Abstract:
A valve structure includes: a valve seat part furnished with a valve hole portion having a valve hole connecting a first gas chamber to a second gas chamber, and a valve-body supporting wall part laterally extending from the valve hole portion; an elastic valve-body member furnished with a first elastic platelike section disposed paralleling the valve hole portion, and a second elastic platelike section extending from the first elastic platelike section, wherein the first elastic platelike section is elastically deformable against the second elastic platelike section under pressure differential between the first gas chamber and the second gas chamber such as to open the valve hole; and an elastic pressing member arranged paralleling the second elastic platelike section such as to elastically deform together with the elastic valve-body member, and being of planar form determined such as to expose the first elastic platelike section.

Description:
INCORPORATION BY REFERENCE 
       [0001]    Priority is claimed med to Japanese Patent Application No. 2015-208613, filed Oct. 23, 2015, the entire content which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present invention in particular embodiments relates to valve structures in valved nonlubricated linear compressors, and to nonlubricated linear compressors having the valve structures. In addition, the present invention in particular embodiments relates to cryogenic refrigerators having the nonlubricated linear compressors. 
         [0004]    Description of Related Art. 
         [0005]    Attempts at applying nonlubricated linear compressors to cryogenic refrigerators have been proposed. 
       SUMMARY 
       [0006]    One embodiment of the present invention affords a valve structure for a valved nonlubricated linear compressor. The valve structure comprises: a valve seat part including a valve hole portion having a valve hole connecting a first gas chamber to a second gas chamber, and a valve-body supporting wail part extending laterally from the valve hole portion; an elastic valve-body member furnished with a first elastic platelike section disposed paralleling the valve hole portion such as to cover the valve hole, and a second elastic platelike section extending from the first elastic platelike section and paralleling the valve-body supporting wall part, wherein the first elastic platelike section is elastically deformable against the second elastic platelike section under pressure differential between the first gas chamber and the second gas chamber such as to uncover the valve hole; and an elastic pressing member arranged paralleling the second elastic platelike section such as to elastically deform together with the elastic valve-body member, the elastic pressing member being of planar form determined such as to expose the first elastic platelike section. 
         [0007]    Another embodiment of the present invention affords a nonlubricated linear compressor including a valve structure as set forth above. 
         [0008]    Still another embodiment of the present invention affords a cryocooler including the just-mentioned nonlubricated linear compressor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic view showing a cryocooler according to an embodiment of the present invention. 
           [0010]      FIG. 2  is a sectional view schematically showing a linear compressor shown in  FIG. 1 . 
           [0011]      FIG. 3  is a sectional view schematical showing a valve structure of a valved nonlubricated linear compressor according to an embodiment of the present invention. 
           [0012]      FIG. 4  is a plan view schematically showing an elastic valve body member shown in  FIG. 3 . 
           [0013]      FIG. 5  is a plan view schematically showing an elastic pressing member shown in  FIG. 3 . 
           [0014]      FIG. 6  is a top view schematically showing the valve structure shown in  FIG. 3 . 
           [0015]      FIG. 7  is a sectional view schematically showing a portion of a reed valve having a stopper. 
           [0016]      FIG. 8  is a sectional view schematically showing a valve structure of a valved nonlubricated linear compressor according to another embodiment of the present invention. 
           [0017]      FIG. 9  is a sectional view schematically showing a valve structure of a valved nonlubricated linear compressor according to still another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    A nonlubricated linear compressor includes a valve therein. A stopper which restricts a movement, amount of a valve body maybe provided in the valve. However, if the movement amount of the valve body is restricted, since a flow rate of gas flowing through the valve decreases, the flow rate of gas which is discharged from a linear compressor also decreases. In addition, noise may occur due to collision of the valve body with respect to the stopper. In this way, there is room for improvement for the nonlubricated linear compressor including the valve having a stopper. 
         [0019]    It is desirable to provide an improved valve structure, a valved nonlubricated linear compressor having the valve structure, and a cryocooler having the nonlubricated linear compressor. 
         [0020]    In addition, arbitrary combinations of the above-described components, or components or expression of the present invention may be replaced by each other in methods, devices, systems, or the like, and these replacements are also included in aspects of the present invention. 
