Abstract:
A rotary valve mechanism includes a stator valve member furnished with one of either a dome-shaped high-pressure recess area made of a polymer or a high-pressure flow path made of metal, and a rotor valve member furnished with the other of either the dome-shaped high-pressure recess area made of a polymer or the high-pressure flow path made of metal, and seals a high-pressure region being the high-pressure flow path communicated with the dome-shaped high-pressure recess area and is disposed adjoining the stator valve member such as to isolate the high-pressure region from its low-pressure surrounding environs.

Description:
INCORPORATION BY REFERENCE 
       [0001]    Priority is claimed to Japanese Patent Application No. 2015-257052, filed Dec. 28, 2015, the Entire Content of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present invention in particular embodiments relates to cryocoolers and rotary valve mechanisms for cryocoolers. 
         [0004]    Description of Related Art 
         [0005]    Cryocoolers, typified by Gifford-McMahon (GM) cryocoolers, include working-gas (also called refrigerant-gas) expanders and compressors. Expanders for the most part include a displacer that is axially reciprocated by a driving means, and a regenerator that is built into the displacer. The displacer is accommodated in a cylinder that guides its reciprocation. The variable volume that by the relative movement of the displacer with respect to the cylinder is formed between the two is employed as the working-gas expansion chamber. By appropriately synchronizing expansion-chamber volume change and pressure change, the expander is able to produce coldness. 
         [0006]    For that purpose, the cryocooler is furnished with a valve unit for controlling the pressure of the expansion chamber. The valve unit is configured so as to switch alternately between supply of high-pressure working gas from the compressor to the expander, and recovery of low-pressure working gas from the expander to the compressor. The usual practice is to employ a rotary valve mechanism as the valve unit. The valve unit is also furnished in other cryocoolers such as pulse-tube refrigerators. 
       SUMMARY 
       [0007]    The present invention in one aspect affords a cryocooler including: a working gas compressor provided with a compressor expulsion port and a compressor suction port; an expander provided with a gas expansion chamber and a low-pressure gas chamber communicated with the compressor suction port; a stator valve member disposed in the low-pressure gas chamber, and provided with a stator-side rotary sliding surface, a high-pressure gas inlet port opening on the stator-side rotary sliding surface and communicated with the compressor expulsion port, and a gas venting port opening on the stator-side rotary sliding surface and communicated with the gas expansion chamber; and a rotor-valve polymer member disposed in the low-pressure gas chamber such as to rotate about an axis with respect to the stator valve member and configured such as to isolate a rotor valve high-pressure recess area from the low-pressure gas chamber, the rotor valve high-pressure recess area being formed such as to communicate the high-pressure gas inlet port with the gas venting port in a portion of a single cycle of rotation of the rotor-valve polymer member and to cut off the high-pressure gas inlet port from the gas venting port in the remainder of the single cycle. The rotor-valve polymer member includes a rotor-valve outer peripheral surface facing the low-pressure gas chamber, a rotor-side rotary sliding surface surrounding the rotor valve high-pressure recess area, and in surface-contact with the stator-side rotary sliding surface, a recess-area bottom wall surface facing the rotor valve high-pressure recess area, a recess-area peripheral wall surface forming a recess-area contour line on the rotor-side rotary sliding surface and extending from the recess-area contour line and directed toward the recess-area bottom wall surface, the polymer&#39;s thickness toward the rotor-valve outer peripheral surface varies running along the recess-area contour line, and a first thin-walled polymer portion having a first minimum polymer thickness from the recess-area peripheral wall surface to the rotor valve outer peripheral surface, and including a first inclination join region connecting the recess-area bottom wall surface to the recess-area peripheral wall surface and being inclined with respect to both the recess-area bottom wall surface and the recess-area peripheral wall surface. 
         [0008]    The present invention in another aspect affords a cryocooler rotary valve mechanism including: a stator valve member disposed in a low-pressure gas chamber of a cryocooler, and provided with a stator-side rotary sliding surface, a high-pressure gas inlet port opening on the stator-side rotary sliding surface, and a gas venting port opening on the stator-side rotary sliding surface; a rotor-valve polymer member disposed in the low-pressure gas chamber such as to rotate about an axis with respect to the stator valve member and configured such as to isolate a rotor valve high-pressure recess area from the low-pressure gas chamber, the rotor valve high-pressure recess area being formed such as to communicate the high-pressure gas inlet port with the gas venting port in a portion of a single cycle of rotation of the rotor-valve polymer member and to cut off the high-pressure gas inlet port from the gas venting port in the remainder of the single cycle. The rotor valve resin member includes a rotor-valve outer peripheral surface facing the low-pressure gas chamber, a rotor-side rotary sliding surface surrounding the rotor valve high-pressure recess area, and in surface-contact with the stator-side rotary sliding surface, a recess-area bottom wall surface facing the rotor valve high-pressure recess area, a recess-area peripheral wall surface forming a recess-area contour line on the rotor-side rotary sliding surface and extending from the recess-area contour line and directed toward the recess-area bottom wall surface, the polymer&#39;s thickness toward the rotor-valve outer peripheral surface varies running along the recess-area contour line, and a thin-walled polymer portion having a minimum polymer thickness from the recess-area peripheral wall surface to the rotor valve outer peripheral surface, and including a first inclination join region connecting the recess-area bottom wall surface to the recess-area peripheral wall surface and being inclined with respect to both the recess-area bottom wall surface and the recess-area peripheral wall surface. 
