Abstract:
A two stage reciprocating compressor includes a casing. A first compressing unit is disposed in the casing and includes a first piston and a first cylinder, the first compressing unit being driven by a reciprocating motor to linearly reciprocate the first piston in the first cylinder to suck in and compress gas. A second compressing unit is disposed in the casing and includes a second piston and a second cylinder, the second compressing unit being driven by vibration of the first compressing unit to linearly reciprocate the second piston in the second cylinder to suck in and compress gas. A vibration transfer member transfers the vibration from the first compressing unit to the second compressing unit. The first and second compressing units extend in parallel and face in the same direction, the second compressing unit being located adjacent to a suction passage of the first compressing unit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The present disclosure relates to subject matter contained in priority Korean Patent Application No. 10-2007-0029856, filed on Mar. 27, 2007, and 10-2007-0057883, filed on Jun. 13, 2007 which are herein expressly incorporated by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a reciprocating compressor, and more particularly, to a two stage reciprocating compressor which may be provided in a refrigerator having two evaporators for efficiently performing gas suction by two compressing units by implementing one compressor having the two compressing units, and a refrigerator having the same. 
   2. Description of the Related Art 
   Generally, compressors convert electric energy into kinetic energy so as to compress a refrigerant by using the kinetic energy. The compressor is a core element of a freezing cycle system, and there are various types of compressors for compressing the refrigerant, such as a rotary compressor, a scroll compressor, a reciprocating compressor, and so on. 
     FIG. 1  is a cross-sectional view of a conventional reciprocating compressor. As shown, the reciprocating compressor includes a casing  100  having a gas suction pipe  110  and a discharge pipe  120 , a frame unit  200  disposed in the casing  100 , a reciprocating motor  300  mounted at the frame unit  200  so as to generate a linear reciprocating driving force, a compressing unit  400  compressing gas by receiving the driving force from the reciprocating motor  300 , and a resonance spring unit  500  for generating resonance by using the driving force of the reciprocating motor  300 . 
   The frame unit  200  includes a front frame  210  supporting one side of the reciprocating motor  300 , a middle frame  220  supporting another side of the reciprocating motor  300 , and a rear frame  230  coupled to the middle frame  220  so as to form a space with the middle frame  220 . 
   The reciprocating motor  300  includes an outer stator  310  fixed between the middle frame  220  and the rear frame  230 , an inner stator  320  inserted into the outer stator  310  so as to be fixedly-coupled to a side of the front frame  210 , a mover  330  movably inserted between the outer stator  310  and the inner stator  320 , and a winding coil  340  coupled to the inside of the outer stator  310 . The mover  330  includes a magnet  331  and a magnet holder  332  supporting the magnet  331 . 
   The compressing unit  400  includes a cylinder  410  fixedly-coupled to the front frame  210 , a piston  420  having one side movably inserted into the cylinder  410  and another side fixedly-coupled to the mover  330 , a discharge valve assembly  430  mounted at one side of the cylinder  410  so as to control the discharge of the refrigerant, and a suction valve  440  mounted at an end portion of the piston  420  so as to control a flow of the refrigerant that is sucked into an inner space of the cylinder  410 . 
   The piston  420  includes a cylindrical body  421  which has specific length and outer diameter, a flange  422  extended from the end of the cylindrical body in a vertical direction so as to be coupled to the magnet holder  332  of the mover, and a suction passage  423  penetratingly formed in the cylindrical body  421 . 
   The discharge valve assembly  430  includes a discharge cover  431  for covering the inner space of the cylinder  410 , a discharge valve  432  inserted into the discharge cover  431  so as to open/close the inner space of the cylinder  410 , and a discharge spring  433  inserted into the discharge cover  431  so as to elastically support the discharge valve  432 . 
   The resonance spring unit  500  includes a spring support  510  fixedly-coupled with the piston  420  and the mover  330 , a front coil spring  520  coupled between the spring support  510  and the middle frame  220 , and a rear coil spring  530  coupled between the spring support  510  and the rear frame  230 . 
   Reference numeral  10  denotes a support spring, and  411  denotes the inner space of the cylinder. 
   An operation of the reciprocating compressor will be described as follows. 
   When power is supplied to the reciprocating compressor, the linear reciprocating driving force is generated by an electromagnetic interaction of the reciprocating motor  300 , and the linear reciprocating driving force is transferred to the piston  420  through the mover  330 . 