         [0021]    According to the present invention, it is possible to provide an improved valve structure, a valved nonlubricated linear compressor having the valve structure, and a cryocooler having the valved nonlubricated linear compressor. 
         [0022]    Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in descriptions thereof, the same reference numerals are assigned to the same elements, and overlapping descriptions thereof are omitted. In addition, configurations described below are exemplified, and do not limit the scope of the present invention. 
         [0023]      FIG. 1  is a schematic view showing a cryocooler  100  according to an embodiment of the present invention. The cryocooler  100  includes a linear compressor  10  and an expander  102 . For example, the expander  102  is a Gifford McMahon type expander, and in this case, the cryocooler  100  is a Gifford McMahon type cryocooler. 
         [0024]    A discharge port of the linear compressor  10  is connected to the expander  102  through a high-pressure pipe  104 . Moreover, a suction port of the linear compressor  10  is connected to the expander  102  through a low-pressure pipe  106 . A high-pressure working gas  36  is supplied from the linear compressor  10  to the expander  102  through the high-pressure pipe  104 . The high-pressure working gas  36  is adiabatically expanded in the expander  102 , and thus, the expander  102  generates coldness. A low-pressure working gas  34  is recovered front the expander  102  to the linear compressor  10  through the low-pressure pipe  106 . The linear compressor  10  compresses the low-pressure working gas  34  and supplies the compressed gas as the high-pressure working gas  36  to the expander  102  again. For example, the working gas is a helium gas. 
         [0025]      FIG. 2  is a sectional view schematically showing the linear compressor  10  shown in  FIG. 1 . The linear compressor  10  includes a compressor case  12 , a compressor container  14 , a piston  16 , a cylinder  18 , a linear actuator  20 , and a leaf spring unit  22 . In the linear compressor  10 , one piston  16 , and one cylinder  18  which accommodates the piston  16  are provided. The linear compressor  10  is configured of a nonlubricated linear compressor (may be referred to as an linear compressor) in which oil is not used so as to lubricate a movable element. 
         [0026]    The compressor case  12  accommodates the compressor container  14 . Dynamic vibration absorbers  24  for preventing vibrations of the compressor container  14  from being transmitted to the outside or decreasing the vibrations are provided between the compressor case  12  and the compressor container  14 . The compressor case  12  may be a cover member which covers the dynamic vibration absorbers  24 . 
         [0027]    The compressor container  14  is a pressure container which is configured so as to airtightly hold a working gas in the linear compressor  10 . The compressor container  14  accommodates the piston.  16 , a cylinder  18 , the linear actuator  20 , and the leaf spring unit  22 . 
         [0028]    The compressor container  14  includes a high-pressure chamber  26  and a low-pressure chamber  28  of a working gas therein. A discharge pipe  30  is connected to the high-pressure chamber  26 , and a suction pipe  32  is connected to the low-pressure chamber  28 . The discharge pipe  30  penetrates the compressor case  12  and the compressor container  14 , and connects the high-pressure pipe  32  penetrates the compressor case  12  and the compressor container  14 , and connects the low-pressure chamber  28  to the outside of the linear compressor  10 . Accordingly, the low-pressure working gas  34  is recovered from the outside of the linear compressor  10  to the low-pressure chamber  28  through the suction pipe  32 . In addition, the high-pressure working gas  36  is supplied from the high-pressure chamber  26  to the outside of the linear compressor  10  through the discharge pipe  30 . 
         [0029]    In addition, with the compressor container  14  or instead of the compressor container  14 , the compressor case  12  may be configured as a pressure container which airtightly holds the working gas in the linear compressor  10 . 
         [0030]    The piston  16  is a movable body which partitions the inside of the compressor container  14  into the high-pressure chamber  26  and the low-pressure chamber  28 . The high-pressure chamber  26  includes a pressurization chamber  38  and a discharge chamber  40 . The pressurization chamber  38  is formed between the piston  16  and the cylinder  18 . The discharge chamber  40  is formed inside the cylinder  18 . The discharge pipe  30  is connected to the discharge chamber  40 . 