         [0009]    The present invention in still another aspect affords a rotary valve mechanism including: a stator valve member furnished with one of either a dome-shaped high-pressure recess area made of a polymer or a high-pressure flow path made of metal; and a rotor valve member furnished with the other of either the dome-shaped high-pressure recess area made of a polymer or the high-pressure flow path made of metal, and seals a high-pressure region being the high-pressure flow path communicated with the dome-shaped high-pressure recess area and is disposed adjoining the stator valve member such as to isolate the high-pressure region from its low-pressure surrounding environs. 
         [0010]    It should be understood that among methods, devices, systems, etc. of the present invention, those in which constituent elements or representations have been interchanged are valid as modes of the present invention as well. 
         [0011]    The present invention enables improved reliability in cryocooler rotary-valve mechanisms. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a view which schematically shows the entire configuration of a cryocooler according to an embodiment of the present invention and schematically shows a cross section of an expander of the cryocooler. 
           [0013]      FIG. 2  is an exploded perspective view schematically showing a main portion of a rotary valve which may be used in the cryocooler shown in  FIG. 1 . 
           [0014]      FIG. 3  is a perspective view schematically showing a rotor valve member which may be used in the cryocooler shown in  FIG. 1 . 
           [0015]      FIG. 4  is a view showing a simulation result of a flow rate of a working gas in a high-pressure flow path with respect to the rotor valve member shown in  FIG. 3 . 
           [0016]      FIG. 5  is a perspective view schematically showing a rotor valve member according to an embodiment of the present invention. 
           [0017]      FIG. 6  is a view showing a simulation result of von Mises stress applied to the rotor valve member shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    It is desirable to improve reliability of a rotary valve mechanism of a cryocooler. 
         [0019]    Hereinafter, an embodiment 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 are appropriately omitted. Moreover, configurations described below are exemplified and do not limit the scope of the present invention. 
         [0020]    In one embodiment, a rotary valve mechanism of a cryocooler includes a stator valve member formed of metal (or a resin) and a rotor valve member which rotationally slides on the stator valve member and is formed of a resin (or metal). The stator valve member and the rotor valve member may be respectively referred to as a stator valve plate and a rotor valve plate. 
         [0021]    The rotary valve mechanism is installed in a low-pressure chamber which is filled with a relatively low-pressure working gas. A metal member includes a high-pressure flow path for a high-pressure working gas, and the high-pressure flow path is formed to penetrate the metal member. A resin member includes a dome-shaped high-pressure recessed portion for a high-pressure working gas. A dome-shaped recessed portion is formed in which a cross section perpendicular in a depth direction of the recessed portion gradually decreases in the depth direction. The dome-shaped recessed portion is formed by an arbitrary processing method. For example, the dome-shaped recessed portion may be formed by fillet processing or chamfering processing. The rotor valve member seals a high-pressure region in which the high-pressure flow path of metal communicates with the dome-shaped high-pressure recessed portion of a resin, and is disposed to be adjacent to the stator valve member to separate the high-pressure region from the a low-pressure surrounding environment. The dome-shaped recessed portion may communicate with the high-pressure flow path in at least a portion of a rotation of one period of the rotary valve mechanism and may block the high-pressure flow path in other portions of the rotation. 
         [0022]    Accordingly, at least a portion (particularly, a portion facing the high-pressure region) of solid portions of the rotor valve member and the stator valve member functions as a pressure partition wall which receives a load of a differential pressure between a high pressure and a low pressure. In the dome-shaped recessed portion, the thickness of the partition wall portion gradually increases in the depth direction. Accordingly, stress which is applied to the surface of the dome-shaped recessed portion or the inside of the partition wall decreases. Particularly, a decrease of stress in a thin portion of the resin member reduces damage risk at the location and improves reliability of the rotary valve mechanism. In addition, since the surface of the dome-shaped recessed portion does not have a sharp corner portion which significantly influences the flow of the working gas, a decrease in pressure loss of the flow of the working gas and improvement in refrigeration performance are realized. 
         [0023]      FIG. 1  is a view schematically showing a cryocooler  10  according to an embodiment of the present invention. The cryocooler  10  includes a compressor  12  which compresses a working gas and an expander  14  which cools the working gas by adiabatic expansion. For example, the working gas is helium gas. The expander  14  may be also referred to as a cold head. A regenerator  16  which pre-cools the working gas is included in the expander  14 . The cryocooler  10  includes a gas pipe  18  which includes a first pipe  18   a  and a second pipe  18   b  which are respectively connected to the compressor  12  and the expander  14 . The shown cryocooler  10  is a single-staged GM cryocooler. 
         [0024]    As is well known, a working gas having a first high pressure is supplied from a discharging port  12   a  of the compressor  12  to the expander  14  through the first pipe  18   a . The pressure of the working gas is decreased from the first high pressure to a second high pressure which is lower than the first high pressure due to adiabatic expansion in the expander  14 . The working gas having the second high pressure is returned from the expander  14  to a suction port  12   b  of the compressor  12  through the second pipe  18   b . The compressor  12  compresses the returned working gas having the second high pressure. Accordingly, the pressure of the working gas increases to the first high pressure again. In general, the first high pressure and the second high pressure are significantly higher than the atmospheric pressure. For convenience of descriptions, the first high pressure and the second high pressure are simply referred to as a high pressure and a low pressure, respectively. Typically, for example, the high pressure is 2 to 3 MPa, and the low pressure is 0.5 to 1.5 MPa. For example, a difference between the high pressure and the low pressure is approximately 1.2 to 2 MPa. 
