Abstract:
A cryogenic refrigerator includes a first cylinder and a second cylinder, a first displacer and a second displacer configured to reciprocate inside the first cylinder and the second cylinder, respectively, an intake and outlet system configured to alternately perform a first operation of supplying gas to the first cylinder and discharging the gas from the second cylinder and a second operation of discharging the gas from the first cylinder and supplying the gas to the second cylinder, a communication path configured to communicate the first cylinder with the second cylinder, and an opening and closing part configured to open and close the communication path.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2012-040635, filed on Feb. 27, 2012, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a cryogenic refrigerator that produces cryogenic temperatures by causing the Simon expansion using a high-pressure refrigerant gas fed from a compressor. 
         [0004]    2. Description of the Related Art 
         [0005]    As cryogenic refrigerators have been used for a wider variety of purposes, there is a demand for increases in their outputs. Conventionally, as a common practice for improving the performance of the cryogenic refrigerator, it has been performed to increase the diameter of a cylinder, the stroke length of a displacer, and the high-low pressure difference of a refrigerant gas of the cryogenic refrigerator. In addition to the above, it has been proposed to combine multiple compressors and multiple expanders as described in, for example, Japanese Laid-Open Patent Application No. 11-257772. 
       SUMMARY OF THE INVENTION 
       [0006]    According to an aspect of the present invention, a cryogenic refrigerator includes a first cylinder and a second cylinder; a first displacer and a second displacer configured to reciprocate inside the first cylinder and the second cylinder, respectively; an intake and outlet system configured to alternately perform a first operation of supplying gas to the first cylinder and discharging the gas from the second cylinder and a second operation of discharging the gas from the first cylinder and supplying the gas to the second cylinder; a communication path configured to communicate the first cylinder with the second cylinder; and an opening and closing part configured to open and close the communication path. 
         [0007]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0008]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and not restrictive of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a schematic diagram illustrating a cryogenic refrigerator according to an embodiment of the present invention; 
           [0011]      FIG. 2  is a schematic diagram illustrating a connection mechanism of the cryogenic refrigerator according to the embodiment; 
           [0012]      FIG. 3  is a diagram illustrating a configuration of a first displacer and a second displacer according to the embodiment; 
           [0013]      FIG. 4  is a schematic diagram illustrating a Scotch yoke mechanism of the cryogenic refrigerator according to the embodiment; 
           [0014]      FIG. 5  is a timing chart illustrating valve timing of valves of the cryogenic refrigerator according to this embodiment; 
           [0015]      FIG. 6  is a timing chart illustrating the valve timing of the cryogenic refrigerator along with the positions of the first and second displacers, the pressures inside first and second cylinders, and pressures on the high-pressure side and the low-pressure side of a compressor according to the embodiment; and 
           [0016]      FIG. 7  is a schematic diagram illustrating a variation of the embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    As described above, it has been proposed to combine multiple compressors and multiple expanders. According to the above-described conventional art, however, the compressor unit including multiple compressors increases in size and decreases in efficiency, and an increase in operational loads on the compressor unit is likely to reduce the useful service life of the compressor unit. That is, the conventional art has yet to provide a cryogenic refrigerator that makes it possible to achieve higher output more efficiently. 
         [0018]    According to an aspect of the present invention, a cryogenic refrigerator is provided that makes it possible to achieve higher output more efficiently. 
         [0019]    According to a cryogenic refrigerator of an embodiment of the present invention, the opening operation of an opening and closing part allows a high-pressure refrigerant gas taken in into one of a first cylinder and a second cylinder from a compressor to be provided to the other one of the first cylinder and the second cylinder. Likewise, a high-pressure refrigerant gas is allowed to be provided from the other one to the one of the first cylinder and the second cylinder. This reduces variations on both the high-pressure side and the low-pressure side of the compressor, so that it is possible to reduce operational loads on the compressor. 
         [0020]    A description is given below, with reference to the accompanying drawings, of one or more embodiments of the present invention. 
         [0021]      FIG. 1  and  FIG. 2  are diagrams for illustrating a cryogenic refrigerator  1  according to an embodiment of the present invention.  FIG. 1  is a diagram illustrating a piping structure of the cryogenic refrigerator  1 .  FIG. 2  is a diagram illustrating a drive structure of the cryogenic refrigerator  1 . The cryogenic refrigerator  1  of this embodiment is a Gifford-McMahon (GM) refrigerator that uses helium gas as a refrigerant gas. 
