Patent Publication Number: US-7588427-B2

Title: Variable capacity rotary compressor

Description:
TECHNICAL FIELD 
   The present invention relates to a rotary compressor, and more particularly, to a mechanism for changing compression capacity of a rotary compressor. 
   BACKGROUND ART 
   In general, compressors are machines that are supplied power from a power generator such as an electric motor, a turbine or the like and apply compressive work to a working fluid, such as air or refrigerant to elevate the pressure of the working fluid. Such compressors are widely used in a variety of applications, from electric home appliances such as air conditioners, refrigerators and the like to industrial plants. 
   The compressors are classified into two types according to their compressing methods: a positive displacement compressor, and a dynamic compressor (a turbo compressor). The positive displacement compressor is widely used in industry fields and configured to increase pressure by reducing its volume. The positive displacement compressors can be further classified into a reciprocating compressor and a rotary compressor. 
   The reciprocating compressor is configured to compress the working fluid using a piston that linearly reciprocates in a cylinder. The reciprocating compressor has an advantage of providing high compression efficiency with a simple structure. However, the reciprocation compressor has a limitation in increasing its rotational speed due to the inertia of the piston and a disadvantage in that a considerable vibration occurs due to the inertial force. The rotary compressor is configured to compress working fluid using a roller eccentrically revolving along an inner circumference of the cylinder, and has an advantage of obtaining high compression efficiency at a low speed compared with the reciprocating compressor, thereby reducing noise and vibration. 
   Recently, compressors having at least two compression capacities have been developed. These compressors have compression capacities different from each other according to the rotational directions (i.e., clockwise direction and counterclockwise direction) by using a partially modified compression mechanism. Since compression capacity can be adjusted differently according to loads required by these compressors, such a compressor is widely used to increase an operation efficiency of several equipments requiring the compression of working fluid, especially household electric appliances such as a refrigerator that uses a refrigeration cycle. 
   However, a conventional rotary compressor has separate a suction portion and discharge portion which communicate with a cylinder. The roller rolls from the suction portion to the discharge portion along an inner circumference of the cylinder, so that the working fluid is compressed. Accordingly, when the roller rolls in an opposite direction (i.e., from the discharge portion to the suction portion), the working fluid is not compressed. In other words, the conventional rotary compressor cannot have different compression capacities if the rotational direction is changed. Accordingly, there is a demand for a rotary compressor having variable compression capacities as well as the aforementioned advantages. 
   DISCLOSURE OF INVENTION 
   Accordingly, the present invention is directed to a rotary compressor that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
   An object of the present invention is to provide a rotary compressor in which the compressing stroke is possibly performed to both or the clockwise and counterclockwise rotations of a driving shaft. 
   Another object of the present invention is to provide a rotary compressor whose compression capacity can be varied. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
   To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a rotary compressor comprising: a driving shaft being rotatable clockwise and counterclockwise, and having an eccentric portion of a predetermined size; a cylinder having a predetermined inner volume; a roller installed rotatably on an outer circumference of the eccentric portion so as to contact an inner circumference of the cylinder, performing a rolling motion along the inner circumference and forming a fluid chamber to suck and compress fluid along with the inner circumference; a vane installed elastically in the cylinder to contact the roller; upper and lower bearings installed respectively in upper and lower portions of the cylinder, for rotatably supporting the driving shaft and hermetically sealing the inner volume; suction and discharge ports communicating with the fluid chamber so as to suck and discharge the fluid; a suction plenum communicating with the suction ports and preliminarily storing the fluid; and a compression mechanism configured to form different sizes of compressive spaces in the fluid chamber depending on the rotational direction of the driving shaft. 
   Preferably, the compression mechanism compresses the fluid using the overall fluid chamber when the driving shaft rotates in any one of the clockwise direction and the counterclockwise direction. 
   In more detail, the compression mechanism compresses the fluid using a portion of the fluid chamber when the driving shaft rotates in the other of the clockwise direction and the counterclockwise direction. 
   In an aspect of the invention, the compression mechanism comprises a valve assembly, which rotates according to the rotational direction of the driving shaft to selectively open at least one of the suction ports. 
   In another aspect of the invention, the compression mechanism comprises a valve assembly selective opening at least one of the suction ports spaced apart from each other by using a pressure difference between the cylinder and inner and outer portions according to the rotational direction of the driving shaft. 
   In still another aspect of the invention, the compression mechanism comprises a first vane and a second vane that divide the fluid chamber into a first space configured such that the fluid is compressed while the driving shaft rotates bidirectionally, and a second space configured such that the fluid is compressed while the driving shaft rotates in any one direction. 
   In yet another aspect of the invention, the compression mechanism is comprised of clearances formed differently according to the rotational direction of the driving shaft between the roller and the inner circumference of the cylinder. 
   Meanwhile, the suction plenum accommodates oil separated from the stored fluid, and is installed at a lower portion of the bearing in the vicinity of the suction port. 
   It is preferable that the suction plenum has 100-400% a volume as large as the fluid chamber. It is also preferable that the suction plenum further comprises a penetration hole through which a sleeve of the bearing passes. 
   The suction plenum could be connected with a suction pipe through a predetermined fluid passage, and this fluid passage penetrates the cylinder and the lower bearing. 
   It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
       FIG. 1  is a partial longitudinal sectional view illustrating a rotary compressor according to a first embodiment of the present invention; 
       FIG. 2  is an exploded perspective view illustrating the compression unit of the rotary compressor according to a first embodiment of the present invention; 
       FIG. 3  is a sectional view illustrating the compressing unit according to a first embodiment of the present invention; 
       FIG. 4  is a cross-sectional view illustrating the inside of the cylinder according to a first embodiment of the present invention; 
       FIGS. 5A and 5B  are plan views illustrating a lower bearing of the rotary compressor according to a first embodiment of the present invention; 
       FIGS. 6A and 6B  illustrate a valve assembly of the rotary compressor according to a first embodiment of the present invention; 
       FIGS. 7A ,  7 B AND  7 C are plan views illustrating modifications of a valve assembly; 
       FIGS. 8A and 8B  are plan views illustrating a revolution control means; 
       FIG. 8C  is a partial sectional view of  FIG. 8B ; 
       FIGS. 9A and 9B  are plan views of modifications of the revolution control means of the valve assembly; 
       FIGS. 10A and 10B  are plan views of another modifications of the revolution control means of the valve assembly; 
       FIGS. 11A and 11B  are plan views of another modifications of the revolution control means of the valve assembly; 
       FIG. 12  is an exploded perspective view of a compressing unit of a rotary compressor including a suction plenum according to a first embodiment of the present invention; 
       FIG. 13  is a cross-sectional view of the compressing unit shown in  FIG. 12 ; 
       FIGS. 14A to 14C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the counterclockwise direction in the rotary compressors according to a first embodiment of the present invention; 
       FIGS. 15A to 15C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the clockwise direction in the rotary compressors according to a first embodiment of the present invention; 
       FIG. 16  is a partial longitudinal sectional view illustrating a rotary compressor according to a second embodiment of the present invention; 
       FIG. 17  is an exploded perspective view illustrating the compression unit of the rotary compressor according to a second embodiment of the present invention; 
       FIG. 18  is a sectional view illustrating the compressing unit according to a second embodiment of the present invention; 
       FIG. 19  is a cross-sectional view illustrating the inside of the cylinder according to a second embodiment of the present invention; 
       FIG. 20  is a plan view illustrating a lower bearing of the rotary compressor according to a second embodiment of the present invention; 
       FIG. 21  is an exploded perspective view of a rotary compressor including a modified valve assembly according to a second embodiment of the present invention; 
       FIG. 22  is a plan view illustrating the valve assembly of  FIG. 6 ; 
       FIGS. 23A and 23B  are sectional views illustrating operation of discharge valves of a rotary compressor according to a second embodiment of the present invention; 
       FIGS. 24A and 24B  are sectional views illustrating operation of a valve assembly of a rotary compressor according to a second embodiment of the present invention; 
       FIG. 25  is an exploded perspective view of a compressing unit of a rotary compressor including a suction plenum according to a second embodiment of the present invention; 
       FIG. 26  is a cross-sectional view of the compressing unit shown in  FIG. 25 ; 
       FIGS. 27A to 27C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the counterclockwise direction in the rotary compressors according to a second embodiment of the present invention; 
       FIGS. 28A to 28C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the clockwise direction in the rotary compressors according to a second embodiment of the present invention; 
       FIG. 29  is a partial longitudinal sectional view illustrating a rotary compressor according to a third embodiment of the present invention; 
       FIG. 30  is an exploded perspective view illustrating the compression unit of the rotary compressor according to a third embodiment of the present invention; 
       FIG. 31  is a sectional view illustrating the compressing unit according to a third embodiment of the present invention; 
       FIG. 32  is a cross-sectional view illustrating the inside of the cylinder according to a third embodiment of the present invention; 
       FIG. 33  is a plan view illustrating a lower bearing of the rotary compressor according to a third embodiment of the present invention; 
       FIGS. 34A and 34B  are sectional views illustrating operation of discharge valves of a rotary compressor according to a third embodiment of the present invention; 
       FIGS. 35A and 35B  are sectional views illustrating operation of suction valves of a rotary compressor according to a third embodiment of the present invention; 
       FIG. 36  is an exploded perspective view of a compressing unit of a rotary compressor including a suction plenum according to a third embodiment of the present invention; 
       FIG. 37  is a cross-sectional view of the compressing unit shown in  FIG. 36 ; 
       FIGS. 38A to 38D  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the counterclockwise direction in the rotary compressors according to a third embodiment of the present invention; 
       FIGS. 39A to 39D  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the clockwise direction in the rotary compressors according to a third embodiment of the present invention; 
       FIG. 40  is a partial longitudinal sectional view illustrating a rotary compressor according to a fourth embodiment of the present invention; 
       FIG. 41  is an exploded perspective view illustrating the compression unit of the rotary compressor according to a fourth embodiment of the present invention; 
       FIG. 42  is a sectional view illustrating the compressing unit according to a fourth embodiment of the present invention; 
       FIG. 43  is a cross-sectional view illustrating the inside of the cylinder according to a fourth embodiment of the present invention; 
       FIG. 44  is a plan view illustrating clearances between the roller and the cylinder in a rotary compressor according to a fourth embodiment of the present invention; 
       FIG. 45  is an exploded perspective view of a compressing unit of a rotary compressor including a suction plenum according to a fourth embodiment of the present invention; 
       FIG. 46  is a cross-sectional view of the compressing unit shown in  FIG. 45 ; 
       FIGS. 47A to 47C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the counterclockwise direction in the rotary compressors according to a fourth embodiment of the present invention; and 
       FIGS. 48A to 48C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the clockwise direction in the rotary compressors according to a fourth embodiment of the present invention. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   Reference will now be made in detail to the preferred embodiments of the present invention to achieve the objects, with examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     FIGS. 1 ,  16 ,  29  and  40  are longitudinal sectional views of rotary compressors according to first to fourth embodiments of the present invention. 
   First, as shown in the drawings, in each embodiment, a rotary compressor of the present invention includes a case  1 , a power generator  10  positioned in the case  1  and a compressing unit  20 . In the referenced figures, the power generator  10  is positioned on the upper portion of the rotary compressor and the compressing unit  20  is positioned on the lower portion of the rotary compressor. However, their positions may be changed if necessary. An upper cap  3  and a lower cap  5  are installed on the upper portion and the lower portion of the case  1  respectively to define a sealed inner space. A suction pipe  7  for sucking working fluid is installed on a side of the case  1  and connected to an accumulator  8  for separating lubricant from refrigerant. A discharge pipe  9  for discharging the compressed fluid is installed on the center of the upper cap  3 . A predetermined amount of the lubricant “0” is filled in the lower cap  5  so as to lubricate and cool members that are moving frictionally. Here, an end of a driving shaft  13  is dipped in the lubricant. 
   The power generator  10  includes a stator  11  fixed in the case  1 , a rotor  12  rotatably supported in the stator  11  and the driving shaft  13  inserted forcibly into the rotor  12 . The rotor  12  is rotated due to electromagnetic force, and the driving shaft  13  delivers the rotation force of the rotor to the compressing unit  20 . To supply external electric power to the stator  20 , a terminal  4  is installed in the upper cap  3 . In the present invention, the rotor  12  is configured to be rotatable clockwise and counterclockwise and accordingly the driving shaft  13  is rotatable together with the rotor  12  bidirectionally, i.e., clockwise and counterclockwise. Since the bidirectionally rotatable motor is conventional, its detailed description will be omitted. 
   The compressing unit  20  includes a cylinder  21  fixed to the case  1 , and upper and lower bearings  24  and  25  respectively installed on upper and lower portions of the cylinder  21 . Also, other elements for compression are included in the cylinder  21  and bearings  24  and  25 , and combination of a part of the elements constitutes compression mechanisms  100 ,  200 ,  300  and  400  in each embodiment. 
   In the compression unit  20 , the compression mechanisms  100 ,  200 ,  300  and  400  compress specific working fluid in all rotational directions (clockwise and counterclockwise) of the driving shaft  13  in combination with other elements. For instance, for bidirectional compression, in addition to the compression mechanisms, the aforementioned bidirectional rotational motor is applied to the compressor of the invention, and suction and discharge ports allow the fluid to be sucked into the compression unit  20  and to be discharged from the compression unit  20  in all rotational directions of the driving shaft  13 . Further, the compression mechanisms  100 ,  200 ,  300  and  400  are configured to form compression spaces having different sizes substantially inside the compression unit  20  according to the rotational direction of the driving shaft  13 . Accordingly, the compressor is allowed to have different compression capacities according to the rotational directions of the shaft  13 . 
   In the rotary compressor of the invention, the power generator  10  is the same as that of a general rotary compressor, and any great modification is not required for the power generator  10  according to the embodiments of the invention. Accordingly, additional description on the power generator  10  is omitted and the compression mechanisms  100 ,  200 ,  300  and  400  schematically described in the above will be described in more detail with reference to drawings related with first to fourth embodiments. 
   First Embodiment 
     FIG. 2  is an exploded perspective view illustrating the compression unit of the rotary compressor according to a first embodiment of the present invention and  FIG. 3  is a sectional view illustrating the compressing unit according to a first embodiment of the present invention. 
   In the compression unit  20  of the first embodiment, the cylinder  21  has a predetermined inner volume and a strength enough to endure the pressure of the fluid. The cylinder  21  accommodates an eccentric portion  13   a  formed on the driving shaft  13  in the inner volume. The eccentric portion  13   a  is a kind of an eccentric cam and has a center spaced by a predetermined distance from its rotation center. The cylinder  21  has a groove  21   b  extending by a predetermined depth from its inner circumference. A vane  23  to be described below is installed in the groove  21   b . The groove  21   b  is long enough to accommodate the vane  23  completely. 
   The roller  22  is a ring member that has an outer diameter less than the inner diameter of the cylinder  21 . As shown in  FIG. 4 , the roller  22  contacts the inner circumference of the cylinder  21  and is rotatably coupled with the eccentric portion  13   a . Accordingly, the roller  22  performs rolling motion on the inner circumference of the cylinder  21  while spinning on the outer circumference of the eccentric portion  13   a  when the driving shaft  13  rotates. The roller  22  revolves spaced apart by a predetermined distance from the rotation center ‘0’ due to the eccentric portion  13   a  while performing the rolling motion. Since the outer circumference of the roller  22  always contacts the inner circumference due to the eccentric portion  13   a , the outer circumference of the roller  22  and the inner circumference of the cylinder form a separate fluid chamber  29  in the inner volume. The fluid chamber  29  is used to suck and compress the fluid in the rotary compressor. 
   The vane  23  is installed in the groove  21   b  of the cylinder  21  as described above. An elastic member  23   a  is installed in the groove  21   b  to elastically support the vane  23 . The vane  23  continuously contacts the roller  22 . In other words, the elastic member  23   a  has one end fixed to the cylinder  21  and the other end coupled with the vane  23 , and pushes the vane  23  to the side of the roller  22 . Accordingly, the vane  23  divides the fluid chamber  29  into two separate spaces  29   a  and  29   b  as shown in  FIG. 4 . While the driving shaft  13  rotates or the roller  22  revolves, the volumes of the spaces  29   a  and  29   b  are changed complementarily. In other words, if the roller  22  rotates clockwise, the space  29   a  gets smaller but the other space  29   b  gets larger. However, the total volume of the spaces  29   a  and  29   b  is constant and approximately the same as that of the predetermined fluid chamber  29 . One of the spaces  29   a  and  29   b  works as a suction chamber for sucking the fluid and the other one works as a compression chamber for compressing the fluid relatively when the driving shaft  13  rotates in one direction (clockwise or counterclockwise). Accordingly, as described above, the compression chamber of the spaces  29   a  and  29   b  gets smaller to compress the previously sucked fluid and the suction chamber expands to suck the new fluid relatively according to the rotation of the roller  22 . If the rotational direction of the roller  22  is reversed, the functions of the spaces  29   a  and  29   b  are exchanged. In the other words, if the roller  22  revolves counterclockwise, the right space  29   b  of the roller  22  becomes a compression chamber, but if the roller  22  revolves clockwise, the left space  29   a  of the roller  22  becomes a discharge chamber. 