         [0025]    The expander  14  includes an expander movable portion  20  and an expander stationary portion  22 . The expander movable portion  20  is configured so as to reciprocate in an axial direction (up-down direction in  FIG. 1 ) with respect to the expander stationary portion  22 . The movement direction of the expander movable portion  20  is indicated by an arrow A in  FIG. 1 . The expander stationary portion  22  is configured so as to support the expander movable portion  20  to be reciprocated in the axial direction. In addition, the expander stationary portion  22  is configured of an airtight container in which the expander movable portion  20  is accommodated along with a high-pressure gas (including first high-pressure gas and second high-pressure gas). 
         [0026]    The expander movable portion  20  includes a displacer  24  and a displacer drive shaft  26  which reciprocates the displacer  24 . A regenerator  16  is built in the displacer  24 . The displacer  24  includes a displacer member  24   a  which surrounds the regenerator  16 . An internal space of the displacer member  24   a  is filled with a regenerator material. Accordingly, the regenerator  16  is formed inside the displacer  24 . For example, the displacer  24  has a substantially columnar shape which extends in the axial direction. The displacer member  24   a  includes an outer diameter and an inner diameter which are substantially constant in the axial direction. Accordingly, the regenerator  16  also has a substantially columnar shape which extends in the axial direction. 
         [0027]    The expander stationary portion  22  approximately has two configurations which includes a cylinder  28  and a drive mechanism housing  30 . The upper portion of the expander stationary portion  22  in the axial direction is the drive mechanism housing  30 , the lower portion of the expander stationary portion  22  in the axial direction is the cylinder  28 , and the drive mechanism housing  30  and the cylinder  28  are firmly connected to each other. The cylinder  28  is configured to guide the reciprocation of the displacer  24 . The cylinder  28  extends in the axial direction from the drive mechanism housing  30 . The cylinder  28  has an inner diameter which is substantially constant in the axial direction. Accordingly, the cylinder  28  has a substantially cylindrical inner surface which extends in the axial direction. The inner diameter is slightly greater than the outer diameter of the displacer member  24   a.    
         [0028]    Moreover, the expander stationary portion  22  includes a cooling stage  32 . The cooling stage  32  is fixed to the terminal of the cylinder  28  on the side opposite to the drive mechanism housing  30  in the axial direction. The cooling stage  32  is provided so as to transfer coldness generated by the expander  14  to other objects. The objects are attached to the cooling stage  32 , and are cooled by the cooling stage  32  during the operation of the cryocooler  10 . 
         [0029]    During the operation of the cryocooler  10 , the regenerator  16  includes a regenerator high-temperature portion  16   a  on one side (upper side in the drawing) in the axial direction, and a regenerator low-temperature portion  16   b  on the side (lower side in the drawing) opposite to the regenerator high-temperature portion  16   a . In this way, the regenerator  16  has a temperature distribution in the axial direction. Similarly, other components (for example, displacer  24  and cylinder  28 ) of the expander  14  which surrounds the regenerator  16  also have axial temperature distributions. Accordingly, the expander  14  includes a high-temperature portion on one side in the axial direction and a low-temperature portion on the other side in the axial direction during the operation of the expander  14 . For example, the high-temperature portion has a temperature such as an approximately room temperature. The cooling temperatures of the low-temperature portion are different from each other according to the use of the cryocooler  10 , and for example, the low-temperature portion is cooled to a temperature which is included in a range from approximately 10 K to approximately 10 0 K. The cooling stage  32  is fixed to the cylinder  28  to enclose the low-temperature portion of the cylinder  28 . 
         [0030]    In the present specification, for convenience of the description, terms such as an axial direction, a radial direction, and a circumferential direction are used. As shown by an arrow A, the axial direction indicates the movement direction of the expander movable portion  20  with respect to the expander stationary portion  22 . The radial direction indicates a direction (horizontal direction in the drawing) perpendicular to the axial direction, and the circumferential direction indicates a direction which surrounds the axial direction. An element of the expander  14  being close to the cooling stage  32  in the axial direction may be referred to “down”, and the element being far from the cooling stage  32  in the axial direction may be referred to as “up.” Accordingly, the high-temperature portion and the low-temperature portion of the expander  14  are respectively positioned on the upper portion and the lower portion in the axial direction. The expressions are used so as to only assist understanding of a relative positional relationship between elements of the expander  14 . Accordingly, the expressions are not related to the disposition of the expander  14  when the expander  14  is installed in site. For example, in the expander  14 , the cooling stage  32  may be installed upward and the drive mechanism housing  30  may be installed downward. Alternatively, the expander  14  may be installed such that the axial direction coincides with the horizontal direction. 
         [0031]    In addition, terms such as the axial direction, the radial direction, and the circumferential direction are used with respect to the rotary valve mechanism. In this case, the axial direction indicates the direction of the rotary shaft of the rotary valve mechanism. 