         [0022]    First, a description is given of the piping structure of the cryogenic refrigerator  1 . As illustrated in  FIG. 1 , the cryogenic refrigerator  1  includes a first cylinder  2 , a first displacer  3 , a second cylinder  4 , a second displacer  5 , an intake and outlet system  6  including a group of pipes and a group of valves V 1 , V 2 , V 3 , and V 4 , a connecting pipe  7  (a communication path), and a communicating valve V 5  (an opening and closing part). The cryogenic refrigerator  1  further includes a microcomputer (not graphically illustrated) as a control part that controls the opening and closing of the valves V 1  through V 4  and the communicating valve V 5 . The group of pipes of the intake and outlet system  6  includes a first supply pipe  61 , a first outlet pipe  62 , a second supply pipe  63 , a second outlet pipe  64 , a first supply and outlet common pipe  65 , and a second supply and outlet common pipe  66 . The first supply pipe  61  has a first end connected to a high-pressure side H of a compressor  8 . The first supply pipe  61  has a second end connected to the first supply and outlet common pipe  65  that is connected to the first cylinder  2 . The first intake valve V 1  is provided in a middle portion of the first supply and outlet common pipe  65 . 
         [0023]    The second supply pipe  63  has a first end connected to a middle portion of the first supply pipe  61 . The second supply pipe  63  has a second end connected to the second supply and outlet common pipe  66  connected to the second cylinder  4 . The second intake valve V 3  is provided in a middle portion of the second supply and outlet common pipe  66 . 
         [0024]    The second outlet pipe  64  has a first end connected to a low-pressure side L of the compressor  8 . The second outlet pipe  64  has a second end connected to the second supply and outlet common pipe  66  connected to the second cylinder  4 . The second outlet valve V 4  is provided in a middle portion of the second supply and outlet common pipe  66 . 
         [0025]    The first outlet pipe  62  has a first end connected to a middle portion of the second outlet pipe  64 . The first outlet pipe  62  has a second end connected to the first supply and outlet common pipe  65  connected to the first cylinder  2 . The first outlet valve V 2  is provided in a middle portion of the first supply and outlet common pipe  65 . 
         [0026]    The connecting pipe  7  has a first end connected to the first supply and outlet common pipe  65 , and has a second end connected to the second supply and outlet common pipe  66 . The communicating valve V 5  is provided in a middle portion of the connecting pipe  7 . 
         [0027]    Next, a description is given, with reference to  FIG. 2 , of the drive structure of the cryogenic refrigerator  1 . The first cylinder  2  has a bottomed cylinder (tube) shape, and encloses the first displacer  3 . The second cylinder  4  has a bottomed cylinder (tube) shape, and encloses the second displacer  5 . 
         [0028]    The first cylinder  2  and the second cylinder  4  include a common flange part  90 . The upper end of the first cylinder  2  and the upper end of the second cylinder  4  are open at the upper surface of the flange part  90 . The upper end of the first cylinder  2  and the upper end of the second cylinder  4  are hermetically closed by a common lid part  9 . 
         [0029]    The first cylinder  2  and the second cylinder  4  are disposed side by side in the rightward and the leftward direction in  FIG. 2 . Further, a columnar support member  21  that extends upward through an insertion hole  9   c  formed in the lid part  9  is provided on a wall face part  8   a  of the upper surface of the flange part  90  between the upper end openings of the first cylinder  2  and the second cylinder  4 . The support member  21  is fixed to the through hole  9   c.    
         [0030]    Next, a description is given, with reference to  FIG. 3 , of a configuration of the first displacer  3  and the second displacer  5  of this embodiment. The first displacer  3  and the second displacer  5  have the same configuration. Therefore, in  FIG. 3 , a description is given using the first displacer  3  and a description of the second displacer  5  is omitted. Further, when necessary, the reference numerals of components of the second displacer  5  are shown in parentheses. 
