better adjust the load balance. At least one balance hole may be provided, or a plurality of balance holes may be provided. For example, as shown in  FIG. 3C , three or more balance holes (balance through-holes  24 A) may be provided. Or, as shown in  FIG. 3D , one balance hole (balance through-hole  24 A) may be provided. In a case where one balance hole (balance through-hole  24 A) is provided for the eccentric location, this balance hole is not point-symmetric or line-symmetric with respect to the rotational axis R of the rotor  22 A. The size of the balance hole, namely, the inner diameter of the balance hole is not particularly limited, and may be set within proper ranges according to conditions. 
     Further, the shape of the balance hole is not particularly limited. The cross-sectional shape (traverse sectional shape) of the balance hole may be a circle as shown in  FIGS. 2A and 2C . Or, the cross-sectional shape (traverse sectional shape) of the balance hole may be an oval, a rectangle, or a polygon. The longitudinal-sectional shape (spatial shape) of the balance hole may be columnar (cylindrical) with an equal diameter as a whole, as shown in  FIGS. 1 and 2B . Or, the inner diameter of the balance hole may be gradually changed, or may be changed in a stepwise manner (the balance hole has a stepped portion). 
     The location of the balance hole formed in the core is not particularly limited. As shown in  FIG. 2C , it is preferable that the balance holes (balance through-holes  24 A) be positioned outward relative to the permanent magnets  23  when viewed from the direction of the rotational axis R of the rotor  22 A (in a plan view). In the present embodiment, each of the permanent magnets  23  is curved so that its center portion is convex toward the inner periphery (toward the rotational axis R of the rotor  22 A), namely, its center portion is concave toward the outer periphery. The entire balance through-holes  24 A are located outward relative to the concave outer peripheral surfaces of the permanent magnets  23 , respectively. 
     In this layout, a lateral (horizontal) distance between the balance holes and the rotational axis R of the rotor  22 A can be increased as much as possible. Therefore, the adjustment amount of load balance by the balance holes can be increased. For example, in a case where the balance through-hole  24 A is located between the permanent magnets  23 , a part of the balance through-hole  24 A may be located outward relative to the permanent magnet  23 . In light of this, the balance holes are preferably positioned to be closest to the outer periphery of the rotor  22 A. 
     In the present embodiment, as shown in  FIGS. 1, 2A and 2B , the rotor  22 A is provided with the balance weight  25 , and the balance through-holes  24 A (balance holes) are provided within a portion of the core of the rotor  22 A to which the balance weight  25  is fastened. This configuration is merely exemplary. For example, as shown in  FIGS. 4A to 4C , the balance weight  25  may be omitted.  FIGS. 4A to 4C  are a plan view, a longitudinal sectional view, and a schematic plan view of  FIGS. 2A to 2C , respectively. The example of  FIGS. 4A to 4C  is the same as that of  FIGS. 2A to 2C  except that the balance weight  25  is omitted in the example of  FIGS. 4A to 4C . 
     Although not shown, the balance weight  25  may be mounted on the crankshaft  40  as well as the rotor  22 A. In other words, as the balance weight  25 , at least one of a rotor balance weight mounted on the rotor  22 A and a crankshaft balance weight mounted on the crankshaft  40  may be used. Moreover, as the balance weight  25 , a balance weight which is mountable at a location that is other than the rotor  22 A and the crankshaft  40  may be used. 
     As described above, in the sealed refrigerant compressor  10 A of the present embodiment, the rotor  22 A includes the core and the permanent magnets  23 , and does not include the magnet protective members covering the outer peripheral surfaces of the permanent magnets  23  provided in the core. In the sealed refrigerant compressor  10 A, the core is preferably provided for the eccentric location with at least one balance hole which is not line-symmetric or point-symmetric with respect to the rotational axis R of the rotor  22 A, in order to adjust the load balance during the rotation of the rotor  22 A. This makes it possible to suppress or avoid the disorder of the magnetic field attributed to the balance holes from substantially affecting the electric component  20 A, even in the configuration in which the balance holes are non-symmetric with respect to the rotational axis R. 
     Therefore, the size of the balance hole(s) can be reduced, and the shape of the balance hole(s) can be simplified. The balance holes may be provided at any locations except a configuration in which the balance holes are symmetric with respect to the rotational axis R of the rotor  22 A. Therefore, depending on the unbalanced load state of the sealed refrigerant compressor  10 A, the balance hole with a simple structure can be provided more flexibly. Since the load of the rotor  22 A can be adjusted into an unbalanced state, the load balance of the whole of the sealed refrigerant compressor  10 A can be adjusted well. As a result, the sealed refrigerant compressor  10 A can realize a lower vibration and a smaller size. 
