Patent Publication Number: US-2007110600-A1

Title: Linear Compressor

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention The present invention relates to a linear compressor, and more particularly, to a linear compressor in which a suction valve performs opening/closing operations as it moves relative to a piston by an inertial force when the piston reciprocally moves.  
      2. Description of the Related Art Generally, a linear compressor is an apparatus configured in such a fashion that a piston reciprocally moves in a cylinder upon receiving a reciprocating drive force of a linear motor, to compress working-fluid received in the cylinder, for example, refrigerant. The linear compressor is mainly used in refrigerators, etc.  
       FIG. 1  is a sectional view illustrating a conventional linear compressor.  FIG. 2  is a view of important parts of the conventional linear compressor, illustrating the advance movement of a piston.  FIG. 3  is a view of important parts of the conventional linear compressor, illustrating the retraction movement of the piston.  
      As shown in FIGS.  1  to  3 , the conventional linear compressor comprises a shell  2  forming the outer appearance of the compressor, a cylinder block  4  and a back cover  6  which are arranged in the shell  2 , and a compression unit provided between the cylinder block  4  and the back cover  6 . The compression unit serves to compress working-fluid by a desired compression ratio.  
      The shell  2  is provided with a fluid suction pipe  8  and a fluid discharge pipe  9 , such that the working-fluid to be compressed is sucked into the compression unit from the outside of the shell  2 , and then, is again discharged out of the shell  2  after being compressed in the compression unit.  
      The compression unit includes a cylinder  10  having a compression chamber  11  in which the working-fluid, having passed through the fluid suction pipe  8 , is compressed, a piston  20  to compress the working-fluid received in the compression chamber  11  of the cylinder  10  while performing reciprocating movements in the cylinder  10 , and a linear motor  30  to reciprocally move the piston  20 .  
      The cylinder  10  is provided with a discharge valve assembly  12 , such that the working-fluid, compressed in the compression chamber  11  of the cylinder  10 , is discharged into the fluid discharge pipe  9  in accordance with the operation of the discharge valve assembly  12 .  
      The piston  20  is internally formed with a suction path  21  for allowing the working-fluid, having passed through the fluid suction pipe  8 , to be sucked into the cylinder  10 . Also, the piston  20  has a suction valve  22  to open or close the suction path  21 .  
      The suction valve  22  is an elastic member fastened to the piston  20  by means of a bolt B. The suction valve  22  is designed to be opened or closed as it is elastically deformed in accordance with a pressure difference between the suction path  21  of the piston  20  and the interior of the cylinder  10 .  
      The linear motor  30  basically includes a stator  32 , and a mover  34 . The mover  34  is adapted to reciprocally move while electromagnetically interacting with the stator  32 . The mover  34  is connected to the piston  20 .  
      The compression unit further includes a main spring assembly  40  for providing the piston  20  with an elastic force in a reciprocating movement direction of the piston  20 . Thus, the main spring assembly  40  allows vibrations of the piston  20  to some extent when the piston  20  reciprocally moves.  
      The main spring assembly  40  consists of a first main spring  42  located between the back cover  6  and the piston  20 , and a second main spring  44  located between the cylinder  10  and the linear motor  30  to be supported by the cylinder block  4  and the piston  20 .  
      The operation of the conventional linear compressor having the above-described configuration will now be explained.  
      If the linear motor  30  is driven, the piston  20  reciprocally moves in the cylinder  10  upon receiving the drive force of the linear motor  30 . Then, the first and second main springs  42  and  44  are repeatedly compressed and tensioned in accordance with the reciprocating movements of the piston  20 , thereby serving to allow vibrations of the piston  20  to some extent while causing the discharge valve assembly  12  and the suction valve  22  to be repeatedly opened or closed.  
      Thereby, the working-fluid is sucked into the compression chamber  11  of the cylinder  10  through the fluid suction pipe  8 , such that it is compressed to a high-pressure state by the piston  20  in the compression chamber  11  of the cylinder  10 . Subsequently, the compressed working-fluid is discharged from the cylinder  10  through the discharge valve assembly  12 , to be discharged out of the shell  2  through the fluid discharge pipe  9 .  