         [0031]    A first expansion space  113 A is formed between the low temperature end of the first displacer  3  and the first cylinder  2 . A second expansion space  113 B is formed between the low temperature end of the second displacer  5  and the second cylinder  4 . Referring to  FIG. 1  and  FIG. 3 , a cooling stage  10  is thermally coupled to the peripheries of the first and second expansion spaces  113 A and  113 B of the first and second cylinders  2  and  4 . The cooling stage  10  is formed of, for example, copper, aluminum, stainless steel or the like. 
         [0032]    The first cylinder  2  accommodates the first displacer  3  in such a manner as to allow the first displacer  3  to reciprocate in the longitudinal directions of the first cylinder  2  (the directions of arrows Z 1  and Z 2  in  FIG. 3 ). The second cylinder  4  accommodates the second displacer  5  in such a manner as to allow the second displacer  5  to reciprocate in the longitudinal directions of the second cylinder  4  (the directions of arrows Z 1  and Z 2  in  FIG. 3 ). For example, stainless steel is used for the first cylinder  2  and the second cylinder  4  in terms of ensuring strength, thermal conductivity, helium blocking capability, etc. 
         [0033]    Each of the first displacer  3  and the second displacer  5  has a cylindrical shape, and has a channel space formed inside where a refrigerant gas flows. The channel space is filled with a regenerator material to form a regenerator  117 . 
         [0034]    A room temperature chamber  108 A is formed between the first cylinder  2  and the high temperature end of the first displacer  3 . A room temperature chamber  108 B is formed between the second cylinder  4  and the high temperature end of the second displacer  5 . 
         [0035]    The room temperature chambers  108 A and  108 B are spaces that change in volume with the reciprocations of the first displacer  3  and the second displacer  5 , respectively. The above-described first supply and outlet common pipe  65  is connected to the room temperature chamber  108 A, and the above-described second supply and outlet common pipe  66  is connected to the room temperature chamber  108 B. An upper flow rectifier  109  that rectifies (regulates) a flow of helium gas is provided on the upper end side, that is, the room temperature chamber  108 A or  108 B side, of each regenerator  117 . A lower flow rectifier  110  is provided on the lower end side of each regenerator  117 . 
         [0036]    An opening  111  through which helium gas flows from the first room temperature chamber  108 A or the second room temperature chamber  108 B into the refrigerator  117  is formed at the high temperature end of each of the first displacer  3  and the second displacer  5 . 
         [0037]    An opening  116  through which helium gas is introduced into or let out of the first expansion space  113 A or the second expansion space  113 B is formed at the low temperature end of each of the first displacer  3  and the second displacer  5 . 
         [0038]    The first expansion space  113 A and the second expansion space  113 B change in volume with the reciprocations of the first displacer  3  and the second displacer  5 , respectively. A seal member  115  is attached between part of the first displacer  3  near its high temperature end and the first cylinder  2  and between part of the second displacer  5  near its high temperature end and the second cylinder  4 . 
         [0039]    For example, Bakelite (phenol containing cloth) or the like is used for the first displacer  3  and the second displacer  5  in view of specific gravity, abrasion resistance, strength, and thermal conductivity. The regenerator material is formed of, for example, a wire mesh. 
         [0040]    The cryogenic refrigerator  1  includes a drive mechanism that drives the first displacer  3  and the second displacer  5  in different phases. The drive mechanism includes a Scotch yoke mechanism  70  and a connection mechanism  80 . 
         [0041]      FIG. 4  is a schematic diagram illustrating the Scotch yoke mechanism  70 . The Scotch yoke mechanism  70  includes a crank member  77  and a Scotch yoke  78 . The crank member  77  is connected to an output shaft (motor shaft)  74  of a motor (a drive part). The crank member  77  includes a crank pin  75  that is eccentric to the output shaft  74  and extends parallel to the output shaft  74 . The Scotch yoke  78  includes a horizontally elongated frame part  32  in which a window part  34  is formed, a drive shaft  31 , and a cylindrical crank pin bearing  11 . The frame part  32  is formed in a middle portion of the drive shaft  31 . That is, the frame part  32  forms part of the drive shaft  31 . 
         [0042]    As illustrated in  FIG. 2 , the lower end of the drive shaft  31  is fixed to an upper part of the first displacer  3 . The crank pin bearing  11  is rollably provided in the window part  34 . The crank pin  75  is slidably received by the inner wall surface of the crank pin bearing  11 . By this configuration, the Scotch yoke mechanism  70  converts the rotational driving force generated by the motor into a driving force to cause the first displacer  3  to reciprocate vertically (in the Z 1  and the Z 2  direction in  FIG. 2 ) through the rotational motion of the crank member  77 . 
