Patent Publication Number: US-7220108-B2

Title: Variable capacity rotary compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 2003-68054, filed Sep. 30, 2003 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates, in general, to rotary compressors and, more particularly, to a variable capacity rotary compressor, in which is a compression operation is executed in either of two compression chambers having different capacities, by an eccentric unit mounted to a rotating shaft. 
   2. Description of the Related Art 
   Generally, a compressor is installed in a refrigeration system, such as an air conditioner and a refrigerator, which operates to cool air in a given space using a refrigeration cycle. In the refrigeration system, the compressor operates to compress a refrigerant which circulates through a refrigeration circuit. A cooling capacity of the refrigeration system is determined according to a compression capacity of the compressor. Thus, when the compressor is designed to vary a compression capacity thereof as desired, the refrigeration system may be operated under an optimum condition considering several factors, such as a difference between a practical temperature and a predetermined temperature, thus allowing air in a given space to be efficiently cooled, and saving energy. 
   A variety of compressors are used in the refrigeration system. The compressors are typically classified into two types, which are rotary compressors and reciprocating compressors. The present invention relates to the rotary compressor, which will be described in the following. 
   The conventional rotary compressor includes a hermetic casing, with a stator and a rotor being installed in the hermetic casing. A rotating shaft penetrates through the rotor. An eccentric cam is integrally provided on an outer surface of the rotating shaft. A roller is provided in a compression chamber to be rotated over the eccentric cam. 
   The rotary compressor constructed as described above is operated as follows. As the rotating shaft rotates, the eccentric cam and the roller execute eccentric rotation in the compression chamber. At the time, a gas refrigerant is drawn into the compression chamber and then compressed, prior to discharging the compressed refrigerant to an outside of the hermetic casing. 
   However, the conventional rotary compressor has a problem in that the rotary compressor is fixed in a compression capacity thereof, so that it is impossible to vary the compression capacity according to a difference between an environmental temperature and a preset reference temperature. 
   In a detailed description, when the environmental temperature is considerably higher than the preset reference temperature, the compressor must be operated in a large capacity compression mode to rapidly lower the environmental temperature. Meanwhile, when the difference between the environmental temperature and the preset reference temperature is not large, the compressor must be operated in a small capacity compression mode so as to save energy. However, it is impossible to change the capacity of the rotary compressor according to the difference between the environmental temperature and the preset reference temperature, so that the conventional rotary compressor does not efficiently cope with a variance in temperature, thus leading to a waste of energy. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an aspect of the present invention to provide a variable capacity rotary compressor which is constructed so that a compression operation is executed in either of two compression chambers having different capacities by an eccentric unit mounted to a rotating shaft, thus varying a compression capacity as desired. 
   It is a further aspect of the present invention to provide a variable capacity rotary compressor, which prevents an eccentric bush from rotating faster than a rotating shaft in a specific range, due to variance in pressure of a compression chamber as the rotating shaft rotates. 
   It is an another aspect of the present invention to provide a variable capacity rotary compressor in which noise generated within the compressor as a result of parts collating with each other is reduced. 
   Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
   The above and/or other aspects are achieved by a variable capacity rotary compressor, including upper and lower compression chambers, a rotating shaft, upper and lower eccentric cams, upper and lower eccentric bushes, a slot, a locking pin, and a restraining unit. The upper and lower compression chambers have different capacities. The rotating shaft passes through the upper and lower compression chambers. The upper and lower eccentric cams are provided on the rotating shaft. The upper and lower eccentric bushes are fitted over the upper and lower eccentric cams, respectively. The slot is provided at a predetermined position between the upper and lower eccentric bushes. The locking pin functions to change a position of the upper or lower eccentric bush to a maximum eccentric position, in cooperation with the slot. The restraining unit is provided at a predetermined position of the slot to restrain the locking pin with a predetermined elastic force when the locking pin is placed at a first or second end of the slot. 
   The restraining unit may include at each end thereof a pair of elastic pieces which are spaced apart from each other by a predetermined interval to restrain the locking pin with the predetermined elastic force. 
   The restraining unit may be set along an edge of the slot, and include an upper lip, a lower lip, and a pair of connecters which connects both ends of the upper and lower lips to each other. 
   The pair of elastic pieces may be provided at positions adjacent to each of the pair of connecters to be inwardly projected from the upper and lower lips, respectively. 