     Embodiment 2 
     The above-described sealed refrigerant compressor  10 A of Embodiment 1 includes the electric component  20 A which is the inner rotor motor. This is merely exemplary. An electric component may be an outer rotor motor. Specifically, as shown in  FIG. 5 , a sealed refrigerant compressor  10 B according to Embodiment 2 includes an electric component  20 B and the compression component  30  (compressor body  12 ) which are accommodated in the sealed container  11 , and the refrigerant gas and the lubricating oil  13  are reserved in the sealed container  11 , as in the sealed refrigerant compressor  10 A according to Embodiment 1. The electric component  20 B is the outer rotor motor. 
     The electric component  20 B includes at least a stator  21 B and a rotor  22 B, as in the electric component  20 A according to Embodiment 1. As can be seen from the plan view of  FIG. 6A  or the longitudinal sectional view of  FIG. 6B , the stator  21 B has a stator shaft hole  29   c  in a center portion thereof. The bearing unit  35  of the compression component  30  is secured to the stator shaft hole  29   c  in a state in which the baring unit  35  is pressingly inserted thereinto. 
     As shown in  FIGS. 5, 6A and 6B , the rotor  22 B is disposed coaxially with the stator  21 B to surround the outer periphery of the stator  21 B. The length of the rotor  22 B in the direction of the rotational axis R of the rotor  22 B is set to be smaller than the diameter of the rotor  22 B. In brief, as in the rotor  22 A of Embodiment 1, the diameter of the rotor  22 B is larger than the length of the rotor  22 B (the rotor  22 B is short in the vertical direction). 
     In the rotor  22 B, the plurality of permanent magnets  23  are arranged uniformly on the inner periphery of a cylindrical yoke  28  which is rotatable around the outer periphery of the stator  21 B. For example, the yoke  28  may have a disc shape with a diameter larger than that of the flange portion  44 , or the cylindrical yoke  28  may be secured to the outer periphery of a frame with a diameter larger than that of the flange portion  44 . As shown in  FIG. 6B  and the bottom view of  FIG. 6C , the yoke  28  (or the frame) of the rotor  22 B has a rotor shaft hole  29   b  in a center portion thereof. The rotor shaft hole  29   b  is secured to the lower end of the main shaft section  41  of the crankshaft  40  by welding or the like. 
     The sealed refrigerant compressor  10 B according to the present embodiment is the same as the sealed refrigerant compressor  10 A according to Embodiment 1 except that the electric component  20 B is the outer rotor motor. Therefore, the constituents of the sealed refrigerant compressor  10 B will not be specifically described. The operation of the sealed refrigerant compressor  10 B is basically the same as that of the sealed refrigerant compressor  10 A. When electric power is supplied from an external power supply to the electric component  20 B, a current flows through the stator  21 B and a magnetic field is generated, which causes the rotor  22 B secured to the main shaft section  41  of the crankshaft  40  to rotate. According to the rotation of the rotor  22 B, the crankshaft  40  rotates, and the piston  33  reciprocates inside the cylinder  32  via the connecting rod  43  rotatably mounted on the eccentric shaft section  42 . Correspondingly, the refrigerant is compressed by the compression component  30 . 
     As in the sealed refrigerant compressor  10 A according to Embodiment 1, in the sealed refrigerant compressor  10 B according to the present embodiment, the rotor  22 B of the electric component  20 B is formed with balance through-holes  24 B. In the rotor  22 B of the present embodiment, the core as the body is configured as the yoke  27 . The plurality of permanent magnets  23  are arranged on the inner peripheral surface of the yoke  28 . Therefore, the electric component  20 B is the SPM motor. The rotor  22 B does not include the magnet protective members covering the inner peripheral surfaces of the plurality of permanent magnets  23  (the rotor  22 B does not require the magnet protective members). 
     The balance through-holes  24 B serve to adjust the load balance during the rotation of the rotor  22 B. In the present embodiment, two balance through-holes  24 B are provided. As shown in  FIGS. 5 and 6B , the balance through-holes  24 B extend in the direction of the rotational axis R of the rotor  22 B. As shown in  FIGS. 6A and 6C , when viewed from the upper surface or lower surface of the rotor  22 B, the two balance through-holes  24 B are eccentrically located in a portion of the rotor  22 B which is in the vicinity of the outer periphery of the rotor  22 B. In other words, in the present embodiment, the plurality of balance through-holes  24 B of the rotor  22 B are provided for the eccentric location in the yoke  28  which is the body of the rotor  22 B in such a manner that the balance through-holes  24 B are not point-symmetric or line-symmetric with respect to the rotational axis R of the rotor  22 B. 
     The specific configuration of the balance through-holes  24 B is the same as that of the balance through-holes  24 A according to Embodiment 1. The balance through-holes  24 B may be configured as the balance blind holes  24 C,  24 D (blind holes having bottoms) of  FIGS. 3A and 3B . As shown in  FIG. 6A , at least a part of each of the balance through-holes  24 B according to the present embodiment 2 is preferably located outward relative to the permanent magnet  23  when viewed from the direction of the rotational axis R of the rotor  22 B (in a plan view), as in the balance through-holes  24 A of Embodiment 1. 