   The piston  420  is linearly reciprocated in the inner space  411  of the cylinder by receiving the linear reciprocating driving force of the mover  330 . By the linear reciprocating motion of the piston  420 , the suction valve  440  and the discharge valve  432  are operated by a difference between a pressure of the inner space  411  and an external pressure of the cylinder. The refrigerant is sucked and compressed so as to be discharged into the inner space  411  of the cylinder. The discharged refrigerant flows outside of the compressor through the discharge cover  431  and the discharge pipe  120 . This procedure is repeated so that the refrigerant is compressed. 
   The front coil spring  520  and the rear coil spring  530  are contracted/relaxed together with the reciprocating motion of the mover  330  and the piston  420 , thereby elastically supporting the mover  330  and the piston  420  and causing the resonance. 
   The reciprocating compressor may be provided in a freezing cycle apparatus and the freezing cycle apparatus may be provided in a refrigerator. 
   Refrigerators may be a type having one evaporator (cooling unit) or another type having two evaporators. 
   In a refrigerator having two evaporators, i.e., a freezing chamber evaporator and a refrigerating chamber evaporator, the temperature of the freezing chamber and the refrigerating chamber is accurately controlled so that it is possible to store foods in fresh state for a long time. However, in a refrigerator having two evaporators and one compressor, the freezing chamber and the refrigerating chamber should be alternately operated. Further, in a refrigerator having two evaporators and two compressors, a large space for a machine chamber for installing the compressors is required, such that the space for storing the foods is made smaller. 
   Meanwhile, when the reciprocating compressor having one compressing unit is applied to a refrigerator having two evaporators, two reciprocating compressors must be mounted in the refrigerator. Accordingly, the space for the machine chamber where the compressor is installed is enlarged, and the storing space of the refrigerator is smaller. 
   SUMMARY OF THE INVENTION 
   Therefore, the present invention is directed to a two stage reciprocating compressor which is capable of being applied to a refrigerator having two evaporators and efficiently performing gas suction by two compressing units by implementing one compressor having the two compressing units, and a refrigerator having the same. 
   According to an aspect of the invention, a two stage reciprocating compressor includes a casing; a first compressing unit disposed in the casing and including a first piston and a first cylinder, the first compressing unit being driven by a reciprocating motor to linearly reciprocate the first piston in the first cylinder to suck in and compress gas; a second compressing unit disposed in the casing and including a second piston and a second cylinder, the second compressing unit being driven by vibration of the first compressing unit to linearly reciprocate the second piston in the second cylinder to suck in and compress gas; and a vibration transfer member that transfers the vibration from the first compressing unit to the second compressing unit. The first and second compressing units extend in parallel and face in the same direction, the second compressing unit being located adjacent to a suction passage of the first compressing unit. 
   The first compressing unit and the second compressing unit may move in a same direction when compressing gas. The suction passage of the first compressing unit may be formed in the first piston of the first compressing unit, and the second compressing unit may be disposed laterally of the first piston of the first compressing unit so as to accelerate the flow of gas into the suction passage of the first compressing unit by the motion of the second compressing unit. 
   The casing may contain gas which has been compressed and discharged from the second compressing unit, such gas being sucked into the first compressing unit. The second piston of the second compressing unit may be fixedly-coupled to the vibration transfer member so as to be located between the vibration transfer member and a sub frame, and a support frame may be coupled with the second cylinder of the second compressing unit. The vibration transfer member may include a disk portion having a through hole therein, and a connecting portion extended from one side of the disk portion. 
   According to another aspect of the invention, a refrigerator includes a refrigerator body; a refrigerating chamber evaporator disposed in the refrigerator body to generate and supply cool air to a refrigerating chamber; a freezing chamber evaporator disposed in the refrigerator body to generate and supply cool air to a freezing chamber; and a two stage reciprocating compressor connected to the refrigerating chamber evaporator and the freezing chamber evaporator. The two stage reciprocating compressor includes a casing; a first compressing unit disposed in the casing and including a first piston and a first cylinder, the first compressing unit being driven by a reciprocating motor to linearly reciprocate the first piston in the first cylinder to suck in and compress gas; a second compressing unit disposed in the casing and including a second piston and a second cylinder, the second compressing unit being driven by vibration of the first compressing unit to linearly reciprocate the second piston in the second cylinder to suck in and compress gas; and a vibration transfer member that transfers the vibration from the first compressing unit to the second compressing unit. The first and second compressing units extend in parallel and face in the same direction, the second compressing unit being located adjacent to a suction passage of the first compressing unit. 