   The upper bearing  24  and the lower bearing  25  are, as shown in  FIG. 2 , installed on the upper and lower portions of the cylinder  21  respectively, and rotatably support the driving shaft  13  using a sleeve and the penetrating holes  24   b  and  25   b  formed inside the sleeve. In more detail, the upper bearing  24 , the lower bearing  25  and the cylinder  21  include a plurality of coupling holes  24   a ,  25   a  and  21   a  formed to correspond to each other respectively. The cylinder  21 , the upper bearing  24  and the lower bearing  25  are coupled with one another to seal the cylinder inner volume, especially the fluid chamber  29  using coupling members such as bolts and nuts. 
   The discharge ports  26   a  and  26   b  are formed on the upper bearing  24 . The discharge ports  26   a  and  26   b  communicate with the fluid chamber  29  so that the compressed fluid can be discharged. The discharge ports  26   a  and  26   b  can communicate directly with the fluid chamber  29  or can communicate with the fluid chamber  29  through a predetermined fluid passage  21   d  formed in the cylinder  21  and the upper bearing  24 . Discharge valves  26   c  and  26   d  are installed on the upper bearing  24  so as to open and close the discharge ports  26   a  and  26   b . The discharge valves  26   c  and  26   d  selectively open the discharge ports  26   a  and  26   b  only when the pressure of the chamber  29  is greater than or equal to a predetermined pressure. To achieve this, it is desirable that the discharge valves  26   c  and  26   d  are leaf springs of which one end is fixed in the vicinity of the discharge ports  26   a  and  26   b  and the other end can be deformed freely. Although not shown in the drawings, a retainer for restricting the deformable amount of the leaf spring may be installed on the upper portion of the discharge valves  26   c  and  26   d  so that the valves  26   c  and  26   d  can operate stably. In addition, a muffler (not shown) can be installed on the upper portion of the upper bearing  24  to reduce a noise generated when the compressed fluid is discharged. 
   The suction ports  27   a ,  27   b  and  27   c  communicating with the fluid chamber  29  are formed on the lower bearing  25 . The suction ports  27   a ,  27   b  and  27   c  guide the compressed fluid to the fluid chamber  29 . The suction ports  27   a ,  27   b  and  27   c  are connected to the suction pipe  7  so that the fluid outside the compressor can flow into the chamber  29 . More particularly, the suction pipe  7  is branched into a plurality of auxiliary pipes  7   a  and the branched auxiliary pipes  7   a  are connected to suction ports  27  respectively. If necessary, the discharge ports  26   a  and  26   b  may be formed on the lower bearing  25  and the suction ports  27   a ,  27   b  and  27   c  may be formed on the upper bearing  24 . 
   The suction and discharge ports  26  and  27  become the important factors in determining compression capacity of the rotary compressor, and will be described referring to  FIGS. 4 and 5 .  FIG. 4  is a cross-sectional view illustrating the inside of the cylinder according to a first embodiment of the present invention. 
   First, the compressor of the present invention includes at least two discharge ports  26   a  and  26   b . As shown in the drawing, even if the roller  22  revolves in any direction, a discharge port should exist between the suction port and vane  23  positioned in the revolution path to discharge the compressed fluid. Accordingly, one discharge port is necessary for each rotational direction. It causes the compressor of the present invention to discharge the fluid regardless of the revolution direction of the roller  22  (that is, the rotational direction of the driving shaft  13 ). Meanwhile, as described above, the compression chamber of the spaces  29   a  and  29   b  gets smaller to compress the fluid as the roller  22  approaches the vane  23 . Accordingly, the discharge ports  26   a  and  26   b  are preferably formed facing each other in the vicinity of the vane  23  to discharge the maximum compressed fluid. In other words, as shown in the drawings, the discharge ports  26   a  and  26   b  are positioned on both sides of the vane  23  respectively. The discharge ports  26   a  and  26   b  are preferably positioned in the vicinity of the vane  23  if possible. 
   The suction port  27  is positioned properly so that the fluid can be compressed between the discharge ports  26   a  and  26   b  and the roller  22 . Actually, the fluid is compressed from a suction port to a discharge port positioned in the revolution path of the roller  22 . In other words, the relative position of the suction port for the corresponding discharge port determines the compression capacity and accordingly two compression capacities can be obtained using different suction ports  27  according to the rotational direction. Accordingly, the compression mechanism of the present invention has first and second suction ports  27   a  and  27   b  corresponding to two discharge ports  26   a  and  26   b  respectively and the suction ports  27   a  and  27   b  are spaced apart by a predetermined angle from each other with respect to the center 0 for two different compression capacities. 
   Preferably, the first suction port  27   a  is positioned in the vicinity of the vane  23 . Accordingly, the roller  22  compresses the fluid from the first suction port  27   a  to the second discharge port  26   b  positioned across the vane  23  in its rotation in one direction (counterclockwise in the drawing). The roller  22  compresses the fluid due to the first suction port  27   a  by using the overall chamber  29  and accordingly the compressor has a maximum compression capacity in the counterclockwise rotation. In other words, the fluid as much as overall volume of the chamber  29  is compressed. The first suction port  27   a  is actually spaced apart by an angle θ 1  of 10° clockwise or counterclockwise from the vane  23  as shown in  FIGS. 4 and 5A . The drawings of the present invention illustrate the first suction port  27   a  spaced apart by the angle θ 1  counterclockwise. At this separating angle θ 1 , the overall fluid chamber  29  can be used to compress the fluid without interference of the vane  23 . 
   The second suction port  27   b  is spaced apart by a predetermined angle from the first suction port  27   a  with respect to the center. The roller  22  compresses the fluid from the second suction port  27   b  to the first discharge port  26   a  in its rotation in counterclockwise direction. Since the second suction port  27   b  is spaced apart by a considerable angle clockwise from the vane  23 , the roller  22  compresses the fluid by using a portion of the chamber  29  and accordingly the compressor has less compression capacity than it has during counterclockwise rotary motion. In other words, the fluid as much as a portion volume of the chamber  29  is compressed. The second suction port  27   b  is preferably spaced apart by an angle θ 2  of a range of 90-180° clockwise or counterclockwise from the vane  23 . The second suction port  27   b  is preferably positioned facing the first suction port  27   a  so that the difference between compression capacities can be made properly and the interference can be avoided for each rotational direction. 
   As shown in  FIG. 5A , the suction ports  27   a  and  27   b  are generally in circular shapes whose diameters are, preferably 6-15 mm. In order to increase a suction amount of fluid, the suction ports  27   a  and  27   b  can also be provided in several shapes, including a rectangle. Further, as shown in  FIG. 5B , the rectangular suction ports  27   a  and  27   b  may have a predetermined curvature. In this case, an interference with adjacent other parts, especially the roller  22 , can be minimized in operation. 
   Meanwhile, in order to obtain desired compression capacity in each rotational direction, suction ports that are available in any one of rotational directions should be single. If there are two suction ports in the rotation path of the roller  22 , compression does not occur between the suction ports. In other words, if the first suction port  27   a  is opened, the second suction port  27   b  should be closed, and vice versa. Accordingly, the valve assembly  100  is installed between the lower bearing  24  and the cylinder  21  to selectively open only one of the suction ports  27   a  and  27   b  according to the revolution direction (i.e., rotational direction of the driving shaft  13 ). Thus, by selectively opening a specific one of the suction ports, different compression spaces can be substantially formed in the fluid chamber  29  according to the rotational direction, so that the valve assembly  100  acts as the inventive compression mechanism previously defined. 
   As shown in  FIGS. 2 ,  3  and  6 A- 6 B, the valve assembly  100  includes first and second valves  110  and  120 , which are installed between the cylinder  21  and the lower bearing  25  so as to allow it to be adjacent to the suction ports. If the suction ports  27   a ,  27   b  and  27   c  are formed on the upper bearing  24 , the first and second valves  110  and  120  are installed between the cylinder  21  and the upper bearing  24 . 
   The first valve  110 , as shown in  FIG. 3 , is a disk member installed so as to contact the eccentric portion  13   a  more accurately than the driving shaft  13 . Accordingly, if the driving shaft  13  rotates (that is, the roller  22  revolves), the first valve  110  rotates in the same direction. Preferably, the first valve  110  has a diameter larger than an inner diameter of the cylinder  21 . As shown in  FIG. 3 , the cylinder  21  supports a portion (i.e., an outer circumference) of the first valve  110  so that the first valve  110  can rotate stably. Preferably, the first valve  110  is 0.5-5 mm thick. 
   Referring to  FIGS. 2 and 6A , the first valve  110  includes first and second openings  111  and  112  respectively communicating with the first and second suction ports  27   a  and  27   b  in a specific rotational direction, and a penetration hole  110   a  into which the driving shaft  13  is inserted. In more detail, when the roller  22  rotates in any one of the clockwise and counterclockwise directions, the first opening  111  communicates with the first suction port  27   a  by the rotation of the first valve  110 , and the second suction port  27   b  is closed by the body of the first valve  110 . When the roller  22  rotates in the other of the clockwise and counterclockwise directions, the second opening  112  communicates with the second suction port  27   b . At this time, the first suction port  27   a  is closed by the body of the first valve  110 . These first and second openings  111  and  112  can be in circular or polygonal shapes. In case the openings  111  and  112  are the circular shapes, it is desired that the openings  111  and  112  are 6-15 mm in diameter. Additionally, the openings  111  and  112  can be rectangular shapes having predetermined curvature as shown in  FIG. 7A , or cut-away portions as shown in  FIG. 7B . As a result, the openings are enlarged, such that fluid is sucked smoothly. If these openings  111  and  112  are formed adjacent to a center of the first valve  110 , a probability of interference between the roller  22  and the eccentric portion  13   a  increases. In addition, there is the probability of the fluid leaking out along the driving shaft  13 , since the openings  111  and  112  communicate with a space between the roller  22  and the eccentric portion  13   a . For these reasons, as shown in  FIG. 7C , it is preferable that the openings  111  and  112  are positioned in the vicinity of the outer circumference of the first valve  110 . Meanwhile, the first opening  111  may open each of the first and second suction ports  27   a  and  27   b  at each rotational direction by adjusting the rotation angle of the first valve  110 . In other words, when the driving shaft  13  rotates in any one of the clockwise and counterclockwise directions, the first opening  111  communicates with the first suction port  27   a  while closing the second suction port  27   b . When the driving shaft  13  rotates in the other of the clockwise and counterclockwise directions, the first opening  111  communicates with the second suction port  27   b  while closing the first suction port  27   a . It is desirable to control the suction ports using such a single opening  111 , since the structure of the first valve  110  is simplified much more. 
   Referring to  FIGS. 2 ,  3  and  6 B, the second valve  120  is fixed between the cylinder  21  and the lower bearing  25  so as to guide a rotary motion of the first valve  110 . The second valve  120  is a ring-shaped member having a site portion  121  which receives rotatably the first valve  110 . The second valve  120  further includes a coupling hole  120   a  through which it is coupled with the cylinder  21  and the upper and lower bearings  24  and  25  by a coupling member. Preferably, the second valve  120  has the same thickness as the first valve  110  in order for a prevention of fluid leakage and a stable support. In addition, since the first valve  110  is partially supported by the cylinder  21 , the first valve  110  may have a thickness slightly smaller than the second valve  120  in order to form a gap for the smooth rotation of the second valve  120 . 
   Meanwhile, referring to  FIG. 4 , in the case of the clockwise rotation, the fluid&#39;s suction or discharge between the vane  23  and the roller  22  does not occur while the roller  22  revolves from the vane  23  to the second suction port  27   b . Accordingly, a region V becomes a vacuum state. The vacuum region V causes a power loss of the driving shaft  13  and a loud noise. Accordingly, in order to overcome the problem in the vacuum region V, a third suction port  27   c  is provided at the lower bearing  25 . The third suction port  27   c  is formed between the second suction port  27   b  and the vane  23 , supplying fluid to the space between the roller  22  and the vane  23  so as not to form the vacuum state before the roller  22  passes through the second suction port  27   b . Preferably, the third suction port  27   c  is formed in the vicinity of the vane  23  so as to remove quickly the vacuum state. However, the third suction port  27   c  is positioned to face the first suction port  27   a  since the third suction port  27   c  operates at a different rotational direction from the first suction port  27   a . In reality, the third suction port  27   c  is positioned spaced by an angle (θ 3 ) of approximately 10° from the vane  23  clockwise or counterclockwise. In addition, as shown in  FIGS. 5A and 5B , the third suction port  27   c  can be circular shapes or curved rectangular shapes. 
   Since the aforementioned third suction port  27   c  operates along with the second suction port  27   b , the suction ports  27   b  and  27   c  should be simultaneously opened while the roller  22  revolves in any one of the clockwise and counterclockwise directions. Accordingly, the first valve  110  further includes a third opening  113  configured to communicate with the third suction port  27   c  at the same time when the second suction port  27   b  is opened. According to the present invention, the third opening  113  can be formed independently, which is represented with a dotted line in  FIG. 6A . However, since the first and third suction ports  27   a  and  27   c  are adjacent to each other, it is desirable to open both the first and third suction ports  27   a  and  27   c  according to the rotational direction of the first opening  111  by increasing the rotation angle of the first valve  110 . 
   The first valve  110  may open the suction ports  27   a ,  27   b  and  27   c  according to the rotational direction of the roller  22 , but the corresponding suction ports should be opened accurately in order to obtain desired compression capacity. The accurate opening of the suction ports can be achieved by controlling the rotation angle of the first valve  110 . Thus, preferably, the valve assembly  100  further includes means for controlling the rotation angle of the first valve  110 , which will be described in detail with reference to  FIGS. 8 to 11 .  FIGS. 8 to 11  illustrate the valve assembly connected with the lower bearing  25  in order to clearly explain the control means. 
   As shown in  FIGS. 8A and 8B , the control means includes a groove  114  formed at the first valve  110  and having a predetermined length, and a stopper  114   a  formed on the lower bearing  25  and inserted into the groove  114 . The groove  114  and the stopper  114   a  are illustrated in  FIGS. 5A ,  5 B and  6 . The groove  114  serves as locus of the stopper  114   a  and can be a straight groove or a curved groove. If the groove  114  is exposed to the chamber  29  during operation, it becomes a dead volume causing a re-expansion of fluid. Accordingly, it is desirable to make the groove  114  adjacent to a center of the first valve  110  so that large portion of the groove  114  can be covered by the revolving roller  22 . Preferably, an angle (α) between both ends of the groove  114  is of 30-120° in the center of the first valve  110 . In addition, if the stopper  114   a  is protruded from the groove  114 , it interferes with the roller  22 . Accordingly, it is desirable that a thickness t 2  of the stopper  114   a  is equal to a thickness t 1  of the valve  110 , as shown in  FIG. 5C . Preferably, a width L of the stopper  114   a  is equal to a width of the groove  114  such that the first valve  110  rotates stably. 
   In case of using the control means, the first valve  110  rotates counterclockwise together with the eccentric portion  13   a  of the driving shaft  13  when the driving shaft  13  rotates counterclockwise. As shown in  FIG. 8A , the stopper  114   a  is then latched to one end of the groove  114  to thereby stop the first valve  110 . At this time, the first opening  111  accurately communicates with the first suction port  27   a , and the second and third suction ports  27   b  and  27   c  are closed. As a result, fluid is introduced into the cylinder  21  through the first suction port  27   a  and the first opening  111 , which communicate with each other. On the contrary, if the driving shaft  13  rotates clockwise, the first valve  110  also rotates clockwise. At the same time, the first and second openings  111  and  112  also rotate clockwise, as represented with a dotted arrow in  FIG. 8A . As shown in  FIG. 8B , if the stopper  114   a  is latched to the other end of the groove  114 , the first and second openings  111  and  112  are opened together with the third and second suction ports  27   c  and  27   b . Then, the first suction port  27   a  is closed by the first valve  110 . Accordingly, fluid is introduced through the second suction port  27   b /the second opening  112  and the third suction port  27   c /the first opening  111 , which communicate with each other. 
   As shown in  FIGS. 9A and 9B , the control means can be provided with a projection  115  formed on the first valve  110  and projecting in a radial direction of the first valve  110 , and a groove  123  formed on the second valve  120  and receiving the projection  115  movably. Here, the groove  123  is formed on the second valve  120  so that it is not exposed to the inner volume of the cylinder  21 . Therefore, a dead volume is not formed inside the cylinder  21 . In addition, as shown in  FIGS. 10A and 10B , the control means can be provided with a projection  124  formed on the second valve  120  and projecting in a radial direction of the second valve  120 , and a groove  116  formed on the first valve  110  and receiving the projection  124  movably. 