     As described above, in the electric component which is the inner rotor type (Embodiment 1) or the electric component which is the outer rotor type (Embodiment 2), the rotor does not include the magnet protective members covering the permanent magnets, the core is provided with at least one balance hole, and this balance hole is preferably eccentrically located not to be line-symmetric or point-symmetric with respect to the rotational axis of the rotor. Thereby, the load of the rotor can be adjusted into an unbalanced state, and the load balance of the whole of the sealed refrigerant compressor can be adjusted well. As a result, the sealed refrigerant compressor can realize a lower vibration and a smaller size. 
     Embodiment 3 
     In Embodiment 3, an example of a refrigeration device including the sealed refrigerant compressor  10 A of Embodiment 1 or the sealed refrigerant compressor  10 B of Embodiment 2 will be described with reference to  FIG. 7 . 
     The sealed refrigerant compressor  10 A or  10 B of the present disclosure can be suitably incorporated into a refrigeration cycle or various devices (refrigeration devices) having a configuration similar to that of the refrigeration cycle. Specifically, for example, the devices may be a refrigerator (refrigerator for household use or refrigerator for business purpose), an ice making machine, a show case, a dehumidifier, a heat pump type hot water supply device, a heat pump type laundry/drying machine, an automatic vending machine, an air conditioner, an air compressor, etc. However, these are merely exemplary. In the present embodiment, the basic configuration of a refrigeration device  50  will be described in conjunction with an article storage device of  FIG. 7 , as an exemplary device into which the sealed refrigerant compressor  10 A or  10 B is incorporated. 
     The refrigeration device  50  of  FIG. 7  includes a refrigeration device body  51  and a refrigerant circuit  60 . The refrigeration device body  51  includes a heat insulating casing having an opening and a door which opens and closes the opening of the casing. The refrigeration device body  51  includes in the interior thereof a storage space  52  for storing articles, a mechanical room  53  for storing the refrigerant circuit  60  and the like, and a partition wall  54  which defines the storage space  52  and the mechanical room  53 . 
     The refrigerant circuit  60  is configured such that the sealed refrigerant compressor  10 A or  10 B, a heat radiator  61 , a pressure-reducing device  62 , a heat absorbing unit  63 , and the like are connected together in an annular shape by use of a pipe  64 . In brief, the refrigerant circuit  60  is an exemplary refrigeration cycle using the sealed refrigerant compressor  10 A or  10 B of the present disclosure. 
     In the refrigerant circuit  60 , the sealed refrigerant compressor  10 A or  10 B, the heat radiator  61 , and the pressure-reducing device  62  are placed in the mechanical room  53 , while the heat absorbing unit  63  is placed in the storage space  52  including a blower (not shown in  FIG. 6 ). As indicated by a broken line arrow, the blower agitates cold of the heat absorbing unit  63  to circulate it in the interior of the storage space  52 . 
     In the above-described manner, the refrigeration device  50  of the present embodiment incorporates the sealed refrigerant compressor  10 A of Embodiment 1 or the sealed refrigerant compressor  10 B according to Embodiment 2. In the sealed refrigerant compressor  10 A or  10 B of the present disclosure, as described above, the core of the rotor  22 A or  22 B of the electric component  20 A or  20 B is not provided with the magnet protective members covering the permanent magnets  23 , the core is provided with at least one balance hole, and this balance hole is preferably eccentrically located not to be line-symmetric or point-symmetric with respect to the rotational axis R of the rotor  22 A or  22 B. 
     In this configuration, the load of the rotor  22 A or  22 B can be adjusted into an unbalanced state, and thus the load balance of the whole of the sealed refrigerant compressor  10 A or  10 B can be adjusted well. As a result, the sealed refrigerant compressor  10 A or  10 B can realize a lower vibration and a smaller size. Since the refrigerant circuit  60  is operated by the sealed refrigerant compressor  10 A or  10 B, the refrigeration device  50  can realize a lower vibration and a smaller size. To adjust the load balance, only the balance hole(s) is/are provided without providing the magnet protective member. Therefore, the number of members is not increased, manufacturing steps are not increased, and manufacturing cost can be reduced. 
     The present invention is not limited to the above embodiments. Various modifications may be made within the scope of the claims. An embodiment obtained by suitably combining technical means disclosed in different embodiments and a plurality of modification examples is included in the technical scope of the present invention. 
     Numerous improvements and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, the description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and/or function may be varied substantially without departing from the spirit of the invention. 
     As described above, the present invention can be widely suitably used in the fields of sealed refrigerant compressor constituting the refrigeration cycle. Further, the present invention can be widely used in the fields of refrigeration devices incorporating the sealed refrigerant compressor, such as refrigeration devices for household uses such as electric freezers/refrigerators or air conditioners, or refrigeration devices for business purposes such as a dehumidifier, a show case for business purpose or an automatic vending machine, etc.