         [0043]    As illustrated in  FIG. 2 , the drive shaft  31  projects upward and outward from the upper part of the first displacer  3  through an insertion hole  9   a  of the lid part  9 . Further, a driven shaft  51  is fixed to an upper part of the second displacer  5 . The driven shaft  51  projects upward and outward from the upper part of the second displacer  5  through an insertion hole  9   b  of the lid part  9 . 
         [0044]    As illustrated in  FIG. 2 , the cryogenic refrigerator  1  includes the connection mechanism  80  that connects the Scotch yoke mechanism  70  (the drive shaft  31 ) and the driven shaft  51 . The connection mechanism  80  includes a first arm (link) part  12 , a second arm (link) part  13 , and the support member  21 . One of the first arm part  12  and the second arm part  13  may be omitted. 
         [0045]    The first arm part  12  has a first end part  12   a,  a second end part  12   b,  and a center part  12   c  rotatably connected to an upper end part of the drive shaft  31 , an upper end part of the driven shaft  51 , and an upper part of the support member  21 , respectively, by connecting members  16  such as pins. 
         [0046]    The second arm part  13  has a first end part  13   a,  a second end part  13   b,  and a center part  13   c  rotatably connected to part of the drive shaft  31  below the frame part  32 , a middle part of the driven shaft  51 , and a middle part of the support member  21 , respectively, by connecting members  17  such as pins. 
         [0047]    That is, the first arm part  12  and the second arm part  13  have their respective center parts  12   c  and  13   c  connected to the support member  21 , being vertically spaced apart from each other, so as to be oscillatable in directions indicated by arrows A 1  and A 2  in  FIG. 2  about the points of connection. 
         [0048]    Referring to  FIG. 4  as well, the crank pin  75  is rotated by the motor, so that the crank pin bearing  11  causes the drive shaft  31  and the first displacer  3  to vertically reciprocate while sliding (rolling) in the longitudinal directions of the window part  34 . 
         [0049]    Following this reciprocation, the first arm part  12  and the second arm part  13 , having their respective first ends  12   a  and  13   a  connected to the drive shaft  31 , oscillate in the A 1  and the A 2  direction of  FIG. 2  about their points of connection to the support member  21 . That is, when the drive shaft  31  slides upward (in the Z 1  direction in  FIG. 2 ), the first arm part  12  and the second arm part  13  oscillate in the direction of arrow A 2  in  FIG. 2 , so that the driven shaft  51 , which is connected to the second end parts  12   b  and  13   b  of the first arm part  12  and the second arm part  13 , slides downward (in the Z 2  direction in  FIG. 2 ). Further, when the drive shaft  31  slides downward, the first arm part  12  and the second arm part  13  oscillate in the direction of arrow A 1  of  FIG. 2 , so that the driven shaft  51  slides upward. As a result of such sliding motions (vertical movements) of the drive shaft  31  and the driven shaft  51  due to the oscillations of the first arm part  12  and the second arm part  13 , the first displacer  3  and the second displacer  5  connected to the drive shaft  31  and the driven shaft  51  vertically reciprocate in antiphase. 
         [0050]    Next, a description is given, with reference to the timing charts of  FIG. 5  and  FIG. 6 , of operations of the first intake valve V 1 , the first outlet valve V 2 , the second intake valve V 3 , the second outlet valve V 4 , and the communicating valve V 5 , that is, the valve timing VT, of the cryogenic refrigerator  1 . For convenience of graphical representation, the valve timing VT, which is indicated by a bold line in  FIG. 5 , is schematically illustrated with blocks in (e) of  FIG. 6 . 