   In case of using such control means, the projections  115  and  124  are latched to one end of each groove  123  and  116  as shown in  FIGS. 9A and 10A  if the driving shaft  13  rotates counterclockwise. Accordingly, the first opening  111  communicates with the first suction port  27   a  so as to allow the suction of fluid, and the second and third suction ports  27   b  and  27   c  are closed. On the contrary, as shown in  FIGS. 9B and 10B , if the driving shaft  13  rotates clockwise, the projections  115  and  124  are latched to the other end of each groove  123  and  116 , and the first and second openings  111  and  112  simultaneously open the third and second suction ports  27   c  and  27   b  so as to allow the suction of fluid. The first suction port  27   a  is closed by the first valve  110 . 
   In addition, as shown in  FIGS. 11A and 11B , the control means can be provided with a projection  125  formed on the second valve  120  and projecting toward a center of the second valve  120 , and a cut-away portion  117  formed on the first valve  110  and movably accommodating the projection  125 . In such control means, a clearance between the projection  125  and the cut-away portion  117  allows the first and second suction ports  27   a  and  27   b  to be opened by forming the cut-away portion  117  largely in a properly large size. Accordingly, the control means decreases the dead volume substantially since the grooves of the above-described control means are omitted. 
   In more detail, if the driving shaft  13  rotates counterclockwise, one end of the projection  125  contacts one end of the cut-away portion  17  as shown in  FIG. 11A . Accordingly, a clearance between the other ends of the projection  125  and the cut-away portion  117  allows the first suction port  27   a  to be opened. In addition, as shown in  FIG. 11B , if the driving shaft  13  rotates clockwise, the projection  125  is latched to the cut-away portion  117 . At this time, the second opening  112  opens the second suction port  27   b , and simultaneously, the clearance between the projection  125  and the cut-away portion  117  allows the third suction port  27   c  to be opened as described above. In such control means, the projection  125  preferably has an angle β 1  of approximately 10° between both ends thereof and the cut-away portion  117  has an angle β 2  of 30-120° between both ends thereof. 
   Meanwhile, as described above with reference to  FIGS. 2 and 3 , the suction ports  27   a ,  27   b  and  27   c  are individually connected with a plurality of suction pipes  7   a  so as to supply fluid to the fluid chamber  29  installed inside the cylinder  21 . However, the number of parts increases due to these suction pipes  7   a , thus making the structure complicated. In addition, fluid may not be properly supplied to the cylinder  21  due to a change in a compression state of the suction pipes  7   a  separated during operation. Accordingly, as shown in  FIG. 12 , it is preferable that the compressor includes a suction plenum  500  for preliminarily storing fluid to be sucked by the compressor. 
   The suction plenum  500  directly communicates with all of the suction ports  27   a ,  27   b  and  27   c  so as to supply the fluid. Accordingly, the suction plenum  500  is installed in a lower portion of the lower bearing  25  in the vicinity of the suction ports  27   a ,  27   b  and  27   c . Although there is shown in the drawing that the suction ports  27   a ,  27   b  and  27   c  are formed at the lower bearing  25 , they can be formed at the upper bearing  24  if necessary. In this case, the suction plenum  500  is installed in the upper bearing  24 . The suction plenum  500  can be directly fixed to the bearing  25  by welding. In addition, a coupling member can be used to couple the suction plenum  500  with the cylinder  21 , the upper and lower bearings  24  and  25  and the valve assembly  100 . In order to lubricate the driving shaft  13 , a sleeve  25   d  of the lower bearing  25  should be soaked into a lubricant which is stored in a lower portion of the case  1 . Accordingly, the suction plenum  500  includes a penetration hole  500   a  for the sleeve  25   d  so that the sleeve  25   d  can reach the lubricant through the hole  500   a . Preferably, the suction plenum  500  has 100-400% a volume as large as the fluid chamber  29  so as to supply the fluid stably. The suction plenum  500  is also connected with the suction pipe  7  so as to store the fluid. In more detail, the suction plenum  500  can be connected with the suction pipe  7  through a predetermined fluid passage. In this case, as shown in  FIG. 12 , the fluid passage penetrates the cylinder  21 , the valve assembly  100  and the lower bearing  25 . In other words, the fluid passage includes a suction hole  21   c  of the cylinder  21 , a suction hole  122  of the second valve, and a suction hole  25   c  of the lower bearing. Alternatively, the fluid passage may penetrate only the cylinder  21  and the lower bearing  25 , and thereby the fluid passage includes a suction hole  21   c  of the cylinder  21  and a suction hole  25   c  of the lower bearing. 
   Such a suction plenum  500  forms a space in which a predetermined amount of fluid is always stored, so that a pressure variation of the sucked fluid is buffered to stably supply the fluid to the suction ports  27   a ,  27   b  and  27   c . In addition, the suction plenum  500  can accommodate oil separated from the stored fluid (for example, the lubricant included in the fluid) and thus assist or substitute for the accumulator  8 . 
   Hereinafter, operation of a rotary compressor according to a first embodiment of the present invention will be described in more detail. 
     FIGS. 14A to 14C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the counterclockwise direction in the rotary compressors according to a first embodiment of the present invention. 
   First, in  FIG. 14A , there are shown states of respective elements inside the cylinder  21  when the driving shaft  13  rotates in the counterclockwise direction. First, the first suction port  27   a  communicates with the first opening  111 , and the remaining second suction port  27   b  and third suction port  27   c  are closed. Detailed description on the state of the suction ports in the counterclockwise direction will be omitted since it has been described with reference to  FIGS. 8A ,  9 A,  10 A and  11 A. 
   In a state that the first suction port  27   a  is opened, the roller  22  revolves counterclockwise with performing a rolling motion along the inner circumference of the cylinder  21  due to the rotation of the driving shaft  13 . As the roller  22  continues to revolve, the size of the space  29   b  is reduced as shown in  FIG. 14B  and thus the fluid that has been sucked is compressed. In this stroke, the vane  23  moves up and down elastically by the elastic member  23   a  to thereby hermetically partition the fluid chamber  29  into the two sealed spaces  29   a  and  29   b . At the same time, new fluid continues to be sucked into the space  29   a  through the first suction port  27   a  (first opening  111 ) so as to be compressed in a next stroke. 
   When the fluid pressure in the space  29   b  is above a predetermined value, the second discharge valve  26   d  shown in  FIG. 2  is opened. Accordingly, as shown in  FIG. 14C , the fluid is discharged through the second discharge port  26   b . As the roller  22  continues to revolve, all the fluid in the space  29   b  is discharged through the second discharge port  26   b . After the fluid is completely discharged, the second discharge valve  26   d  closes the second discharge port  26   b  by its self-elasticity. 
   Thus, after a single stroke is ended, the roller  22  continues to revolve counterclockwise and discharges the fluid by repeating the same stroke. In the counterclockwise stroke, the roller  22  compresses the fluid with revolving from the first suction port  27   a  to the second discharge port  26   b . As aforementioned, since the first suction port  27   a  (the first opening  111 ) and the second discharge port  26   b  are positioned in the vicinity of the vane  23  to face each other, the fluid is compressed using the overall volume of the fluid chamber  29  in the counterclockwise stroke. In other words, a compressive space corresponding to the entire volume of the fluid chamber  29  is created during the counterclockwise stroke, so that a maximal compression capacity is obtained. 
     FIGS. 15A to 15C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the clockwise direction in the rotary compressors according to a first embodiment of the present invention. 
   First, in  FIG. 15A , there are shown states of respective elements inside the cylinder  21  when the driving shaft  13  rotates in the clockwise direction. The first suction port  27   a  is closed, and the second suction port  27   b  and third suction port  27   c  communicate with the second opening  112  and the first opening  111  respectively. If the first valve  110  has the third opening  113  additionally (refer to  FIG. 6A ), the third suction port  27   c  communicates with the third opening  113 . Detailed description on the state of the suction ports in the clockwise direction will be omitted since it has been described with reference to  FIGS. 5B ,  9 B,  10 B and  11 B. 
   In a state that the second and third suction ports  27   b  and  27   c  are opened (i.e., a state that the first and second openings  111  and  112  communicate), the roller  22  begins to revolve clockwise with performing a rolling motion along the inner circumference of the cylinder  21  due to the clockwise rotation of the driving shaft  13 . In such an initial stage revolution, the fluid sucked until the roller  22  reaches the second suction port  27   b  is not compressed but is forcibly exhausted outside the cylinder  21  by the roller  22  through the second suction port  27   b  as shown in  FIG. 15A . Accordingly, the fluid begins to be compressed after the roller  22  passes the second suction port  27   b  as shown in  FIG. 15B . At the same time, a space between the second suction port  27   b  and the vane  23 , i.e., the space  29   b  is made in a vacuum state. However, as aforementioned, as the revolution of the roller  22  starts, the third suction port  27   c  communicates with the first opening  111  (or third opening  113 ) so as to suck the fluid and thus is opened. Accordingly, the vacuum state is eliminated by the sucked fluid and thus occurrence of noise and loss of power are suppressed. 
   As the roller  22  continues to revolve, the size of the space  29   a  is reduced and the fluid that has been sucked is compressed. In this compression stroke, the vane  23  moves up and down elastically by the elastic member  23   a  to thereby partition the fluid chamber  29  into the two sealed spaces  29   a  and  29   b . Also, new fluid is continuously sucked into the space  29   b  through the second and third suction ports  27   b  and  27   c  (first and second openings  111  and  112 ) so as to be compressed in a next stroke. 
   When the fluid pressure in the space  29   a  is above a predetermined value, the first discharge valve  26   c  (see  FIG. 2 ) is opened as shown in  FIG. 15C  and accordingly the fluid is discharged through the first discharge port  26   a . After the fluid is completely discharged, the first discharge valve  26   c  closes the first discharge port  26   a  by its self-elasticity. 
   Thus, after a single stroke is ended, the roller  22  continues to revolve clockwise and discharges the fluid by repeating the same stroke. In the counterclockwise stroke, the roller  22  compresses the fluid with revolving from the second suction port  27   b  to the first discharge port  26   a . Accordingly, the fluid is compressed using a part of the overall fluid chamber  29  in the clockwise stroke, so that a compression space that is different in size than that in the counterclockwise stroke is obtained. In more detail, a compression space smaller than that in the counterclockwise stroke is formed and thus a compression capacity smaller than that in the counterclockwise stroke is obtained. 
   In each of the aforementioned strokes (i.e., the clockwise stroke and the counterclockwise stroke), the discharged compressive fluid moves upward through the space between the rotor  12  and the stator  11  inside the case  1  and the space between the stator  11  and the case  1 . Finally, the compressed fluid is discharged through the discharge pipe  9  out of the compressor. 
   In the above first embodiment, the inventive rotary compressor has suction and discharge ports properly arranged, and valve assembly having the simple structure and for selectively opening the suction ports according to the rotational direction of the driving shaft. Accordingly, although the driving shaft rotates in any one of the counterclockwise direction and clockwise direction, the fluid can be compressed. And, different sizes of compression spaces are formed depending on the rotational direction of the driving shaft such that different compression capacities are obtained in its operation. In particular, any one of the compression capacities is formed using the predesigned entire fluid chamber. In addition, the compressor of the present invention has the plenum for preliminarily storing the fluid so that this fluid could be stably provided to the cylinder. 
   Second Embodiment 
     FIG. 17  is an exploded perspective view illustrating the compression unit of the rotary compressor according to a second embodiment of the present invention and  FIG. 18  is a sectional view illustrating the compressing unit according to a second embodiment of the present invention. 
   In the compression unit  20  of the second embodiment, the cylinder  21  has a predetermined inner volume and a strength enough to endure the pressure of the fluid to be compressed. The cylinder  21  accommodates an eccentric portion  13   a  formed on the driving shaft  13  in the inner volume. The eccentric portion  13   a  is a kind of an eccentric cam and has a center spaced by a predetermined distance from its rotation center. The cylinder  21  has a groove  21   b  extending by a predetermined depth from its inner circumference. A vane  23  to be described below is installed in the groove  21   b . The groove  21   b  is long enough to accommodate the vane  23  completely. 
   The roller  22  is a ring member that has an outer diameter less than the inner diameter of the cylinder  21 . As shown in  FIG. 19 , the roller  22  contacts the inner circumference of the cylinder  21  and is rotatably coupled with the eccentric portion  13   a . Accordingly, the roller  22  performs rolling motion on the inner circumference of the cylinder  21  while spinning on the outer circumference of the eccentric portion  13   a  when the driving shaft  13  rotates. The roller  22  revolves spaced apart by a predetermined distance from the rotation center ‘0’ due to the eccentric portion  13   a  while performing the rolling motion. Since the outer circumference of the roller  22  always contacts the inner circumference due to the eccentric portion  13   a , the outer circumference of the roller  22  and the inner circumference of the cylinder  21  form a separate fluid chamber  29  in the inner volume. The fluid chamber  29  is used to suck and compress the fluid in the rotary compressor. 
   The vane  23  is installed in the groove  21   b  of the cylinder  21  as described above. An elastic member  23   a  is installed in the groove  21   b  to elastically support the vane  23 . The vane  23  continuously contacts the roller  22 . In other words, the elastic member  23   a  has one end fixed to the cylinder  21  and the other end coupled with the vane  23 , and pushes the vane  23  to the side of the roller  22 . Accordingly, the vane  23  divides the fluid chamber  29  into two separate spaces  29   a  and  29   b  as shown in  FIG. 19 . While the driving shaft  13  rotates or the roller  22  revolves, the volumes of the spaces  29   a  and  29   b  are changed complementarily. In other words, if the roller  22  rotates clockwise, the space  29   a  gets smaller but the other space  29   b  gets larger. However, the total volume of the spaces  29   a  and  29   b  is constant and approximately same as that of the predetermined fluid chamber  29 . One of the spaces  29   a  and  29   b  works as a suction chamber for sucking the fluid and the other one works as a compression chamber for compressing the fluid relatively when the driving shaft  13  rotates in one direction (clockwise or counterclockwise). Accordingly, as described above, the compression chamber of the spaces  29   a  and  29   b  gets smaller to compress the previously sucked fluid and the suction chamber expands to suck the new fluid relatively according to the rotation of the roller  22 . If the rotational direction of the roller  22  is reversed, the functions of the spaces  29   a  and  29   b  are exchanged. In the other words, if the roller  22  revolves counterclockwise, the right space  29   b  of the roller  22  becomes a compression chamber, but if the roller  22  revolves clockwise, the left space  29   a  of the roller  22  becomes a discharge chamber. 
   The upper bearing  24  and the lower bearing  25  are, as shown in  FIG. 17 , installed on the upper and lower portions of the cylinder  21  respectively, and rotatably support the driving shaft  12  using a sleeve and the penetrating holes  24   b  and  25   b  formed inside the sleeve. In more detail, the upper bearing  24 , the lower bearing  25  and the cylinder  21  include a plurality of coupling holes  24   a ,  25   a  and  21   a  formed to correspond to each other respectively. The cylinder  21 , the upper bearing  24  and the lower bearing  25  are coupled with one another to seal the cylinder inner volume, especially the fluid chamber  29  using coupling members such as bolts and nuts. 
   Referring to  FIGS. 17 and 18 , discharge ports  26   a  and  26   b  are formed on the upper bearing  24 . The discharge ports  26   a  and  26   b  communicate with the fluid chamber  29  so that the compressed fluid can be discharged. The discharge ports  26   a  and  26   b  can communicate directly with the fluid chamber  29  or can communicate with the fluid chamber  29  through a predetermined fluid passage  21   d  formed in the cylinder  21  and the upper bearing  24 . As shown in the drawings, the discharge ports  26   a  and  26   b  are formed on the upper bearing  24 , but if necessary, may be formed on the lower bearing  25 . Also, the discharge ports  26   a  and  26   b  may be formed in the cylinder  21  so as to communicate with the inside of the cylinder  21  easily. Discharge valves  26   c  and  26   d  are installed in the upper bearing  24  so as to open and close the discharge ports  26   a  and  26   b.    
     FIGS. 23A and 23B  are sectional views illustrating operations of these discharge valves  26   c  and  26   d.    