         [0031]    The linear compressor  10  is configured of a valved linear compressor. An intake valve  42  for supplying the low-pressure working gas  34  from the low-pressure chamber  28  to the high-pressure chamber  26  is provided in the piston  16 . The intake valve  42  is opened and closed by a pressure difference between the high-pressure chamber  26  and the low-pressure chamber  28 . The intake valve  42  is opened when the pressure difference exceeds a predetermined threshold value, and is closed when the pressure difference is dower than the threshold value. A discharge valve  14  for discharging the high-pressure working gas  36  from the pressurization chamber  38  to the discharge chamber  40  is provided in the cylinder  18 . The discharge valve  44  is opened and closed by a pressure difference between the pressurization chamber  38  and the discharge chamber  40 . The discharge valve  44  is opened when the pressure difference exceeds a predetermined threshold value, and is closed when the pressure difference is lower than the threshold value. For example, the intake valve  42  and the discharge valve  44  are reed valve type valves. 
         [0032]    The piston  16  is a hollow cylindrical member which extends in an axial direction (a vertical direction in  FIG. 2 ) The piston.  16  includes a piston tip portion  46  which faces the pressurization chamber  38 , and a piston main body portion  48  which extends from the piston tip portion  46  toward the side opposite to the pressurization chamber  38  in the axial direction. 
         [0033]    A first piston recessed portion  50  is formed in the piston tip portion  46 , and a second piston recessed portion  52  is formed in the piston main body portion  48 . The first piston recessed portion  50  is a hollow portion of the piston tip portion  46 , piston recessed portion  52  is a hollow portion of the piston main body portion  48 , and forms a portion of the low-pressure chamber  28 . 
         [0034]    A piston partition portion  54  is provided between the piston tip portion  46  and the piston main body portion  48 . The piston partition portion  54  is a wall which partitions the piston into the first piston recessed portion  50  and the second piston recessed portion  52 . A piston communication hole  56  is formed at the center of the piston partition portion  54 . The piston communication hole  56  communicates with the first piston recessed portion  50  and the second piston recessed portion  52 . The intake valve  42  is accommodated in the first piston recessed portion  50 . The intake valve  42  is configured so as to open and close the piston communication hole  56  by a pressure difference between the first piston recessed portion  50  and the second piston recessed portion  52 . 
         [0035]    The piston  16  is supported to the compressor container  14  in a reciprocation-enable manner (for example, a vibration-enable manner) in the axial direction by the leaf spring unit  22 . A radial inner portion of the leaf spring unit  22  is attached to the base end portion of the piston main body portion  48  so as to circumferentially surround the piston  16 . A radial outer portion of the leaf spring unit  22  is attached to the compressor container  14 . 
         [0036]    Moreover, the piston  16  includes a piston drive portion  49  which is driven by the linear actuator  20 . The piston drive portion  49  is attached to the piston main body portion  48 . 
         [0037]    The cylinder  18  is a hollow cylindrical member which extends in the axial direction so as to accommodate the piston  16 . The cylinder  18  is supported so as to be fixed to the compressor container  14 . The cylinder  18  includes a cylinder fixing end portion  58  which is fixed to the compressor container  14 , and a cylinder main body portion  60  which extends from the cylinder fixing end portion  58  toward the piston  16  in the axial direction. The discharge chamber  40  is formed in the cylinder fixing end portion  58 . The cylinder main body portion  60  includes a cylinder inner surface  62  which slidably supports the piston  16  in the axial direction. A cylinder partition portion  64  is provided between the cylinder fixing end portion  58  and the cylinder main body portion  60 . A cylinder communication hole  66  is formed at the center of the cylinder partition portion  64 . The cylinder communication hole  66  communicates with the discharge chamber  40  and the pressurization chamber  38 . The discharge valve  44  is accommodated in the discharge chamber  40 , and is configured so as to open and close the cylinder communication hole  66  by a pressure difference between the discharge chamber  40  and the pressurization chamber  38 . 
         [0038]    The linear actuator  20  is configured to be driven so as to reciprocate the piston  16  in the axial direction. A forward movement and a backward movement of the piston  16  in the axial direction are periodically repeated by the driving of the linear actuator  20 . The forward movement of the piston  16  is a upward movement in  FIG. 2 , and the backward movement of the piston  16  is a downward movement in  FIG. 2 . For example, the linear actuator  20  is a linear vibration actuator which vibrates the piston  16  in the axial direction. 
