Abstract:
A cryogenic refrigerator includes a pressure switching valve with a rotational element for switching between channels. The cryogenic refrigerator includes a first member located on one side in a direction of a rotational axis of the rotational element; a second member located on another side in the direction of the rotational axis of the rotational element; a bearing rotatably supporting the rotational element; and an elastic element. The first and second members sandwich the bearing via the elastic element.

Description:
FIELD 
       [0001]    The disclosures herein relate to a cryogenic refrigerator including a bearing which holds a pressure switching valve whose rotational element is rotated to switch between channels. 
       BACKGROUND 
       [0002]    Japanese Laid-open Patent Publication No. 2004-53157 discloses a pressure switching valve whose rotational element for switching between channels is held by a bearing, wherein an elastic element is inserted between the rotational element and the bearing in a radial direction such that the rotation of the rotational element rotates the bearing with reliability. 
         [0003]    In the case of a configuration in which an outer race of the bearing is secured by sandwiching the outer race of the bearing between two members disposed in a direction of a rotational axis, there may be a case where the outer race of the bearing is not secured with reliability due to processing tolerances, etc., unless these two members are processed with high accuracy. If the outer race of the bearing is not secured and thus is rotated, wear occurs in a member which supports the outer race of the bearing from an outer surface side in the radial direction, which results in a problem that complicated processes are necessary for the processing of these two members. 
       SUMMARY 
       [0004]    According to an aspect of the embodiment, a cryogenic refrigerator is provided. The cryogenic refrigerator includes 
         [0005]    a pressure switching valve with a rotational element for switching between channels; 
         [0006]    a first member located on one side in a direction of a rotational axis of the rotational element; 
         [0007]    a second member located on another side in the direction of the rotational axis of the rotational element; 
         [0008]    a bearing rotatably supporting the rotational element; and 
         [0009]    an elastic element, wherein 
         [0010]    the first and second members sandwich the bearing therebetween via the elastic element. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a drawing illustrating an example of an overall configuration related to a cryogenic refrigerator; 
           [0012]      FIG. 2  is a cross-section view of an example of a main portion of a cryogenic refrigerator  14 ; and 
           [0013]      FIG. 3  is a cross-section view of another example of a main portion of a cryogenic refrigerator  14 ′. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0014]    In the following, embodiments will be described with reference to the accompanying drawings. 
         [0015]      FIG. 1  is a drawing illustrating an example of an overall configuration related to a cryogenic refrigerator. 
         [0016]    The configuration illustrated in  FIG. 1  includes a gas compressor (merely referred to as a compressor, hereinafter)  10  which includes a suction port  10 A for receiving operation gas (a refrigerant gas) and a discharge port  10 B for discharging the compressed operation gas; and a cryogenic refrigerator  14  coupled to the compressor  10 . In  FIG. 1 , a low-pressure pipe is indicated by the numeral reference  16  and a high-pressure pipe is indicated by the numeral reference  18 . 
         [0017]      FIG. 2  is a cross-section view of an example of a main portion of the cryogenic refrigerator  14 . 
         [0018]    The cryogenic refrigerator  14  is a Gifford McMahon cycle (GM) refrigerator. The GM refrigerator utilizes a change in volume of space induced by a displacer reciprocating in a cylinder to obtain a cooling effect based on the Gifford McMahon refrigeration cycle. It is noted that according to the GM refrigerator, a high-pressure refrigerant gas (He gas, etc.) is supplied to the cylinder in which the gas is adiabatically expanded to obtain a cryogenic temperature. The expanded cryogenic-temperature refrigerant gas absorbs heat from the surroundings and is exhausted from the cylinder after the temperature of the refrigerant gas is increased to a room temperature by thermal exchange with a storage medium. In this way, the inside of the cylinder is kept at a cryogenic temperature. The refrigerant gas exhausted from the cylinder is supplied to the compressor in which it is compressed to be the high-pressure refrigerant gas. The high-pressure refrigerant gas is supplied to the cylinder of the GM refrigerator again. 
         [0019]    The cryogenic refrigerator  14  mainly includes a cylinder section  20 , a valve body  30 , a valve plate  34 , a bearing  36 , a lid member  50 , a housing  60 , and a motor  46 , as illustrated in  FIG. 2 . 
         [0020]    The cylinder section  20  may define any number of stages such as one stage, two stages, etc. It is noted that a configuration of the cylinder section  20  itself may be arbitrary and is not explained in detail here. 