   The discharge valves  26   c  and  26   d  are configured to open the discharge ports  26   a  and  26   b  when a positive pressure which is greater than or equal to a predetermined pressure is generated in the inside of the cylinder  21 . To achieve this, it is desirable that the discharge valves  26   c  and  26   d  are a plate valve of which one end is fixed in the vicinity of the discharge ports  26   a  and  26   b  and the other end can be deformed freely. These discharge valves  26   c  and  26   d  are deformed toward a relatively low pressure by a relatively high pressure. However, in case a relatively high pressure is generated outside the cylinder  21 , the discharge valves  26   c  and  26   d  are confined by the upper bearing  24 . In more detail, as shown in  FIG. 23A , if a negative pressure is generated inside the cylinder  21 , the discharge valves  26   c  and  26   d  are deformed toward the cylinder  21  due to the pressure (atmospheric pressure) outside the cylinder  21  that is relatively high. However, the discharge valves  26   c  and  26   d  are confined by the upper bearing  24  and are not deformed but close the discharge ports  26   a  and  26   b  more firmly on its behalf. Also, in case a relatively low positive pressure is generated in the cylinder  21 , the discharge ports  26   a  and  26   b  continue to be closed by the self-elasticity of the discharge valves  26   c  and  26   d . After that, if a positive pressure above a predetermined value, i.e., a positive pressure that is larger than the elasticity of the discharge valves  26   c  and  26   d  is generated, the discharge valves  26   c  and  26   d  are deformed so as to open the discharge ports  26   a  and  26   b  as shown in  FIG. 23B . Accordingly, only when the pressure of the chamber  29  is above a predetermined positive pressure, the discharge valves  26   c  and  26   d  selectively open the discharge ports  26   a  and  26   b . Although not shown in the drawings, a retainer for limiting the deformable amount may be installed on the upper portion of the discharge valves  26   c  and  26   d  so that the valves can operate stably. In addition, a muffler (not shown) may be installed on the upper portion of the upper bearing  24  to reduce a noise generated when the compressed fluid is discharged. 
   Referring to  FIGS. 17 and 18 , suction ports  27   a ,  27   b  and  27   c  communicating with the fluid chamber  29  are formed on the lower bearing  25 . The suction ports  27   a ,  27   b  and  27   c  guide the fluid to be compressed to the fluid chamber  29 . The suction ports  27   a ,  27   b  and  27   c  are connected to the suction pipe  7  so that the fluid outside the compressor can flow into the chamber  29 . More specifically, the suction pipe  7  is branched into a plurality of auxiliary pipes  7   a  and the auxiliary pipes  7   a  are connected to suction ports  27   a  and  27   b  respectively. If necessary, the discharge ports  26   a  and  26   b  may be formed in the cylinder  21  so as to communicate with the inside of the cylinder  21  with ease like the aforementioned discharge ports  26   a  and  26   b . Also, the discharge ports  26   a  and  26   b  may be formed on the lower bearing  25  and the suction ports  27   a ,  27   b  and  27   c  may be formed on the upper bearing  24 . 
   These suction and discharge ports  26  and  27  become the important factors in determining compression capacity of the rotary compressor, and will be described referring to  FIGS. 19 and 20 .  FIG. 19  is a cross-sectional view illustrating the inside of the cylinder according to a second embodiment of the present invention. 
   First, the compressor of the present invention includes at least two discharge ports  26   a  and  26   b . As shown in the drawing, even if the roller  22  revolves in any direction, a discharge port should exist between the suction port and vane  23  positioned in the revolution path to discharge the compressed fluid. Accordingly, one discharge port is necessary for each rotational direction, and allows the compressor of the present invention to discharge the fluid regardless of the revolution direction of the roller  22  (that is, the rotational direction of the driving shaft  13 ). Meanwhile, as described above, the compression chamber of the spaces  29   a  and  29   b  gets smaller to compress the fluid as the roller  22  approaches the vane  23 . Accordingly, the discharge ports  26   a  and  26   b  are preferably formed facing each other in the vicinity of the vane  23  to discharge the maximum compressed fluid. In other word, as shown in the drawings, the discharge ports  26   a  and  26   b  are positioned on both sides of the vane  23  respectively. The discharge ports  26   a  and  26   b  are preferably positioned in the vicinity of the vane  23  if possible. 
   The suction port  27  is positioned properly so that the fluid can be compressed between the discharge ports  26   a  and  26   b  and the roller  22 . Actually, the fluid is compressed from a suction port to a discharge port positioned in the revolution path of the roller  22 . In other words, the relative position of the suction port for the corresponding discharge port determines the compression capacity and accordingly two compression capacities can be obtained using different suction ports  27  according to the rotational direction. Accordingly, the compression of the present invention has first and second suction ports  27   a  and  27   b  corresponding to two discharge ports  26   a  and  26   b  respectively and the suction ports are spaced apart by a predetermined angle from each other with respect to the center 0 for two different compression capacities. 
   Preferably, the first suction port  27   a  is positioned in the vicinity of the vane  23 . Accordingly, the roller  22  compresses the fluid from the first suction port  27   a  to the second discharge port  26   b  positioned across the vane  23  in its rotation in one direction (counterclockwise in the drawing). The roller  22  compresses the fluid due to the first suction port  27   a  by using the overall chamber  29  and accordingly the compressor has a maximum compression capacity in the counterclockwise rotation. In other words, the fluid as much as overall volume of the chamber  29  is compressed. The first suction port  27   a  is actually spaced apart by an angle θ 1  of 10° clockwise or counterclockwise from the vane  23  as shown in  FIGS. 19 and 20 . The drawings of the present invention illustrate the first suction port  27   a  spaced apart by the angle θ 1  counterclockwise. At this separating angle θ 1 , the overall fluid chamber  29  can be used to compress the fluid without interference of the vane  23 . 
   The second suction port  27   b  is spaced apart by a predetermined angle from the first suction port  27   a  with respect to the center. The roller  20  compresses the fluid from the second suction port  27   b  to the first discharge port  26   a  in its rotation in counterclockwise direction. Since the second suction port  27   b  is spaced apart by a considerable angle clockwise from the vane  23 , the roller  22  compresses the fluid by using a portion of the chamber  29  and accordingly the compressor has less compression capacity than it has during counterclockwise rotary motion. In other words, the fluid as much as a portion volume of the chamber  29  is compressed. The second suction port  27   b  is preferably spaced apart by an angle θ 2  of a range of 90-180° clockwise or counterclockwise from the vane  23 . The second suction port  27   b  is preferably positioned facing the first suction port  27   a  so that the difference between compression capacities can be made properly and the interference can be avoided for each rotational direction. 
   As shown in  FIG. 20 , the suction ports  27   a  and  27   b  are generally in circular shapes whose diameters are, preferably, 6-15 mm. In order to increase a suction amount of fluid, the suction ports  27   a  and  27   b  can also be provided in several shapes, including a rectangle. Further, the rectangular suction ports  27   a  and  27   b  may have a predetermined curvature. 
   Meanwhile, in order to obtain desired compression capacity in each rotational direction, suction ports that are available in any one of rotational directions should be single. If there are two suction ports in revolution path of the roller  22 , the compression does not occur between the suction ports. In other words, if the first suction port  27   a  is opened, the second suction port  27   b  should be closed, and vice versa. Accordingly, a valve assembly  200  is installed between the lower bearing  24  and the cylinder  21  to selectively open only one of the suction ports  27   a  and  27   b  according to the revolution direction (i.e., rotational direction of the driving shaft  13 ). Thus, by selectively opening a specific one of the suction ports, different compression spaces can be substantially formed in the fluid chamber  29  according to the rotational direction, so that the valve assembly  200  acts as the inventive compression mechanism previously defined. 
   As shown in  FIGS. 17 and 18 , the valve assembly  200  includes first and second valves  210  and  220 , which are installed between the cylinder  21  and the lower bearing  25  so as to allow it to be adjacent to the suction ports. If the suction ports  27   a ,  27   b  and  27   c  are formed on the upper bearing  24 , the first and second valves  210  and  220  are installed between the cylinder  21  and the upper bearing  24 . 
   Basically, to allow fluid to be sucked into the inside of the cylinder  21 , i.e., into the inside of the fluid chamber  29 , the inner pressure of the cylinder  21  should be lower than the outer pressure (atmospheric pressure) of the cylinder  21 . Accordingly, the first and second valves  210  and  220  are configured to open the suction ports  27   a  and  27   b  when a pressure difference between the inside and the outside of the cylinder  21 , more precisely, a negative pressure above a predetermined pressure is generated in the cylinder  21 . To achieve this, the first and second valves  210  and  220  may be a check valve allowing one directional flow due to a pressure difference, i.e., fluid flow into the inside of the cylinder  21 . In the meanwhile, the first and second valves  210  and  220  may be a plate valve similarly with the discharge valves  26   c  and  26   d . In the invention, the plate valve is preferable since it can perform the same function with more simple and higher response. The first and second valves  210  and  220  as the plate valves have second ends  210   b  and  220   b  fixed around the discharge ports  26   a  and  26   b  and first ends  210   a  and  220   a  that are freely deformable. The first and second valves  210  and  220  are deformable by an external pressure of the cylinder  21  that is relatively high, only when a negative pressure is generated inside the cylinder  21 . On the contrary, in case a positive pressure is generated inside the cylinder  21 , the first and second valves  210  and  220  are confined by the lower bearing  25  so as not to be deformed. Also, the first and second valves  210  and  220  may be provided with a retainer for restricting deformation of the first ends  210   a  and  220   a . In the present invention, the retainer may be an independent member but is preferably simple structured grooves  211 ,  221  formed in the cylinder  21 . The grooves  211 ,  221  extend with a slope in the length direction of the valves  210  and  220 , and the valves  210  and  220 , more accurately, the first ends  210   a  and  220   a , are received in the grooves  211  and  221  as deformed. Accordingly, the grooves  211  and  221  restrict an excessive deformation due to an abrupt pressure variation to thereby allow the valves  210  and  220  to operate stably. 
   In the meanwhile, referring to  FIG. 19 , in the case of the clockwise rotation, the fluid&#39;s suction or discharge between the vane  23  and the roller  22  does not occur while the roller  22  revolves from the vane  23  to the second suction port  27   b . Accordingly, a region V becomes a vacuum state. The vacuum region V causes a power loss of the driving shaft  13  and a loud noise. Accordingly, in order to overcome the problem in the vacuum region V, a third suction port  27   c  is provided at the lower bearing  25 . The third suction port  27   c  is formed between the second suction port  27   b  and the vane  23 , supplying fluid to the space between the roller  22  and the vane  23  so as not to form the vacuum state before the roller  22  passes through the second suction port  27   b . Preferably, the third suction port  27   c  is formed in the vicinity of the vane  23  so as to remove quickly the vacuum state. However, the third suction port  27   c  is positioned to face the first suction port  27   a  since the third suction port  27   c  operates at a different rotational direction from the first suction port  27   a . In reality, the third suction port  27   c  is positioned spaced by an angle (θ 3 ) of approximately 10° from the vane  23  clockwise or counterclockwise. Also, the third suction port  27   c  may be a circular shape or a curved rectangular shape like the first and second suction ports  27   a  and  27   b.    
   Since the aforementioned third suction port  27   c  operates along with the second suction port  27   b , the suction ports  27   b  and  27   c  should be simultaneously opened while the roller  22  revolves in any one of the clockwise and counterclockwise directions. Accordingly, the valve assembly  200  further includes a third valve  230  configured to open the third suction port  27   c  as soon as the second suction port  27   b  is opened. Like the first and second valves  210  and  220 , the third valve  230  is configured to open the third suction port  27   c  when a negative pressure above a predetermined pressure is generated in the cylinder  21 . The third valve  230  may be a check valve or a plate valve. In case the third valve  230  is a plate valve, it has a first end  230   a  and a second end  230   b  like the first and second valves  210  and  220 . Also, the third valve  230  as the plate valve may have a groove  231  as a retainer. Since characteristics of this third valve  230  are the same as those of the first and second valves  210  and  220  as described above, its detailed description will be omitted. 
   In  FIGS. 17 and 18 , the valve assembly  200  is shown as divided valves  210 ,  220  and  230 . In case the valves  210 ,  220  and  230  are a plate valve, the valve assembly  200  is preferably a single plate member which the plurality of valves  210 ,  220  and  230  are connected with one another as shown in  FIGS. 21 and 22 . In more detail, the valves  210 ,  220  and  230  of the valve assembly  200  can be easily formed by grooves  200   c  formed in the plate member. Also, the valve assembly  200  includes a penetration hole  200   a  through which the driving shaft  13  passes. Further, the valve assembly  200  has a coupling hole  200   b  corresponding to coupling holes  21   a ,  24   a  and  25   a  of the cylinder  21  and the upper and lower bearings  25  and  25 , and can be coupled with the cylinder  21  and the upper and lower bearings  24  and  25  by using a proper coupling member. Since the valve assembly  200  can be assembled or fabricated with ease, it is possible to decrease production costs and enhance productivity. 
   In the aforementioned valve assembly  200 , as shown in  FIG. 24A , if a positive pressure is generated in the chamber  29 , the valves  210 ,  220  and  230  are deformed toward the lower bearing  25 . However, the valves  210 ,  220  and  230  are confined by the upper bearing  24  and are not deformed, but close the suction ports  27   a ,  27   b  and  27   cb  more firmly on its behalf. Also, in case a relatively low negative pressure is generated in the cylinder  21 , the suction ports  27   a ,  27   b  and  27   c  continue to be closed by the self-elasticity of the valves  210 ,  220  and  230 . After that, if a negative pressure above a predetermined value, i.e., a negative pressure that is larger than the elasticity of the valves  210 ,  220  and  230  is generated, the valves  210 ,  220  and  230  are deformed toward the cylinder  21  as shown in  FIG. 24B , so that the suction ports  27   a  and  27   b  are opened. Accordingly, the valves  210 ,  220  and  230  selectively open the suction ports  27   a ,  27   b  and  27   c  by using a pressure difference between the inside and the outside of the cylinder  21 . 
   In more detail, as shown in  FIG. 19 , if the driving shaft  13  rotates any one direction (counterclockwise on the drawing), space  29   b  in front of the rotational direction is gradually reduced and thus the fluid is compressed. In the meanwhile, a negative pressure is formed in a space  29   a  formed at an opposite place to the rotational direction. Accordingly, as aforementioned, the first valve  210  opens the first suction port  27   a . Likewise, if the driving shaft  13  rotates in other direction (clockwise on the drawing), a negative pressure is formed in the space  29   b , and the second valve  220  opens the second suction port  27   b . Like the second valve  220 , the third valve  230  is influenced by the negative pressure to open the third suction port  27   c  in the clockwise rotation of the driving shaft  13 . Resultantly, the first to third valves  210 ,  220  and  230  in the valve assembly  200  of the invention selectively open the corresponding suction ports  27   a ,  27   b  and  27   c  according to the rotational direction of the driving shaft  13 . 
   Meanwhile, as described above with reference to  FIGS. 17 and 18 , the suction ports  27   a ,  27   b  and  27   c  are individually connected with a plurality of suction pipes  7   a  so as to supply fluid to the fluid chamber  29  inside the cylinder  21 . However, the number of parts increases due to these suction pipes  7   a , thus making the structure complicated. In addition, fluid may not be properly supplied to the cylinder  21  due to a change in a compression state of the suction pipes  7   a  separated during operation. Accordingly, as shown in  FIG. 25  and  FIG. 26 , it is desirable that the compressor includes a suction plenum  500  for preliminarily storing fluid to be sucked into the compressor. 
   The suction plenum  500  directly communicates with all of the suction ports  27   a ,  27   b  and  27   c  so as to supply the fluid. Accordingly, the suction plenum  500  is installed in a lower portion of the lower bearing  25  in the vicinity of the suction ports  27   a ,  27   b  and  27   c . Although there is shown in the drawing that the suction ports  27   a ,  27   b  and  27   c  are formed at the lower bearing  25 , they can be formed at the upper bearing  24  if necessary. In this case, the suction plenum  500  is installed in the upper bearing  24 . The suction plenum  500  can be directly fixed to the bearing  25  by welding. In addition, a coupling member can be used to couple the suction plenum  500  with the cylinder  21 , the upper and lower bearings  24  and  25  and the valve assembly  200 . In order to lubricate the driving shaft  13 , a sleeve  25   d  of the lower bearing  25  should be soaked into a lubricant which is stored in a lower portion of the case  1 . Accordingly, the suction plenum  500  includes a penetration hole  500   a  for the sleeve  25   d  so that the sleeve  25   d  can reach the lubricant through the hole  500   a . Preferably, the suction plenum  500  has 100-400% a volume as large as the fluid chamber  29  so as to supply the fluid stably. The suction plenum  500  is also connected with the suction pipe  7  so as to store the fluid. In more detail, the suction plenum  500  can be connected with the suction pipe  7  through a predetermined fluid passage. In this case, as shown in  FIG. 26 , the fluid passage penetrates the cylinder  21  and the lower bearing  25 . In other words, the fluid passage includes a suction hole  21   c  of the cylinder  21  and a suction hole  25   c  of the lower bearing. 
   Such a suction plenum  500  forms a space in which a predetermined amount of fluid is always stored, so that a pressure variation of the sucked fluid is buffered to stably supply the fluid to the suction ports  27   a ,  27   b  and  27   c . In addition, the suction plenum  500  can accommodate oil extracted from the stored fluid (for example, the lubricant included in the fluid) and thus assist or substitute for the accumulator  8 . 
   Hereinafter, operation of a rotary compressor according to a second embodiment of the present invention will be described in more detail. 
     FIGS. 27A to 27C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the counterclockwise direction in the rotary compressors according to a second embodiment of the present invention. 