      The suction, compression, and discharge operations of the working fluid as stated above are continuously repeated in this sequence so long as the linear motor  30  is driven.  
      A problem of the above-described conventional linear compressor is that the suction valve  22  of the linear compressor is adapted to use an elastic force thereof, and therefore, may exhibit different elastic strains in accordance with a pressure difference between the suction path  21  of the piston  20  and the interior of the cylinder  10 . This makes it impossible for the linear compressor to achieve improved constant compression efficiency, and results in deterioration of reliability.  
      In particular, the suction valve  22  using an elastic force may exhibit excessive elastic deformation as shown in  FIG. 3  when a pressure difference between the suction path  21  of the piston  20  and the interior of the cylinder  10  is large or liquid phase working-fluid is introduced into the cylinder  10 . Accordingly, there is a high risk in that the suction valve  22  may be plastically deformed or damaged due to an increased stress. Furthermore, the suction valve  22  suffers from deterioration of durability with the lapse of time, and consequently has a poor response property.  
      Excessive elastic deformation of the suction valve  22  also exposes the piston  20  to severe shock. This is due to an increase of stress as well as inordinate vibration and noise.  
      Another problem of the conventional linear compressor is that, when the bolt B is used to fasten the suction valve  22  to the piston  20 , a bolt head inevitably protrudes into the compression chamber  11  of the cylinder  10 , increasing the dead volume of the compression chamber  11  of the cylinder  10 . This results in deterioration of compression efficiency. Also, if the bolt head directly collides with the discharge valve assembly  12 , the bolt head may be severely damaged, and excessive vibration and noise may be generated.  
      Recently, high-density nitrogen dioxide is widely used as working fluid. However, the use of the nitrogen dioxide working fluid requires a relatively reduced diameter of the piston  20 . Thus, in this case, it is very difficult to fasten the suction valve  22  to the piston  20  by use of the bolt B, and the piston  20  suffers from an increased flow resistance.  
     SUMMARY OF THE INVENTION  
      Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a linear compressor in which a suction valve performs opening/closing operations as it moves relative to a piston by an inertial force, rather than an elastic force, when the piston reciprocally moves, whereby the suction valve can always exhibit an even opening/closing stroke, achieving several advantageous effects, for example, improved constant compression efficiency, little risk of deformation or damage, high response and durability, and minimized vibration and noise.  
      In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a linear compressor comprising: a piston adapted to reciprocally move in a cylinder, the piston being internally formed with a suction path; and a suction valve inserted in the suction path of the piston to move relative to the suction path, the suction valve performing opening/closing operations as it moves relative to the piston when the piston reciprocally moves.  
      Preferably, a suction valve may be adapted to open or close the suction path of the piston as it moves relative to the suction path when the piston reciprocally moves, the suction valve including: a suction valve body formed with an elongated slot extending in a reciprocating movement direction of the piston; and a suction valve guide pin fitted through the piston and the slot of the suction valve body to move relative to the suction valve body while being fixed to the piston.  
      Preferably, the suction valve body may have: a head portion disposed to protrude out of the suction path of the piston; and a body portion configured to move into or out of the suction path of the piston, the body portion having a partially cut-away cross sectional shape to allow the passage of working-fluid.  
      Preferably, the body portion may have a D-cut shape for the passage of the working-fluid.  
      Preferably, the suction valve body may have: a head portion disposed to protrude out of the suction path of the piston; and a body portion configured to have a diameter smaller than a diameter of the suction path of the piston to move into or out of the suction path of the piston.  
      Preferably, the suction valve body may have: a head portion disposed to protrude out of the suction path of the piston; and a body portion configured to move into or out of the suction path of the piston, the body portion having holes for allowing the passage of working-fluid.  
      Preferably, the holes of the body portion may be integrally formed with a slot of the suction valve body.  
      Preferably, the piston may be also formed with a suction valve recess such that the suction valve is completely inserted into the piston.  
      Preferably, the piston may be also formed with a suction valve recess such that the suction valve is completely inserted into the piston, the suction valve recess being configured to gradually widen away from the suction path of the piston toward a distal end of the piston.  