   The pair of elastic pieces may have an elastic force which is larger than a slip-rotating force of the upper and lower eccentric bushes but is smaller than a rotating force of the rotating shaft. 
   The upper lip may be provided with a first locking projection which is vertically upwardly projected from an inside end of the upper lip to be locked by the slot, and the lower lip may be provided with a second locking projection which is vertically downwardly projected from an inside end of the lower lip to be locked by the slot, to prevent the restraining unit from being removed from the slot. 
   Each of the pair of connecters may be provided with a third locking projection which is rearwardly projected from an inside end of the connecter to be locked by the slot, to prevent the restraining unit from moving in a horizontal direction. 
   The restraining unit may be fabricated through a pressing process to have a single structure. 
   The locking pin may be provided at a predetermined position between the upper and lower eccentric cams to be projected from the rotating shaft. The slot may be provided at the predetermined position between the upper and lower eccentric bushes to receive the locking pin therein, and may have a length to allow, an angle between a first line extending from the first end of the slot to a center of the rotating shaft and a second line extending from the second end of the slot to the center of the rotating shaft, to be 180°. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a sectional view to show an interior construction of a variable capacity rotary compressor, according to an embodiment of the present invention; 
       FIG. 2  is a perspective view of an eccentric unit included in the compressor of  FIG. 1 , in which upper and lower eccentric bushes of the eccentric unit are separated from a rotating shaft; 
       FIG. 3  is a perspective view to show a restraining unit fitted into the eccentric unit of  FIG. 2 ; 
       FIG. 4  is a sectional view taken along a line A—A of  FIG. 2  to show a state immediately before a locking pin is restrained by the restraining unit of  FIG. 3  as the rotating shaft rotates in a first direction; 
       FIG. 5  is a sectional view taken along the line A—A of  FIG. 2  to show a state when the locking pin is restrained by the restraining unit of  FIG. 3  as the rotating shaft rotates in the first direction; 
       FIG. 6  is a sectional view to show an upper compression chamber where a compression operation is executed without slippage by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in the first direction; 
       FIG. 7  is a sectional view, corresponding to  FIG. 6 , to show a lower compression chamber where an idle operation is executed by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in the first direction; 
       FIG. 8  is a sectional view to show the lower compression chamber where the compression operation is executed without the slippage by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in a second direction; and 
       FIG. 9  is a sectional view, corresponding to  FIG. 8 , to show the upper compression chamber where the idle operation is executed by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in the second direction. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiment is described below in order to explain the present invention by referring to the figures. 
   A variable capacity rotary compressor is explained in U.S. patent application Ser. No. 10/352,000, the content of which is incorporated herein by reference. Before presenting a detailed description of the present invention, the variable capacity rotary compressor is briefly discussed. 
   The construction of the variable capacity rotary compressor is as follows. The compressor includes first and second compression chambers. An eccentric unit is installed in the first and second compression chambers to execute the compression operation in either of the compression chambers, according to a rotating direction of a rotating shaft. The eccentric unit includes first and second eccentric cams, first and second eccentric bushes, first and second rollers, and a locking pin. The first and second eccentric cams are provided on an outer surface of the rotating shaft which passes through the first and second compression chambers. The first and second eccentric bushes are rotatably fitted over the first and second eccentric cams, respectively. The first and second rollers are rotatably fitted over the first and second eccentric bushes, respectively, to compress a gas refrigerant. The locking pin is installed to change a position of one of the first and second eccentric bushes to a position eccentric from a central axis of the rotating shaft, while changing a position of a remaining one of the first and second eccentric bushes to a position concentric with the central axis of the rotating shaft, according to the rotating direction of the rotating shaft. 
   Thus, when the rotating shaft rotates in a first direction which is counterclockwise in the drawings or a second direction which is clockwise in the drawings, the compression operation is executed in either of the first and second compression chambers having different capacities by the eccentric unit constructed as described above, thus varying the compression capacity of the compressor as desired. 
   A detailed description of the present invention is now presented. 