   According to another aspect of the invention, a two stage reciprocating compressor includes a casing; a first compressing unit disposed in the casing and including a first piston and a first cylinder, the first compressing unit being driven by a reciprocating motor to linearly reciprocate the first piston in the first cylinder to suck in and compress gas; a second compressing unit disposed in the casing and including a second piston and a second cylinder, the second compressing unit being driven by vibration of the first compressing unit to linearly reciprocate the second piston in the second cylinder to suck in and compress gas; and a vibration transfer member that transfers the vibration from the first compressing unit to the second compressing unit. The second compressing unit is located adjacent to a suction passage of the first compressing unit so that motion of the second compressing unit accelerates the flow of gas into the suction passage of the first compressing unit. 
   The first compressing unit and the second compressing unit may move in a same direction when compressing gas. The suction passage of the first compressing unit may be formed in the first piston of the first compressing unit, and the second compressing unit may be disposed laterally of the first piston of the first compressing unit so as to accelerate the flow of gas into the suction passage of the first compressing unit by the motion of the second compressing unit. 
   The casing may contain gas which has been compressed and discharged from the second compressing unit, such gas being sucked into the first compressing unit. The second piston of the second compressing unit may be fixedly-coupled to the vibration transfer member so as to be located between the vibration transfer member and a sub frame, and a support frame may be coupled with the second cylinder of the second compressing unit. The vibration transfer member may include a disk portion having a through hole therein, and a connecting portion extended from one side of the disk portion. 
   According to another aspect of the invention, a refrigerator includes a refrigerator body; a refrigerating chamber evaporator disposed in the refrigerator body to generate and supply cool air to a refrigerating chamber; a freezing chamber evaporator disposed in the refrigerator body to generate and supply cool air to a freezing chamber; and a two stage reciprocating compressor connected to the refrigerating chamber evaporator and the freezing chamber evaporator. The two stage reciprocating compressor includes a casing; a first compressing unit disposed in the casing and including a first piston and a first cylinder, the first compressing unit being driven by a reciprocating motor to linearly reciprocate the first piston in the first cylinder to suck in and compress gas; a second compressing unit disposed in the casing and including a second piston and a second cylinder, the second compressing unit being driven by vibration of the first compressing unit to linearly reciprocate the second piston in the second cylinder to suck in and compress gas; and a vibration transfer member that transfers the vibration from the first compressing unit to the second compressing unit. The second compressing unit is located adjacent to a suction passage of the first compressing unit so that motion of the second compressing unit accelerates the flow of gas into the suction passage of the first compressing unit. 
   According to another aspect of the invention, a method of compressing gas with a compressor having a first compressing unit with a first piston and a first cylinder, and a second compressing unit with a second piston and a second cylinder, includes driving the first compressing unit to linearly reciprocate the first piston in the first cylinder to suck in and compress gas; transferring vibration from the first compressing unit to the second compressing unit; driving the second compressing unit by vibration of the first compressing unit to linearly reciprocate the second piston in the second cylinder to suck in and compress gas; and accelerating the flow of gas into a suction passage of the first compressing unit by motion of the second compressing unit. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE 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 specification, illustrate preferred embodiments of the invention and together with the description serve to explain the principles of the invention. 
     In the drawings: 
       FIG. 1  is a cross-sectional view of a conventional reciprocating compressor; 
       FIG. 2  is a cross-sectional view of one embodiment of a two stage reciprocating compressor in accordance with the present invention; 
       FIG. 3  is a perspective view of one embodiment of a refrigerator in accordance with the present invention; 
       FIG. 4  is a cross-sectional view showing an operation state of the two reciprocating compressor of  FIG. 2 ; and 
       FIG. 5  is a cross-sectional view showing gas suction in the two stage reciprocating compressor of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Description will now be given in detail of the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 2  is a cross-sectional view showing one embodiment of the two stage reciprocating compressor in accordance with the present invention. 
   As shown in the drawing, a first compressing unit may be disposed in the casing  100  having a certain inner space so as to suck gas and compress same by receiving a reciprocating driving force from a reciprocating motor M. 