      Preferably, the piston may be also formed with a suction valve recess such that the suction valve is completely inserted into the piston, the suction valve recess having an inclined region where it comes into contact with the suction valve; and the suction valve has an inclined surface to come into surface contact with the inclined region of the suction valve recess when the suction valve is inserted into the suction valve recess.  
      In accordance with another aspect of the present invention, the above and other objects can be accomplished by the provision of a linear compressor comprising: a piston adapted to reciprocally move in a cylinder, the piston being internally formed with a suction path; and a suction valve adapted to open or close the suction path of the piston as it moves relative to the suction path when the piston reciprocally moves, the suction valve including: a suction valve body formed with an elongated slot extending in a reciprocating movement direction of the piston; and a suction valve guide pin fitted through the piston and the slot of the suction valve body to move relative to the suction valve body while being fixed to the piston, wherein: the piston is also formed with a suction valve recess such that the suction valve is completely inserted into the piston, the suction valve recess having an inclined region where it comes into contact with the suction valve; and the suction valve has an inclined surface to come into surface contact with the inclined region of the suction valve recess when the suction valve is inserted into the suction valve recess.  
      In the linear compressor of the present invention having the above-described configuration, the suction valve is inserted in the suction path of the piston to move relative to the suction path, thereby performing opening/closing operations as it moves relative to the piston by an inertial force when the piston reciprocally moves, whereby the suction valve always exhibits an even opening/closing stroke, and therefore, can achieve various advantageous effects, such as for example, improved constant compression efficiency, little deformation or damage due to excessive stress applied to the suction valve, an improvement in response and durability, and minimized vibration and noise caused by the opening/closing operations of the suction valve.  
      Further, as a result of providing the suction valve guide pin in the piston in a radial direction of the piston to couple the suction valve to the piston, it is possible to minimize the dead volume of the compression chamber of the cylinder, to enable the suction valve to be easily mounted to the piston even if the piston has a small diameter, and to reduce the flow resistance of working-fluid due to the existence of the suction valve.  
      Furthermore, since the piston is formed with the suction valve recess such that the suction valve is completely inserted into the piston when the suction valve closes the suction path of the piston, the dead volume of the cylinder chamber of the cylinder can be more effectively eliminated, and there is no risk of interference between the suction valve and a discharge valve assembly.  
      Finally, by providing the suction valve with an inclined head portion, the head portion of the suction valve can come into surface contact with the suction valve recess of the piston, whereby the suction valve can smoothly move into or out of the suction valve recess of the piston, and in particular, the head portion of the suction valve can achieve an improved stiffness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a sectional view illustrating a conventional linear compressor;  
       FIG. 2  is a view of important parts of the conventional linear compressor, illustrating the advance movement of a piston;  
       FIG. 3  is a view of important parts of the conventional linear compressor, illustrating the retraction movement of the piston;  
       FIG. 4  is a sectional view illustrating a linear compressor according to a first embodiment of the present invention;  
       FIG. 5  is an exploded perspective view illustrating a suction valve and a piston included in the linear compressor according to the first embodiment of the present invention;  
       FIG. 6  is a view illustrating an initially retracted state of the piston of the linear compressor according to the first embodiment of the present invention;  
       FIG. 7  is a view illustrating a completely retracted state of the piston of the linear compressor according to the first embodiment of the present invention;  
       FIG. 8  is a view illustrating an initially advanced state of the piston of the linear compressor according to the first embodiment of the present invention;  
       FIG. 9  is a view illustrating a completely advanced state of the piston of the linear compressor according to the first embodiment of the present invention;  
       FIG. 10  is a configuration view of important parts of a linear compressor according to a second embodiment of the present invention, illustrating a retracted state of a piston included in the linear compressor;  
       FIG. 11  is a configuration view of important parts of the linear compressor according to the second embodiment of the present invention, illustrating an advanced state of the piston;  
       FIG. 12  is a configuration view of important parts of a linear compressor according to a third embodiment of the present invention, illustrating a retracted state of a piston included in the linear compressor;  
       FIG. 13  is a configuration view of important parts of the linear compressor according to the third embodiment of the present invention, illustrating an advanced state of the piston;  
       FIG. 14  is a configuration view of important parts of a linear compressor according to a fourth embodiment of the present invention, illustrating a retracted state of a piston included in the linear compressor; and  
       FIG. 15  is a configuration view of important parts of the linear compressor according to the fourth embodiment of the present invention, illustrating an advanced state of the piston. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Now, preferred embodiments of the present invention will be explained with reference to the accompanying drawings.  