     FIG. 1  is a sectional view to show a variable capacity rotary compressor, according to an embodiment of the present invention. As shown in  FIG. 1 , the variable capacity rotary compressor includes a hermetic casing  10 , with a driving unit  20  and a compressing unit  30  being installed in the hermetic casing  10 . The driving unit  20  generates a rotating force, and the compressing unit  30  compresses gas using the rotating force of the driving unit  20 . The driving unit  20  includes a cylindrical stator  22 , a rotor  23 , and a rotating shaft  21 . The stator  22  is fixedly mounted to an inner surface of the hermetic casing  10 . The rotor  23  is rotatably installed in the stator  22 . The rotating shaft  21  is installed to pass through a center of the rotor  23 , and rotates along with the rotor  23  in a first direction which is counterclockwise in the drawings or in a second direction which is clockwise in the drawings. 
   The compressing unit  30  includes a housing  33 , upper and lower flanges  35  and  36 , and a partition  34 . The housing  33  defines upper and lower compression chambers  31  and  32 , which are both cylindrical but have different capacities, therein. The upper and lower flanges  35  and  36  are mounted to upper and lower ends of the housing  33 , respectively, to rotatably support the rotating shaft  21 . The partition  34  is interposed between the upper and lower compression chambers  31  and  32  to partition the upper and lower compression chambers  31  and  32  from each other. 
   The upper compression chamber  31  is taller than the lower compression chamber  32 , thus the upper compression chamber  31  has a larger capacity than the lower compression chamber  32 . Therefore, a larger amount of gas is compressed in the upper compression chamber  31  in comparison with the lower compression chamber  32 , thus allowing the rotary compressor to have a variable capacity. 
   Meanwhile, when the lower compression chamber  32  is taller than the upper compression chamber  31 , the lower compression chamber  32  has a larger capacity than the upper compression chamber  31 , to allow a larger amount of gas to be compressed in the lower compression chamber  32 . 
   Further, an eccentric unit  40  is placed in the upper and lower compression chambers  31  and  32  to execute a compressing operation in either the upper or lower compression chamber  31  and  32 , according to a rotating direction of the rotating shaft  21 . According to the present invention, a restraining unit  80  is provided at a predetermined position of the eccentric unit  40  to allow the eccentric unit  40  to be smoothly operated without slippage. The construction and operation of the eccentric unit  40  and the restraining unit  80  will be described later herein, with reference to  FIGS. 2 to 8 . 
   Upper and lower rollers  37  and  38  are placed in the upper and lower compression chambers  31 , respectively, to be rotatably fitted over the eccentric unit  40 . The upper inlet and outlet  63  and  65  (refer to  FIG. 6 ) are formed at predetermined positions of the housing  33  to communicate with the upper compression chamber  31 . The lower inlet and outlet  64  and  66  (refer to  FIG. 8 ) are formed at predetermined positions of the housing  33  to communicate with the lower compression chamber  32 . 
   An upper vane  61  is positioned between the upper inlet and outlet  63  and  65 , and is biased in a radial direction by an upper support spring  61   a  to be in close contact with the upper roller  37  (refer to  FIG. 6 ). Further, a lower vane  62  is positioned between the lower inlet and outlet  64  and  66 , and is biased in a radial direction by a lower support spring  62   a  to be in close contact with the lower roller  38  (refer to  FIG. 8 ). 
   A refrigerant outlet pipe  69   a  extends from an accumulator  69  which contains a refrigerant therein. Of the refrigerant contained in the accumulator  69 , only a gas refrigerant flows into the compressor through the refrigerant outlet pipe  69   a . A path controller  70  is included at a predetermined position of the refrigerant outlet pipe  69   a . The path controller  70  opens an intake path  67  or  68  to supply the gas refrigerant to the upper or lower inlet  63  or  64  of the upper or lower compression chamber  31  or  32  in which a compression operation is executed. A valve  71  is installed in the path controller  70  to be movable in a horizontal direction. The valve  71  opens either the intake paths  67  or  68  by a difference in pressure between the intake path  67  connected to the upper inlet  63  and the intake path  68  connected to the lower inlet  64  to supply the gas refrigerant to the upper inlet  63  or lower inlet  64 . 
   The construction of the rotating shaft  21 , the eccentric unit  40 , and the restraining unit  80  according to an embodiment of the present invention will be described in the following with reference to  FIGS. 2 and 3 . 
     FIG. 2  is a perspective view of the eccentric unit included in the compressor of  FIG. 1 , in which upper and lower eccentric bushes of the eccentric unit are separated from the rotating shaft.  FIG. 3  is a perspective view to show the restraining unit fitted into the eccentric unit of  FIG. 2 . 
