Patent Publication Number: US-7223081-B2

Title: Variable capacity rotary compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Application No. 2003-50983, filed Jul. 24, 2003, in the Korean Intellectual Property Office, the disclosure of which is 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, which is designed such that a compression operation is executed in either of two compression chambers having different capacities thereof, by an eccentric unit mounted to a rotating shaft. 
   2. Description of the Related Art 
   Generally, a compressor is installed in refrigeration systems, such as air conditioners and refrigerators, which operate to cool air in a given space using a refrigeration cycle. In refrigeration systems, 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 operates under an optimum condition considering several factors, such as a difference between a practical temperature and a predetermined temperature, thus, allowing air in the given space to be efficiently cooled, and saving energy. 
   A variety of compressors are used in the refrigeration systems. The compressors are typically classified into two types, (i.e., 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 an eccentric rotation in the compression chamber. 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 thereof by an eccentric unit mounted to a rotating shaft, thus varying a compression capacity as desired. 
   It is another aspect to provide a variable capacity rotary compressor, which is designed to prevent an eccentric bush from rotating faster than a rotating shaft in a specific range, due to a variance in a pressure of a compression chamber as the rotating shaft rotates. 
   The above and/or other aspects are achieved by providing 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 upper and lower brake units. The upper and lower compression chambers have different interior capacities thereof. 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 operates to change a position of the upper or lower eccentric bush to a maximum eccentric position, in cooperation with the slot. The upper and lower brake units simultaneously operate to prevent either of the upper and lower eccentric bushes from slipping over the upper or lower eccentric cam, respectively. 
   The upper brake unit may include first and second upper pockets formed at first predetermined positions of the upper eccentric cam, first and second upper brake balls movably set in the first and second upper pockets, respectively, and first and second upper brake holes formed at second predetermined positions of the upper eccentric bush to have a diameter smaller than that of each of the first and second upper brake balls. The lower brake unit may include first and second lower pockets formed at third predetermined positions of the lower eccentric cam, first and second lower brake balls movably set in the first and second lower pockets, respectively, and first and second lower brake holes formed at fourth predetermined positions of the lower eccentric bush to have a diameter smaller than that of each of the first and second lower brake balls. 
   The locking pin may project from the rotating shaft at a position between the upper and lower eccentric cams. The slot may be provided between the upper and lower eccentric bushes to engage with the locking pin, and may have a length to allow, an angle between a first line extending from a first end of the slot to a center of the rotating shaft and a second line extending from a second end of the slot to the center of the rotating shaft, to be 180°. 
   The first and second upper pockets may be formed on the upper eccentric cam to be opposite to each other, and the first and second lower pockets may be formed on the lower eccentric cam to be opposite to each other at common angular positions as that of the first and second upper pockets. 
   Similarly, the first and second upper brake holes may be formed on the upper eccentric bush to be opposite to each other, and the first and second lower brake holes may be formed on the lower eccentric bush to be opposite to each other at common angular positions as that of the first and second upper brake holes. 
   Therefore, when the locking pin contacts the first end of the slot and the upper eccentric bush rotates to be maximally eccentrically from the rotating shaft, the first and second upper brake balls may be inserted into the first and second upper brake holes, respectively, and the first and second lower brake balls may be inserted into the first and second lower brakes holes, respectively, by a centrifugal force, thus preventing the upper eccentric bush from slipping. 
   When the locking pin contacts the second end of the slot and the lower eccentric bush rotates to be maximally eccentrically from the rotating shaft, the first and second upper brake balls may be inserted into the second and first upper brake holes, respectively, and the first and second lower brake balls may be inserted into the second and first lower brakes holes, respectively, by the centrifugal force, thus preventing the lower eccentric bush from slipping. 
   Further, an oil passage may be axially formed along the rotating shaft. In this case, the first and second upper pockets may communicate with the oil passage via first and second upper connecting passages, and the first and second lower pockets may communicate with the oil passage via first and second lower connecting passages, thus allowing an oil pressure and the centrifugal force to act on the first and second upper brake balls and the first and second lower brake balls. 