         [0039]    The leaf spring unit  22  is a bearing which allows reciprocation of the piston  16  in the axial direction and restricts the movements of the piston  16  in the radial direction and the circumferential direction. The leaf spring unit  22  includes a plurality of leaf springs  23 . The plurality of leaf springs  23  are arranged in series in the axial direction, and for example, include at least ten leaf springs  23 . In the plurality of leaf springs  23 , each leaf spring  23  elastically supports the piston  16  to the compressor container  14  such that the piston  16  can reciprocate in the axial direction. Each leaf spring  23  extends along a plane perpendicular to the axial direction. The leaf spring  23  is referred to as a flexure spring, is soft in the reciprocation direction of the piston  16 , and is rigid in the direction perpendicular to the reciprocation direction. 
         [0040]    The plurality of leaf springs  23  are disposed so as to be adjacent to each other with gaps in the axial direction. The leaf springs  23  are disposed with gaps in the axial direction such that the leaf springs  23  do not come into contact with each other. For example, the gas between two leaf springs  23  adjacent to each other in the axial direction is determined such that the two leaf springs  23  do not come into contact with each other by elastic deformation generated by the reciprocation of the piston  16 . In order to maintain an appropriate gap, a spacer or a pressing member may be provided between two leaf springs  23 . 
         [0041]    In this way, an axial vibration system is configured in which the piston.  16  is provided as a mass element and the leaf spring unit  22  is provided as an elastic element. For example, the vibration system is designed so as to provide a desired resonant frequency by appropriately setting axial stiffness of each leaf spring  23  of the leaf spring unit  22 . The vibration system is driven by the linear actuator  20 . 
         [0042]    An axial movable region on design of the piston  16  is determined so as to apply a cycle of a desired volume change to the high-pressure chamber  26  (for example, pressurization chamber  38 ). For example, the axial movable region of the piston  16  may be determined such that the piston  16  (for example, piston tip portion  46 ) abuts on or comes into contact with a facing portion (for example, cylinder partition portion  64 ) of the cylinder  18  at a top dead center when the piston  16  moves forward, and the tip surface of the piston  16  is separated from the facing portion of the cylinder  18  by a predetermined distance at a bottom dead center when the piston  16  moves backward. Alternatively, the axial movable region may be determined to a predetermined separation distance such that the tip surface of the piston  16  does not come into contact with the facing portion of the cylinder  18  at the top dead center. 
         [0043]    Here, a basic operation of the linear compressor  10  will be described. As described above, the low-pressure working gas  34  is recovered from the outside of the linear compressor  10  to the low-pressure chamber  28  through the suction pipe  32 . When the piston  16  moves to the bottom dead center or the vicinity thereof, the intake valve  42  is opened and the discharge valve  44  is closed. The low-pressure working gas  34  is supplied from the second piston recessed portion  52  to the pressurization chamber  38  through the piston communication hole  56 . When the piston  16  moves forward from the bottom dead center to the top dead center, the intake valve  42  is closed, and the working gas inside the pressurization chamber  38  and the discharge chamber  40  is compressed so as to be boosted. 
         [0044]    When the piston  16  moves to the top dead center or the vicinity thereof, the discharge valve  44  is opened, and the high-pressure working gas  36  is supplied from the discharge chamber  40  to the outside of the linear compressor  10  through the discharge pipe  30 . When the piston  16  moves backward from the top dead center to the bottom dead center, the discharge valve  44  is closed, and the working gas inside the pressurization chamber  38  and the discharge chamber  40  is expanded so as to be decompressed. When the piston  16  is returned to the bottom dead center or the vicinity thereof, the intake valve  42  is opened, and the low-pressure working gas  34  is supplied to the pressurization chamber  38  again. In this way, a compression cycle is repeated in the linear compressor  10 . 