   As shown in  FIG. 2 , the eccentric unit  40  includes upper and lower eccentric cams  41  and  42 . The upper and lower eccentric cams  41  and  42  are provided on the rotating shaft  21  to be placed in the upper and lower compression chambers  31  and  32 , respectively. The upper and lower eccentric bushes  51  and  52  are fitted over the upper and lower eccentric cams  41  and  42 , respectively. A locking pin  43  is provided at a predetermined position between the upper and lower eccentric cams  41  and  42 . A slot  53  of a predetermined length is provided at a predetermined position between the upper and lower eccentric bushes  51  and  52  to engage with the locking pin  43 . The eccentric unit  40  also includes the restraining unit  80 . The restraining unit  80  prevents the upper or lower eccentric bush  51  or  52  from slipping over the upper or lower eccentric cam  41  or  42  at a predetermined position. 
   The upper and lower eccentric cams  41  and  42  are integrally fitted over the rotating shaft  21  to be eccentric from the central axis C 1 —C 1  of the rotating shaft  21 . The upper and lower eccentric cams  41  and  42  are positioned to correspond an upper eccentric line L 1 —L 1  of the upper eccentric cam  41  to a lower eccentric line L 2 —L 2  of the lower eccentric cam  42 . In this case, the upper eccentric line L 1 —L 1  is defined as a line to connect a maximum eccentric part of the upper eccentric cam  41 , which is maximally projected from the rotating shaft  21 , to a minimum eccentric part of the upper eccentric cam  41 , which is minimally projected from the rotating shaft  21 . Meanwhile, the lower eccentric line L 2 —L 2  is defined as a line to connect a maximum eccentric part of the lower eccentric cam  42 , which is maximally projected from the rotating shaft  21 , to a minimum eccentric part of the lower eccentric cam  42 , which is minimally projected from the rotating shaft  21 . 
   The locking pin  43  includes a threaded shank  44  and a head  45 . The head  45  has slightly larger diameter than the shank  44 , and is formed at an end of the shank  44 . Further, a threaded hole  46  is formed on the rotating shaft  21  between the upper and lower eccentric cams  41  and  42  to be at about 90° with the maximum eccentric parts of the upper and lower eccentric cams  41  and  42 . The threaded shank  44  of the locking pin  43  is inserted into the threaded hole  46  in a screw-fastening method to lock the locking pin  43  to the rotating shaft  21 . 
   The upper and lower eccentric bushes  51  and  52  are integrated with each other by a connecting part  54  which connects the upper and lower eccentric bushes  51  and  52  to each other. The slot  53  is formed around a part of the connecting part  54 , and has a slightly larger width than a diameter of the head  45  of the locking pin  43 . 
   Thus, when the upper and lower eccentric bushes  51  and  52  which are integrally connected to each other by the connecting part  54  are fitted over the rotating shaft  21  and the locking pin  43  is inserted to the threaded hole  46  of the rotating shaft  21  through the slot  53 , the locking pin  43  is mounted to the rotating shaft  21  while engaging with the slot  53 . 
   When the rotating shaft  21  rotates in the first or second direction in such a state, the locking pin  43  comes into contact with the first or second end  53   a  or  53   b  of the slot  53  and causes the upper and lower eccentric bushes  51  and  52  rotate in the first or second direction along with the rotating shaft  21 . 
   In this case, an eccentric line L 3 —L 3 , which connects the maximum eccentric part of the upper eccentric bush  51  to the minimum eccentric part thereof, is placed at about 90° with a line which connects the first end  53   a  of the slot  53  to a center of the connecting part  54 . Meanwhile, an eccentric line L 4 —L 4 , which connects the maximum eccentric part of the lower eccentric bush  52  to the minimum eccentric part thereof, is placed at about 90° with a line which connects the second end  53   b  of the slot  53  to the center of the connecting part  54 . 
   Further, the eccentric line L 3 —L 3  of the upper eccentric bush  51  and the eccentric line L 4 —L 4  of the lower eccentric bush  52  are positioned on a same plane, but the maximum eccentric part of the upper eccentric bush  51  is arranged to be opposite to the maximum eccentric part of the lower eccentric bush  52 . An angle between a line extending from the first end  53   a  of the slot  53  to a center of the rotating shaft  21  and a line extending from the second end  53   b  of the slot  53  to the center of the rotating shaft  21  is 180°. The slot  53  is formed around a part of the connecting part  54 . 