   
     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 showing an interior construction of a variable capacity rotary compressor, according to an embodiment of the present invention; 
       FIG. 2  is an exploded perspective view of an eccentric unit included in the variable capacity rotary 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 sectional view showing an upper compression chamber in which a compression operation is executed without a slippage by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in a first direction; 
       FIG. 4  is a sectional view, corresponding to  FIG. 3 , which shows a lower compression chamber in which an idle operation is executed by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in the first direction; 
       FIG. 5  is a sectional view showing an upper eccentric bush when the rotating shaft rotates in the first direction, in which the upper eccentric bush does not slip at a first predetermined position by the eccentric unit of  FIG. 2 ; 
       FIG. 6  is a sectional view showing a lower compression chamber in which the compression operation is executed without the slippage by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in a second direction; 
       FIG. 7  is a sectional view, corresponding to  FIG. 6 , which shows the upper compression chamber in which the idle operation is executed by the eccentric unit of  FIG. 2 , when the rotating shaft rotates in the second direction; and 
       FIG. 8  is a sectional view showing a lower eccentric bush when the rotating shaft rotates in the second direction, in which the lower eccentric bush does not slip at a second predetermined position by the eccentric unit of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the 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 to explain the present invention by referring to the figures. 
     FIG. 1  is a sectional view showing a variable capacity rotary compressor, according to an embodiment of the present invention. As illustrated in  FIG. 1 , the variable capacity rotary compressor includes a hermetic casing  10 , with a drive unit  20  and a compressing unit  30  being installed in the hermetic casing  10 . The drive unit  20  generates a rotating force, and the compressing unit  30  compresses gas using the rotating force of the drive unit  20 . The drive unit  20  includes a cylindrical stator  22 , a rotor  23 , and a rotating shaft  21 . The cylindrical stator  22  is fixedly mounted to an inner surface of the hermetic casing  10 . The rotor  23  is rotatably installed in the cylindrical 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 plate  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 plate  34  is interposed between the upper and lower compression chambers  31  and  32  to partition the upper and lower compression chambers  31  and  32  thereby. 
   The upper compression chamber  31  may be higher in a vertical direction than that of the lower compression chamber  32 , thus the upper compression chamber  31  may have a larger capacity than that of the lower compression chamber  32 . Therefore, a larger amount of gas may be compressed in the upper compression chamber  31  in comparison with the lower compression chamber  32 , thus allowing the variable capacity rotary compressor to have a variable capacity. 
   Further, when the lower compression chamber  32  is higher than that of the upper compression chamber  31 , the lower compression chamber  32  has a larger capacity than that of the upper compression chamber  31 , thus allowing 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  or  32 , according to a rotating direction of the rotating shaft  21 . Upper and lower brake units  80  and  90  are provided at predetermined positions of the eccentric unit  40  to smoothly operate the eccentric unit  40 . A construction and an operation of the eccentric unit  40  and the upper and lower brake units  80  and  90  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  and  32 , respectively, to be rotatably fitted over the eccentric unit  40 . Upper inlet and upper outlet ports  63  and  65  (see  FIG. 3 ) are formed at predetermined positions of the housing  33  to communicate with the upper compression chamber  31 . Lower inlet and lower outlet ports  64  and  66  (see  FIG. 6 ) 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 upper outlet ports  63  and  65 , and is biased in a radial direction by an upper support spring  61   a  to be in a close contact with the upper roller  37  (see  FIG. 3 ). Further, a lower vane  62  is positioned between the lower inlet and lower outlet ports  64  and  66 , and is biased in a radial direction by a lower support spring  62   a  to be in a close contact with the lower roller  38  (see  FIG. 6 ). 
   Further, 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 variable capacity rotary compressor through the refrigerant outlet pipe  69   a . At a predetermined position of the refrigerant outlet pipe  69   a  is installed a path control unit  70 . The path control unit  70  operates to open or to close first or second intake paths  67  or  68 , thus supplying the gas refrigerant to one of the upper inlet port  63  of the upper compression chamber  31  and the lower inlet port  64  of the lower compression chamber  32  in which a compression operation is executed. A valve unit  71  is installed in the path control unit  70  to be movable in a horizontal direction. The valve unit  71  operates to open either the first or second intake paths  67  or  68  by a difference in a pressure between the first intake path  67  connected to the upper inlet port  63  and the second intake path  68  connected to the lower inlet port  64 , thus supplying the gas refrigerant to the upper inlet port  63  or lower inlet port  64 . 