         [0032]    The configuration of the flow path of the working gas in the expander  14  is described. The expander  14  includes a valve portion  34 , a housing gas flow path  36 , an upper gas chamber  37 , a displacer upper-lid gas flow path  38 , a displacer lower-lid gas flow path  39 , a gas expansion chamber  40 , and a low-pressure gas chamber  42 . A high-pressure gas flows from the first pipe  18   a  to the gas expansion chamber  40  via the valve portion  34 , the housing gas flow path  36 , the upper gas chamber  37 , the displacer upper-lid gas flow path  38 , the regenerator  16 , and the displacer lower-lid gas flow path  39 . The gas returned to the gas expansion chamber  40  flows to the low-pressure gas chamber  42  via the displacer lower-lid gas flow path  39 , the regenerator  16 , the displacer upper-lid gas flow path  38 , the upper gas chamber  37 , the housing gas flow path  36 , and the valve portion  34 . 
         [0033]    Although it is described below in detail, the valve portion  34  is configured to control the pressure of the gas expansion chamber  40  to be synchronized with the reciprocation of the displacer  24 . The valve portion  34  functions as a portion of a supply path for supplying a high-pressure gas to the gas expansion chamber  40 , and function as a portion of a discharging path for discharging a low-pressure gas from the gas expansion chamber  40 . The valve portion  34  is configured to end the discharging of the low-pressure gas and to start the supply of the high-pressure gas when the displacer  24  passes a bottom dead center or the vicinity thereof. The valve portion  34  is configured to end the supply of the high-pressure gas and to start the discharging of the low-pressure gas when the displacer  24  passes a top dead center or the vicinity thereof. In this way, the valve portion  34  is configured to switch the supply function and the discharging function of the working gas to be synchronized with the reciprocation of the displacer  24 . 
         [0034]    The housing gas flow path  36  is formed so as to penetrate the drive mechanism housing  30  such that gas flows between the expander stationary portion  22  and the upper gas chamber  37 . 
         [0035]    The upper gas chamber  37  is formed between the expander stationary portion  22  and the displacer  24  on the regenerator high-temperature portion  16   a  side. More specifically, the upper gas chamber  37  is interposed between the drive mechanism housing  30  and the displacer  24  in the axial direction, and is surrounded by the cylinder  28  in the circumferential direction. The upper gas chamber  37  is adjacent to the low-pressure gas chamber  42 . The upper gas chamber  37  is also referred to as a room temperature chamber. The upper gas chamber  37  is a variable volume which is formed between the expander movable portion  20  and the expander stationary portion  22 . 
         [0036]    The displacer upper-lid gas flow path  38  is at least one opening of the displacer member  24   a  which is formed to allow the regenerator high-temperature portion  16   a  to communicate with the upper gas chamber  37 . The displacer lower-lid gas flow path  39  is at least one opening of the displacer member  24   a  which is formed to allow the regenerator low-temperature portion  16   b  to communicate with the gas expansion chamber  40 . A seal portion  44  which seals a clearance between the displacer  24  and the cylinder  28  is provided on the side surface of the displacer member  24   a . The seal portion  44  may be attached to the displacer member  24   a  so as to surround the displacer upper-lid gas flow path  38  in the circumferential direction. 
         [0037]    The gas expansion chamber  40  is formed between the cylinder  28  and the displacer  24  on the regenerator low-temperature portion  16   b  side. Similarly to the upper gas chamber  37 , the gas expansion chamber  40  is a variable volume which is formed between the expander movable portion  20  and the expander stationary portion  22 , and the volume of the gas expansion chamber  40  is complementarily changed with the volume of the upper gas chamber  37  by the relative movement of the displacer  24  with respect to the cylinder  28 . Since the seal portion  44  is provided, a direct gas flow (that is, the flow of gas which bypasses the regenerator  16 ) between the upper gas chamber  37  and the gas expansion chamber  40  is not generated. 
         [0038]    The low-pressure gas chamber  42  defines the inside of the drive mechanism housing  30 . The second pipe  18   b  is connected to the drive mechanism housing  30 . Accordingly, the low-pressure gas chamber  42  communicates with the suction port  12   b  of the compressor  12  through the second pipe  18   b . Therefore, the low-pressure gas chamber  42  is always maintained to a low pressure. 
         [0039]    The displacer drive shaft  26  protrudes from the displacer  24  to the low-pressure gas chamber  42  through the upper gas chamber  37 . The expander stationary portion  22  includes a pair of drive shaft guides  46   a  and  46   b  which support the displacer drive shaft  26  in the axial direction in a movable manner. Each of the drive shaft guides  46   a  and  46   b  is provided in the drive mechanism housing  30  so as to surround the displacer drive shaft  26 . The drive shaft guide  46   b  positioned on the lower side in the axial direction or the lower end section of the drive mechanism housing  30  is airtightly configured. Accordingly, the low-pressure gas chamber  42  is separated from the upper gas chamber  37 . The direct gas flow between the low-pressure gas chamber  42  and the upper gas chamber  37  is not generated. 
         [0040]    The expander  14  includes a drive mechanism  48  which is accommodated in the low-pressure gas chamber  42  and drives the displacer  24 . The drive mechanism  48  includes a motor  48   a  and a scotch yoke mechanism  48   b . The displacer drive shaft  26  forms a portion of the scotch yoke mechanism  48   b . In addition, the scotch yoke mechanism  48   b  includes a crank pin  49  which extends to be parallel to the output shaft of the motor  48   a  and is eccentric to the output shaft. The displacer drive shaft  26  is connected to the scotch yoke mechanism  48   b  to be driven in the axial direction by the scotch yoke mechanism  48   b . Accordingly, the displacer  24  is reciprocated in the axial direction by the rotation of the motor  48   a . The scotch yoke mechanism  48   b  is interposed between the drive shaft guides  46   a  and  46   b , and the drive shaft guides  46   a  and  46   b  are positioned at different positions from each other in the axial direction. 