         [0045]      FIG. 3  is a sectional view schematically showing a valve structure  70  of a valved nonlubricated linear compressor according to an embodiment of the present invention. The valve structure  70  includes a valve seat portion  74  having a valve hole  72 , an elastic valve body member  76 , an elastic pressing member  78 , and a fixing member  80 . The valve structure  70  is disposed between a first gas chamber  82  and a second gas chamber  84 . The first gas chamber  82  communicates with the second gas chamber  84  through the valve hole  72 . When the valve structure  70  is closed, the valve structure  70  blocks the first gas chamber  82  from the second gas chamber  84 . The valve structure  70  blocks a flow of a working gas between the first gas chamber  82  and the second gas chamber  84  through the valve hole  72 . Meanwhile, the valve structure  70  is open, the valve structure  70  allows the first gas chamber  82  to communicate with the second gas chamber  84 . The valve structure  70  allows the flow of a working gas between the first gas chamber  82  and the second gas chamber  84  through the valve hole  72 . 
         [0046]    The valve structure  70  may be the above-described intake valve  42 . In this case, the valve hole  72  and the valve seat portion  74  respectively correspond to the piston communication hole  56  and the piston partition portion  54  shown in  FIG. 2 . The first gas chamber  82  and the second gas chamber  84  respectively correspond to the high-pressure chamber  26  and the low-pressure chamber  28 . Alternatively, the valve structure  70  may be the above-described discharge valve  44 . In this case, the valve hole  72  and the valve seat portion  74  respectively correspond to the cylinder communication on hole  66  and the cylinder partition portion  64  shown in  FIG. 2 . The first gas chamber  82  and the second gas chamber  84  respectively correspond to the discharge chamber  40  and the pressurization chamber  38 . 
         [0047]    The valve seat portion  74  includes a valve hole portion  74   a  having a valve hole  72 , and a valve body support wall portion  74   b  which extends laterally from the valve hole portion  74   a . The valve hole portion  74   a  is a portion of the valve seat portion  74  which defines the valve hole  72 , and the valve body support wall portion  74   b  which is a portion of other portions of the valve seat portion  74  which does not have the valve hole  72 . Accordingly, the valve hole portion  74   a  and the valve body support wall portion  74   b  may be respectively referred to as a wall portion with a hole and a wall portion without a hole of the valve seat portion  74 . 
         [0048]    The valve seat portion  74  extends to be flat along a surface perpendicular to the axial direction (similarly to  FIG. 2 , vertical direction in  FIG. 3 ). The valve body support wall portion  74   b  is continuous to the valve hole portion  74   a  such that the flat surface of the valve body support wall portion  74   b  is formed along with the valve hole portion  74   a . For example, in a case where the valve seat portion  74  have a circular plate shape, the valve hole portion  74   a  may occupy a semicircular region (alternatively, a fan-shaped region or an arc-shaped region) which is positioned on one side of the circular plate, and the valve body support wall portion  74   b  may occupy a semicircular region (alternatively, a fan-shaped region or an arc-shaped region) positioned on a side opposite to the valve hole portion  74   a.    
         [0049]    The elastic valve body member  76  includes a first elastic plate-shaped portion  76   a  and a second elastic plate-shaped portion.  76   b . The first elastic plate-shaped portion  76   a  is disposed along the valve hole portion  74   a  so as to cover the valve hole  72 . The second elastic plate-shaped portion  76   b  extends laterally from the first elastic plate-shaped portion  76   a  and is disposed along the valve body support wall portion  74   b . The first elastic plate-shaped portion  76   a  can be elastically deformed with respect to the second elastic plate-shaped portion  76   b  so as to open the valve hole  72  by a pressure difference between the first gas chamber  82  and the second gas chamber  84 . The elastic valve body member  76  may be a leaf spring which is soft in the axial direction and is rigid movement of the first elastic plate-shaped portion  76   a  with respect to the valve hole  72  is shown by broken lines in  FIG. 3 . The elastic valve body member  76  operates as a valve body which can be elastically displaced so as to open and close the valve hole  72 . 
         [0050]    The first elastic plate-shaped portion  76   a  and the second elastic plate-shaped portion  76   b  form an integral member (that is, elastic valve body member  76 ) which is continuous to each other. For example, in a case where the elastic valve body member  76  has a circular plate shape, the first elastic plate-shaped portion  76   a  may be a semicircular portion. (alternatively, a fan-shaped region or an arc-shaped region) which is positioned on one side of the circular plate, and the second elastic plate-shaped portion  76   b  may be a semicircular portion (alternatively, a fan-shaped region or an arc-shaped region) positioned on a side opposite to the first elastic plate-shaped portion  76   a . In addition, the elastic valve body member  76  includes a slit  76   c  which is positioned between the first elastic plate-shaped portion  76   a  and the second elastic plate-shaped portion  76   b.    