   Further, a predetermined amount of oil  11  is contained in a lower portion of the hermetic casing  10  to lubricate and to cool several contact parts of the compressing part  30 . An oil passage  12  is axially formed along the rotating shaft  21  to be eccentric from a central axis C 1 -C 1  of the rotating shaft  21 , and operates to move the oil  11  upward by a centrifugal force resulting from a rotation of the rotating shaft  21 . A plurality of oil supply holes  13  are formed in the rotating shaft  21  in radial directions to communicate with the oil passage  12 , thus supplying the oil  11 , which flows upward through the oil passage  12 , to the contact parts. 
   A construction of the rotating shaft  21  and the eccentric unit  40  according to the embodiment of the present invention will be described in the following with reference to  FIG. 2 . 
     FIG. 2  is an exploded perspective view of the eccentric unit  40  included in the variable capacity rotary compressor of  FIG. 1 , in which upper and lower eccentric bushes  51  and  52  of the eccentric unit  40  are separated from the rotating shaft  21 . As illustrated 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. 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 upper and lower brake units  80  and  90 . The upper and lower brake units  80  and  90  operate to prevent the upper eccentric bush  51  and lower eccentric bush  52  from slipping over the upper eccentric cam  41  and lower eccentric cam  42 , respectively, at corresponding predetermined positions. This slipping may be due to variance in pressure of one or both of the upper and lower compression chambers  31  and  32  as the rotating shaft  21  rotates. 
   The upper and lower eccentric cams  41  and  42  integrally are 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  and 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 maximally projects from the rotating shaft  21 , to a minimum eccentric part of the upper eccentric cam  41 , which minimally projects from the rotating shaft  21 . Further, 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 maximally projects from the rotating shaft  21 , to a minimum eccentric part of the lower eccentric cam  42 , which minimally projects from the rotating shaft  21 . 
   The locking pin  43  includes a threaded shank  44  and a head  45 . The head  45  has a slightly larger diameter than the threaded shank  44 , and is formed at an end of the threaded 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-type 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 width which is slightly larger 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 direction or the second direction in such a state, the upper and lower eccentric bushes  51  and  52  are not rotated until the locking pin  43  comes into contact with one of first and second ends  53   a  and  53   b  of the slot  53 . When the locking pin  43  comes into contact with the first end  53   a  or the second end  53   b  of the slot  53 , the upper and lower eccentric bushes  51  and  52  rotate in the first direction or the second direction along with the rotating shaft  21 . 
   In this case, a first eccentric line L 3 -L 3 , which connects a maximum eccentric part of the upper eccentric bush  51  to a 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 . Further, a second eccentric line L 4 -L 4 , which connects a maximum eccentric part of the lower eccentric bush  52  to a 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 first eccentric line L 3 -L 3  of the upper eccentric bush  51  and the second eccentric line L 4 -L 4  of the lower eccentric bush  52  are positioned on a common 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 . 
   In the eccentric unit  40  constructed as described above, the upper brake unit  80  is provided between the upper eccentric cam  41  and the upper eccentric bush  51 , while the lower brake unit  90  is provided between the lower eccentric cam  42  and the lower eccentric bush  52 . 
   The upper brake unit  80  includes first and second upper pockets  81  and  82 . The first and second upper pockets  81  and  82  are bored on an outer surface of the upper eccentric cam  41  to be opposite to each other. First and second upper brake balls  85  and  86  are set in the first and second upper pockets  81  and  82 , respectively. First and second upper brake holes  87  and  88  are bored on an inner surface of the upper eccentric bush  51  to be opposite to each other. 
   The first and second upper brake balls  85  and  86  are slightly smaller than the first and second upper pockets  81  and  82  while being slightly larger than the first and second upper brake holes  87  and  88 , respectively, in a diameter thereof. Thus, the first and second upper brake balls  85  and  86  are movably set in the first and second upper pockets  81  and  82 , respectively. When a centrifugal force is generated in such a state, the first and second upper brake balls  85  and  86  move outward to be inserted into the first and second upper brake holes  87  and  88 , respectively, thus preventing one of the upper eccentric bush  51  from slipping over the upper eccentric cam  41  and the lower eccentric bush  52  from slipping over the lower eccentric cam  42 . 