         [0041]    The valve portion  34  is connected to the drive mechanism  48  and is accommodated in the drive mechanism housing  30 . The valve portion  34  is a rotary valve type. The valve portion  34  includes a rotor valve resin member (hereinafter, may be simply referred to as a rotor valve member)  34   a  and a stator valve metal member (hereinafter, may be simply referred to as a stator valve member)  34   b . That is, the rotor valve member  34   a  is formed of a resin material (for example, engineering plastic material or fluoropolymer material), and the stator valve member  34   b  is formed of metal (for example, aluminum material or steel material). Conversely, the rotor valve member  34   a  may be formed of metal and the stator valve member  34   b  is formed of a resin. 
         [0042]    The rotor valve member  34   a  is connected to the output shaft of the motor  48   a  so as to be rotated by the rotation of the motor  48   a . The rotor valve member  34   a  is in surface-contact with the stator valve member  34   b  so as to rotationally slide on the stator valve member  34   b . The stator valve member  34   b  is fixed to the drive mechanism housing  30 . The stator valve member  34   b  is configured so as to receive the high-pressure gas which enters the drive mechanism housing  30  from the first pipe  18   a.    
         [0043]    The operation of the cryocooler  10  having the above-described configuration is described. When the displacer  24  moves to the bottom dead center of the cylinder  28  or the position around the bottom dead center, the valve portion  34  is switched to connect the discharging port  12   a  of the compressor  12  to the gas expansion chamber  40 . An intake process of the cryocooler  10  starts. The high-pressure gas enters the regenerator high-temperature portion  16   a  through the housing gas flow path  36 , the upper gas chamber  37 , and the displacer upper-lid gas flow path  38  from the valve portion  34 . The gas is cooled while passing through the regenerator  16  and enters the gas expansion chamber  40  through the displacer lower-lid gas flow path  39  from the regenerator low-temperature portion  16   b . While the gas flows into the gas expansion chamber  40 , the displacer  24  moves toward the top dead center of the cylinder  28 . Accordingly, the volume of the gas expansion chamber  40  increases. In this way, the gas expansion chamber  40  is filled with a high-pressure gas. 
         [0044]    When the displacer  24  moves to the top dead center of the cylinder  28  or the position around the top dead center, the valve portion  34  is switched so as to connect the suction port  12   b  of the compressor  12  to the gas expansion chamber  40 . The intake process ends and an exhaust process starts. The high-pressure gas is expanded in the gas expansion chamber  40 . The expanded gas enters the regenerator  16  through the displacer lower-lid gas flow path  39  from the gas expansion chamber  40 . The gas is cooled while passing through the regenerator  16 . The gas is returned from the regenerator  16  to the compressor  12  via the housing gas flow path  36 , the valve portion  34 , and the low-pressure gas chamber  42 . While the gas flows out from the gas expansion chamber  40 , the displacer  24  moves toward the bottom dead center of the cylinder  28 . Accordingly, the volume of the gas expansion chamber  40  decreases and a low-pressure gas is discharged from the gas expansion chamber  40 . If the exhaust process ends, the intake process starts again. 
         [0045]    The above-described process is one-time cooling cycle in the cryocooler  10 . The cryocooler  10  repeats the cooling cycle and cools the cooling stage  32  to a desired temperature. Accordingly, the cryocooler  10  can cool an object which is thermally connected to the cooling stage  32  to a cryogenic temperature. 
         [0046]      FIG. 2  is an exploded perspective view schematically showing a main portion of an exemplary rotary valve used in the cryocooler  10  shown in  FIG. 1 . A dashed line Y shown in  FIG. 2  indicates a rotary shaft of the valve portion  34 . 
         [0047]    The stator valve member  34   b  has a flat stator-side rotary sliding surface  50 , and similarly to the stator valve member  34   b  and a rotor valve member  134   a  has a flat rotor-side rotary sliding surface  52 . The stator-side rotary sliding surface  50  and the rotor-side rotary sliding surface  52  are perpendicular to the rotation axis Y. Since the stator-side rotary sliding surface  50  and the rotor-side rotary sliding surface  52  are in surface-contact with each other, leakage of a refrigerant gas is prevented. 
         [0048]    The stator valve member  34   b  is fixed to the inside of the drive mechanism housing  30  by a stator valve fixing pin  54 . The stator valve fixing pin  54  engages with a stator valve end surface  51  which is positioned on the side opposite to the stator-side rotary sliding surface  50  of the stator valve member  34   b  in the rotation axis direction, and regulates the rotation of the stator valve member  34   b.    
         [0049]    The rotor valve member  134   a  is rotatably supported by a rotor valve bearing  56  shown in  FIG. 1 . An engagement hole (not shown) which engages with the crank pin  49  is formed on a rotor valve end surface  58  which is positioned on the rotor-side rotary sliding surface  52  of the rotor valve member  134   a  in the rotation axis direction. The motor  48   a  rotates the crank pin  49 , and thereby, the rotor valve member  134   a  rotates so as to be synchronized with the scotch yoke mechanism  48   b . Moreover, the rotor valve member  134   a  includes a rotor valve outer peripheral surface  60  which connects the rotor-side rotary sliding surface  52  to the rotor valve end surface  58 . The rotor valve outer peripheral surface  60  is supported by the rotor valve bearing  56  and faces the low-pressure gas chamber  42 . 