   First, in  FIG. 27A , there are shown states of respective elements inside the cylinder  21  when the driving shaft  13  begins to rotate in the counterclockwise direction. Since there is no pressure variation in the cylinder  21 , the suction and discharge ports are closed by the respective valves. Since operations of the respective valves in the counterclockwise rotation have been described with reference to  FIGS. 23A to 24B  in the above, its detailed description will be omitted. 
   The roller  22  revolves counterclockwise with performing a rolling motion along the inner circumference of the cylinder  21  due to the rotation of the driving shaft  13 . As the roller  22  continues to revolve, the size of the space  29   b  is reduced as shown in  FIG. 27B  and thus the fluid that has been sucked is compressed. Due to the compression, a positive pressure is generated in the space  29   b  and accordingly the second and third suction ports  27   b  and  27   c  are more firmly closed. At the same time, as a negative pressure is generated in the space  29   a , the first suction port  27   a  is opened and the first discharge port  26   a  is closed. New fluid continues to be sucked into the space  29   a  through the first suction port  27   a  so as to be compressed in a next stroke. In this stroke, the vane  23  moves up and down elastically by the elastic member  23   a  to thereby hermetically partition the fluid chamber  29  into the two sealed spaces  29   a  and  29   b.    
   When the fluid pressure in the space  29   b  is above a predetermined value, the second discharge port  26   b  is opened and as shown in  FIG. 27C , the fluid is discharged through the second discharge port  26   b . As the roller  22  continues to revolve, all the fluid in the space  29   b  is discharged through the second discharge port  26   b . After the fluid is completely discharged, the second discharge valve  26   d  closes the second discharge port  26   b  by its self-elasticity. 
   Thus, after a single stroke is ended, the roller  22  continues to revolve counterclockwise and discharges the fluid by repeating the same stroke. In the counterclockwise stroke, the roller  22  compresses the fluid with revolving from the first suction port  27   a  to the second discharge port  26   b . As aforementioned, since the first suction port  27   a  and the second discharge port  26   b  are positioned in the vicinity of the vane  23  to face each other, the fluid is compressed using the overall volume of the fluid chamber  29  in the counterclockwise stroke and thus a maximal compression capacity is obtained. 
     FIGS. 28A to 28C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the clockwise direction in the rotary compressors according to a second embodiment of the present invention. 
   First, in  FIG. 28A , there are shown states of respective elements inside the cylinder when the driving shaft  13  rotates in the clockwise direction. Since there is no pressure variation in the cylinder  21 , the suction and discharge ports are closed by the respective valves as aforementioned. Since operations of the respective valves in the counterclockwise rotation have been described with reference to  FIGS. 23A to 24B  in the above, its detailed description will be omitted. 
   The roller  22  begins to revolve clockwise with performing a rolling motion along the inner circumference of the cylinder  21  due to the rotation of the driving shaft  13 . In such an initial stage revolution, the fluid sucked until the roller  22  reaches the second suction port  27   b  is not compressed but is forcibly exhausted outside the cylinder  21  by the roller  22  through the second suction port  27   b  as shown in  FIG. 28A . For this purpose, it is preferable that a predetermined clearance is always formed between the second valve  220  and the lower bearing  25 . Before a relatively large positive pressure is applied, the fluid is leaked to the outside through the clearance and the second suction port  27   b . If a large positive pressure is generated, the second valve  220  closes the second suction port  27   b  firmly such that the compressed fluid is not leaked. Accordingly, the fluid begins to be compressed as shown in  FIG. 28B  after the roller  22  passes through the second suction port  27   b . At the same time, a space  29   b  between the second suction port  27   b  and the vane  23  becomes a negative pressure state, the second discharge port  26   b  is closed but the third suction port  27   c  is opened. Accordingly, the vacuum state in the space  29   b  is eliminated by the sucked fluid and thus occurrence of noise and loss of power are suppressed. Also, the space  29   a  is in a relatively positive pressure state and the first suction port  27   a  is closed such that the compressed fluid is not leaked. 
   As the roller  22  continues to revolve, the size of the space  29   a  is reduced and the fluid that has been sucked is further compressed. In this compression stroke, the vane  23  moves up and down elastically by the elastic member  23   a  to thereby partition the fluid chamber  29  into the two sealed spaces  29   a  and  29   b . Also, while the negative pressure state of the space  29   b  is held, the second suction port  27   c  as well as the third suction port  27   b  is opened, so that new fluid is continuously sucked into the space  29   b  so as to be compressed in a next stroke. 
   When the fluid pressure in the space  29   a  is above a predetermined value, the first discharge port  26   a  is opened as shown in  FIG. 28C  and accordingly the fluid is discharged through the first discharge port  26   a . After the fluid is completely discharged, the first discharge valve  26   c  closes the first discharge port  26   a  by its self-elasticity. 
   Thus, after a single stroke is ended, the roller  22  continues to revolve clockwise and discharges the fluid by repeating the same stroke. In the clockwise stroke, the roller  22  compresses the fluid with revolving from the second suction port  27   b  to the first discharge port  26   a . Accordingly, the fluid is compressed using a part of the overall fluid chamber  29  in the counterclockwise stroke, so that a compression capacity that is smaller than that in the clockwise direction is obtained. 
   In the aforementioned strokes (i.e., the clockwise stroke and the counterclockwise stroke), the discharged compressive fluid moves upward through the space between the rotor  12  and the stator  11  inside the case  1  and the space between the stator  11  and the case  1 . Finally, the compressed fluid is discharged through the discharge pipe  9  out of the compressor. 
   In the aforementioned second embodiment, the inventive rotary compressor has suction and discharge ports properly arranged, and valve assembly having the simple structure and for selectively opening the suction ports according to the rotational direction of the driving shaft using the pressure difference between the inside and the outside of the cylinder. Accordingly, although the driving shaft rotates in any one of the counterclockwise direction and clockwise direction, the fluid can be compressed. And, different sizes of compression spaces are formed depending on the rotational direction of the driving shaft such that different compression capacities are obtained in its operation. In particular, any one of the compression capacities is formed using the predesigned entire fluid chamber. In addition, the compressor of the present invention has the plenum for preliminarily storing the fluid so that the fluid could be stably provided to the cylinder. 
   Third Embodiment 
     FIG. 30  is an exploded perspective view illustrating the compression unit of the rotary compressor according to a third embodiment of the present invention and  FIG. 31  is a sectional view illustrating the compressing unit according to a third embodiment of the present invention. 
   In the third embodiment, the cylinder  21  has a predetermined inner volume and the strength enough to endure the pressure of the fluid to be compressed. The cylinder  21  accommodates an eccentric portion  13   a  formed on the driving shaft  13  in the inner volume. The eccentric portion  13   a  is a kind of an eccentric cam and has a center spaced by a predetermined distance from its rotation center. The cylinder  21  has a groove  21   b  and a groove  21   c  extending by a predetermined depth from its inner circumference to accommodate a vane assembly  300 . Vanes  310  and  320  to be described below are installed in the grooves  21   b  and  21   c . The grooves  21   b  and  21   c  are long enough to accommodate the vanes  310  and  320  completely. 
   The roller  22  is a ring member that has an outer diameter less than the inner diameter of the cylinder  21 . As shown in  FIG. 32 , the roller  22  contacts, the inner circumference of the cylinder  21  and rotatably coupled with the eccentric portion  13   a . Accordingly, the roller  22  performs rolling motion on the inner circumference of the cylinder  21  while spinning on the outer circumference of the eccentric portion  13   a  when the driving shaft  13  rotates. The roller  22  revolves spaced apart by a predetermined distance from the rotation center ‘0’ due to the eccentric portion  13   a  while performing the rolling motion. Since the outer circumference of the roller  22  always contacts the inner circumference due to the eccentric portion  13   a , the outer circumference of the roller  22  and the inner circumference of the cylinder  21  form a separate fluid chamber  29  in the inner volume. The fluid chamber  29  is used to suck and compress the fluid in the rotary compressor. 
   The upper bearing  24  and the lower bearing  25  are, as shown in  FIGS. 30 and 31 , installed on the upper and lower portions of the cylinder  21  respectively, and rotatably support the driving shaft  12  using a sleeve and the penetrating holes  24   b  and  25   b  formed inside the sleeve. In more detail, the upper bearing  24 , the lower bearing  25  and the cylinder  21  include a plurality of coupling holes  24   a ,  25   a  and  21   a  formed to correspond to each other respectively. The cylinder  21 , the upper bearing  24  and the lower bearing  25  are firmly coupled with one another to seal the cylinder inner volume, especially the fluid chamber  29  using coupling members such as bolts and nuts. 
   The vane assembly  300  includes two first and second vanes  310  and  320  installed in the cylinder  21 . As aforementioned, the first and second vanes  310  and  320  are installed within the grooves  21   b  and  21   c  of the cylinder  21 . Elastic members  310   a  and  320   a  are also installed in the grooves  21   b  and  21   c  to elastically support the vanes  310  and  320 . The vanes  310  and  320  continuously contact the roller  22 . In other words, the elastic members  310   a  and  320   a  have one ends fixed to the cylinder  21  and the other ends coupled with the vanes  310  and  320 , and pushes the vanes  310  and  320  toward the roller  22 . Accordingly, the vanes  310  and  320  divide the fluid chamber  29  into two separate first and second spaces  29   a  and  29   b  as shown in  FIG. 32 . Since the vanes  310  and  320  are always in contact with the roller  22 , the first and second spaces  29   a  and  29   b  are separated completely independently with the revolution direction (the rotational direction of the driving shaft  13 ) of the roller  22 . In other words, the first and second spaces  29   a  and  29   b  can suck, compress and discharge independently. Thus, since the first and second spaces  29   a  and  29   b  are independent from each other, the compression in the first and second spaces  29   a  and  29   b  in each rotational direction of the driving shaft  13  can be adjusted so as to change the compression capacity of the compressor. In other words, the first space  29   a  is configured to compress the fluid in both of the clockwise direction and the counterclockwise direction, whereas the second space  29   b  is configured to compress the fluid in any one of the clockwise direction and the counterclockwise direction of the driving shaft. Accordingly, according to the rotational direction of the driving shaft  13 , the compression capacity is varied, so that the vane  300  acts as the predefined compression mechanism of the invention. 
   In more detail, for the compression of the fluid in bidirections of the driving shaft  13 , discharge and suction ports  26   a ,  26   b ,  27   a ,  27   b  to suck and discharge the fluid depending on the rotational direction of the driving shaft  13  are provided in the first space  29   a.    
   First, discharge ports  26   a  and  26   b  are formed on the upper bearing  24 . The discharge ports  26   a  and  26   b  communicate with the first space  29   a  such that the compressed fluid is discharged. The discharge ports  26   a  and  26   b  can communicate directly with the first space  29   a , and can communicate with the fluid chamber  29  through a predetermined length of passage  21   d  formed on the cylinder  21  and the upper bearing  24 . 
   As specifically shown in  FIG. 32 , the inventive compressor includes at least two first and second discharge ports  26   a  and  26   b . Although the roller  22  revolves any one of the clockwise direction and the counterclockwise direction within the first space  29   a , it is required that one discharge port should be provided between the suction port and the vane assembly  300  located within the revolution path so as to discharge the compressed fluid. Accordingly, one discharge port is needed every rotational direction (clockwise direction and the counterclockwise direction). For this purpose, the respective first and second discharge ports  26   a  and  26   b  are located so as to discharge the fluid in the corresponding rotational direction. The aforementioned first and second discharge ports  26   a  and  26   b  allow the inventive compressor to discharge the fluid regardless of the revolution direction (i.e., rotational direction of the driving shaft  13 ) of the roller  22 . In other words, in the first space  29   a , the fluid is discharged from the first discharge port  26   a  while the driving shaft rotates in any one direction (clockwise direction on the drawing) and is discharged from the second discharge port  26   b  while the driving shaft  13  rotates in other directional rotation (counterclockwise direction on the drawing). Also, the discharge ports  26   a  and  26   b  are preferably formed in the vicinity of the vane assembly  300  to discharge the maximum compressed fluid in each rotational direction of the driving shaft  13 . In other words, as shown in the drawings, the first discharge port  26   a  is located in the vicinity of the first vane  310  and the second discharge port  26   b  is located in the vicinity of the second vane  320 . The discharge ports  26   a  and  26   b  are preferably positioned in the vicinity of the vanes  310  and  320  if possible. 
   Suction ports  27   a  and  27   b  communicating with the first space  29   a  are formed on the lower bearing  25 . The suction ports  27   a  and  27   b  guide the fluid to be compressed to the first space  29   a . The suction ports  27   a  and  27   b  are connected to the suction pipe  7  so that the fluid outside the compressor can be introduced into the chamber  29 . More specifically, the suction pipe  7  is branched into a plurality of auxiliary pipes  7   a  and the auxiliary pipes  7   a  are connected to suction ports  27   a  and  27   b  respectively. If necessary, the discharge ports  26   a  and  26   b  may be formed on the lower bearing  25  and the suction ports  27   a  and  27   b  may be formed on the upper bearing  24 . 
   As shown in detail in  FIG. 32 , the suction ports  27   a  and  27   b  are positioned properly so that the fluid can be compressed between the discharge ports  26   a  and  26   b  and the roller  22 . Actually, the fluid is compressed from any one of the suction ports to any one of the discharge ports positioned in the revolution path of the roller  22 . Accordingly, in order to obtain a compression capacity from the first space  29   a  in all rotational directions (clockwise and counterclockwise directions) of the driving shaft  13 , at least one suction port for corresponding discharge port in each rotational direction of the driving shaft  13  is requested. To this end, the compression of the present invention has first and second suction ports  27   a  and  27   b  corresponding to two discharge ports  26   a  and  26   b  respectively and for sucking the fluid into the first space  29   a  in a corresponding rotational direction of the driving shaft  13 . 
   Also, as described above, since the fluid is compressed between the suction port and the discharge port that are operably linked while the driving shaft  13  rotates in any one direction, relative position of the suction port to the corresponding discharge port determines the compression capacity. In other words, once the position of the discharge valve is determined, the position of the suction port determines the compression capacity. Accordingly, in order to secure a compression capacity as large as possible in each directional rotation of the driving shaft  13 , it is preferable that the first and second suction ports  26   a  and  26   b  are located in the vicinity of the vane assembly  300 . In other words, as shown in the drawings, like the discharge ports  26   a  and  26   b , the suction ports  27   a  and  27   b  are respectively located in the vicinity of the first and second vanes  310  and  320 . In more detail, as shown in  FIGS. 32 and 33 , the first suction port  27   a  is actually spaced apart by an angle θ 1  of 10° clockwise or counterclockwise from the first vane  310 . In the drawings of the present invention, there is shown the first suction port  27   a  spaced apart by the angle θ 1  counterclockwise. Similarly to the first suction port  27   a , the second suction port  27   b  is spaced apart by an angle θ 1  of 10° clockwise or counterclockwise from the second vane  320 . The second suction port  27   b  is located communicating with the first space  29   a , i.e., spaced apart from the second vane  320  clockwise on the drawings such that the fluid is compressed in all rotational directions in the first space  29   a . These suction ports are generally a circular shape and preferably have a diameter 6-15 mm. In order to increase a suction amount of fluid, the suction ports  27   a  and  27   b  can also be provided in several shapes, including a rectangle. Resultantly, the roller  22  compresses the fluid from the first suction port  27   a  to the second discharge port  26   b  in any one directional rotation (counterclockwise direction on the drawing). And, the roller  22  compresses the fluid from the second suction port  27   b  to the first discharge port  26   a  in any other directional rotation (clockwise direction on the drawing). By the aforementioned discharge and suction ports, compression is carried out in the first space  29   a  while the driving shaft  13  rotates bidirectionally. Also, the roller  22  compresses the fluid in the first space  29   a  by using the entire portion of the fluid chamber  29 . In other words, refrigerant of an amount corresponding to the entire volume of the fluid chamber  29  can be compressed. 
   Also, in the second space  29   b , there are provided discharge and suction ports  26   e  and  27   c  for sucking and discharging the fluid to be compressed only in any one direction of the driving shaft  13 . 
   As shown in  FIGS. 30 ,  31  and  32 , the discharge port  26   e  and the suction port  27   c  are respectively formed on the upper bearing  24  and the lower bearing  25  so as to communicate with the second space  29   b . The discharge port  26   c  can communicate directly with the second space  29   b  or can communicate with the second space  29   b  through a predetermined fluid passage  21   d  formed on the upper bearing  24 . The suction port  27   c  can be connected directly with the suction pipe  7  or be connected with one of a plurality of auxiliary pipes  7   a  branched from the suction pipe  7  like the suction ports  27   a  and  27   b . If necessary, the discharge port  26  may be formed on the lower bearing  25  and the suction port  27   c  may be formed on the upper bearing  24 . 