   The first and second upper pockets  81  and  82  are designed to communicate with the oil passage  12  which is axially formed along the rotating shaft  21 , via first and second upper connecting passages  83  and  84 , to enhance operational effects of the first and second upper brake balls  85  and  86  and to prevent the upper and lower eccentric bushes  51  and  52  from slipping. According to the above-mentioned construction, the oil  11  is supplied from the oil passage  12  through the first and second upper connecting passages  83  and  84  to the first and second upper pockets  81  and  82 . At this time, an oil pressure resulting from the oil  11  acts on the first and second upper brake balls  85  and  86  to move the first and second upper brake balls  85  and  86  in an outward direction. Thus, the first and second upper brake balls  85  and  86  come into a closer contact (i.e., a pressure contact) with the first and second upper brake holes  87  and  88 , respectively, thus effectively preventing the upper eccentric bush  51  from slipping over the upper eccentric cam  41  or the lower eccentric bush  52  from slipping over the lower eccentric cam  42 . 
   Since each of the first and second upper brake holes  87  and  88  is bored from an inner surface of the upper eccentric bush  51  to an outer surface thereof, the oil  11  fed into the first and second upper pockets  81  and  82  flows to an exterior of the upper eccentric bush  51  through gaps between the first and second upper brake balls  85  and  86  and the first and second upper brake holes  87  and  88 . Such a construction prevents the first and second upper brake balls  85  and  86  from being fixed in the first and second upper brake holes  87  and  88 , respectively, by an oil pressure, while allowing a contact part between the upper eccentric bush  51  and the upper roller  37  (see  FIG. 3 ) fitted over the upper eccentric bush  51  to be lubricated. 
   The first and second upper pockets  81  and  82 , which are formed along the upper eccentric line L 1 -L 1  of the upper eccentric cam  41  to be opposite to each other, are arranged at positions which are angularly spaced apart from the locking pin  43  by about 90°. Further, the first and second upper brake holes  87  and  88 , which are formed along the first eccentric line L 3 -L 3  of the upper eccentric bush  51  to be opposite to each other, are arranged at positions which are angularly spaced apart from the first end  53   a  of the slot  53  by about 90°. 
   When the rotating shaft  21  rotates in the first direction, which is counterclockwise in  FIG. 2 , the first upper pocket  81  is positioned leading the locking pin  43  while being angularly spaced apart from the locking pin  43  by a first angle of 90°. Further, the second upper pocket  82  is positioned following the locking pin  43  while being angularly spaced apart from the locking pin  43  by a second angle of 90°. Further, the first upper brake hole  87  is positioned leading the first end  53   a  of the slot  53  while being angularly spaced apart from the first end  53   a  by a third angle of 90°. The second upper brake hole  88  is positioned following the first end  53   a  of the slot  53  while being angularly spaced apart from the first end  53   a  by a fourth angle of 90°. 
   Thus, when the locking pin  43  contacts the first end  53   a  of the slot  53  and the rotating shaft  21  rotates along with the upper and lower eccentric bushes  51  and  52  in the first direction, the first upper pocket  81  is aligned with the first upper brake hole  87  and the second upper pocket  82  is aligned with the second upper brake hole  88 . At this time, the first and second upper brake balls  85  and  86  are inserted into the first and second upper brake holes  87  and  88 , respectively, thus preventing the upper eccentric bush  51  from slipping. 
   Conversely, when the locking pin  43  contacts the second end  53   b  of the slot  53  and the rotating shaft  21  rotates along with the upper and lower eccentric bushes  51  and  52  in the second direction, the first upper pocket  81  is aligned with the second upper brake hole  88  and the second upper pocket  82  is aligned with the first upper brake hole  87 . At this time, the first and second upper brake balls  85  and  86  are inserted into the second and first upper brake holes  88  and  87 , respectively, thus preventing the lower eccentric bush  52  from slipping. 
   A general construction of the lower brake unit  90  remains the same as that of the upper brake unit  80 , except that the lower brake unit  90  is provided between the lower eccentric cam  42  and the lower eccentric bush  52 . 