   When the locking pin  43  is locked by the first end  53   a  of the slot  53  and the upper eccentric bush  51  rotates along with the rotating shaft  21  in the first direction (of course, the lower eccentric bush  52  also rotates), the maximum eccentric part of the upper eccentric cam  41  contacts the maximum eccentric part of the upper eccentric bush  51 . Thus, the upper eccentric bush  51  rotates along with the rotating shaft  21  in the first direction while being maximally eccentric from the rotating shaft  21  (refer to  FIG. 6 ). Meanwhile, in the case of the lower eccentric bush  52 , the maximum eccentric part of the lower eccentric cam  42  contacts the minimum eccentric part of the lower eccentric bush  52 . Thus, the lower eccentric bush  52  rotates along with the rotating shaft  21  in the first direction while being concentric with the rotating shaft  21  (refer to  FIG. 7 ). 
   When the locking pin  43  is locked by the second end  53   b  of the slot  53  and the lower eccentric bush  52  rotates along with the rotating shaft  21  in the second direction, the maximum eccentric part of the lower eccentric cam  42  contacts the maximum eccentric part of the lower eccentric bush  52 . Thus, the lower eccentric bush  51  rotates along with the rotating shaft  21  in the second direction while being maximally eccentric from the rotating shaft  21  (refer to  FIG. 8 ). Meanwhile, in the case of the upper eccentric bush  51 , the maximum eccentric part of the upper eccentric cam  41  contacts the minimum eccentric part of the upper eccentric bush  51 . Thus, the upper eccentric bush  51  rotates along with the rotating shaft  21  in the second direction while being concentric with the rotating shaft  21  (refer to  FIG. 9 ). 
   The restraining unit  80  is provided at the predetermined position of the eccentric unit  40  which is constructed as described above, to allow the upper and lower eccentric bushes  51  and  52  to rotate at a same speed as the rotating shaft  21  without slippage. The restraining unit  80  is made of a ring-shaped thin plate. The ring-shaped thin plate is folded to have a similar shape as an edge of the slot  53 , and then is fitted into the slot  53 . After the restraining unit  80  is fitted into the slot  53 , the locking pin  43  is fastened to the rotating shaft  21  through the slot  53 . 
   According to the present invention, the restraining unit  80  includes upper and lower lips  81  and  82  which come into contact with the edge of the slot  53 . The restraining unit  80  also includes a pair of connecters  83  which connect opposite ends of the upper and lower lips  81  and  82  to each other. The restraining unit  80  further includes a pair of first elastic pieces  84  which are provided at positions adjacent to one of the connecters  83  to be inwardly projected from the upper and lower lips  81  and  82 . Further, a pair of second elastic pieces  85  are provided at positions adjacent to a remaining one of the connecters  83  to be inwardly projected from the upper and lower lips  81  and  82 . 
   The upper and lower lips  81  and  82 , the connecters  83 , and the first and second elastic pieces  84  and  85  are integrated with each other into a single structure, through a pressing process or other processes, to have a predetermined elastic force. Thus, when the restraining unit  80  is fitted into the slot  53  while the upper and lower lips  81  and  82  are slightly compressed, as shown in  FIG. 3 , the upper lip  81  comes into close contact with the upper edge of the slot  53 , and the lower lip  82  comes into close contact with the lower edge of the slot  53 . Further, the pair of connecters  83 , respectively, come into close contact with the first and second ends  53   a  and  53   b  of the slot  53 . 
   At positions adjacent to the first end  53   a  of the slot  53 , the upper and lower lips  81  and  82  are cut and bent to form the pair of first elastic pieces  84 . The pair of first elastic pieces  84  are placed to be spaced apart from each other by a predetermined interval, to elastically restrain or release the locking pin  43 . Thus, when the rotating shaft  21  rotates in the first direction and the locking pin  43  moves to the first end  53   a  of the slot  53 , the locking pin  43  is elastically restrained by the pair of first elastic pieces  84 . 
   Similarly, at positions adjacent to the second end  53   b  of the slot  53 , the upper and lower lips  81  and  82  are cut and bent to form the pair of second elastic pieces  85 . The pair of second elastic pieces  85  are placed to be spaced apart from each other by a predetermined interval, to elastically restrain or release the locking pin  43 . Thus, when the rotating shaft  21  rotates in the second direction and the locking pin  43  moves to the second end  53   b  of the slot  53 , the locking pin  43  is elastically restrained by the pair of second elastic pieces  85 . 