         [0050]    The stator valve member  34   b  includes a high-pressure gas inlet port  62  and a gas flow port  64 . The high-pressure gas inlet port  62  is opened to the center portion of the stator-side rotary sliding surface  50 , and is formed to penetrate the center portion of the stator valve member  34   b  in the rotation axis direction. The high-pressure gas inlet port  62  communicates with the discharging port  12   a  of the compressor  12  through the first pipe  18   a . The gas flow port  64  is opened outside the high-pressure gas inlet port  62  in the radial direction on the stator-side rotary sliding surface  50 . The gas flow port  64  is formed in an approximately arc-shaped groove with the high-pressure gas inlet port  62  as a center. 
         [0051]    The stator valve member  34   b  includes a communication path  66  which is formed so as to penetrate the stator valve member  34   b  to connect the gas flow port  64  to the housing gas flow path  36 . Accordingly, the gas flow port  64  finally communicates with the gas expansion chamber  40  via the communication path  66  and the housing gas flow path  36 . One end of the communication path  66  is opened to the gas flow port  64  and the other end thereof is opened to the side surface of the stator valve member  34   b . While the portion of the communication path  66  on the gas flow port  64  side extends in the rotation axis direction, the portion of the communication path  66  on the housing gas flow path  36  side which is orthogonal to the portion of communication path  66  on the gas flow port  64  side extends in the radial direction. 
         [0052]    The low-pressure returned gas flows from the gas expansion chamber  40  to the gas flow port  64  in the exhaust process while the high-pressure gas flows to the gas flow port  64  in the intake process of the cryocooler  10 . 
         [0053]    The rotor valve member  134   a  includes a rotor valve high-pressure recessed portion  68  and a rotor valve opening portion  70 . The rotor-side rotary sliding surface  52  is in surface-contact with the stator-side rotary sliding surface  50  around the rotor valve high-pressure recessed portion  68 . Similarly, the rotor-side rotary sliding surface  52  is in surface-contact with the stator-side rotary sliding surface  50  around the rotor valve opening portion  70 . 
         [0054]    The rotor valve high-pressure recessed portion  68  is opened to the rotor-side rotary sliding surface  52  and is formed in an elliptical groove. The rotor valve high-pressure recessed portion  68  extends from the center portion of the rotor-side rotary sliding surface  52  to the outside in the radial direction. The depth of the rotor valve high-pressure recessed portion  68  is smaller than the length of the rotor valve member  134   a  in the rotation axis direction, and the rotor valve high-pressure recessed portion  68  does not penetrate the rotor valve member  134   a . One end of the rotor valve high-pressure recessed portion  68  in the radial direction is positioned at the location corresponding to the high-pressure gas inlet port  62  on the rotor-side rotary sliding surface  52 . Accordingly, the rotor valve high-pressure recessed portion  68  is connected to the high-pressure gas inlet port  62  always. The other end in the radial direction of the rotor valve high-pressure recessed portion  68  is formed so as to be positioned on approximately the same circumference as that of the gas flow port  64  of the stator valve member  34   b.    
         [0055]    In this way, the intake valve is configured in the valve portion  34 . The rotor valve high-pressure recessed portion  68  is configured so as to allow the high-pressure gas inlet port  62  to communicate with the gas flow port  64  in a portion (for example, intake process) of one period of the rotation of the rotor valve member  134   a , and allow the high-pressure gas inlet port  62  not to communicate with the gas flow port  64  in a remaining portion (for example, exhaust process) of the one period. Two areas configured of the rotor valve high-pressure recessed portion  68  and the high-pressure gas inlet port  62 , or three areas configured of the rotor valve high-pressure recessed portion  68 , the high-pressure gas inlet port  62 , and the gas flow port  64  form high-pressure regions (or high-pressure flow paths) which communicate with each other in the valve portion  34 . The rotor valve member  134   a  seals the high-pressure region and is disposed to be adjacent to the stator valve member  34   b  so as to separate the high-pressure region from the low-pressure surrounding environment (that is, low-pressure gas chamber  42 ). The rotor valve high-pressure recessed portion  68  is provided as a flow direction changing portion or a flow path folding portion in the high-pressure flow path of the valve portion  34 . 
         [0056]    Meanwhile, the rotor valve opening portion  70  is an arc-shaped hole which penetrates from the rotor-side rotary sliding surface  52  of the rotor valve member  134   a  to the rotor valve end surface  58 , and forms a low-pressure flow path which communicates with the low-pressure gas chamber  42 . The rotor valve opening portion  70  is positioned on approximately the side opposite to the outer end section of the rotor valve high-pressure recessed portion  68  in the radial direction with respect to the center portion of the rotor-side rotary sliding surface  52 . The rotor valve opening portion  70  is formed so as to be positioned on approximately the same circle as that of the gas flow port  64  of the stator valve member  34   b . In this way, the exhaust valve is configured in the valve portion  34 . The rotor valve member  134   a  is configured to allow the gas flow port  64  to communicate with the low-pressure gas chamber  42  in at least a portion (for example, exhaust process) of the period in which the high-pressure gas inlet port  62  does not communicate with the gas flow port  64 . 
         [0057]      FIG. 3  is a perspective view schematically showing a rotor valve member  234   a  which is used in the cryocooler  10  shown in  FIG. 1 . Similarly to the rotor valve member  134   a  shown in  FIG. 2 , the rotor valve member  234   a  includes the rotor valve high-pressure recessed portion  68  and the rotor valve opening portion  70  and functions as an intake/exhaust valve. 