   As aforementioned, compression capacity in any one directional rotation of the driving shaft  13  in a rotary compressor is obtained between one suction port and one discharge port that are located on the revolution path of the roller  22 . Since the second space  29   b  is for compressing the fluid in any one direction of the driving shaft  13 , only one suction port and one discharge port that are functionally linked with each other so as to be able to compress the fluid are requested. Owing to the aforementioned reason, in the inventive compressor, the second space  29   b  has a third discharge port  26   e  and a third suction port  27   c.    
   As shown in  FIG. 32 , these third discharge and suction ports  26   e  and  27   c  are spaced apart by a predetermined distance within the second space  29   b  such that the fluid can be compressed therebetween. First, the third discharge port  26   e  is preferably formed in the vicinity of one of the vanes  310  and  320  within the range of the second space  29   b  so as to discharge the fluid compressed to the maximum. In  FIG. 32 , there is shown the third discharge port  26   e  arranged in the vicinity of the first vane  310  and accordingly the fluid compressed while the driving shaft  13  rotates counterclockwise is discharged. The third discharge port  26   e  is preferably located as close as possible. Also, as aforementioned, once the location of the discharge valve is determined, the location of the suction port determines the compression capacity. Accordingly, in order to secure a compression capacity as large as possible in the second space  29   b , the third suction port  27   c  is preferably located in the vicinity of any one of the vanes  310  and  320 . Here, the third suction port  27   c  should be spaced apart by a predetermined angle from the third discharge port  26   e  for the compression of the fluid. Accordingly, since the third discharge port  26   e  is placed in the vicinity of the first vane  310  in  FIG. 32 , the third suction port  27   c  is placed in the vicinity of the second vane  320 . In more detail, the third suction port  27   c  is substantially spaced apart by an angle θ 3  of 10° clockwise or counterclockwise from the second vane  320 . In the drawings of the invention, there is shown the first suction port  27   a  spaced apart by the angel θ 3  of 10° clockwise or counterclockwise so as to be placed within the second space  29   b . Like the suction ports  27   a  and  27   b , this suction port  27   c  is generally a circular shape and preferably has a diameter 6-15 mm. Also, in order to increase a suction amount of fluid, the suction port  27   c  can also be provided in several shapes, including a rectangle. Resultantly, the roller  22  compresses the fluid from the third suction port  27   c  to the third discharge port  26   e  in any one directional rotation (counterclockwise direction on the drawing). On the contrary, since the roller  22  rotates from the third discharge port  26   e  to the third suction port  27   c  in any other directional rotation (clockwise direction on the drawing) of the driving shaft  13 , the fluid is not compressed. By the aforementioned discharge and suction ports, compression is carried out in the second space  29   b  while the driving shaft  13  rotates only in any one direction. However, since the suction and discharge ports  27   c  and  26   e  are placed in the vicinity of the vanes  310  and  320 , the roller  22  compresses the fluid by using the entire portion of the second space  29   b  while the driving shaft  13  rotates only in any one direction. In other words, refrigerant of an amount corresponding to the entire volume of the second space  29   b  can be compressed. 
   Consequently, in the third embodiment, the suction and discharge ports selectively supply the first and second spaces  29   a  and  29   b  with fluid and discharge the fluid from the first and second spaces  29   a  and  29   b  such that each of compressions in the first and second spaces  29   a  and  29   b  is independently performed depending on the rotational direction of the driving shaft  13 . Accordingly, the suction and discharge ports substantially and auxiliary assist the function of the vane assembly  300  that is the compression mechanism. 
   In order to open and close these discharge ports  26   a ,  26   b  and  26   e , discharge valves  26   c ,  26   d  and  26   f  are installed on the upper bearing  24  as shown in  FIGS. 30 and 31 . The first discharge valve  26   c  opens and closes the first discharge port  26   a , the second discharge valve  26   d  opens and closes the second discharge port  26   b , and the third discharge valve  26   f  opens and closes the third discharge port  26   e , respectively.  FIGS. 34A and 34B  are sectional views illustrating operations of these discharge valves  26   c ,  26   d  and  26   f . The discharge valves  26   c ,  26   d  and  26   f  are configured to open the discharge ports  26   a ,  26   b  and  26   e  when a positive pressure which is greater than or equal to a predetermined pressure is generated in the inside of the cylinder  21 . To achieve this, it is desirable that the discharge valves  26   c ,  26   d  and  26   f  are a check valve allowing only a flow of fluid to the outside of the cylinder  21 . Also, the discharge valves  26   c ,  26   d  and  26   f  may be a plate valve of which one end is fixed in the vicinity of the discharge ports  26   a ,  26   b  and  26   e  and the other end can be deformed freely. Then, in case a relatively high pressure is generated outside the cylinder  21 , the discharge valves  26   c ,  26   d  and  26   f  functioning as a plate valve are installed to be confined by the upper bearing  24 . In more detail, as shown in  FIG. 34A , if a negative pressure is generated inside the first space  29   a  or the second space  29   b , the discharge valves  26   c ,  26   d  and  26   f  are deformed toward the cylinder  21  due to the pressure (atmospheric pressure) outside the cylinder  21  that is relatively high. However, the discharge valves  26   c ,  26   d  and  26   f  are confined by the upper bearing  24  and are not deformed but are placed closely around the discharge ports  26   a ,  26   b  and  26   e  on its behalf to close the discharge ports  26   a ,  26   b  and  26   e  more firmly. Also, in case a relatively low positive pressure is generated in the cylinder  21 , the discharge ports  26   a ,  26   b  and  26   e  continue to be closed by the self-elasticity of the discharge valves. After that, if a positive pressure above a predetermined value, i.e., a positive pressure that is larger than the elasticity of the discharge valves  26   c ,  26   d  and  26   f  is generated, the discharge valves  26   c ,  26   d  and  26   f  are deformed so as to open the discharge ports  26   a ,  26   b  and  26   e  as shown in  FIG. 34B . Accordingly, only when the pressures of the first and second spaces  29   a  and  29   b  are above a predetermined positive pressure, the discharge valves  26   c ,  26   d  and  26   f  selectively open the discharge ports  26   a ,  26   b  and  26   e . Although not shown in the drawings, a retainer for restricting the deformable amount of the valves may be installed on the upper portion of the discharge valves  26   c ,  26   d  and  26   f  so that the valves can operate stably. In addition, a muffler (not shown) may be installed on the upper portion of the upper bearing  24  to reduce a noise generated when the compressed fluid is discharged. 
   In order to close the suction ports  27   a  and  27   b , suction valves  27   d  and  27   e  are installed between the cylinder  21  and the lower bearing  25  as shown in  FIGS. 30 and 31 . In other words, the first suction valve  27   d  is installed to open and close the first suction port  27   a , and the second suction valve  27   e  is installed to open and close the second suction port  27   b . If the suction ports  27   a  and  27   b  are formed on the upper bearing  24 , the first and second suction valves  27   d  and  27   e  are installed between the cylinder and the upper bearing  24 . In the meanwhile, since the fluid compression does not occur in the second space  29   b  in the other directional rotation (clockwise direction on  FIG. 32 ) of the driving shaft  13 , the third suction port  27   c  is not necessarily closed to prevent the fluid from being leaked outside the cylinder  21  during such a rotation. Accordingly, it is preferable for a simple structure that the suction valve such as the first and second suction valves  27   d  and  27   e  are not installed in the third suction port  27   c . By the same reason, the third suction port  27   c  may be formed to penetrate a sidewall of the cylinder  21  instead of the lower bearing  25  as shown in the drawings. 
   Basically, so as for the fluid to be sucked into the inside of the cylinder  21 , i.e., into the first and second spaces  29   a  and  29   b , the inner pressure of the cylinder  21  should be lower than the outer pressure (atmospheric pressure) of the cylinder  21 . Accordingly, the suction valves  27   d  and  27   e  are configured to open the suction ports  27   a  and  27   b  when a pressure difference between the inside and the outside of the cylinder  21 , more precisely, a negative pressure above a predetermined pressure is generated in the cylinder  21 . To achieve this, the suction valves  27   d  and  27   e  may be a check valve allowing one directional flow due to a pressure difference, i.e., fluid flow into the inside of the cylinder  21 . In the meanwhile, the suction valves  27   d  and  27   e  may be a plate valve similarly with the discharge valves  26   c ,  26   d  and  26   f . In the invention, the plate valve is preferable since it can perform the same function with more simple and higher response. The suction valves  27   d  and  27   e  are deformable by the external pressure of the cylinder  21  that is relatively high only in case a negative pressure is generated within the cylinder  21 . On the contrary, in case a positive pressure is generated inside the cylinder  21 , the suction valves  27   d  and  27   e  are confined by the lower bearing  25  so as not to be deformed. Also, the suction valves  27   d  and  27   e  may be provided with a retainer for restricting deformation of the second ends. In the present invention, the retainer may be an independent member, but is preferably simple structured grooves  28  formed in the cylinder  21 . The grooves  28  extend with a slope in the length direction of the valves  27   d  and  27   e , and the valves, more accurately, the second ends are received in the grooves  28  as deformed. Accordingly, the grooves  28  restrict an excessive deformation of the valves  27   d  and  27   e  due to an abrupt pressure variation to thereby allow the valves  27   d  and  27   e  to operate stably. 
   As shown in  FIG. 35A , if a positive pressure is generated inside the first space  29   a , the valves  27   d  and  27   e  are deformed toward the lower bearing  25 . However, the valves  27   d  and  27   e  are confined by the upper bearing  24  and are not deformed, but close the suction ports  27   a  and  27   b  more firmly. Also, in case a relatively low negative pressure is generated in the cylinder  21 , the suction ports  27   a  and  27   b  continue to be closed by the self-elasticity of the suction valves  27   d  and  27   e . After that, if a negative pressure above a predetermined value, i.e., a negative pressure that is larger than the elasticity of the valves  27   d  and  27   e  is generated, the valves  27   d  and  27   e  are deformed toward the cylinder  21  as shown in  FIG. 35B  such that the suction ports  27   a  and  27   b  are opened to suck fluid. Resultantly, the suction valves  27   d  and  27   e  open the suction ports  27   a  and  27   b  by using the negative pressure of the inside of the cylinder  21 . 
   Meanwhile, as described above with reference to  FIGS. 30 and 31 , the suction ports  27   a ,  27   b  and  27   c  are individually connected with a plurality of suction pipes  7   a  so as to supply fluid to the fluid chamber  29  inside the cylinder  21 . However, the number of parts increases due to these suction pipes  7   a , thus making the structure complicated. In addition, fluid may not be properly supplied to the cylinder  21  due to a change in a compression state of the suction pipes  7   a  separated during operation. Accordingly, as shown in  FIG. 36  and  FIG. 37 , it is desirable that the compressor includes a suction plenum  500  for preliminarily storing fluid to be sucked by the compressor. 
   The suction plenum  500  directly communicates with all of the suction ports  27   a  and  27   b  so as to supply the fluid. Accordingly, the suction plenum  500  is installed in a lower portion of the lower bearing  25  in the vicinity of the suction ports  27   a  and  27   b . Although there is shown in the drawing that the suction ports  27   a  and  27   b  are formed at the lower bearing  25 , they can be formed at the upper bearing  24  if necessary. In this case, the suction plenum  500  is installed in the upper bearing  24 . The suction plenum  500  can be directly fixed to the bearing  25  by welding. In addition, a coupling member can be used to couple the suction plenum  500  with the cylinder  21 , the upper and lower bearings  24  and  25  and the valve assembly  300 . In order to lubricate the driving shaft  13 , a sleeve  25   d  of the lower bearing  25  should be soaked into a lubricant which is stored in a lower portion of the case  1 . Accordingly, the suction plenum  500  includes a penetration hole  500   a  for the sleeve so that the sleeve  25   d  reach the lubricant through the hole  500   a . Preferably, the suction plenum  500  has 100-400% a volume as large as the fluid chamber  29  so as to supply the fluid stably. The suction plenum  500  is also connected with the suction pipe  7  so as to store the fluid. In more detail, the suction plenum  500  can be connected with the suction pipe  7  through a predetermined fluid passage. In this case, as shown in  FIG. 36 , the fluid passage penetrates the cylinder  21  and the lower bearing  25 . In other words, the fluid passage includes a suction hole  21   e  of the cylinder  21  and a suction hole  25   c  of the lower bearing. Further, if the third suction port  27   c  is formed in the cylinder  21 , this suction port  27   c  may diverge from the suction hole  21   e  so as to communicate with the inner space of the cylinder  21 , as shown in  FIG. 37 . It is preferable that such a suction hole  21   e  is formed near the vane  320  so that the suction port  27   c  diverging therefrom is located near the vane  320 . With such suction port  27   c , the fluid in the suction pipe  7  could be simultaneously provided to the cylinder  21  and the suction plenum  500  through the suction port  27   c  and the suction holes  21   e / 25   c . Alternatively, the fluid in the suction plenum  500  could be provided to the cylinder  21 , serially passing through the suction hole  25   c  and the suction port  27   c . Therefore, the fluid could be more stably provided with the cylinder  21 . Also, such a suction port  27   c  is advantageous, as it simplifies the structure of the compressor of the present invention and does not reduce the strength of the cylinder  21 . 
   The suction plenum  500  as described above, forms a space in which a predetermined amount of fluid is always stored, so that a pressure variation of the sucked fluid is buffered to stably supply the fluid to the suction ports  27   a ,  27   b  and  27   c . In addition, the suction plenum  500  can accommodate oil extracted from the stored fluid (for example, the lubricant included in the fluid) and thus assist or substitute for the accumulator  8 . 
   Hereinafter, operation of a rotary compressor according to a third embodiment of the present invention will be described in more detail. 
     FIGS. 38A to 38D  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the counterclockwise direction in the rotary compressors according to a third embodiment of the present invention. 
   First, in  FIG. 38A , there are shown states of respective elements inside the cylinder when the driving shaft  13  begins to rotate in the counterclockwise direction. Since there is no pressure variation in the cylinder  21 , the suction and discharge ports are closed by the respective valves. Since operations of the respective valves in the counterclockwise rotation have been described with reference to  FIGS. 34A to 35B  in the above, its detailed description will be omitted. 
   The roller  22  revolves counterclockwise with performing a rolling motion along the inner circumference of the cylinder  21  due to the rotation of the driving shaft  13 . As the roller  22  continues to revolve, the size of the space  29   b  is reduced as shown in  FIG. 38B  and thus the fluid that has been sucked is compressed. Due to the compression, a positive pressure is generated in the space  29   b  around the second discharge and suction ports  26   b  and  27   b  and accordingly the second suction port  27   b  is more firmly closed. At the same time, as a negative pressure is generated in the space  29   a  around the first discharge and suction ports  26   a  and  27   a , the first suction port  27   a  is opened and the first discharge port  26   a  is closed. New fluid continues to be sucked into the space  29   a  through the first suction port  27   a  so as to be compressed in a next stroke. 
   When the fluid pressure in the space  29   a  is above a predetermined value, the second discharge port  26   b  is opened and as shown in  FIG. 38B , the fluid is discharged through the second discharge port  26   b . After the fluid is completely discharged, the second discharge valve  26   d  closes the second discharge port  26   b  by its self-elasticity. 
   As the roller  22  continues to revolve, the size of the space  29   b  is reduced as shown in  FIG. 38C  and thus the fluid that has been sucked into the second space  29   b  begins to be compressed. Due to the compression, a positive pressure is generated in the second space  29   b  around the third discharge port  26   e . At the same time, as a negative pressure is generated in the second space  29   b  around the third suction port  27   c , new fluid continues to be sucked into the second space  29   b  through the opened third suction port so as to be compressed in a next stroke. 
   When the fluid pressure in the space  29   b  is above a predetermined value, the third discharge port  26   e  is opened and as shown in  FIG. 38D , the fluid is discharged through the third discharge port  26   e . As the roller  22  continues to revolve, all the fluid in the space  29   b  is discharged through the third discharge port  26   e . After the fluid is completely discharged, the third discharge valve  26   f  closes the third discharge port  26   e  by its self-elasticity. In the series of steps, the first and second vanes  310  and  320  moves up and down elastically by the elastic members  310   a  and  320   a  to thereby partition the fluid chamber  29  into the two sealed spaces  29   a  and  29   b . Accordingly, the suction and compression of the fluid in the first and second spaces  29   a  and  29   b  are performed independently. 
   Thus, after a single stroke is ended, the roller  22  continues to revolve counterclockwise and discharges the fluid by repeating the same stroke. In the counterclockwise stroke, the roller  22  compresses the fluid with revolving from the first suction port  27   a  to the second discharge port  26   b  in the first space  29   a . In the second space  29   b , the roller  22  compresses the fluid with revolving from the third suction port  27   c  to the third discharge port  26   e . Also, as aforementioned, the first and third suction ports  27   a  and  27   c  and the second and third discharge ports  26   b  and  26   e  are positioned in the vicinity of the corresponding vanes  310  and  320 . Accordingly, the fluid is substantially compressed using the overall volume of the fluid chamber  29  in the counterclockwise stroke and thus a maximal compression capacity is obtained. 