         [0051]    The elastic pressing member  78  is disposed along the second elastic plate-shaped portion  76   b  so as to be elastically deformed along with the elastic valve body member  76 . The elastic pressing member  78  has a planar shape which is defined so as to expose the first elastic plate-shaped portion  76   a . In this way, the elastic pressing member  78  is positioned at a location corresponding to the valve body support wall portion  74   b  (that is, a wall portion without a hole) of the valve seat portion  74 . The elastic pressing member  78  is not present on the valve hole portion  74   a , and thus, an upward space of the first elastic plate-shaped portion  76   a  in the axial direction is open. 
         [0052]    The elastic pressing member  78  may have the same thickness as that of the elastic valve, body member  76 . Alternatively, the elastic pressing member  78  may have a thickness different from that of the elastic valve body member  76 . By adjusting the thickness of the elastic pressing member  78 , it is possible to adjust axial stiffness of the elastic pressing member  78 . 
         [0053]    One surface of the elastic valve body member  76  is in contact with the valve seat portion  74 , and the other surface of the elastic valve body member  76  is in contact with the elastic pressing member  78 . More specifically, one surface of the first elastic plate-shaped portion  76   a  is in contact with the valve hole portion  74   a , and the other surface thereof is not in contact with any member. One surface of the second elastic plate-shaped portion  76   b  is in contact with the valve body support wall portion  74   b , and the other surface thereof is in contact with the elastic pressing member  78 . 
         [0054]    Moreover, if necessary, any plate-shaped or film-shaped member may be interposed between the elastic valve body member  76  and the valve seat portion  74 . In addition, any plate-shaped or film-shaped member may be interposed between the elastic valve body member  76  and the elastic pressing member 
         [0055]    The fixing member  80  fixes the elastic valve body member  76  and the elastic pressing member  78  to the valve seat portion.  74  in a state where the elastic valve body member  76  is interposed between the elastic pressing member  78  and the valve seat portion  74 . For example, the fixing member  80  may be a fastening member such as a bolt. Each of the valve seat portion  74 , the elastic valve body member  76 , and the elastic pressing member  78  may have a through-hole (for example, bolt hole) through which the fixing member 80 passes. 
         [0056]      FIG. 4  is a plan view schematically showing the elastic valve body member  76  shown in  FIG. 3 . The elastic valve body member  76  includes a fulcrum portion  76   d  and a connecting portion  76   e  in addition to the first elastic plate-shaped portion.  76   a  and the second elastic plate-shaped portion  76   b . The fulcrum portion  76   d  is separated from the first elastic plate-shaped portion  76   a  by the slit  76   c . The slit  76   c  is an arc-shaped slit., and partially surrounds the fulcrum portion  76   d . The connecting portion  76   e  radially extends from the fulcrum portion  76   d  to the side opposite to the slit  76   c . The connecting portion  76   e  connects the fulcrum portion  76   d  to the second elastic plate-shaped portion  76   b . The second elastic plate-shaped portion  76   b  is continuous to the first elastic plate-shaped portion  76   a  in the circumferential direction. Since a center angle of the arc-shaped slit is greater than 180°, a center angle of the connecting portion  76   e  is smaller than 180°. According to this, the first elastic plate-shaped portion  76   a  has a fan shape having a center angle which is greater than 180°, and the second elastic plate-shaped portion  76   b  has a fan shape having a center angle which is smaller than 180°. 
         [0057]    The fulcrum portion  76   d  is positioned at the center of the elastic valve body member  76 . The fulcrum portion  76   d  has a through-hole  76   f , through which the fixing member  80  passes, at the center of the fulcrum portion  76   d . Accordingly, the fulcrum portion  76   d  has an annular shape which surrounds the through-hole  76   f . The fulcrum portion  76   d  is fixed to the valve body support wall portion  74   b  by the above-described fixing member  80 . 