         [0021]    The housing  60  accommodates therein various components of a rotary valve (the valve body  30 , the valve plate  34 , the bearing  36 , etc.), etc. 
         [0022]    The lid member  50  is provided such that it covers an opening on one side of the housing  60  (in the illustrated example, an opening on an upper side). The lid member  50  is fastened to the housing with bolts  80 . The bolts  80  are tighten with a relatively high tightening torque so as to prevent looseness of the bolts  80 . Further, O-rings  72 A,  72 B are provided between the lid member  50  and the housing  60  so as to ensure hermeticity. A high-pressure channel  50 A to be coupled to the high-pressure pipe  18  is formed in the lid member  50 . 
         [0023]    The motor  46  is provided such that it covers an opening on another side of the housing  60  (in the illustrated example, an opening on a lower side). An O-ring  46 C is provided between a motor housing of the motor  46  and the housing  60  so as to ensure hermeticity. It is noted that the inside of the motor  46  is coupled to the suction port  10 A on the low-pressure side of the compressor  10  via the low-pressure pipe  16 . The motor  46  includes a rotational shaft  46 A. The rotational movement of the rotational shaft  46 A of the motor  46  causes a rotational movement of the valve plate  34  via a crank  46 B and an eccentric pin  46 D, and a reciprocating movement of a displacer  21  via a Scotch yoke  92 . 
         [0024]    The cylinder section  20  is hermetically coupled to a side portion of the housing  60 . A fluid channel  60 B is formed in the side portion of the housing  60 . A fluid channel  50 B corresponding to the fluid channel  60 B is formed in the lid member  50 . 
         [0025]    The valve body  30  is disposed in a concave portion formed on the inner side (i.e., a lower surface) of the lid member  50 . The valve body  30  is installed such that it is not rotatable with respect to the lid member  50 . O-rings  32  are provided between the outer surface of the valve body  30  and the lid member  50 . A high-pressure fluid channel  30 B is formed in the valve body  30  such that it passes through a center portion of the valve body  30 . The high-pressure fluid channel  30 B is in fluid communication with the high-pressure pipe  18  via the high-pressure fluid channel  50 A of the lid member  50 . The valve body  30  has a valve side fluid channel  30 C and a cylinder side fluid channel  30 A formed therein which are in fluid communication with the fluid channels  60 B and  50 B. The valve body  30  is biased toward the valve plate  34  with a spring  31  which is provided between the valve body  30  and the lid member  50 . 
         [0026]    The valve plate  34  is a rotational element coupled to the rotational shaft  46 A of the motor  46 . The valve plate  34  is provided such that it slidably abuts the valve body  30 . The side of the valve plate  34 , which comes into contact with the valve body  30 , has a high-pressure fluid channel  34 B formed therein which has a bottom (a form of a groove or a concave portion). The high-pressure fluid channel  34 B of the valve plate  34  is in fluid communication with the high-pressure pipe  18  via the high-pressure fluid channel  30 B of the valve body  30  and the high-pressure fluid channel  50 A of the lid member  50 . Further, the valve plate  34  has a low-pressure fluid channel  34 A formed therein which passes through the valve plate  34  in a direction parallel with the direction of the rotational axis. When the valve plate  34  rotates, the valve side fluid channel  30 C and the cylinder side fluid channel  30 A of the valve body  30  come in fluid communication with the high-pressure fluid channel  34 B and the low-pressure fluid channel  34 A alternately, thereby the directions of the refrigeration medium gas are switched alternately. 
         [0027]    When the valve side fluid channel  30 C and the cylinder side fluid channel  30 A of the valve body  30  are in fluid communication with the high-pressure fluid channel  34 B, the refrigerant gas from the compressor  10  is introduced into an upper chamber  90  of the cylinder section  20 . When the valve side fluid channel  30 C and the cylinder side fluid channel  30 A of the valve body  30  are in fluid communication with the low-pressure fluid channel  34 A, the refrigerant gas in the upper chamber  90  is collected by the compressor  10  via the inside of the motor  46 . Thus, when the valve plate  34  is rotated, the introduction of the refrigerant gas into the upper chamber  90  (charging) and the recovery of the refrigerant gas from the upper chamber  90  (exhaust) are repeated. The repetition of introduction and recovery of the refrigerant gas and the reciprocating movement of the displacer  21  of the cylinder section  20  are synchronized with the rotation of the crank  46 B. If a phase of the repetition of introduction and recovery of the refrigerant gas and a phase of the reciprocating movement of the displacer  21  are adjusted appropriately, the temperature of the refrigerant gas in an expansion chamber (not illustrated) of the cylinder section  20  reaches a cryogenic temperature and an endothermic effect is generated. 