     FIGS. 39A to 39D  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the clockwise direction in the rotary compressors according to a third embodiment of the present invention. 
   First, in  FIG. 39A , there are shown states of respective elements inside the cylinder when the driving shaft  13  rotates in the clockwise direction. Since there is no pressure variation in the cylinder  21 , the suction and discharge ports are closed by the respective valves as aforementioned. Since operations of the respective valves in the counterclockwise rotation have been described with reference to  FIGS. 34A to 35B  in the above, its detailed description will be omitted. 
   The roller  22  begins to revolve clockwise with performing a rolling motion along the inner circumference of the cylinder  21  due to the rotation of the driving shaft  13 . In such a revolution, the fluid that has been sucked into the second space  29   b  is not compressed but is forcibly exhausted outside the cylinder  21  by the roller  22  through the opened second suction port  27   b  as shown in  FIG. 39B . Accordingly, the fluid cannot be compressed in the second space  29   b.    
   As the roller  22  continues to revolve, the fluid that has been sucked into the first space  29   a  is compressed, as shown in  FIG. 39C . Due to the compression, a positive pressure is generated in the first space  29   a  around the first discharge and suction ports  26   a  and  27   a . Accordingly, the first suction port  27   a  is closed more firmly. At the same time, a negative pressure is generated in the first space  29   a  around the second discharge and suction ports  26   b  and  27   b , so that the second suction port  27   b  is opened and the second discharge port  26   b  is closed more firmly. New fluid continues to be sucked into the first space  29   a  through the opened second suction port  27   b  so as to be compressed in a next stroke. 
   When the fluid pressure in the space  29   b  is above a predetermined value, the first discharge port  26   a  is opened and as shown in  FIG. 39D , the fluid is discharged through the first discharge port  26   a . As the roller  22  continues to revolve, all the fluid in the space  29   a  is discharged through the first discharge port  26   a . After the fluid is completely discharged, the first discharge valve  26   c  closes the first discharge port  26   a  by its self-elasticity. 
   In the series of steps, the first and second vanes  310  and  320  moves up and down elastically by the elastic members  310   a  and  320   a  to thereby partition the fluid chamber  29  into the two sealed spaces  29   a  and  29   b . Accordingly, the suction and compression of the fluid in the first and second spaces  29   a  and  29   b  are performed independently. 
   Thus, after a single stroke is ended, the roller  22  continues to revolve clockwise and discharges the fluid by repeating the same stroke. In the clockwise stroke, the roller  22  compresses the fluid with revolving from the second suction port  27   b  to the first discharge port  26   a  in the first space  29   a . On the contrary, the fluid compression in the second space  29   a  does not occur. Accordingly, the fluid is compressed using a part (i.e., first space  29   a ) of the overall fluid chamber  29  in the clockwise stroke, so that a compression capacity that is smaller than that in the clockwise direction is obtained. In the meanwhile, since the second vane  320  is located spaced apart by an angle of 180° so as to face the first vane  310 , the sizes of the first space  29   a  and the second space  29   b  are equal to each other. Thus, since the second space  29   b  is used for the compression in the clockwise rotation, the compression capacity in the clockwise direction corresponds to half a compression capacity in the counterclockwise direction. However, as indicated by a dotted line on  FIG. 32 , if the second vane  320  is spaced apart by a predetermined angle (less than 180°) from the first vane  310  clockwise or counterclockwise along with the second and third suction ports  27   b  and  27   c  and the second discharge port  26   b , the size of the second space  29   b  increases or decreases. Accordingly, since the compression capacity in the clockwise rotation is in inverse proportional to the size of the second space  29   b , it becomes small or large. Resultantly, by controlling the relative position of the second vane  320  to the first vane  310 , it is possible to adjust the compression capacity in the clockwise direction. 
   In the aforementioned strokes (i.e., the clockwise stroke and the counterclockwise stroke), the discharged compressive fluid moves upward through the space between the rotor  12  and the stator  11  inside the case  1  and the space between the stator  11  and the case  1 . Finally, the compressed fluid is discharged through the discharge pipe  9  out of the compressor. 
   In the third embodiment described above, the inventive rotary compressor has two vanes partitioning the fluid chamber and suction and discharge ports for selectively sucking and discharging the fluid into the partitioned spaces according to the rotational direction of the driving shaft. Accordingly, although the driving shaft rotates in any one of the counterclockwise direction and clockwise direction, the fluid can be compressed. And, different sizes of compression spaces are formed depending on the rotational direction of the driving shaft such that different compression capacities are obtained in its operation. In particular, any one of the compression capacities is formed using the predesigned entire fluid chamber. In addition, the rotary compressor of the present invention has the plenum for preliminarily storing the fluid such that the fluid could be stably provided to the cylinder. 
   Fourth Embodiment 
     FIG. 41  is an exploded perspective view illustrating the compression unit of the rotary compressor according to a fourth embodiment of the present invention and  FIG. 42  is a sectional view illustrating the compressing unit according to a fourth embodiment of the present invention. 
   In the fourth embodiment, the cylinder  21  has a predetermined inner volume and a strength enough to endure the pressure of the fluid to be compressed. The cylinder  21  accommodates an eccentric portion  13   a  formed on the driving shaft  13  in the inner volume. The eccentric portion  13   a  is a kind of an eccentric cam and has a center spaced by a predetermined distance from its rotation center. The cylinder  21  has a groove  21   b  extending by a predetermined depth from its inner circumference. A vane  23  to be described below is installed in the groove  21   b . The groove  21   b  is long enough to accommodate the vane  23  completely. 
   The roller  22  is a ring member that has an outer diameter less than the inner diameter of the cylinder  21 . As shown in  FIG. 43 , the roller  22  contacts the inner circumference of the cylinder  21  and rotatably coupled with the eccentric portion  13   a . Accordingly, the roller  22  performs a rolling motion on the inner circumference of the cylinder  21  while spinning on the outer circumference of the eccentric portion  13   a  when the driving shaft  13  rotates. The roller  22  revolves spaced apart by a predetermined distance from the rotation center ‘0’ due to the eccentric portion  13   a  while performing the rolling motion. Since the outer circumference of the roller  22  always contacts the inner circumference due to the eccentric portion  13   a , the outer circumference of the roller  22  and the inner circumference of the cylinder  21  form a separate fluid chamber  29  in the inner volume. The fluid chamber  29  is used to suck and compress the fluid in the rotary compressor. 
   The vane  23  is installed in the groove  21   b  of the cylinder  21  as described above. An elastic member  23   a  is installed in the groove  21   b  to elastically support the vane  23 . The vane  23  continuously contacts the roller  22 . In other words, the elastic member  23   a  has one end fixed to the cylinder  21  and the other end coupled with the vane  23 , and pushes the vane  23  to the side of the roller  22 . Accordingly, the vane  23  divides the fluid chamber  29  into two separate spaces  29   a  and  29   b  as shown in  FIG. 43 . While the driving shaft  13  rotates or the roller  22  revolves, the volumes of the spaces  29   a  and  29   b  are changed complementarily. In other words, if the roller  22  rotates clockwise, the space  29   a  gets smaller but the other space  29   b  gets larger. However, the total volume of the spaces  29   a  and  29   b  is constant and approximately same as that of the predetermined fluid chamber  29 . One of the spaces  29   a  and  29   b  works as a suction chamber for sucking the fluid and the other one works as a compression chamber for compressing the fluid relatively when the driving shaft  13  rotates in one direction (clockwise or counterclockwise). Accordingly, as described above, the compression chamber of the spaces  29   a  and  29   b  gets smaller to compress the previously sucked fluid and the suction chamber expands to suck the new fluid relatively according to the rotation of the roller  22 . If the rotational direction of the roller  22  is reversed, the functions of the spaces  29   a  and  29   b  are exchanged. In the other words, if the roller  22  revolves counterclockwise, the right space  29   b  of the roller  22  becomes a compression space, but if the roller  22  revolves clockwise, the left space  29   a  of the roller  22  becomes the compression space. 
   The upper bearing  24  and the lower bearing  25  are, as shown in  FIG. 41 , installed on the upper and lower portions of the cylinder  21  respectively, and rotatably support the driving shaft  12  using a sleeve and the penetrating holes  24   b  and  25   b  formed inside the sleeve. In more detail, the upper bearing  24 , the lower bearing  25  and the cylinder  21  include a plurality of coupling holes  24   a ,  25   a  and  21   a  formed to correspond to each other respectively. The cylinder  21 , the upper bearing  24  and the lower bearing  25  are coupled with one another to seal the cylinder inner volume, especially the fluid chamber  29  using coupling members such as bolts and nuts. 
   Discharge ports  26   a  and  26   b  are formed on the upper bearing  24 . The discharge ports  26   a  and  26   b  communicate with the fluid chamber  29  such that the compressed fluid can be discharged. The discharge ports  26   a  and  26   b  can communicate directly with the fluid chamber  29  or can communicate with the fluid chamber  29  through a predetermined fluid passage  21   d  formed in the cylinder  21  and the upper bearing  24 . 
   As shown more detail in  FIG. 43 , the compressor of the present invention includes at least two discharge ports  26   a  and  26   b . Even if the roller  22  revolves in any direction, a discharge port should exist between the suction port and vane  23  positioned in the revolution path to discharge the compressed fluid. Accordingly, one discharge port is necessary for each rotational direction (clockwise and counterclockwise). To achieve this, the first and second discharge ports  26   a  and  26   b  are positioned to discharge the fluid in the corresponding rotational direction. These first and second discharge ports  26   a  and  26   b  cause the compressor of the present invention to discharge the fluid regardless of the revolution direction of the roller  22  (that is, the rotational direction of the driving shaft  13 ). In other words, the fluid is discharged from the first discharge port  26   a  when rotating in any one direction (clockwise in the drawing) of the driving shaft  13 . Meanwhile, as described above, the compression chamber of the spaces  29   a  and  29   b  gets smaller to compress the fluid as the roller  22  approaches the vane  23 . Accordingly, the discharge ports  26   a  and  26   b  are preferably formed facing each other in the vicinity of the vane  23  to discharge the maximum compressed fluid. In other words, as shown in the drawings, the discharge ports  26   a  and  26   b  are positioned on both sides of the vane  23  respectively. The discharge ports  26   a  and  26   b  are preferably positioned in the vicinity of the vane  23  if possible. 
   Referring to  FIGS. 41 and 42  again, the suction ports  27   a  and  27   b  communicating with the fluid chamber  29  are formed on the lower bearing  25 . The suction ports  27   a  and  27   b  guide the fluid to be compressed to the fluid chamber  29 . The suction ports  27   a  and  27   b  are connected to the suction pipe  7  so that the fluid outside of the compressor can flow into the chamber  29 . More particularly, the suction pipe  7  is branched into a plurality of auxiliary pipes  7   a  and the branched auxiliary pipes  7   a  are connected to the suction ports  27  respectively. If necessary, the discharge ports  26   a  and  26   b  may be formed on the lower bearing  25  and the suction ports  27   a  and  27   b  may be formed on the upper bearing  24 . 
   As shown in  FIG. 43  in detail, these suction ports  27   a  and  27   b  are positioned properly so that the fluid can be compressed between the discharge ports  26   a  and  26   b  and the roller  22 . Actually, the fluid is compressed from a suction port to a discharge port positioned in the revolution path of the roller  22 . Accordingly, to obtain compression capacity in all rotational directions (clockwise and counterclockwise) of the driving shaft  13 , at least one suction port is required for the corresponding discharge port in each rotational direction of the driving shaft  13 . For the same reasons, the compressor of the present invention includes the first and second suction ports  27   a  and  27   b  for sucking the fluid in the corresponding rotational direction of the driving shaft  13  for each of the two discharge ports  26   a  and  26   b.    
   As described above, since the fluid is compressed between the suction port and the discharge port functionally connected with each other in rotation of the driving shaft in one direction, the relative position of the suction port for the corresponding discharge port determines the compression capacity. In other words, once the position of the discharge valve is determined, the position of the suction port determines compression capacity. To obtain large compression capacity as possible in the rotation of the driving shaft in each direction, the first and second suction ports  27   a  and  27   b  are preferably positioned in the vicinity of the vane  23 . In other words, as shown in drawings, the suction ports  27   a  and  27   b  are positioned on both sides of the vane  23 . More particularly, the first suction port  27   a  is actually spaced apart by an angle θ 1  of 10° clockwise or counterclockwise from the vane  23  as shown in  FIG. 43 . The drawings of the present invention illustrates the first suction port  27   a  spaced apart by the angle θ 1  counterclockwise. The second suction port  27   b  is spaced apart by an angle θ 2  of 10° clockwise or counterclockwise from the vane  23  as the first suction port  27   a . The second suction port  27   b  is preferably positioned facing the first suction port  27   a  or separated from the vane  23  on drawings clockwise so that the fluid can be compressed for each rotational direction. The suction ports  27   a  and  27   b  are generally circular shapes whose diameters are, preferably, 6-15 mm. In order to increase a suction amount of fluid, the suction ports  27   a  and  27   b  can also be provided in several shapes, including a rectangle. As a result, the roller  22  compresses the fluid from the first suction port  27   a  to the second discharge port  26   b  positioned across the vane  23  in its rotation in one direction (counterclockwise in the drawing). The roller  22  compresses the fluid from the second discharge port  26   b  to the first suction port  27   a  positioned across the vane  23  in its rotation in the other direction (clockwise in the drawing). The roller  22  compresses the fluid due to the first and second suction ports  27   a  and  27   b  by using the overall chamber  29  in rotations of the driving shaft in both directions. In other words, the refrigerant as much as overall volume of the chamber  29  is compressed. 
   As shown in  FIG. 41  and  FIG. 42 , the discharge valves  26   c  and  26   d  are installed on the upper bearing  24  so as to open and close the discharge ports  26   a  and  26   b . The discharge valves  26   c  and  26   d  are configured to open the discharge ports  26   a  and  26   b  when a positive pressure which is greater than or equal to a predetermined pressure is generated in the inside of the cylinder  21 . To achieve this, it is desirable that the discharge valves  26   c  and  26   d  are plate valves one end of which is fixed in the vicinity of the discharge ports  26   a  and  26   b  and the other end of which can be deformed freely. The discharge valves  26   c  and  26   d  may be check valves allowing fluid flow to the outside of the cylinder  21 . When a relatively high pressure is generated outside the cylinder  21  as shown in the drawing, the discharge valves  26   c  and  26   d  are confined to the upper bearing  24  in order not to be deformed. In more detail, as shown in  FIG. 42 , if a negative pressure is generated inside the chamber  29 , the discharge valves  26   c  and  26   d  are deformed toward the cylinder  21  due to the relatively high pressure (atmospheric pressure) outside the cylinder  21 . However, the discharge valves  26   c  and  26   d  are confined to the upper bearing  24  and are not deformed but close the discharge ports  26   a  and  26   b  more firmly on its behalf. Also, when a relatively low positive pressure is generated in the cylinder  21 , the discharge ports  26   a  and  26   b  continue to be closed by the self-elasticity of the discharge valves  26   c  and  26   d . After that, if a positive pressure higher than a predetermined value, i.e., the positive pressure that is larger than the elasticity of the discharge ports  26   a  and  26   b  is generated, the discharge valves  26   c  and  26   d  are deformed so as to open the discharge ports  26   a  and  26   b . Accordingly, only when the pressure of the chamber  29  is higher than a predetermined positive pressure, the discharge valves  26   c  and  26   d  selectively open the discharge ports  26   a  and  26   b . Although not shown in the drawings, a retainer for limiting the deformable amount may be installed on the upper portion of the discharge valves  26   c  and  26   d  so that the valves can operate stably. In addition, a muffler (not shown) may be installed on the upper portion of the upper bearing  24  to reduce a noise generated when the compressed fluid is discharged. 
   The first and second suction valves  27   d  and  27   e  are installed between the cylinder  21  and the lower bearing  25  so as to open and close the suction ports  27   a  and  27   b . If the suction ports  27   a  and  27   b  are formed on the upper bearing  24 , the first and second suction valves  27   d  and  27   e  are installed between the cylinder  21  and the upper bearing  24 . 