       FIG. 4  is a sectional view illustrating a linear compressor according to a first embodiment of the present invention.  FIG. 5  is an exploded perspective view illustrating a suction valve and a piston included in the linear compressor according to the first embodiment of the present invention. FIGS.  6  to  9  are views illustrating, in this sequence, an initially retracted state, a completely retracted state, an initially advanced state, and a completely advanced state of the piston of the linear compressor according to the first embodiment of the present invention.  
      As shown in FIGS.  4  to  9 , the linear compressor according to the first embodiment of the present invention comprises a shell  50  configured to allow introduction and discharge of working fluid, a cylinder block  60  and a back cover  62  arranged in the shell  50 , and a compression unit P provided between the cylinder block  60  and the back cover  62 . The working-fluid, introduced into the shell  50 , is compressed by a desired compression ratio while passing through the compression unit P, thereby being discharged in a high-pressure state.  
      A fluid suction pipe  52  is connected to the shell  50  such that the working-fluid is sucked into the shell  50  from an external station. Also, a fluid discharge pipe  54  is connected to the shell  50  such that the compressed working-fluid, discharged from the compression unit P, is guided out of the shell  50 .  
      A damper  56  is mounted in the shell  50  to elastically support the compression unit P.  
      A lubricating oil pumping device  58  is arranged in the shell  50  to pump lubricating oil G in the bottom of the shell  50  to the compression unit P.  
      The back cover  62  is located closer to the fluid suction pipe  52  than the cylinder block  60 .  
      A muffler (not shown) is mounted to the back cover  62  to reduce the noise of the working-fluid generated when the working-fluid passes through the fluid suction pipe  52 .  
      The compression unit P includes a linear motor  90  to generate a reciprocating drive force, a cylinder  70  fixedly mounted to the cylinder block  60 , the cylinder  70  internally defining a compression chamber  71  for the compression of the working-fluid, a piston  80  which performs reciprocating movements in the cylinder  70  using the reciprocating drive force of the linear motor  90  to compress the working-fluid received in the compression chamber  71  of the cylinder  70 , and first and second resonance springs  110  and  112  to allow vibrations of the piston  80  to some extent in a reciprocating movement direction of the piston  80  when the piston  80  reciprocally moves.  
      The linear motor  90  is located around the cylinder  70 , and is supported by the cylinder block  60  and the back cover  62 .  
      Considering the configuration of the linear motor  90 , it basically consists of a mover connected to the piston  80  to work in conjunction with the piston  80 , and a stator adapted to electromagnetically interact with the mover for inducing reciprocating movements of the mover.  
      The mover includes a magnet  92  arranged inside the stator in a reciprocally movable manner, and a magnet frame  94  for the fixation of the magnet  92 , the magnet frame  94  being connected to the piston  80  to work in conjunction with the piston  80 . The magnet frame  94  serves to transmit the reciprocating drive force of the linear motor  90  to the piston  80 .  
      The stator includes an outer core  95  located on the outer circumference of the mover, a coil  96  provided in the outer core  95  to generate a magnetic field, and an inner core  97  located on the inner circumference of the mover.  
      The cylinder  70  has a cylindrical structure having open front and rear ends. The piston  80  is inserted into the open rear end of the cylinder  70 . After being compressed in the compression chamber  71  of the cylinder  70 , the working-fluid is discharged from the open front end of the cylinder  70 .  
      The open front end of the cylinder  70  is covered with the discharge valve assembly  75 , such that the working-fluid, compressed in the compression chamber  71  of the cylinder  70 , is discharged into the fluid discharge pipe  54 .  