         [0051]    The vertical axis represents the opening and closing states of the five valves V 1  through V 5  in  FIG. 5 , and the horizontal axis represents time in  FIG. 5  and  FIG. 6 . The starting point of the horizontal axis is time t 0 . The operations of the five valves V 1  through V 5  are determined based on the positions of the first displacer  3  and the second displacer  5  illustrated in Position DP of (a) of  FIG. 6 . In (a) of  FIG. 6 , the position DP of the first displacer  3  is indicated by a solid line, and the position DP of the second displacer  5  is indicated by a broken line. As is clear from (a) of  FIG. 6 , the first displacer  3  and the second displacer  5  are driven to be opposite in phase. With respect to Pressure P illustrated in (b) of  FIG. 6 , the pressure inside the expansion space  113 A of the first cylinder  2  is indicated by a solid line, and the pressure inside the expansion space  113 B of the second cylinder  4  is indicated by a broken line. 
         [0052]    Time t 1  of  FIG. 5  and  FIG. 6  is slightly before the time at which the position DP of the second displacer  5  is at the bottom dead center D. At time t 1 , the communicating valve V 5  is opened by the control part, and continues to be open for a predetermined period of time so as to allow high-pressure helium gas inside the second cylinder  4  to be supplied into the first cylinder  2  via the connecting pipe  7 . 
         [0053]    This predetermined period of time is determined based on the time taken for the pressure P inside the second cylinder  4  to lower from high pressure H to low pressure L (lowering time) or the time taken for the pressure P inside the first cylinder  2  to rise from low pressure L to high pressure H (rising time) illustrated in (b) of  FIG. 6 . This lowering time or rising time may be determined by, for example, an experiment or a simulation, and in general, the predetermined period of time is determined to be approximately the half of the lowering time or rising time. That is, at time t 2 , when the predetermined period of time has passed, the pressure P inside the second cylinder  4  and the pressure P inside the first cylinder  2  are substantially equal. 
         [0054]    At time t 2 , that is, after continuation of the open state of the communicating valve V 5  for the predetermined period of time, the communicating valve V 5  is closed by the control part. Further, at time t 2 , the first intake valve V 1  is opened to allow high-pressure helium gas to be supplied from the high-pressure side H of the compressor  8  into the first cylinder  2  via the first supply pipe  61  and the first supply and outlet common pipe  65 , so that the pressure P inside the first cylinder  2  is caused to be high H. Further, at time t 3 , when a predetermined period of time has passed since time t 2 , the first intake valve V 1  is closed. 
         [0055]    Likewise, at time t 2 , the second outlet valve V 4  is opened to allow helium gas inside the second cylinder  4  to be discharged to the low-pressure side L of the compressor  8  via the second supply and outlet common pipe  66  and the second outlet pipe  64 , so that the pressure P inside the second cylinder  4  is caused to be low L. Further, at time t 3 , when the predetermined period of time has passed since time t 2 , the second outlet valve V 4  is closed. 
         [0056]    Time t 4  in  FIG. 5  and  FIG. 6  is slightly before the time at which the position DP of the first displacer  3  is at the bottom dead center D. At time t 4 , the communicating valve V 5  is opened by the control part, and continues to be open for a predetermined period of time so as to allow high-pressure helium gas inside the first cylinder  2  to be supplied into the second cylinder  4  via the connecting pipe  7 . At time t 5 , when the predetermined period of time has passed since time t 4 , the pressure P inside the second cylinder  4  and the pressure P inside the first cylinder  2  are substantially equal. 
         [0057]    At time t 5 , that is, after continuation of the open state of the communicating valve V 5  for the predetermined period of time, the communicating valve V 5  is closed by the control part. Further, at time t 5 , the second intake valve V 3  is opened to allow high-pressure helium gas to be supplied from the high-pressure side H of the compressor  8  into the second cylinder  4  via the second supply pipe  63  and the second supply and outlet common pipe  66 , so that the pressure P inside the second cylinder  4  is caused to be high H. Further, at time t 6 , when a predetermined period of time has passed since time t 5 , the second intake valve V 3  is closed. 
         [0058]    Likewise, at time t 5 , the first outlet valve V 2  is opened to allow helium gas inside the first cylinder  2  to be discharged to the low-pressure side L of the compressor  8  via the first supply and outlet common pipe  65  and the first outlet pipe  62 , so that the pressure P inside the first cylinder  2  is caused to be low L. Further, at time t 6 , when the predetermined period of time has passed since time t 5 , the first outlet valve V 2  is closed. 