   The first compressing unit may include a main frame  610  having a certain shape, a sub frame  620  spaced from the main frame  610  with a constant interval therebetween, the reciprocating motor M coupled between the main frame  610  and the sub frame  620 , a first cylinder  630  penetratingly coupled to the main frame  610 , a first piston  640  inserted into the first cylinder  630  to be reciprocated, a first discharge valve assembly C 1  mounted at one side of the first cylinder  630  so as to control discharging of a refrigerant, and a first suction valve  650  mounted at an end portion of the first piston  640  so as to control a flow of the refrigerant sucked into an inner space of the first cylinder  630 . 
   The first cylinder  630  may have a cylindrical shape and be provided with a cylinder hole  631  into which the first piston  640  is inserted. The first cylinder  630  may be coupled to the main frame  610  so as to be perpendicular with the main frame  610 . 
   The first piston  640  may include a body portion  641  having a certain length and outer diameter, a flange portion  642  curvedly extended from one side of the body portion  641 , and a suction passage  643  penetratingly formed in the body portion  641 . The body portion  641  of the first piston  640  may be inserted into the cylinder hole  631  of the first cylinder  630 . 
   The reciprocating motor M may include an outer stator  661  coupled between the main frame  610  and the sub frame  620 , an inner stator  662  coupled to an outer circumferential surface of the first cylinder  630  spaced from the outer stator  661  with a constant interval therebetween, and a magnet  663  located between the outer stator  661  and the inner stator  662 . The magnet  663  may be coupled to a magnet holder  664 , and the magnet holder  664  may be coupled to the flange portion  642  of the first piston  640 . A winding coil  665  may be provided at the outer stator  661 . The magnet holder  664  and the magnet  663  may be referred to as a mover. 
   The first discharge valve assembly C 1  may include a first discharge cover  671  covering one side of the first cylinder  630 , a first discharge valve  672  located in the first discharge cover  671  so as to open/close the first cylinder  630 , and a first valve spring  673  elastically supporting the first discharge valve  672 . 
   A first discharge pipe  674  for discharging gas may be connected to one side of the first discharge cover  672 , and be penetratingly coupled to the casing  100 . 
   A first resonance spring unit  680  may be provided to elastically support the first piston  640 . The first resonance spring unit  680  may include a spring support member  681  coupled to the sub frame  620 , a spring holder  682  coupled to the flange portion  642  of the first piston  640 , a front resonance spring  683  disposed between one side of the spring holder  682  and the sub frame  620 , and a rear resonance spring  684  disposed between the spring holder  682  and the spring support member  681 . Preferably, the front and rear resonance springs  683 ,  684  may be formed of a plurality of coil springs. 
   A vibration transfer member  700  may be coupled to the sub frame  620 . 
   The vibration transfer member  700  may include a disk portion  702  having a certain area and provided with a through hole  701  therein and a connecting portion  703  extended from one side of the disk portion  702  in a certain length. The connecting portion  703  of the vibration transfer member  700  may be coupled to the sub frame  620 , and a certain space may be formed between the vibration transfer member  700  and the sub frame  620 . 
   A second compressing unit may be provided at the vibration transfer member  700  so as to compress gas by using vibration transferred through the vibration transfer member  700 . 
   The second compressing unit and the first compressing unit may be positioned on the same line. Particularly, the second compressing unit may be disposed at a rear side of the first piston  640  so as to accelerate sucking of the refrigerant into the suction passage  643  that is formed in the first piston  640  of the first compressing unit by using the vibration of the second compressing unit. 
   The second compressing unit may include a second piston  710  fixedly-coupled to the vibration transfer member  700  so as to be located between the vibration transfer member  700  and the sub frame  620 , a second cylinder  720  into which the second piston  710  is inserted, a support frame  730  coupled to the second cylinder  720 , a second discharge valve assembly C 2  mounted at one side of the second cylinder  720  so as to control discharging of the refrigerant, and a second suction valve  740  mounted at the end portion of the second piston  710  so as to control the flow of the refrigerant sucked into the inner space of the second cylinder  720 . 
   The second piston  710  may include a body portion  711  having a certain outer diameter and length, a suction passage  712  penetratingly formed in the body portion  711 , and a ring-shaped flange portion  713  extended from the outer circumferential surface of one side of the body portion  711  in a certain thickness and length. The end portion of one side of the body portion  711  of the second piston  710  may be inserted into the disk portion through hole  701  of the vibration transfer member  700 . 