      The discharge valve assembly  75  includes a valve cover  76  mounted to cover the open front end of the cylinder  70  while being connected to the fluid discharge pipe  54 , a discharge valve body  77  mounted to reciprocally move in front of the open front end of the cylinder  70  within the discharge valve cover  76 , and a discharge valve spring  78  to elastically support the discharge valve body  77 .  
      The discharge valve cover  76  may have a dual structure. Specifically, the discharge valve cover  76  includes an inner cover  76   b  having a discharge hole  76   a  for the discharge of the working-fluid, and an outer cover  76   c  located at the outside of the inner cover  76   b  to surround the inner cover  76   b,  the outer cover  76   c  being connected to the fluid discharge pipe  54 .  
      A suction path  81  is formed in the piston  80  to extend longitudinally throughout the interior of the piston  80 , such that the suction path  81  is connected to both the fluid suction pipe  52  and the compression chamber  71  of the cylinder  70 .  
      The suction path  81  of the piston  80  is designed to be selectively connected to the compression chamber  71  of the cylinder  70  by the suction valve  84 , which performs opening/closing operations in accordance with the reciprocating movements of the piston  80 .  
      The suction valve  84  is disposed in the suction path  81  of the piston  80  such that it is movable relative to the suction path  81 . Thus, the suction valve  84  is able to perform opening/closing operations as it moves relative to the piston  80  by an inertial force when the piston  80  reciprocally moves.  
      The suction valve  84  includes a suction valve body  85  inserted in the suction path  81  of the piston  80  to move relative to the suction path  81 , the suction valve body  85  having an elongated slot  85 ′ extending in the reciprocating movement direction of the piston  80 , and a suction valve guide pin  86  fitted through the piston  80  and the slot  85 ′ of the suction valve body  85  to move relative to the slot  85 ′ while being fixed to the piston  80 .  
      The suction valve body  85  has a head portion  85   a  disposed to protrude out of the suction path  81  of the piston  80 , and a body portion  85   b  inserted in the suction path  81  of the piston  80  to move into or out of the suction path  81 .  
      The head portion  85   a  of the suction valve body  85  may take the form of a disk having a diameter smaller than a diameter of the piston  80 , but larger than a diameter of the suction path  81  of the piston  80 .  
      Preferably, the head portion  85   a  of the suction valve body  85  has a flat outer surface  85   a ′ at an opposite side of the piston  80 , to ensure even compression of the working-fluid in the compression chamber  71  of the cylinder  70 .  
      The body portion  85   b  of the suction valve body  85  may have a D-cut shape, in order to allow the working-fluid to pass through a space between the body portion  85   b  of the suction valve body  85  and the suction path  81  of the piston  80  when the suction valve  84  moves to open the suction path  81  of the piston  80 .  
      Specifically, the body portion  85   b  of the suction valve body  85  has a partially cut-away cross sectional shape of a circle having approximately the same size as the suction path  81  of the piston  80 .  
      The slot  85 ′ is formed in the body portion  85   b  of the suction valve body  85 , such that the suction valve guide pin  86  is fitted through the slot  85 ′ to move relative to the slot  85 ′.  
      In a relative movement of the suction valve guide pin  86 , one end of the slot  85 ′ toward the head portion  85   a  of the suction valve body  85  is a top dead point, and the opposite end of the slot  85 ′ is a bottom dead point.  
      The suction valve guide pin  86  has a rod shape having a diameter smaller than a length of the slot  85 ′ of the suction valve  84 .  
      The suction valve guide pin  86  may be arranged in the piston  80  in a radial direction of the piston  80 .  
      With this configuration, the suction valve guide pin  86  may be press fitted to the piston  80 . The suction valve guide pin  86  may have approximately the same length as a diameter of the piston  80  such that opposite ends thereof straddle the piston  80 .  
      The suction valve  84  is configured such that it can be completely inserted in the piston  80  when it is desired to close the suction path  81  of the piston  80 .  
      Specifically, a suction valve recess  87  is formed in a front end region of the piston  80  to be connected to the suction path  81  of the piston  80 , such that the head portion  85   a  of the suction valve body  85  is inserted in the suction valve recess  87 .  