   Further, a first locking projection  86  is vertically upwardly projected from a center of an inside end of the upper lip  81 , and a second locking projection  87  is vertically downwardly projected from a center of an inside end of the lower lip  82 , and a third locking projection  88  is rearwardly projected from an inside end of each of the connecters  83 , to allow the restraining unit  80  to be securely fitted into the slot  53 . 
   As shown in  FIG. 3 , when the restraining unit  80  is fitted into the slot  53  while slightly compressing the upper and lower lips  81  and  82 , the first and second locking projections  86  and  87  are respectively locked by the upper and lower edges of the slot  53  to prevent the restraining unit  80  from being undesirably removed from the slot  53 . The third locking projections  88  inwardly extend from the first and second ends  53   a  and  53   b  of the slot  53 , respectively, to prevent the restraining unit  80  from moving to right and left. 
   The pair of first elastic pieces  84  and the pair of second elastic pieces  85  have an elastic force which is larger than a slip-rotating force of the upper and lower eccentric bushes  51  and  52  but is smaller than a rotating force of the rotating shaft  21 . As the rotating shaft  21  rotates, the locking pin  43  moves to be restrained by or released from the first and second elastic pieces  84  and  85 . Conversely, when the upper or lower eccentric bush  51  or  52  respectively slips over the upper or lower eccentric cam  41  or  42 , the locking pin  43  is restrained by the first or second elastic pieces  84  or  85  to allow the upper or lower eccentric bush  51  and  52  to rotate at the same speed as the rotating shaft  21  without slipping over the upper or lower eccentric cam  41  and  42 , respectively. 
   The operation of compressing a gas refrigerant in the upper or lower compression chamber by the eccentric unit according to an embodiment of the present invention will be described in the following with reference to  FIGS. 4 to 9 . 
     FIG. 4  shows a state immediately before the moment when the locking pin  43  is restrained by the restraining unit  80  as the rotating shaft  21  rotates in the first direction.  FIG. 5  shows a state when the locking pin  43  is restrained by the restraining unit  80  as the rotating shaft  21  rotates in the first direction.  FIG. 6  shows the upper compression chamber  31  where the compression operation is executed without slippage by the eccentric unit  40 , when the rotating shaft  21  rotates in the first direction.  FIG. 7  is a sectional view, corresponding to  FIG. 6 , to show the lower compression chamber where the idle operation is executed by the eccentric unit  40 , when the rotating shaft  21  rotates in the first direction. 
   As shown in  FIG. 4 , when the rotating shaft  21  rotates in the first direction, which in this case is counterclockwise, in  FIG. 6 , the locking pin  43 , projected from the rotating shaft  21 , is guided within the slot  53 , in which the restraining unit  80  is fitted, to move toward the first end  53   a  of the slot  53 . By the movement of the locking pin  43 , the locking pin  43  moves close to the first elastic pieces  84  of the restraining unit  80 , which are provided adjacent to the first end  53   a  of the slot  53 . When the locking pin  43  further moves in a same direction, the head  45  of the locking pin  43  passes between the first elastic pieces  84  to be inserted into a position between the first elastic pieces  84  and a corresponding connecter  83 . 
   When the locking pin  43  passes between the first elastic pieces  84 , the first elastic pieces  84  are elastically deformed. Thereafter, as shown in  FIG. 4 , the locking pin  43  is inserted into the position between the first elastic pieces  84  and the corresponding connecter  83 . After the locking pin  43  has passed between the first elastic pieces  84 , the first elastic pieces  84  are elastically restored to original states to restrain the locking pin  43  with a predetermined elastic force. 
   When the locking pin  43  is restrained by the first elastic pieces  84  with the predetermined elastic force so as to be held at the first end  53   a  of the slot  53 , the maximum eccentric part of the upper eccentric cam  41  contacts the maximum eccentric part of the upper eccentric bush  51 . The upper eccentric bush  51  rotates while being maximally eccentric from the central axis C 1 —C 1  of the rotating shaft  21 . Thus, as shown in  FIG. 6 , the upper roller  37  rotates while being in contact with an inner surface of the housing  33  which defines the upper compression chamber  31 , to execute the compression operation. 