         [0028]    The valve plate  34  is rotatably supported by the housing  60  via the bearing  36 , as illustrated in  FIG. 2 . The valve plate  34  has an outer surface fitted into an inner race  36 B of the bearing  36 . It is noted that the valve plate  34  includes a flange portion  34 F at a rim on the valve body  30  side, and an axial registration is made at the flange portion  34 F by a pressing force from the fitted inner race  36 B. 
         [0029]    The bearing  36  includes an outer race  36 A, the inner race  36 B and balls  36 C. The bearing  36  is provided between the lid member  50  and the housing  60 , as illustrated in  FIG. 2 . Specifically, the bearing  36  is fitted in the housing  60  such that the outer surface of the outer race  36 A comes in contact with the inner surface of the housing  60 . The inner surface of the housing  60  has a support surface  60 A formed therein which projects toward the center side. The end surface of the outer race  36 A of the bearing  36  is supported by the support surface  60 A and the load in the direction of the rotational axis is carried by the housing  60  via the support surface  60 A. The lid member  50  is provided such that the outer race  36 A of the bearing  36  is sandwiched between the lid member  50  and the support surface  60 A of the housing  60 . The lid member  50  is provided such that it comes into contact with the end surface of the outer race  36 A in the direction of the rotational axis via the O-ring  70 , as illustrated in  FIG. 2 . In other words, the end surface of the outer race  36 A comes into contact with the lid member  50  not directly but via the O-ring  70 . The O-ring  70  is provided such that it comes into contact with the inner surface of the housing  60 . The O-ring  70  has substantially the same diameter as the inner surface of the housing  60 . 
         [0030]    In this way, according to the embodiment, in order to support the bearing  36  between the lid member  50  and the housing  60  in the direction of the rotational axis, the O-ring  70  is provided between the lid member  50  and the housing  60  in the direction of the rotational axis. Thus, even in the case where there could be a clearance (space) between the housing  60  and the lid member  50  due to the processing tolerance, etc., of the housing  60  and the lid member  50 , the clearance is filled with the O-ring  70 . Thus, when the outer race  36 A of the bearing  36  is installed, it is possible to appropriately apply a preload to the outer race  36 A of the bearing  36  via the O-ring  70 . Correspondingly, it is possible to prevent problems due to the space between the housing  60  and the lid member  50 . In particular, the problems include such that the outer race  36 A of the bearing  36  is not secured and thus is rotated, resulting in abrasion of the housing  60 . It is noted that the preload acting on the outer race  36 A of the bearing  36  can be easily adjusted by adjusting the distance between the housing  60  and the lid member  50  (i.e., the distance in the direction of the rotational axis) or the elastic property of the O-ring  70 . 
         [0031]    According to the embodiment described above, the following effect among others can be obtained. 
         [0032]    According to the embodiment, as described above, by providing the elastic element such the O-ring  70  between the housing  60  and the lid member  50 , an appropriate preload can be applied to the outer race  36 A of the bearing  36 . As a result of this, it is possible to prevent with reliability the problems which could be induced due the dimensional tolerance or the processing tolerance of the housing  60  and the lid member  50  while reducing the processing cost. 
         [0033]    Further, according to the embodiment, the lid member  50  is provided such that it has not only a function of covering the housing but also a function of securing the outer race  36 A of the bearing  36 . With this arrangement, it is possible to obviate the need for a plate for securing the bearing outer race and thus reduce the number of parts and the cost. Here, the lid member  50  may be fastened using a relatively great number of the bolts  80  in order that the lid member  50  can function safely as a lid of a pressure container. If an imbalance occurs between the tightening torques of these bolts  80 , the bearing  36  may tilt. In this connection, according to the embodiment, as described above, when the bearing  36  is supported between the lid member  50  and the housing  60  in the direction of the rotational axis, the O-ring  70  is provided between the lid member  50  and the housing in the direction of the rotational axis. Thus, the O-ring  70  is deformed elastically when the bolts are tighten. Therefore, it is possible to prevent an excessive load from acting on the outer race  36 A of the bearing  36 . Further, the O-ring  70  is deformed elastically even when the imbalance occurs between the tightening torques. Therefore, it is possible to prevent the bearing  36  from tilting. 