      The suction valve recess  87  may be formed in the piston  80  such that it gradually widens from the suction path  81  of the piston  80  toward a front distal end of the piston  80 .  
      Hereinafter, the operation of the linear compressor according to the present invention having the above-described configuration will be explained.  
      If the linear motor  90  is driven, the magnet  92  reciprocally moves along with the magnet frame  94  via the electromagnetic interaction of both the stator and the mover. The resulting reciprocating drive force of the linear motor  90  is transmitted to the piston  80  that is connected to the magnet frame  94 . Thereby, the piston  80  reciprocally moves in the cylinder  70  upon receiving the drive force of the linear motor  90 . Simultaneously, the first and second main springs  110  and  112  are repeatedly compressed and tensioned, causing the suction, compression, discharge of the working-fluid to be repeated in this sequence.  
      Specifically, as shown in  FIG. 6 , if the piston  80  begins to retract out of the cylinder  70 , the suction valve  84  shows a relative movement to the piston  80  by an inertial force, thereby being protruded from the piston  80  into the compression chamber  71  of the cylinder  70 .  
      Just prior to beginning the retraction of the piston  80  out of the cylinder  70 , the suction valve  84  is completely inserted in the piston  80 , and thus, the suction valve guide pin  86  of the suction valve  84  is located at the top dead point of the slot  85 ′ of the suction valve  84  (See.  FIG. 4 ).  
      Accordingly, if the piston  80  begins to retract out of the cylinder  70 , only the piston  80  retracts, while the suction valve  84  remains stationary. As a result, the suction valve  84  is protruded from the piston  80 .  
      In this case, the suction valve guide pin  86  moves along the slot  85 ′ of the suction valve  84  from the top dead point to the bottom dead point of the slot  85 ′.  
      If the piston  80  continuously retracts after the suction valve guide pin  86  reaches the bottom dead point of the slot  85 ′ of the suction valve  84 , as shown in  FIG. 7 , the suction valve guide pin  86  is retracted along with the piston  80 , thereby pulling the suction valve  84 .  
      Thereby, the suction valve  84  is retracted along with the piston  80  while being protruded from the piston  80 .  
      In a state wherein the suction valve  84  is protruded from the piston  80 , the suction path  81  of the piston  80  is opened, thereby allowing the working-fluid in the suction path  81  of the piston  80  to be sucked into the compression chamber  71  of the cylinder  70 .  
      In succession, if the piston  80  advances toward the interior of the cylinder  70 , the suction valve  84  shows a relative movement to the piston  80  by an inertial force, thereby being inserted into the piston  80 .  
      Specifically, if the piston  80  begins to advance into the compression chamber  71  of the cylinder  70 , as shown in  FIG. 8 , the piston  80  approaches the suction valve  84 , and simultaneously, the suction valve  84  retracts toward the piston  80  by the pressure of the working-fluid in the compression chamber  71  of the cylinder  70 . Thereby, the suction valve  84  is rapidly inserted into the piston  80 , thereby closing the suction path  81  of the piston  80 .  
      In this case, the suction valve guide pin  86  moves along the slot  85 ′ of the suction valve  84  from the bottom dead point to the top dead point of the slot  85 ′. If the piston  80  continuously advances after the suction valve guide pin  86  reaches the top dead point of the slot  85 ′ of the suction valve  84 , the suction valve  84  advances along with the piston  80 .  
      Of course, the suction valve  84  is continuously inserted in the piston  80  by the pressure of the working-fluid in the compression chamber  71  of the cylinder  70 .  
      As the piston  80  advances in a state wherein the suction path  81  of the piston  80  is closed by the suction valve  84  as stated above, the working-fluid in the compression chamber  71  of the cylinder  70  is compressed to a high-pressure state.  
      If the working-fluid in the compression chamber  71  of the cylinder  70  is compressed to the high-pressure state, as shown in  FIG. 9 , the discharge valve assembly  75  opens the compression chamber  71  of the cylinder  70  in accordance with the force equilibrium relationship between the pressure of the working-fluid in the compression chamber  71  of the cylinder  70  and the discharge valve spring  78  of the discharge valve assembly  75 .  