   The lower brake unit  90  includes first and second lower pockets  91  and  92 . The first and second lower pockets  91  and  92  are bored on an outer surface of the lower eccentric cam  42  to be opposite to each other. First and second lower brake balls  95  and  96  are set in the first and second lower pockets  91  and  92 , respectively. First and second lower brake holes  97  and  98  are bored on an inner surface of the lower eccentric bush  52  to be opposite to each other. 
   The first and second lower brake balls  95  and  96  have a diameter slightly smaller than those of the first and second lower pockets  91  and  92  while the diameter of the first and second lower brake balls are slightly larger than those of the first and second lower brake holes  97  and  98 , respectively. Thus, the first and second lower brake balls  95  and  96  are movably set in the first and second lower pockets  91  and  92 , respectively. When a centrifugal force is generated in such a state, the first and second lower brake balls  95  and  96  move outward to be inserted into the first and second lower brake holes  97  and  98 , respectively, thus preventing the upper eccentric bush  51  or the lower eccentric bush  52  from slipping over the upper eccentric cam  41  or the lower eccentric cam  42 , respectively. 
   The first and second lower pockets  91  and  92  are designed to communicate with the oil passage  12  which is axially formed along the rotating shaft  21 , via first and second lower connecting passages  93  and  94 , to enhance operational effects of the first and second lower brake balls  95  and  96  which, respectively, prevents the upper and lower eccentric bushes  51  and/or  52  from slipping. According to the above-mentioned construction, the oil  11  is supplied from the oil passage  12  through the first and second lower connecting passages  93  and  94  to the first and second lower pockets  91  and  92 . At this time, an oil pressure resulting from the oil  11  acts on the first and second lower brake balls  95  and  96  to move the first and second lower brake balls  95  and  96  in an outward direction. Thus, the first and second lower brake balls  95  and  96  come into a closer contact (i.e., a pressure contact) with the first and second lower brake holes  97  and  98 , respectively, thus effectively preventing the upper eccentric bush  51  or the lower eccentric bush  52  from slipping over the upper eccentric cam  41  or the lower eccentric cam  42 , respectively. 
   Since each of the first and second lower brake holes  97  and  98  is bored from the an inner surface of the lower eccentric bush  52  to an outer surface thereof, the oil  11  fed into the first and second lower pockets  91  and  92  flows to an exterior of the lower eccentric bush  52  through gaps between the first and second lower brake balls  95  and  96  and the first and second lower brake holes  97  and  98 . Such a construction prevents the first and second lower brake balls  95  and  96  from being fixed in the first and second lower brake holes  97  and  98 , respectively, by an oil pressure, while allowing a contact part between the lower eccentric bush  52  and the lower roller  38  (see  FIG. 6 ) fitted over the lower eccentric bush  52  to be lubricated. 
   The first and second lower pockets  91  and  92 , which are formed along the upper eccentric line L 2 -L 2  of the lower eccentric cam  42  to be opposite to each other, are arranged at positions which are angularly spaced apart from the locking pin  43  by about 90°. Further, the first and second lower brake holes  97  and  98 , which are formed along the first eccentric line L 3 -L 3  of the lower eccentric bush  52  to be opposite to each other, are arranged at positions which are angularly spaced apart from the second end  53   b  of the slot  53  by about 90°. 
   When the rotating shaft  21  rotates in the second direction, which is clockwise in  FIG. 2 , the first lower pocket  91  is positioned leading the locking pin  43  while being angularly spaced apart from the locking pin  43  by a fifth angle of 90°. Further, the second lower pocket  92  is positioned following the locking pin  43  while being angularly spaced apart from the locking pin  43  at a sixth angle of 90°. Further, the first lower brake hole  97  is positioned leading the second end  53   b  of the slot  53  while being angularly spaced apart from the second end  53   b  by a seventh angle of 90°. The second lower brake hole  98  is positioned following the second end  53   b  of the slot  53  while being angularly spaced apart from the second end  53   b  by an eighth angle of 90°. 