         [0059]    The valve operations between time t 7  and time t 9  are equal to but are delayed by one cycle of the reciprocation of the first displacer  3  or the second displacer  5  relative to the valve operations between time t 1  and time t 3 . Further, the valve operations between time t 10  and time t 12  are equal to but are delayed by one cycle of the reciprocation of the first displacer  3  or the second displacer  5  relative to the valve operations between time t 4  and time t 6 . 
         [0060]    Next, a description is given, with reference to  FIG. 1  through  FIG. 3  as well, of an operation of the cryogenic refrigerator  1  of this embodiment as a refrigerator. For convenience of description, a description is given of a refrigerating operation performed by the first cylinder  2  and the first displacer  3 . In the following description, the position of the first displacer  3  that maximizes the volume of the expansion space  113 A is determined as the bottom dead center D, and the position of the first displacer  3  that minimizes the volume of the expansion space  113 A is determined as the top dead center U. 
         [0061]    At some point in the helium gas supply process, the second displacer  5  is positioned at the top dead center U in the second cylinder  4 . At a time slightly before that point, that is, between time t 1  and time t 2  of  FIG. 5  and  FIG. 6 , the communicating valve V 5  is opened for a predetermined period of time by the control part. 
         [0062]    High-pressure helium gas inside the second cylinder  4  flows into the first cylinder  2  via the communicating valve V 5  and the connecting pipe  7 , so that the pressure inside the second cylinder  4  decreases and the pressure inside the first cylinder  2  increases. After passage of a predetermined period of time since the communicating valve V 5  is opened, the communicating valve V 5  is closed, the first intake valve V 1  is opened, and the second outlet valve V 4  is opened by the control part. 
         [0063]    High-pressure helium gas flows from the high-pressure side H of the compressor  8  into the first cylinder  2  via the first supply pipe  61  and the first supply and outlet common pipe  65 . High-pressure helium gas inside the second cylinder  4  flows into the low-pressure side L of the compressor  8  via the second supply and outlet common pipe  66  and the second outlet pipe  64 . 
         [0064]    The high-pressure helium gas is supplied into the first cylinder  2  to flow into the regenerator  117  inside the first displacer  3  through the opening  111  positioned at the top of the first displacer  3 . The high-pressure helium gas that has flown into the regenerator  117  is fed into the first expansion space  113 A via the opening  116  positioned at the bottom of the displacer  3  while being cooled by the regenerator material. 
         [0065]    Thus, the first expansion space  113 A is filled with the high-pressure helium gas, and the first intake valve V 1  is closed as described above. At this time, the first displacer  3  is positioned at the bottom dead center D inside the first cylinder  2 . When the first outlet valve V 2  is opened slightly before this time, the helium gas of the first expansion space  113 A adiabatically expands. The helium gas of the first expansion space  113 A whose temperature has been lowered by the adiabatic expansion absorbs the heat of the cooling stage  10 . 
         [0066]    The first displacer  3  moves toward the top dead center U, so that the volume of the first expansion space  113 A decreases. The helium gas inside the first expansion space  113 A is returned to the intake side, that is, the low-pressure side L, of the compressor  8  via the opening  116 , the regenerator  117 , and the opening  111 . At this point, the regenerator material is cooled by the helium gas. This process is employed as one cycle, and the cryogenic refrigerator  1  cools the cooling stage  10  by repeating this cooling cycle. 
         [0067]    According to the cryogenic refrigerator  1  of this embodiment, using the first displacer  3  and the corresponding first cylinder  2  and the second displacer  5  and the corresponding second cylinder  4  as a pair, it is possible to cause the paired first and second cylinders  2  and  4  to supply a high-pressure refrigerant gas to each other without the intervention of the compressor  8  based on suitable opening and closing of the communicating valve V 5  by causing the first displacer  3  and cylinder  2  and the second displacer  5  and cylinder  4  to operate in antiphase to each other. 
         [0068]    In  FIG. 6 , as a reference example, valve timing VT( 4 V) in a four-valve GM refrigerator that is not provided with the communicating valve V 5  and the connecting pipe  7  of this embodiment is illustrated in (c). According to this valve timing VT( 4 V), the first intake valve V 1  is open and the second outlet valve V 4  is open between time t 1  and time t 3 , and the second intake valve V 3  is open and the first outlet valve V 2  is open between time t 4  and time t 6 . 