   Simultaneously, the maximum eccentric part of the lower eccentric cam  42  contacts the minimum eccentric part of the lower eccentric bush  52 . The lower eccentric bush  52  rotates while being concentric with the central axis C 1 —C 1  of the rotating shaft  21 . Thus, as shown in  FIG. 7 , the lower roller  38  rotates while being spaced apart from the inner surface of the housing  33 , which defines the lower compression chamber  32 , by a predetermined interval. As a result, the compression operation is not executed. 
   When the rotating shaft  21  rotates in the first direction, the gas refrigerant flowing to the upper compression chamber  31  through the upper inlet  63  is compressed by the upper roller  37  in the upper compression chamber  31  having a larger capacity, and subsequently is discharged from the upper compression chamber  31  through the upper outlet  65 . On the other hand, the compression operation is not executed in the lower compression chamber  32  having a smaller capacity. Therefore, the rotary compressor is operated in a larger capacity compression mode. 
   Meanwhile, as shown in  FIG. 6 , when the upper roller  37  comes into contact with the upper vane  61 , the operation of compressing the gas refrigerant is completed and an operation of drawing the gas refrigerant is started. At this time, some of the compressed gas, which was not discharged from the upper compression chamber  31  through the upper outlet  65 , returns to the upper compression chamber  31  and expands again to apply a pressure to the upper roller  37  and the upper eccentric bush  51  in a rotating direction of the rotating shaft  21 . 
   If the upper eccentric bush  51  rotates faster than the rotating shaft  21 , the upper eccentric bush  51  slips over the upper eccentric cam  41 . When the rotating shaft  21  further rotates in such a state, the locking pin  43  collides with the first end  53   a  of the slot  53  to make the upper eccentric bush  51  rotate at a same speed as that of the rotating shaft  21 . Noise may be generated and the locking pin  43  and the slot  53  may be damaged, due to the collision between the locking pin  43  and the slot  53 . 
   However, the eccentric unit  40  according to the present invention prevents the upper eccentric bush  51  from slipping by the operation of the restraining unit  80 . 
   When the upper roller  37  comes into contact with the upper vane  61 , some of the gas refrigerant returns to the upper compression chamber  31  through the upper outlet  65  and expands again, to generate a pressure. The pressure acts on the upper eccentric bush  51  in the rotating direction of the rotating shaft  21  which is the first direction, thus the upper eccentric bush  51  slips over the upper eccentric cam  41 . However, as shown in  FIG. 5 , the locking pin  43  is restrained by the first elastic pieces  84  of the restraining unit  80  which are provided at positions adjacent to the first end  53   a  of the slot  53 , with the elastic force which is larger than the slip-rotating force of the upper eccentric bush  51  to allow the upper eccentric bush  51  to rotate at the same speed as the rotating shaft  21  without the slippage. 
   To execute the compression operation in the lower compression chamber  32  after the upper eccentric bush  51  has executed the compression operation in the upper compression chamber  31  without the slippage, the rotating shaft  21  is stopped to change the rotating direction thereof to the second direction. The compression operation executed in the lower compression chamber  32  will be described in the following with reference to  FIGS. 4 ,  5 ,  8 , and  9 . 
     FIG. 8  is a sectional view to show the lower compression chamber where the compression operation is executed without the slippage by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in the second direction.  FIG. 9  is a sectional view, corresponding to  FIG. 8 , to show the upper compression chamber where the idle operation is executed by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in the second direction. 
   When the rotating shaft  21  rotates in the second direction to execute the compression operation in the lower compression chamber  32 , the locking pin  43  which is restrained at the first end  53  of the slot  53  by the first elastic pieces  84  as shown in  FIG. 5 , rotates along with the rotating shaft  21 . In the above state, a rotating force of the locking pin  43  acts on the first elastic pieces  84  in the second direction. Thus, as shown in  FIG. 4 , the first elastic pieces  84  are depressed to increase the distance between the pair of first elastic pieces  84 , so that the locking pin  43  passes between the first elastic pieces  84 . 
   As the rotating shaft  21  further rotates in such a state, the locking pin  43  rotates toward the second end  53   b  of the slot  53 . Thereafter, the locking pin  43  is restrained by the second elastic pieces  85 , which are provided at the positions adjacent to the second end  53   b  of the slot  53 , in a same manner as the locking pin  43  is restrained by the first elastic pieces  84 , which are provided at the positions adjacent to the first end  53   a  of the slot  53 . 