   Thus, when the locking pin  43  contacts the second end  53   b  of the slot  53  and the rotating shaft  21  rotates along with the upper and lower eccentric bushes  51  and  52  in the second direction, the first lower pocket  91  is aligned with the second lower brake hole  98  and the second lower pocket  92  is aligned with the first lower brake hole  97 . At this time, the first and second lower brake balls  95  and  96  are inserted into the second and first lower brake holes  98  and  97 , respectively, thus preventing the lower eccentric bush  52  from slipping. 
   Conversely, when the locking pin  43  contacts the first end  53   a  of the slot  53  and the rotating shaft  21  rotates along with the upper and lower eccentric bushes  51  and  52  in the first direction, the first lower pocket  91  is aligned with the first lower brake hole  97  and the second lower pocket  92  is aligned with the second lower brake hole  98 . At this time, the first and second lower brake balls  95  and  96  are inserted into the first and second lower brake holes  97  and  98 , respectively, thus preventing the upper eccentric bush  51  from slipping. 
   The operation of compressing a gas refrigerant in the upper or lower compression chamber  31  or  32  by the eccentric unit  40  according to the embodiment of the present invention will be described in the following with reference to  FIGS. 3 to 8 . 
     FIG. 3  is a sectional view showing an upper compression chamber  31  in which a compression operation is executed without a slippage by the eccentric unit  40  of  FIG. 2 , when the rotating shaft  21  rotates in a first direction.  FIG. 4  is a sectional view, corresponding to  FIG. 3 , which shows a lower compression chamber  32  in which an idle operation is executed by the eccentric unit  40  of  FIG. 2 , when the rotating shaft  21  rotates in the first direction.  FIG. 5  is a sectional view showing an upper eccentric bush  51  when the rotating shaft  21  rotates in the first direction, in which the upper eccentric bush  51  does not slip at a predetermined position by the eccentric unit  40  of  FIG. 2 . 
   As illustrated in  FIG. 3 , when the rotating shaft  21  rotates in the first direction, which is counterclockwise in  FIG. 3 , the locking pin  43  projecting from the rotating shaft  21 , rotates at a predetermined angle while engaging with the slot  53  which is provided at a predetermined position between the upper and lower eccentric bushes  51  and  52 . When the locking pin  43  rotates at the predetermined angle, and is locked by the first end  53   a  of the slot  53 , the upper eccentric bush  51  rotates along with the rotating shaft  21 . At this time, since the lower eccentric bush  52  is integrally connected to the upper eccentric bush  51  by the connecting part  54 , the lower eccentric bush  52  rotates along with the upper eccentric bush  51 . 
   When the locking pin  43  contacts the first end  53   a  of the slot  53 , the maximum eccentric part of the upper eccentric cam  41  is aligned with the maximum eccentric part of the upper eccentric bush  51 . In this case, the upper eccentric bush  51  rotates while being maximally eccentric from the central axis C 1 -C 1  of the rotating shaft  21 . Thus, the upper roller  37  rotates while being in contact with an inner surface of the housing  33  defining the upper compression chamber  31 , thus executing the compression operation. 
   Further, the first and second upper pockets  81  and  82  of the upper brake unit  80  are aligned with the first and second upper brake holes  87  and  88 , respectively. The first and second upper brake balls  85  and  86  come into close contact with the first and second upper brake holes  87  and  88 , respectively, by the pressure of the oil  11  fed through the oil passage  12  to the first and second upper connecting passages  83  and  84  and by the centrifugal force, thus the upper eccentric bush  51  rotates while being restrained by the upper eccentric cam  41 . 
   Simultaneously, as illustrated in  FIG. 4 , the maximum eccentric part of the lower eccentric cam  42  contacts with the minimum eccentric part of the lower eccentric bush  52 . In this case, the lower eccentric bush  52  rotates while being concentric with the central axis C 1 -C 1  of the rotating shaft  21 . Thus, 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, thus the compression operation is not executed and, otherwise, an idle operation occurs therein. 
   Further, the first and second lower pockets  91  and  92  of the lower brake unit  90  are aligned with the first and second lower brake holes  97  and  98 , respectively. At this time, the first and second lower brake balls  95  and  96  come into close contact with the first and second lower brake holes  97  and  98 , respectively, by the pressure of the oil  11  fed through the oil passage  12  to the first and second lower connecting passages  93  and  94  and by the centrifugal force, thus the upper eccentric cam  41  rotates along with the upper eccentric bush  51  while being further restrained by the upper brake unit  80 . 