         [0058]      FIG. 5  is a plan view schematically showing the elastic pressing member  78  shown in  FIG. 3 . The elastic pressing member  78  has the same shape as that of a portion of the elastic valve body member  76  in a plan view. The elastic pressing member  78  includes the elastic plate-shaped portion  78   b , the fulcrum portion  78   d , and the connecting portion  78   e , which respectively have shapes similar to those of the second elastic plate-shaped portion  76   b , the fulcrum portion  76   d , and the connecting portion  78   e  of the elastic valve body member  76  in a plan view. In addition, the elastic pressing member  78  includes notches  78   c  corresponding to both ends of the slit  76   c  of the elastic valve body member  76 , and a through-hole  78   f  corresponding to the through-hole  76   f  of the elastic valve body member  76 . The fulcrum portion  78   d  of the elastic pressing member  78  is fixed to the valve body support wall portion  74   b  along with the fulcrum portion  76   d  of the elastic valve body member  76  by the above-described fixing member  80 . 
         [0059]      FIG. 6  is a top view schematically showing the valve structure  70  shown in  FIG. 3 . Accordingly, the elastic valve body member  76 , the elastic pressing member  78  and the fixing member  80  are shown in  FIG. 6 . In addition, for easy understanding, the valve holes  72  are by broken lines in  FIG. 6 . In this example, the valve structure  70  includes three valve holes  72 . 
         [0060]    As shown in  FIGS. 3 and 6 , the first elastic plate-shaped portion  76   a  is disposed so as to cover the valve holes  72 , and the second elastic plate-shaped portion  76   b  is disposed in the region in which the valve holes  72  are not present. The elastic pressing member  78  is superposed on the elastic valve body member  76 , and similarly to the second elastic plate-shaped portion  76   b , is disposed in the region in which the valve holes  72  are not present. The fixing member  80  fixes the elastic valve body member  76  and the elastic pressing member  78 . 
         [0061]    An operation of the valve structure  70  having the above-described configuration will be described. The valve structure  70  is opened and closed by the pressure difference between the first gas chamber  82  and the second gas chamber  84 . When the pressure of the first gas chamber  82  increases with respect to the pressure of the second gas chamber  84  and the pressure difference between two chambers exceeds a predetermined threshold value, the first elastic plate-shaped portion  76   a  is elastically displaced with respect to the second elastic plate-shaped portion  76   b  (arrow D in  FIG. 3 ). The first elastic plate-shaped portion  76   a  is separated from the valve hole portion  74   a . As a result, a working gas flows (arrow G in  FIG. 3 ) from the second gas chamber  84  into the first gas chamber  82  through the valve holes  72 . Accordingly, the valve structure  70  is opened. 
         [0062]    Thereafter, when the pressure difference between the two chambers is lower than the predetermined threshold value, the first elastic plate-shaped portion  76   a  is returned (arrow E in  FIG. 3 ) to the initial position by a restoring force. The first elastic plate-shaped portion  76   a  comes into contact with the valve hole portion  74   a  again. The flow of the working gas from the second gas chamber  84  to the first gas chamber  82  is blocked. Accordingly, the valve structure  70  is closed. 
         [0063]      FIG. 7  is a sectional view schematically showing a portion of a reed valve having a stopper  86 . The stopper  86  is disposed such that the tip portion thereof is separated from the valve hole  88  in the axial direction. A reed valve body  90  is separated from the stopper  86  so as to cover the valve hole  88 . As shown by broken lines, when the reed valve body  90  opens the valve hole  88 , an axial movement of the reed valve body  90  is restricted by the stopper  86 . Since a lift amount of the reed valve body  90  is limited, a flow rate of the gas flowing through the valve is relatively small. In addition, collision of the reed valve body  90  with respect to the stopper  86  may generate noise. 
         [0064]    However, according to the embodiment described with reference to  FIGS. 1 to 6 , the above of the first elastic plate-shaped portion  76   a  in the axial direction is open, and the valve structure  70  does not have the stopper which limits the movement of the elastic valve body member  76 . Accordingly, it is possible to relatively increase the lift amount of the elastic valve body member  76 . The flow rate of the gas flowing through the valve structure  70  increases, and the flow rate of the gas discharged by the linear compressor  10  increases. In addition, since the stopper is not present, collision noise generated by opening and closing of the valve structure  70  decreases. 