   A covering member  750  having a certain area may be fixedly-coupled to the disk portion  702  of the vibration transfer member  700  so as to cover one side of the suction passage  712  of the second piston  710 . A through hole may be formed at the covering member  750  to be communicated with the suction passage  712  of the second piston  710 . A first suction pipe  760  may be connected to the through hole and penetratingly coupled to the casing  100 . 
   The second cylinder  720  may have the cylindrical shape having a certain length and include a cylinder body  722  in which a cylinder hole  721  is penetratingly formed therein, and a flange portion  723  formed at the outer circumferential surface of one side of the cylinder body  722 . 
   The body portion  711  of the second piston  710  may be inserted into the cylinder hole  721  of the second cylinder  720 . Since the second piston  710  is fixed to the vibration transfer member  700 , the second cylinder  720  may be reciprocated. Preferably, the second piston  710  and the second cylinder  720  may be on the same line with the first piston  640  of the first compressing unit and located toward the flange portion  642  of the first piston  640 . 
   Since the second cylinder  720  is on the same line with the first piston  640  and located toward the flange portion  642  of the first piston  640 , the second cylinder  720  may be reciprocated following the second piston  710 , and thereby accelerating sucking of the refrigerant into the suction passage  643  of the first piston  640  by flowing of the refrigerant. 
   The support frame  730  may include a body portion  731  having a coupling hole therein and a support portion  732  extended from the body portion  731 . The second cylinder  720  may be coupled to the coupling hole of the support frame  730 . 
   The second discharge valve assembly C 2  may include a second discharge cover  771  covering one side of the second cylinder  720 , a second discharge valve  772  disposed in the second discharge cover  771  so as to open/close the second cylinder  720 , and a second valve spring  773  elastically supporting the second discharge valve  772 . 
   Discharge holes H may be formed at one side of the second discharge cover  771  to discharge gas. 
   Further, a second resonance spring unit  780  may be provided to elastically support the second cylinder  720  and the support frame  730 . 
   The second resonance spring unit  780  may include a front resonance spring  781  disposed between the spring support member  681  and the flange portion  732  of the support frame  730 , and a rear resonance spring  782  disposed between the flange portion  732  of the support frame  730  and the disk portion  702  of the vibration transfer member  700 . 
   Preferably, the front and rear resonance springs  781 ,  782  may be formed of a plurality of coil springs which are disposed with a constant interval therebetween. 
   The first and second compressing units may be supported at a lower surface of the casing  100  by an elastic support unit, such as by springs. 
   The lower surface of the inside of the casing  100  may be filled with a certain amount of oil. 
   And, a second suction pipe  790  may be coupled to one side of the casing  100  so as to suck the refrigerant into the casing  100 . 
     FIG. 3  is a perspective view showing a refrigerator in accordance with the present invention. 
   As shown in the drawing, the refrigerator in accordance with the present invention may include a refrigerator body  200  provided with a refrigerating chamber R and a freezing chamber F, a refrigerating chamber evaporator E 1  mounted at the refrigerating body  200  so as to generate cool air to be supplied to the refrigerating chamber R, and a freezing chamber evaporator E 2  mounted at the refrigerator body  200  so as to generate cool air to be supplied to the freezing chamber F, the two stage reciprocating compressor connected to the refrigerating chamber evaporator E 1  and the freezing chamber evaporator E 2 , a condenser D connected to the two reciprocating compressor so that the refrigerant discharged therefrom may be condensed and supplied to the refrigerating chamber evaporator E 1  and the freezing chamber evaporator E 2 , a first expanding unit G 1  for expanding the refrigerant flown into the refrigerating chamber evaporator E 1 , and a second expanding unit G 2  for expanding the refrigerant flown into the freezing chamber evaporator E 2 . 
   The two stage reciprocating compressor is as described above. 
   The discharge pipe  674  of the two stage reciprocating compressor may be connected to the condenser D. The first suction pipe  760  may be connected to the freezing chamber evaporator E 2  disposed at the side of the freezing chamber and the second suction pipe  790  may be connected to the refrigerating chamber evaporator E 1  disposed at the side of the refrigerating chamber. 
   Reference numeral  210  denotes a machine chamber, and  300  denotes a door. 
   Hereafter, the operations of the two stage reciprocating compressor and the refrigerator having the same will be described. 