      With the opening operation of the discharge valve assembly  75 , the working-fluid, compressed in the compression chamber  71  of the cylinder  70 , is discharged out of the shell  50  by passing through the discharge cover  76  and the fluid discharge pipe  54  in this sequence.  
       FIGS. 10 and 11  are configuration views of important parts of a linear compressor according to a second embodiment of the present invention,  FIG. 10  illustrating a retracted state of a piston included in the linear compressor, and  FIG. 11  illustrating an advanced state of the piston.  
      As shown in  FIGS. 10 and 11 , the linear compressor according to the second embodiment of the present invention employs a suction valve  150 , which includes a suction valve body  152  inserted in a suction path  161  of a piston  160  to move relative to the suction path  161 , the suction valve body  152  having an elongated slot  150 ′ extending in a reciprocating movement direction of the piston  160 , and a suction valve guide pin  154  fitted through the piston  160  and the slot  150 ′ of the suction valve body  152  to move relative to the slot  150 ′ while being fixed to the piston  160 .  
      The suction valve body  152  may be divided into a head portion  152   a  disposed to protrude out of the suction path  161  of the piston  160 , and a body portion  152   b  configured to have a diameter smaller than a diameter of the suction path  161  of the piston  160  to move into or out of the suction path  161 .  
      In the present embodiment, the suction valve  150  may further include a guide for allowing the center of the suction valve  150  to continuously align with the center of the piston  160  during a relative movement between the suction valve  150  and the piston  160 .  
      Other configurations of the second embodiment of the present invention are identical to those of the first embodiment except for the above-described configurations, and thus, their description will be omitted.  
      Now, the opening/closing operations of the above-described suction valve  150  of the linear compressor according to the second embodiment of the present invention will be explained.  
      When the piston  160  retracts, the suction valve  150  is protruded from the piston  160 , such that the working-fluid in the suction path  161  of the piston  160  flows through a space between the body portion  152   b  of the suction valve body  152  and the suction path  161  of the piston  160 .  
      When the piston  160  advances, the suction valve  150  is inserted into the piston  160 , thereby closing the suction path  161  of the piston  160 .  
       FIGS. 12 and 13  are configuration views of important parts of a linear compressor according to a third embodiment of the present invention,  FIG. 12  illustrating a retracted state of a piston included in the linear compressor, and  FIG. 13  illustrating an advanced state of the piston.  
      As shown in  FIGS. 12 and 13 , the linear compressor according to the third embodiment of the present invention employs a suction valve  200 , which includes a suction valve body  202  inserted in a suction path  211  of a piston  210  to move relative to the suction path  211 , the suction valve body  202  having an elongated slot  200 ′ extending in a reciprocating movement direction of the piston  210 , and a suction valve guide pin  204  fitted through the piston  210  and the slot  200 ′ of the suction valve body  202  to move relative to the slot  200 ′ while being fixed to the piston  210 .  
      The suction valve body  202  may be divided into a head portion  202   a  disposed to protrude out of the suction path  201  of the piston  210 , and a body portion  202   b  configured to have approximately the same diameter as a diameter of the suction path  211  of the piston  210  to move into or out of the suction path  211 , the body portion  202   b  having holes  202   c  for the passage of the working-fluid in the suction path  211  of the piston  210 .  
      The body portion  202   b  of the suction valve body  202  internally defines a path  202   d,  which connects the holes  202   c  of the suction valve body  202  to the suction path  211  of the piston  210 .  
      The holes  202   c  of the suction valve body  202  may be integrally formed with the slot  200 ′ of the suction valve  200 .  
      Other configurations of the third embodiment of the present invention are identical to those of the first embodiment except for the above-described configurations, and thus, their description will be omitted.  
      Now, the opening/closing operations of the above-described suction valve  200  of the linear compressor according to the third embodiment of the present invention will be explained.  
      When the piston  210  retracts, the suction valve  200  is protruded from the piston  210 . Thereby, the holes  202   c  of the suction valve body  202  are opened, such that the working-fluid in the suction path  211  of the piston  210  passes through the suction valve body  202 .  