         [0058]    The rotor valve member  234   a  includes a recessed portion bottom wall surface  72  and the recessed portion peripheral wall surface  74 . The recessed portion bottom wall surface  72  faces the rotor valve high-pressure recessed portion  68  and determines the depth of the rotor valve high-pressure recessed portion  68 . The recessed portion bottom wall surface  72  is parallel to the rotor-side rotary sliding surface  52  and is perpendicular to the rotation axis direction. The recessed portion peripheral wall surface  74  forms an elliptical recessed portion outline  76  on the rotor-side rotary sliding surface  52  and extends from the recessed portion outline  76  to the recessed portion bottom wall surface  72 . The recessed portion peripheral wall surface  74  intersects the recessed portion bottom wall surface  72  so as to be perpendicular to the recessed portion bottom wall surface  72 , and forms an edge line  78 . Accordingly, the edge line  78  has the same dimension and shape as those of the recessed portion outline  76 . The rotor valve opening portion  70  is formed in a fan-shaped through hole. 
         [0059]    The resin thickness of the rotor valve member  234   a  is changed along the recessed portion outline  76  from the recessed portion peripheral wall surface  74  to the rotor valve outer peripheral surface  60 , and the rotor valve member  234   a  includes a first thinned-wall resin portion  80  and a second thinned-wall resin portion  82 . The first thinned-wall resin portion  80  has a first minimum resin thickness  84  from the recessed portion peripheral wall surface  74  to the rotor valve outer peripheral surface  60 . The second thinned-wall resin portion  82  has a second minimum resin thickness  86  from the recessed portion peripheral wall surface  74  to the rotor valve opening portion  70 . The first minimum resin thickness  84  and the second minimum resin thickness  86  may be the same as each other or may be different from each other. The first minimum resin thickness  84  may be larger than or may be smaller than the second minimum resin thickness  86 . 
         [0060]    The recessed portion outline  76  includes a first arc-shaped portion  76   a , a second arc-shaped portion  76   b , a first linear portion  76   c , and a second linear portion  76   d . The first arc-shaped portion  76   a  and the second arc-shaped portion  76   b  are respectively positioned on the first thinned-wall resin portion  80  and the second thinned-wall resin portion  82 . The first linear portion  76   c  and the second linear portion  76   d  connect the first arc-shaped portion  76   a  to the second arc-shaped portion  76   b . The first linear portion  76   c  and the second linear portion  76   d  extends from the center portion on the rotor-side rotary sliding surface  52  to the outside in the radial direction, and the gap between the first linear portion  76   c  and the second linear portion  76   d  gradually increases from the center portion toward the outside in the radial direction. The width of the outer portion of the rotor valve high-pressure recessed portion  68  in the radial direction is wider than that of the center portion. Since the gas flow port  64  of the stator valve member  34   b  is positioned on the outside in the radial direction, according to the shape of the rotor valve high-pressure recessed portion  68 , it is possible to extend the intake period of the cryocooler  10  to some extent. 
         [0061]      FIG. 4  is a view showing a simulation result of a flow rate of a working gas in the high-pressure flow path in the valve portion  34  with respect to the rotor valve member  234   a  shown in  FIG. 3 . In the drawing, a region in which the flow rate is small is indicated by a dark gray, and a region in which the flow rate is great is indicated by a light gray. 
         [0062]    As understood from the drawing, the flow of the working gas from the high-pressure gas inlet port  62  of the stator valve member  34   b  to the gas flow port  64  is folded at the rotor valve high-pressure recessed portion  68 , a region  92  having a small flow rate is generated in the vicinity of the edge line  78 . The region  92  is little used as a flow path, and generates pressure loss in the flow. A fillet surface-shaped boundary  94  is formed between the region  92  and the gas flow region inside the rotor valve high-pressure recessed portion  68 . 
         [0063]      FIG. 5  is a perspective view schematically showing the rotor valve member  34   a  according to an embodiment of the present invention. Similarly to the rotor valve member  134   a  shown in  FIG. 2  and the rotor valve member  234   a  shown in  FIG. 3 , the rotor valve member  34   a  includes the rotor valve high-pressure recessed portion  68  and the rotor valve opening portion  70 , and functions as an intake/exhaust valve. 
         [0064]    The first thinned-wall resin portion  80  and the second thinned-wall resin portion  82  respectively include a first inclination joint region  88  and the second inclination joint region  90 . The first inclination joint region  88  connects the recessed portion bottom wall surface  72  to the recessed portion peripheral wall surface  74  and is inclined with respect to each of the recessed portion bottom wall surface  72  and the recessed portion peripheral wall surface  74 . The second inclination joint region  90  connects the recessed portion bottom wall surface  72  to the recessed portion peripheral wall surface  74  and is inclined with respect to each of the recessed portion bottom wall surface  72  and the recessed portion peripheral wall surface  74 . 
         [0065]    As shown in the drawing, the rotor valve member  34   a  includes a fillet surface which connects the recessed portion bottom wall surface  72  to the recessed portion peripheral wall surface  74  over the entire periphery of the recessed portion peripheral wall surface  74 . The first inclination joint region  88  and the second inclination joint region  90  form a portion of the fillet surface. In this way, the recessed portion bottom wall surface  72  of the rotor valve member  34   a  is formed in a dome shape. The rotor valve high-pressure recessed portion  68  does not have the edge line  78  which is included in the rotor valve member  234   a  shown in  FIG. 3 , and is smoothly curved from the recessed portion peripheral wall surface  74  to the recessed portion bottom wall surface  72 . 