   First, when a power supplied to the two stage reciprocating compressor is applied to the reciprocating motor M, the mover may be linearly reciprocated by an interaction between flux formed by an electric current flowing the winding coil  665  and the flux of the magnet  663 . By the linear reciprocating motion of the mover, as shown in  FIG. 4 , the first piston  640  connected to the mover may be linearly reciprocated in the first cylinder  630 . 
   The mover and the first piston  640  may be supported by an elastic force of the first resonance spring unit  680  so as to generate the resonance. 
   As the first piston  640  is linearly reciprocated in the first cylinder  630 , the first suction valve  650  and the first discharge valve  672  may be operated by a difference between internal pressure and external pressure of the first cylinder  630 . Accordingly the refrigerant filled in the casing  100  may be sucked into the first cylinder  630  through the suction passage  643  of the first piston  640  and the sucked refrigerant may be compressed, thereby being discharged in a pre-set pressurized state. 
   The refrigerant having high temperature and pressure which has been discharged from the first cylinder  630  may be flowed outside of the casing  100  through the first discharge cover  671  and the discharge pipe  674 . 
   At the same time, the mover of the first compressing unit and the first piston  640  may be reciprocated, accordingly sucking the refrigerant and compressing same. The refrigerant may be discharged, and vibration may be generated. The vibration may be transferred to the second compressing unit by the vibration transfer member  700 . 
   As the vibration generated from the first compressing unit is transferred to the second compressing unit through the vibration transfer member  700 , the second cylinder  720  elastically supported by the second resonance spring unit  780  and the support frame  730  may be reciprocated by the vibration transferred to the second compressing unit. The second cylinder  720  may be reciprocated along the second piston  710 , and the second resonance spring unit  780  may cause the resonance of the second cylinder  720  and the support frame  730 . 
   By the reciprocating motion of the second cylinder  720 , the second suction valve  740  and the second discharge valve  772  may be operated by the difference between the internal pressure and the external pressure of the second cylinder  720 . Accordingly the refrigerant may be sucked into the second cylinder  720  through the first suction pipe  760  and the suction passage  712  of the second piston  710 , and the sucked refrigerant may be compressed, thereby being discharged in the pre-set pressurized state. The discharged refrigerant may be flowed into the casing  100  through the discharge holes H of the second discharge cover  771 . 
   As the second cylinder  720  and the support frame  730  which are coupled to each other are reciprocated laterally of the first piston  640 , as shown in  FIG. 5 , flowing of the refrigerant may be generated, thereby accelerating suction of the refrigerant into the suction passage  643  of the first piston  640 . 
   Meanwhile, when the first suction pipe  760  is connected to the evaporator disposed at the side of the freezing chamber of the refrigerator, and the second suction pipe  790  is connected to the evaporator disposed at the side of the refrigerating chamber of the refrigerator, the refrigerant having passed through the freezing chamber evaporator may be compressed at the second compressing unit through the first suction pipe  760  so that the refrigerant may be discharged into the casing  100 , and the refrigerant having passed through the refrigerating chamber may be sucked into the casing  100  through the second suction pipe  790 . 
   The refrigerants which are discharged from the second compressing unit and sucked into the casing  100  through the second suction pipe  790 , respectively, may be sucked into the first compressing unit so as to be compressed and discharged. The discharged refrigerant which has high temperature and pressure may be flowed toward the evaporator through the discharge pipe  674 . 
   A compressing ratio of the first compressing unit and the second compressing unit can be variable according to an operation voltage and an operation frequency. 
   As such, in accordance with the present invention, the first and second compressing units which respectively perform the compression of gas are disposed in the casing  100  on the same line. Accordingly interference therebetween can be minimized, enabling an overall structure to be compact. Also, the motion of the second compact unit accelerates gas suction of the first compressing unit, thereby enabling the gas suction efficiency of the first compressing unit to be enhanced. 
   Further, in accordance with the present invention, when applied to the refrigerator having the evaporators disposed in the freezing chamber and the refrigerating chamber, respectively, the freezing chamber and the refrigerating chamber can be consecutively operated by using one compressor. 
   The two stage reciprocating compressor in accordance with the present invention, by being implemented as a compressor having two compressing units and compact structure, minimizes the space for the refrigerator machine chamber when applied to the refrigerator having two evaporators, and enhances gas suction efficiency by accelerating the gas suction, thereby enabling the performance of the compressor to be improved. 
   The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present disclosure. The present teachings can be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. 
   As the present inventive features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.