   Therefore, when the rotating shaft  21  rotates in the first direction, the gas refrigerant flowing to the upper compression chamber  31  through the upper inlet port  63  is compressed by the upper roller  37  in the upper compression chamber  31  having a larger capacity than that of the lower compression chamber  32 , and subsequently is discharged from the upper compression chamber  31  through the upper outlet port  65 . However, the compression operation is not executed in the lower compression chamber  32  having a smaller capacity than that of the upper compression chamber  31 . Therefore, the variable capacity rotary compressor is operated in a larger capacity compression mode. 
   Further, as shown in  FIG. 3 , 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 port  65 , returns to the upper compression chamber  31  and is re-expanded, thus applying a pressure to the upper roller  37  and the upper eccentric bush  51  in a rotating direction of the rotating shaft  21 . The upper eccentric bush  51  rotates faster than the rotating shaft  21 , thus causing the upper eccentric bush  51  to slip 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 . At this time, noise may be generated and the locking pin  43  and the slot  53  may be damaged, due to a collision between the locking pin  43  and the slot  53 . 
   However, the eccentric unit  40  prevents the upper eccentric bush  51  from slipping by an operation of the upper and lower brake units  80  and  90 . 
   As illustrated in  FIG. 5 , 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 port  65  and is re-expanded, thus generating a force F s . The force F s  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, since the first and second upper brake balls  85  and  86  (see  FIG. 3 ) come into close contact with the first and second upper brake holes  87  and  88  and the first and second lower brake balls  95  and  96  (see  FIG. 4 ) come into close contact with the first and second lower brake holes  97  and  98  by the centrifugal force and the oil pressure, the upper and lower eccentric cams  41  and  42  and the upper and lower eccentric bushes  51  and  52  rotate while being restrained by each other. Thus, a resistance force F r  to prevent a slippage of the upper eccentric bush  51  is generated by the first and second upper brake balls  85  and  86  and the first and second lower brake balls  95  and  96 , thus maximally preventing the upper eccentric bush  51  from slipping. 
   Further, when the rotating shaft  21  stops rotating, the first and second upper brake balls  85  and  86  and the first and second lower brake balls  95  and  96  are not affected by the centrifugal force and the oil pressure. At this time, the first and second upper brake balls  85  and  86  move into the first and second upper pockets  81  and  82 , respectively, while the first and second lower brake balls  95  and  96  move into the first and second lower pockets  91  and  92 , respectively. In such a state, when the rotating shaft  21  rotates in the second direction, the locking pin  43  contacts the second end  53   b  of the slot  53 , thus the compression operation is executed in the lower compression chamber  32 . The compression operation executed in the lower compression chamber  32  will be described as follows. 
     FIG. 6  is a sectional view showing a lower compression chamber  32  where the compression operation is executed without a slippage by the eccentric unit  40  of  FIG. 2 , when the rotating shaft  21  rotates in a second direction.  FIG. 7  is a sectional view, corresponding to  FIG. 6 , which shows the upper compression chamber  31  where an idle operation is executed by the eccentric unit  40  of  FIG. 2 , when the rotating shaft  21  rotates in the second direction.  FIG. 8  is a sectional view showing a lower eccentric bush  52  when the rotating shaft  21  rotates in the second direction, in which the lower eccentric bush  52  does not slip at a predetermined position by the eccentric unit  40  of  FIG. 2 . 
   As illustrated in  FIG. 6 , when the rotating shaft  21  rotates in the second direction, which is clockwise in  FIG. 6 , the variable capacity rotary compressor is operated oppositely to the operation shown in  FIGS. 3 and 4 , thus causing the compression operation to be executed in only the lower compression chamber  32 . 
   That is, while the rotating shaft  21  rotates in the second direction, the locking pin  43  projecting from the rotating shaft  21  comes into contact with the second end  53   b  of the slot  53 , thus causing the upper and lower eccentric bushes  51  and  52  to rotate in the second direction. 
   In this case, 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  52  rotates while being maximally eccentric from the central axis C 1 -C 1  of the rotating shaft  21 . Therefore, the lower roller  38  rotates while being in contact with the inner surface of the housing  33  which defines the lower compression chamber  32 , thus executing the compression operation. 