         [0069]    The waveform of pressure variations on the high-pressure side and the waveform of pressure variations on the low-pressure side of a compressor in this case of the four-valve GM refrigerator are illustrated as PV( 4 V) in (d) of  FIG. 6 . Further, the waveform of pressure variations on the high-pressure side H and the waveform of pressure variations on the low-pressure side L of the compressor  8  in the five-valve cryogenic refrigerator  1  of this embodiment are illustrated as PV in (f) of  FIG. 6 . 
         [0070]    The comparison of these waveforms shows that the pressure range of PV is reduced to approximately the half of the pressure range of PV( 4 V). Specifically, a pressure range ΔH 1  on the high-pressure side H of this embodiment illustrated in (f) of  FIG. 6  is smaller than a pressure range ΔH 2  on the high-pressure side of the reference example illustrated in (d) of  FIG. 6  (ΔH 1 &lt;ΔH 2 ). The same applies to the pressure range on the low-pressure side L of this embodiment. 
         [0071]    That is, according to this embodiment, it is possible to reduce the pressure variations of the compressor  8  by feeding high-pressure helium gas from a high-pressure side cylinder to a low-pressure side cylinder at the initial stage of the intake and the outlet operation. 
         [0072]    Therefore, according to the cryogenic refrigerator  1  of this embodiment, it is possible to reduce operational loads on the compressor  8 . Accordingly, a compressor unit including the compressor  8  is prevented from increasing in size or degrading in efficiency. Further, according to this embodiment, it is possible to reduce pressure variations, so that it is possible to control reduction in the useful service life of the compressor unit due to an increase in its operational loads. In addition, it is possible to reduce the workload of the compressor  8 , so that it is possible to save energy. 
         [0073]    In this embodiment, the configuration is illustrated where the first through fourth valves V 1  through V 4  and the communicating valve V 5  included in the intake and outlet system  6  are independent solenoid valves, while these valves V 1  through V 5  may be replaced with a valve plate and an valve body that form a known rotary valve. 
         [0074]    In this case, the rotary valve may be configured by connecting the valve plate to the output shaft  74  of the motor (drive part) that drives the Scotch yoke mechanism  70  positioned above the lid part  9  of the first cylinder  2  and the second cylinder  4  illustrated in  FIG. 2 , and suitably fixing the valve body above the lid part  9 . That is, the control part may be omitted in the case of using a rotary valve. 
         [0075]    All examples and conditional language provided herein are intended for pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority or inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 
         [0076]    For example, in the above-described embodiment, the case is illustrated where the number of stages is one in the cryogenic refrigerator  1 , while this number of stages may be suitably selected from two, three, etc. Further, the number of pairs of displacers is not limited to one, and may be two or more. 
         [0077]      FIG. 7  is a diagram illustrating a configuration where multiple pairs of displacers are provided according to a variation of the above-described embodiment. It is possible to drive multiple pairs of displacers with the single Scotch yoke mechanism  70  by connecting the connection mechanisms  80  by connecting members  85  as indicated by one-dot chain lines in  FIG. 7 . In this case, the intake and outlet system  6  including the compressor  8  may be shared by the multiple pairs of displacers. 
         [0078]    Further, in the above-described embodiment, a description is given of the case where the cryogenic refrigerator is a GM refrigerator. However, the present invention is not limited to this, and embodiments of the present invention may also be applied to any refrigerators having a displacer, such as Stirling refrigerators and Solvay cycle refrigerators. Further, the definitions of the top dead center and the bottom dead center may be opposite to the above-described definitions. Further, the above-illustrated method of determining a predetermined period of time or a fixed time is a mere example, and a predetermined period of time or a fixed time may be defined as another proportion based on the lowering time or rising time. 
         [0079]    According to an aspect of the present invention, it is possible to reduce operational loads on a compressor by using one or more pairs of displacers and corresponding cylinders and causing a high-pressure refrigerant gas to be fed between the paired cylinders without the intervention of the compressor in cryogenic refrigerators. That is, according to an aspect of the present invention, a compressor unit including the compressor is prevented from increasing in size or degrading in efficiency. Further, according to an aspect of the present invention, it is possible to prevent reduction in the useful service life of the compressor unit due to an increase in its operational loads. Therefore, embodiments of the present invention may be applied to various kinds of cryogenic refrigerators.