   Basically, so as for the fluid to be sucked into the inside of the cylinder  21 , i.e., into the inside of the fluid chamber  29 , the pressure inside the cylinder  21  should be lower than the pressure (atmospheric pressure) outside the cylinder  21 . Accordingly, the suction valves  27   d  and  27   e  are configured to open the suction ports  27   a  and  27   b  when a pressure difference between the inside and the outside of the cylinder  21 , more precisely, a negative pressure higher than a predetermined pressure is generated in the cylinder  21 . To achieve this, the suction valves  27   d  and  27   e  may be check valves allowing one directional flow due to a pressure difference, i.e., fluid flow into the inside of the cylinder  21 . In the meanwhile, the suction valves  27   d  and  27   e  may be plate valves similarly with the discharge valves  26   c  and  26   d . In the present invention, the plate valve is preferable since it can perform the same function with more simple and higher response. The suction valves  27   d  and  27   e  as shown in the drawings have first ends fixed around the suction ports  27   a  and  27   b  and second ends that are freely deformable. The suction valves  27   d  and  27   e  can be deformed due to a relatively high external pressure of the cylinder  21  only when a negative pressure is generated inside the cylinder  21 . On the contrary, in case a positive pressure is generated inside the cylinder  21 , the suction valves  27   d  and  27   e  are confined to the lower bearing  25  so as not to be deformed. Also, the suction valves  27   d  and  27   e  may be provided with a retainer for restricting deformation of the second ends. In the present invention, the retainer may be an independent member but is preferably simple structured grooves  28  formed in the cylinder  21 . The grooves  28  extend with a slope in the length direction of the valves  27   d  and  27   e , and the valves, more precisely, the second ends are received in the grooves  28  as deformed. Accordingly, the grooves  27   e  and  27   f  restrict an excessive deformation of the valves  27   d  and  27   e  due to an abrupt pressure variation to thereby allow the valves  210  and  220  to operate stably. 
   In the aforementioned suction valves  27   d  and  27   e , if a positive pressure is generated in the cylinder  21 , the suction valves  27   d  and  27   e  are deformed toward the lower bearing  25 . However, the valves  27   d  and  27   e  are confined to the lower bearing  25  and are not deformed, but close the suction ports  27   a  and  27   b  more firmly on its behalf. Also, when a relatively low negative pressure is generated in the cylinder  21 , the suction ports  27   a  and  27   b  continue to be closed by the self-elasticity of the suction valves  27   d  and  27   e . After that, if a negative pressure higher than a predetermined value, i.e., a negative pressure that is larger than the elasticity of the valves  27   d  and  27   e  is generated, the valves  27   d  and  27   e  are deformed toward the cylinder  21  and the suction ports  27   a  and  27   b  are opened to suck the fluid. Accordingly, the suction valves  27   d  and  27   e  selectively open the suction ports  27   a  and  27   b  by using a pressure difference between the inside and the outside of the cylinder  21 , that is, a predetermined negative pressure. 
   Using the ports and valves, the fluid can be compressed in both clockwise direction and counterclockwise direction of the driving shaft  13  of the compressor of the present invention. However, the same compression capacities are created in the both rotational directions. Accordingly, as shown in  FIG. 44 , for different compression capacities in each direction, clearances  400  between the inner surface of the cylinder  21  and the roller  22  are formed different from each other according to the rotational direction of the driving shaft. In the present invention, the amounts of the fluid leaked in compression are different from each other according to the rotational direction due to the clearances  400  and accordingly the compression capacities results in getting different from each other. This different leakage amount brings the substantially same results in which compression space is made differently according to the rotational direction in the fluid chamber  29 . As a result, the clearances  400  act as the compression mechanism of the present invention previously defined. 
   As shown in  FIG. 43 , in the rotary compressor, a predetermined clearance  400  is formed between the roller  22  and cylinder  21  to prevent excessive friction between the inner surfaces of the roller  22  and cylinder  21  in operation. The clearance  400  is continuously varied between the roller  22  and the cylinder  21  so that the fluid is leaked more. It is actually difficult to form a continuous clearance and such a continuous clearance can cause malfunction of the rotary compressor. The clearance  400  is preferably varied when the roller  22  is positioned at a predetermined position of the cylinder  21 . More particularly, the clearance  400  of the present invention is a first clearance  410  formed to be comparatively wide at a predetermined position so as for the fluid to be leaked. When the roller  13  contacts a predetermined position of the cylinder  21 , the first clearance  410  can adjust to move the driving shaft  13  towards or away from the position (depicted by an arrow mark). As described above, as the roller  22  approaches to the discharge ports  26   a  and  26   b  (that is, vane  23 ), the fluid is compressed and its pressure gets higher. Accordingly, the first clearance  410  is preferably formed in the vicinity of any one of the discharge ports  26   a  and  26   b  so as to effectively leak the compressed fluid in rotation of the driving shaft  13  in any one direction. Substantially, if the first clearance  410  is spaced apart by an angle α 1  in the range of 60°-90° from the vane  23  clockwise or counterclockwise, it is proper to leak the fluid.  FIG. 44  shows the first clearance  410  spaced apart by the angle α 1  counterclockwise. In addition, the first clearance  410  depends a little on the specification of the compressor and is preferably 90-100 μm. 
   Meanwhile, since the cylinder  21  has a circular inner circumference, the sum of clearances at the positions facing each other, i.e., the positions spaced apart by 180° from each other is constant. Accordingly, the sum of the first clearance  410  and the first facing clearance  410   a  formed at the position (A) facing the first clearance is also constant. As a result, the first facing clearance  410   a  is formed to be narrow and the first clearance  410  is formed to be large as about five times as the first facing clearance  410   a . It is preferable that the first facing clearance  410   a  is substantially 20-30 μm. The entire clearance of about 120 μm is formed with the first clearance  410 . 
   In addition, the clearance  400  to assist the first clearance  410  can further a second clearance  420  formed to be comparatively wide. The second clearance  420  is spaced apart by a predetermined angle from the first clearance  410  and actually spaced apart by the angle α 2  in the range of 150′-180′ from the vane  23 . The second clearance  420  depends a little on the specification of the compressor and is preferably 90-100 μm similar to the first clearance. Similarly, the second clearance  420  has the second facing clearance  420   a  formed on the position B facing the second clearance  420  and the characteristics of the second facing clearance  420   a  is substantially the same as the first facing clearance  410   a . So, the detailed description on the second facing clearance  420   a  will be omitted. Except for these clearances  410 ,  420 ,  410   a  and  420   a , the other clearances are formed to be the same as their facing clearances. 
   Due to the clearances  410 ,  420 ,  410   a  and  420   a , the clearances  400  vary along the inner circumference of the cylinder  21  and differ from each other at especially the vane  23 , that is, around discharge ports  26   a  and  26   b . More particularly, the clearance  400  is partially wide (clearances  410  and  420 ) at initial of the counterclockwise rotation of the driving shaft  13  and is partially narrow (clearances  410   a  and  420   a ) at last of the counterclockwise rotation of the driving shaft  13 . The clearance  400  is partially narrow (clearances  410   a  and  420   a ) at initial of the clockwise rotation of the driving shaft  13  and is partially wide (clearances  410  and  420 ) at last of the clockwise rotation of the driving shaft  13 . In view of the foregoing reasons, the clearances  400  are resultantly varied depending on the rotational direction of the driving shaft  13 . 
   Meanwhile, as described above with reference to  FIGS. 41 and 42 , the suction ports  27   a  and  27   b  are individually connected with a plurality of suction pipes  7   a  so as to supply fluid to the fluid chamber  29  inside the cylinder  21 . However, these suction pipes  7   a  increase the number of parts, thus making the structure complicated. Also, fluid may not be properly supplied to the cylinder  21  due to a change in a compression state of the suction pipes  7   a  separated during operation. Accordingly, as shown in  FIG. 45  and  FIG. 46 , it is desirable that the compressor includes a suction plenum  500  for preliminarily storing fluid to be sucked by the compressor. 
   The suction plenum  500  directly communicates with all of the suction ports  27   a  and  27   b  so as to supply the fluid. Accordingly, the suction plenum  500  is installed in a lower portion of the lower bearing  25  in the vicinity of the suction ports  27   a  and  27   b . Although there is shown in the drawing that the suction ports  27   a  and  27   b  are formed at the lower bearing  25 , they can be formed at the upper bearing  24  if necessary. In this case, the suction plenum  500  is installed in the upper bearing  24 . The suction plenum  500  can be directly fixed to the bearing  25  by welding. In addition, a coupling member can be used to couple the suction plenum  500  with the cylinder  21 , the upper and lower bearings  24  and  25  and the valve assembly  400 . In order to lubricate the driving shaft  13 , a sleeve  25   d  of the lower bearing  25  should be soaked into a lubricant which is stored in a lower portion of the case  1 . Accordingly, the suction plenum  500  includes a penetration hole  500   a  for the sleeve so that the sleeve  25   d  reach the lubricant through the hole  500   a . Preferably, the suction plenum  500  has 100-400% a volume as large as the fluid chamber  29  so as to supply the fluid stably. The suction plenum  500  is also connected with the suction pipe  7  so as to store the fluid. In more detail, the suction plenum  500  can be connected with the suction pipe  7  through a predetermined fluid passage. In this case, as shown in  FIG. 46 , the fluid passage penetrates the cylinder  21  and the lower bearing  25 . In other words, the fluid passage includes a suction hole  21   c  of the cylinder  21  and a suction hole  25   c  of the lower bearing. 
   Such a suction plenum  500  forms a space in which a predetermined amount of fluid is always stored, so that a pressure variation of the sucked fluid is buffered to stably supply the fluid to the suction ports  27   a  and  27   b . In addition, the suction plenum  500  can accommodate oil extracted from the stored fluid (for example, the lubricant included in the fluid) and thus assist or substitute for the accumulator  8 . 
   Hereinafter, operation of a rotary compressor according to a fourth embodiment of the present invention will be described in more detail. 
     FIGS. 47A to 47C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the counterclockwise direction in the rotary compressors according to a fourth embodiment of the present invention. 
   First, in  FIG. 47A , there are shown states of respective elements inside the cylinder when the driving shaft  13  begins to rotate in the counterclockwise direction. Since there is no pressure variation in the cylinder  21 , the suction and discharge ports are closed by the respective valves. Since operations of the respective valves in the counterclockwise rotation have been described in the above, its detailed description will be omitted. 
   The roller  22  revolves counterclockwise with performing a rolling motion along the inner circumference of the cylinder  21  due to the rotation of the driving shaft  13 . As the roller  22  continues to revolve, the size of the space  29   b  is reduced as shown in  FIG. 47B  and thus the fluid that has been sucked is compressed. Due to the compression, a positive pressure is generated in the space  29   b  and accordingly the second port  27   b  is more firmly closed. At the same time, as a negative pressure is generated in the space  29   a , the first suction port  27   a  is opened and the first discharge port  26   a  is closed. New fluid continues to be sucked into the space  29   a  through the first suction port  27   a  so as to be compressed in a next stroke. In this stroke, the vane  23  moves up and down elastically by the elastic member  23   a  to thereby hermetically partition the fluid chamber  29  into the two sealed spaces  29   a  and  29   b . Also, since the first facing clearance  410   a  is formed narrower than other surrounding clearances, the compressed fluid having a high pressure can be continuously compressed without being leaked to the clearance. 
   When the fluid pressure in the space  29   b  is above a predetermined value, the second discharge port  26   b  is opened and as shown in  FIG. 47C , the fluid is discharged through the second discharge port  26   b . As the roller  22  continues to revolve, all the fluid in the space  29   b  is discharged through the second discharge port  26   b . Herein, the pressure of the fluid shows the highest value but since the second facing clearance  420   a  is narrower than other surrounding clearances, the fluid can be discharged stably. After the fluid is completely discharged, the second discharge valve  26   d  closes the second discharge port  26   c  by its self-elasticity. 
   Thus, after a single stroke is ended, the roller  22  continues to revolve counterclockwise and discharges the fluid by repeating the same stroke. In the counterclockwise stroke, the roller  22  compresses the fluid with revolving from the first suction port  27   a  to the second discharge port  26   b . As aforementioned, since the first suction port  27   a  and the second discharge port  27   b  are positioned in the vicinity of the vane  23  to face each other, the fluid is compressed using the overall volume of the fluid chamber  29  in the counterclockwise stroke and thus a maximal compression capacity is obtained. 
     FIGS. 48A to 48C  are cross-sectional views sequentially illustrating insides of the cylinder when the roller revolves in the clockwise direction in the rotary compressors according to a fourth embodiment of the present invention. 
   First, in  FIG. 48A , there are shown states of respective elements inside the cylinder when the driving shaft  13  rotates in the clockwise direction. Since there is no pressure variation in the cylinder  21 , the suction and discharge ports are closed by the respective valves as aforementioned. Since operations of the respective valves in the counterclockwise rotation have been described in advance in the above, its detailed description will be omitted. 
   The roller  22  begins to revolve clockwise with performing a rolling motion along the inner circumference of the cylinder  21  due to the rotation of the driving shaft  13 . By such an initial stage revolution, the size of the space  29   a  is reduced and the fluid in the space  29   a  is gradually compressed such that pressure is elevated. In this compression stroke, the vane  23  moves up and down elastically by the elastic member  23   a  to thereby partition the fluid chamber  29  into the two sealed spaces  29   a  and  29   b . At the same time, the space  29   a  becomes a positive pressure state relatively and accordingly, the first suction port  27   a  is closed such that the compressed fluid is not leaked. However, as shown in  FIG. 48B , since the first clearance  410  is formed wider than other surrounding clearances while the roller  22  revolves, a part of the fluid which compression is initiated is leaked through the clearance  410 . Accordingly, pressure as well as fluid amount in the space  29   a  decreases considerably. 
   When the fluid pressure in the space  29   a  is above a predetermined value, the first discharge port  26   a  is opened as shown in  FIG. 48C  and accordingly the fluid is discharged through the first discharge port  26   a . Herein, the fluid shows the highest pressure value but since the first clearance  410  is formed wider than other surrounding clearances, the leakage of the fluid is generated more seriously than in the second clearance  420 . After the fluid is completely discharged, the first discharge valve  26   c  closes the first discharge port  26   a  by its self-elasticity. 
   Thus, after a single stroke is ended, the roller  22  continues to revolve clockwise and discharges the fluid by repeating the same stroke. In the clockwise stroke, the roller  22  compresses the fluid with revolving from the second suction port  27   b  to the first discharge port  26   a . Accordingly, like the counterclockwise stroke, the fluid in the clockwise stroke is compressed using the entire portion of the fluid chamber  29 . However, much fluid is leaked due to the first and second clearances  410  and  420 . Accordingly, in the counterclockwise stroke, a compression capacity that is smaller than that in the clockwise direction is obtained, which brings the same result as that of when the fluid is compressed only using a part of the entire fluid chamber  29 . 
   In the aforementioned strokes (i.e., the clockwise stroke and the counterclockwise stroke), the discharged compressive fluid moves upward through the space between the rotor  12  and the stator  11  inside the case  1  and the space between the stator  11  and the case  1 . Finally, the compressed fluid is discharged through the discharge pipe  9  out of the compressor. 
   In the fourth embodiment, the inventive rotary compressor has suction and discharge ports for sucking and discharging fluid in bidirectional rotation of the driving shaft, and clearances located between the roller and the cylinder and varied with the rotational direction of the driving shaft. Accordingly, due to these clearances, fluid may be leaked while the fluid is compressed in a specific rotational direction, which causes a result that the fluid is compressed using the entire portion of the fluid chamber in any one directional rotation and is compressed using a part of the fluid chamber in other directional rotation. Accordingly, the fluid can be compressed although the driving shaft rotates in any one of the counterclockwise direction and clockwise direction. Also, different sizes of compression spaces are formed depending on the rotational direction of the driving shaft such that different compression capacities are obtained in its operation. In particular, any one of the compression capacities is formed using the predesigned entire fluid chamber. Further, the rotary compressor of the present invention has the plenum for preliminarily storing the fluid so that the fluid could be stably supplied to the cylinder. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 
   INDUSTRIAL APPLICABILITY 
   The rotary compressor according to each embodiment as above provides following advantages. 
   First, according to the related art, several devices are combined in order to achieve the dual-capacity compression. For example, an inverter and two compressors having different compression capacities are combined in order to obtain the dual compression capacities. In this case, the structure becomes complicated and the cost increases. However, according to the present invention, the dual-capacity compression can be achieved using only one compressor. Particularly, the present invention can achieve the dual-capacity compression by changing parts of the conventional rotary compressor to the minimum. 
   Second, the conventional compressor having a single compression capacity cannot provide the compression capacity that is adaptable for various operation conditions of air conditioner or refrigerator. In this case, power consumption may be wasted unnecessarily. However, the present invention can provide a compression capacity that is adaptable for the operation conditions of equipments. 
   Third, the rotary compressor of the present invention uses the entire portion of the predesigned fluid chamber in producing a dual-compression capacity. This means that the compressor of the present invention has at least the same compression capacity as the conventional rotary compressor having the same sized cylinder and fluid chamber. In other words, the inventive rotary compressor can substitute for the conventional rotary compressor without modifying designs of basic parts, such as cylinder size or the like. Accordingly, the inventive rotary compressor can be freely applied to required systems without any consideration of the compression capacity and any increase in unit cost of production. 
   Fourth, the rotary compressor of the present invention has the suction plenum for constantly storing a predetermined amount of fluid. This plenum buffers a pressure variation of the sucked fluid and stably supplies the fluid to the cylinder. Therefore, the reliability and stability of the compressor are greatly improved.