   Simultaneously, as illustrated in  FIG. 7 , the maximum eccentric part of the upper eccentric cam  41  contacts with the minimum eccentric part of the upper eccentric bush  51 . In this case, the upper eccentric bush  51  rotates while being concentric with the central axis C 1 -C 1  of the rotating shaft  21 . Thus, 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, thus the compression operation is not executed and otherwise an idle operation is executed. 
   Therefore, the gas refrigerant flowing to the lower compression chamber  32  through the lower inlet port  64  is compressed by the lower roller  38  in the lower compression chamber  32  having a smaller capacity than that of the upper compression chamber  31 , and subsequently is discharged from the lower compression chamber  32  through the lower outlet port  66 . However, the compression operation is not executed in the upper compression chamber  31  having a larger capacity than that of the lower compression chamber  32 . Therefore, the rotary compressor is operated in a smaller capacity compression mode. 
   Further, as shown in  FIG. 6 , when the lower roller  38  comes into contact with the lower vane  62 , an operation of compressing the gas refrigerant is completed and an operation of drawing the gas refrigerant starts. At this time, some of the compressed gas, which was not discharged from the lower compression chamber  32  through the lower outlet port  66 , returns to the lower compression chamber  32  and is re-expanded, thus applying a pressure to the lower roller  38  and the lower eccentric bush  52  in a rotating direction of the rotating shaft  21 . The lower eccentric bush  52  rotates faster than the rotating shaft  21 , thus causing 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 . Further, 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 upper and lower eccentric bushes  51  and  52  are restrained in a common manner as those of the upper and lower eccentric bushes  51  and  52 , which are restrained by the upper and lower brake units  80  and  90  when the rotating shaft  21  rotates in the first direction, thus preventing the slippage and the collision. 
   Thus, the eccentric unit  40  prevents the lower eccentric bush  52  from slipping by the operation of the upper and lower brake units  80  and  90 . 
   As illustrated in  FIG. 8 , 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 port  66  and is re-expanded, thus generating the force F s.  The force F s  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, since the second and first lower brake balls  96  and  95  (see  FIG. 6 ) come into close contact with the first and second lower brake holes  97  and  98  and the second and first upper brake balls  86  and  85  (see  FIG. 7 ) come into close contact with the first and second upper brake holes  87  and  88  by the centrifugal force and the oil pressure, the lower and upper eccentric cams  42  and  41  and the lower and upper eccentric bushes  52  and  51  are rotated while being restrained by each other. Thus, a resistance force F r  to prevent the slippage of the lower eccentric bush  52  is generated by the first and second lower brake balls  95  and  96  and the first and second upper brake balls  85  and  86 , thus maximally preventing the lower eccentric bush  52  from slipping. 
   Further, when the rotating shaft  21  stops rotating, the first and second lower brake balls  95  and  96  and the first and second upper brake balls  85  and  86  are not affected by the centrifugal force and the oil pressure. At this time, the first and second upper brake balls  85  and  86  are moved into the first and second upper pockets  81  and  82 , respectively, while the first and second lower brake balls  95  and  96  are moved into the first and second lower pockets  91  and  92 , respectively. In such a state, when the rotating shaft  21  is rotated again in the first direction, the locking pin  43  contacts the first end  53   a  of the slot  53 , thus the compression operation is executed in the upper compression chamber  31 . 
   As is apparent from the above description, a variable capacity rotary compressor is provided, which is designed to execute a compression operation in either of upper and lower compression chambers having different interior capacities thereof by an eccentric unit which rotates in the first direction or the second direction, thus varying a compression capacity of the variable capacity rotary compressor as desired. 
   Further, a variable capacity rotary compressor is provided, which has an upper brake unit between an upper eccentric cam and an upper eccentric bush, and has a lower brake unit between a lower eccentric cam and a lower eccentric bush, thus preventing the upper eccentric bush or lower eccentric bush from slipping when an eccentric unit rotates in the first direction or the second direction, therefore allowing the upper and lower eccentric bushes to smoothly rotate. 
   Although an embodiment of the present invention has been shown and described, it would be appreciated by those skilled in the art that changes may be made in the embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.