   As such, when the locking pin  43  is restrained at the second end  53   b  of the slot  53  by the second elastic pieces  85 , the maximum eccentric part of the lower eccentric cam  42  contacts the maximum eccentric part of the lower eccentric bush  52 , and thereby the lower eccentric bush  52  rotates while being maximally eccentric from the central axis C 1 —C 1  of the rotating shaft  21 . Thus, as shown in  FIG. 8 , the lower roller  38  rotates while being in contact with the inner surface of the housing  33  which defines the lower compression chamber  32  to execute the compression operation. 
   Simultaneously, the maximum eccentric part of the upper eccentric cam  41  contacts the minimum eccentric part of the upper eccentric bush  51 . The upper eccentric bush  51  rotates while being concentric with the central axis C 1 —C 1  of the rotating shaft  21 . Thus, as shown in  FIG. 9 , the upper roller  37  rotates while being spaced apart from the inner surface of the housing  33 , which defines the upper compression chamber  31 , by a predetermined interval to not execute the compression operation. 
   The gas refrigerant flowing to the lower compression chamber  32  through the lower inlet  64  is compressed by the lower roller  38  in the lower compression chamber  32  having a smaller capacity, and subsequently is discharged from the lower compression chamber  32  through the lower outlet  66 . On the other hand, the compression operation is not executed in the upper compression chamber  31  having a larger capacity. Therefore, the rotary compressor is operated in a smaller capacity compression mode. 
   Meanwhile, as shown in  FIG. 8 , when the lower roller  38  comes into contact with the lower vane  62 , the operation of compressing the gas refrigerant is completed and an operation of drawing the gas refrigerant is started. At this time, some of the compressed gas, which was not discharged from the lower compression chamber  32  through the lower outlet  66 , returns to the lower compression chamber  32  and expands again to apply a pressure to the lower roller  38  and the lower eccentric bush  52  in a rotating direction of the rotating shaft  21 . At this time, the lower eccentric bush  52  rotates faster than the rotating shaft  21  and causes the lower eccentric bush  52  to slip over the lower eccentric cam  42 . 
   When the rotating shaft  21  further rotates in such a state, the locking pin  43  collides with the second end  53   b  of the slot  53  to make the lower eccentric bush  52  rotate at a same speed as that of the rotating shaft  21 . Noise may be generated and the locking pin  43  and the slot  53  may be damaged, due to the collision between the locking pin  43  and the slot  53 . 
   However, the lower eccentric bush  52  is restrained by the restraining unit  80  in a same manner as the upper eccentric bush  51  is restrained by the restraining unit  80  when the rotating shaft  21  rotates in the first direction to prevent the slippage, the collision and, as a result, the noise. 
   When the lower roller  38  comes into contact with the lower vane  62 , some of the gas refrigerant returns to the lower compression chamber  32  through the lower outlet  66  and expands again, thus generating a pressure. The pressure acts on the lower eccentric bush  52  in the rotating direction of the rotating shaft  21  which is the second direction, thus the lower eccentric bush  52  slips over the lower eccentric cam  42 . However, in a same manner as shown in  FIG. 5 , the locking pin  43  is restrained by the second elastic pieces  85  which are provided at positions adjacent to the second end  53   b  of the slot  53 , with the elastic force which is larger than the slip-rotating force of the lower eccentric bush  52  to allow the lower eccentric bush  52  to rotate at the same speed as the rotating shaft  21  without the slippage. 
   As described above, when the rotating shaft  21  rotates in the first or second direction, the restraining unit  80  allows the upper or lower eccentric bush  51  or  52  to execute the compression operation in the upper or lower compression chamber  31  or  32  without the slippage. 
   As is apparent from the above description, the present invention provides a variable capacity rotary compressor, which is designed to execute a compression operation in either of upper and lower compression chambers having different capacities by an eccentric unit which rotates in the first or second direction to vary a compression capacity of the compressor as desired. 
   Further, the present invention provides a variable capacity rotary compressor, which has a restraining unit to prevent the upper or lower eccentric bush from slipping when an eccentric unit rotates in the first or second direction to allow the upper and lower eccentric bushes to rotate smoothly. 
   Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.