         [0065]    When the first elastic plate-shaped portion  76   a  is axially displaced, the second elastic plate-shaped portion  76   b  is elastically deformed. The elastic pressing member  78  is elastically deformed according the elastic deformation of the second elastic plate-shaped portion  76   b  In this way, the elastic pressing member  78  is integrally deformed with elastic valve body member  76 , compared with a case where the elastic pressing member  78  is not present, it is possible to alleviate stress when the elastic valve body member  76  is elastically deformed. For example, stress concentration in the connection portion  76   e  and the second elastic plate-shaped portion  76   b  is alleviated. Accordingly, it is possible to prolong a service life of the elastic valve body member  76 . 
         [0066]    In addition, the planar shape of the elastic valve body member  76  contributes an increase in the lift amount. The first elastic plate-shaped portion  76   a  is separated from the fulcrum portion  76   d  by the slit  76   c  and the first elastic plate-shaped portion  76   a  is connected to the fulcrum portion  76   d  by the second elastic plate-shaped portion  76   b  and the connecting portion  76   e . In addition, the fulcrum portion  76   d  is positioned at the center of the elastic valve body member  76 . In this way, it is possible to lengthen the spring length of the elastic valve body member  76 . Accordingly, the valve structure  70  having a large lift amount is obtained. 
         [0067]      FIG. 8  is a sectional view schematically showing the valve structure  70  of a valved nonlubricated linear compressor according to another embodiment of the present invention. As shown in  FIG. 8 , the elastic valve body member  76  includes a fluoropolymer layer  92 . A contact surface between the elastic valve body member  76  and the valve seat portion  74  is covered with the fluoropolymer layer  92 . Moreover, both surfaces of the elastic valve body member  76  may be covered with the fluoropolymer layers  92 . For example, the fluoropolymer layer  92  is formed of polytetrafluoroethylene (PTFE). Accordingly, it is possible to decrease collision noise between the elastic valve body member  76  and the valve seat portion  74 . In addition, seal performance during closing of the valve structure  70 , that is, sealability of the valve hole  72   b  the elastic valve body member  76  is improved. 
         [0068]      FIG. 9  is a sectional view schematically showing the valve structure  70  of a valved nonlubricated linear compressor according to still another embodiment of the present invention. The valve structure  70  includes a fluoropolymer member  94  which is disposed between the valve seat portion  74  and the elastic valve body member  76 . The fluoropolymer member  94  may be a film, a sheet, or a plate which is formed of a fluoropolymer such as polytetrafluoroethylene (PTFE). The fluoropolymer member  94  is disposed along the valve seat portion  74 . One surface of the fluoropolymer member  94  is in contact with the valve seat portion  74 , and the other surface of the fluoropolymer member  94  is in contact with the elastic valve body member  76 . 
         [0069]    The fluoropolymer member  94  has a planar shape similar to the elastic valve body member  76  except for having the opening portion  96 . The opening portion  96  is formed at the location corresponding to the valve hole  72 . Accordingly, the working gas passes through the valve hole  72  and the opening portion  96 . The opening portion  96  may be a hole, a slit, or other opening portions. 
         [0070]    The fluoropolymer member  94  may have the same thickness as that of the elastic valve body member  76 . Alternatively, the fluoropolymer member  94  may have a thickness different from that of the elastic valve body member  76 . In this way, the thickness of the fluoroplymer member  94  can be greater than that of the fluoropolymer layer  92  shown in  FIG. 8 . This contributes a decrease in collision noise between the elastic valve body member  76  and the valve seat portion  74 . 
         [0071]    The opening portion  96  may be a hole having the same shape as that of the valve hole  72 . The opening portion  96  may be a hole having a shape different from that of the valve hole  72 . For example, the opening portion  96  may be a hole which is smaller than the valve hole  72 . In a case where the fluoropolymer member  94  has flexibility in the axial direction, and it is possible to axially lift the fluoropolymer member  94  by interaction between the working gas passing through the valve hole  72  and the fluoropolymer member  94 . This contributes a decrease in noise during opening and closing of the valve structure  70 . 
         [0072]    It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.