         [0034]      FIG. 3  is a cross-section view of another example of a main portion of a cryogenic refrigerator  14 ′. 
         [0035]    The cryogenic refrigerator  14 ′ illustrated in  FIG. 3  is the same as the cryogenic refrigerator  14  illustrated in  FIG. 2  except for the location of the O-ring  70 . Specifically, the cryogenic refrigerator  14  illustrated in  FIG. 2  has the O-ring  70  between the housing  60  and the lid member  50  such that the O-ring  70  comes into contact with the lid member  50 . To the contrary, the cryogenic refrigerator  14 ′ illustrated in  FIG. 3  has the O-ring  70  between the housing  60  and the lid member  50  such that the O-ring  70  comes into contact with the housing  60 . In other words, according to the cryogenic refrigerator  14  illustrated in  FIG. 2 , the outer race  36 A of the bearing  36  is directly supported by the support surface  60 A of the housing  60 . To the contrary, according to the cryogenic refrigerator  14 ′ illustrated in  FIG. 3 , the outer race  36 A of the bearing  36  is supported by the support surface  60 A of the housing  60  via the O-ring  70 . According to the cryogenic refrigerator  14 ′ illustrated in  FIG. 3 , it is possible to obtain the same effects as is the case with the cryogenic refrigerator  14  illustrated in  FIG. 2 . However, according to the cryogenic refrigerator  14  illustrated in  FIG. 2 , since the outer race  36 A of the bearing  36  is directly supported by the support surface  60 A of the housing  60 , there is an advantage that the axial position of the bearing  36  with respect to the housing  60  can be determined precisely. 
         [0036]    Preferably, in the cryogenic refrigerator  14  illustrated in  FIG. 2 , the O-ring  70  is provided such that it contributes to the hermeticity between the housing  60  and the lid member  50 . In the illustrated example, the O-ring  70  is elastically deformed between the housing  60  and the lid member and thus contributes to the hermeticity between the housing  60  and the lid member  50 . Specifically, when the high-pressure refrigerant gas is supplied to the cryogenic refrigerator, the O-ring  70  provides a function of preventing a leak of the high-pressure refrigerant gas between the housing  60  and the lid member  50  (i.e., between the fluid channel  60 B of the housing  60  and the fluid channel  50 B of the lid member  50 ) to the low-pressure side space (i.e., the space within the housing  60  which is in fluid communication with the inside of the motor  46 ). Thus, if such a sealing function of the O-ring  70  is sufficient, it is possible to eliminate the O-ring  72 A (see  FIGS. 2 and 3 ) which implements the same function. 
         [0037]    The present invention is disclosed with reference to the preferred embodiments. However, it should be understood that the present invention is not limited to the above-described embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
         [0038]    For example, according to the embodiment, the O-ring  70  is disclosed as an example of an elastic element; however, elastic elements other than the O-ring  70  may be used as long as they are elastic parts (for example, parts made of a resin, rubber or the like). For example, a wave washer, a sealing member having a cross section of U-shape, such as a U-seal (registered trade mark) or the like may be used. 
         [0039]    Further, according to the embodiment, the lid member  50  is provided such that it provides a function of securing the outer race  36 A of the bearing  36 , thereby the plate for securing the bearing outer race is eliminated. However, the configuration in which the outer race  36 A of the bearing  36  is secured using another member, such as the plate for securing the bearing outer race, instead of the lid member  50  is also applicable. In this case, the outer race  36 A of the bearing  36  may be secured between the other member, such as the plate for securing the bearing outer race, and the housing  60  via the O-ring  70 . Further, the housing  60  may be replaced with the other member. 
         [0040]    Further, according to the embodiment, the configuration in which the Gifford McMahon cycle (GM) is adopted is described as an example; however, any type of a cryogenic refrigerator, such as a pulse tube refrigerator, for example, is also applicable. In the case of the pulse tube refrigerator, the configuration described above may be applied in a rotary valve accommodating section (i.e., a housing section) upstream of the pulse tube refrigerator. 
         [0041]    The present application is based on Japanese Priority Application No. 2010-194989, filed on Aug. 31, 2010, the entire contents of which are hereby incorporated by reference.