      When the piston  210  advances, the suction valve  200  is inserted into the piston  210 , thereby closing the suction path  211  of the piston  210 .  
       FIGS. 14 and 15  are configuration views of important parts of a linear compressor according to a fourth embodiment of the present invention,  FIG. 14  illustrating a retracted state of a piston included in the linear compressor, and  FIG. 15  illustrating an advanced state of the piston.  
      As shown in  FIGS. 14 and 15 , the linear compressor according to the fourth embodiment of the present invention includes a suction valve  250 , which includes a suction valve body  252  inserted in a suction path  261  of a piston  260  to move relative to the suction path  261 , the suction valve body  252  having an elongated slot  250 ′ extending in a reciprocating movement direction of the piston  260 , and a suction valve guide pin  254  fitted through the piston  260  and the slot  250 ′ of the suction valve body  252  to move relative to the suction valve body  252  while being fixed to the piston  260 .  
      The piston  260  is formed in a front end region thereof with a suction valve recess  262  to be connected to the suction path  261  of the piston  260 , such that a head portion  252   a  of the suction valve body  252  is inserted in the suction valve recess  262 .  
      The suction valve recess  262  of the piston  260  may have an inclined structure on at least the region where the piston  260  comes into contact with the suction valve  250 . Specifically, the suction valve recess  262  of the piston  260  may gradually widen away from the suction path  261  of the piston  260  toward a front distal end of the piston  260 .  
      The suction valve body  252  may be divided into the head portion  252   a  disposed to protrude out of the suction path  261  of the piston  260 , and a body portion  252   b  having a D-cut shape and adapted to move into or out of the suction path  261  of the piston  260 .  
      Preferably, the head portion  252   a  of the suction valve body  252  has an inclined outer surface, such that the head portion  252   a  comes into surface contact with the suction valve recess  262  of the piston  160  when it is completely inserted into the suction valve recess  262  of the piston  260 .  
      Other configurations of the fourth embodiment of the present invention are identical to those of the first embodiment except for the above-described configurations, and thus, their description will be omitted.  
      Now, the opening/closing operations of the suction valve  250 , employed in the linear compressor having the above-described configuration according to the fourth embodiment of the present invention, will be explained.  
      When the piston  260  retracts, the suction valve  250  is protruded from the piston  260 , such that working-fluid in the suction path  261  of the piston  260  passes through the suction valve body  252 .  
      When the piston  260  advances, the suction valve  250  is inserted into the piston  260 , thereby closing the suction path  261  of the piston  210 .  
      As is apparent from the above description, the present invention provides a linear compressor having the following several advantages.  
      Firstly, the linear compressor of the present invention is configured in such a fashion that a suction valve is inserted in a suction path of a piston to move relative to the suction path, thereby performing opening/closing operations as it moves relative to the piston by an inertial force when the piston reciprocally moves. The suction valve configured as stated above can always exhibit an even opening/closing stroke, and therefore, can achieve various advantageous effects, such as for example, improved constant compression efficiency, little deformation or damage due to excessive stress applied to the suction valve, an improvement in response and durability, and minimized vibration and noise caused by the opening/closing operations of the suction valve.  
      Secondly, according to the present invention, a suction valve guide pin is provided in the piston in a radial direction of the piston, to couple the suction valve to the piston. The use of the suction valve guide pin has the effects of minimizing the dead volume of a compression chamber of a cylinder, enabling the suction valve to be easily mounted to the piston even if the piston has a small diameter, and reducing the flow resistance of working-fluid due to the existence of the suction valve.  
      Thirdly, the piston is formed with a suction valve recess such that the suction valve is completely inserted into the piston when the suction valve closes the suction path of the piston. This more effectively eliminates the dead volume of the cylinder chamber of the cylinder, and can prevent interference between the suction valve and a discharge valve assembly.  
      Fourthly, by providing the suction valve with an inclined head portion, the head portion of the suction valve can come into surface contact with the suction valve recess of the piston, whereby the suction valve can smoothly move into or out of the suction valve recess of the piston, and in particular, the head portion of the suction valve can achieve an improved stiffness.  
      Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.