         [0066]    The dome-shaped recessed portion bottom wall surface  72  determines the maximum depth of the rotor valve high-pressure recessed portion  68  from the rotor-side rotary sliding surface  52 . The first minimum resin thickness  84  and the second minimum resin thickness  86  is smaller than the maximum depth. In this way, the resin thickness of the rotor valve member  34   a  is relatively thin. This contributes to a decrease in the size of the rotor valve member  34   a.    
         [0067]    From the viewpoint of easiness of fillet processing, the fillet surface has a fillet radius which is smaller than the radius of the first arc-shaped portion  76   a  or the second arc-shaped portion  76   b . In addition, the fillet radius is greater than 1/10 of the radius of the arc-shaped portion. Accordingly, it is possible to obtain stress alleviation effects in the first thinned-wall resin portion  80  and the second thinned-wall resin portion  82 . It is possible to obtain greater stress alleviation effects by increasing the fillet radius. 
         [0068]    Similarly to the rotor valve member  234   a  shown in  FIG. 3 , the first linear portion  76   c  and the second linear portion  76   d  extends from the center portion on the rotor-side rotary sliding surface  52  to the outside in the radial direction, and the gap between the first linear portion  76   c  and the second linear portion  76   d  gradually increases from the center portion toward the outside in the radial direction. 
         [0069]    As described above, the rotor valve member  34   a  may be formed of a fluoropolymer material. In this case, the fillet surface may have a fillet radius which is determined such that the maximum value of von Mises Stress applied to the recessed portion peripheral wall surface  74  is smaller than ⅓ (or ⅕) of the tensile strength of the fluoropolymer material. The fillet radius may be determined such that the maximum value of von Mises stress applied to the recessed portion peripheral wall surface  74  is smaller than ⅕ of the tensile strength of the fluoropolymer material. In this way, it is possible to sufficiently decrease a damage risk of the rotor valve member  34   a  in the first thinned-wall resin portion  80  and the second thinned-wall resin portion  82  in the practical use by designing the rotor valve high-pressure recessed portion  68  as described above. In addition, the fillet radius may be determined such that the maximum value of von Mises stress applied to the recessed portion peripheral wall surface  74  is larger than ⅙ (or ⅛) of the tensile strength of the fluoropolymer material. 
         [0070]      FIG. 6  is a view showing a simulation result of the von Mises stress applied to the rotor valve member  34   a  shown in  FIG. 5 .  FIG. 6  shows the simulation result during the operation of the cryocooler  10  (that is, a state where the pressure of the region inside the rotor valve high-pressure recessed portion  68  is high and the pressure of the region (low-pressure gas chamber  42 ) around the rotor valve member  34   a  is low). In the drawing, a region in which the stress is great is indicated by dark gray, and a region in which the stress is small is indicated by light gray. In this simulation model, the rotor valve opening portion  70  is omitted. 
         [0071]    As understood from the drawing, the maximum value of the von Mises stress is generated in the inner surface of the first thinned-wall resin portion  80  facing the rotor valve high-pressure recessed portion  68 . The maximum value is approximately 6.66 MPa. Here, the tensile strength of the used fluoropolymer material is approximately 37 MPa. Accordingly, the maximum value of the von Mises stress is smaller than ⅕ of the tensile strength of the used material. 
         [0072]    Meanwhile, according to the simulation result under the same conditions, in the rotor valve member  234   a  shown in  FIG. 3  having the edge line  78 , similarly, the maximum value of the von Mises stress is generated on the inner surface of the first thinned-wall resin portion  80 , and the value is approximately 8.5 MPa. 
         [0073]    In this way, according to the present embodiment, it is possible to decrease the stress applied to the thin portion by providing the inclination joint region on the thinned-wall resin portion of the rotor valve member  34   a . The damage risk is decreased by the thin portion, and it is possible to improve reliability of the rotary valve mechanism. In addition, the dome-shaped recessed portion bottom wall surface  72  is formed along the boundary  94  shown in  FIG. 4 . The region  92  contributing to the pressure loss is embedded in the material so as to form a smooth curved surface. Accordingly, it is possible to decrease the pressure loss of the flow of the working gas and improve refrigeration performance of the cryocooler  10 . 
         [0074]    Hereinbefore, the present invention is described based on the embodiment. The present invention is not limited to the embodiment, and a person skilled in the art understands various design modifications can be applied, various modification examples can be applied, and the modification examples are also included in the scope of the present invention. 
         [0075]    In the above-described embodiment, the first inclination joint region  88  and the second inclination joint region  90  are formed on the fillet surface. However, the present invention is not limited to this. The first inclination joint region  88  and/or the second inclination joint region  90  may be a flat inclined surface (for example, a surface which is chamfered by 45°, or a surface which is chamfered by an arbitrary angle). 
         [0076]    In the above-described example, the embodiment is described in which the cryocooler is a single-stage GM cryocooler. However, the present invention is not limited to this, and the configuration of the flow path of the working gas according to the embodiment can be applied to a two-stage or a multiple-stage GM cryocooler, or can be applied to other cryocoolers such as a pulse tube cryocooler. 
         [0077]    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.