How to disassemble a cryogenic refrigerator

Abstract

To provide a disassembling method for a cryogenic refrigerator in order to replace a scotch yoke guide.SOLUTION: A disassembling method for a cryogenic refrigerator is provided. The cryogenic refrigerator comprises: a housing 20 comprising a lower opening 21; a lower cover closing the lower opening 21; a scotch yoke shaft 45 housed in the housing 20, passing through the lower cover, and extending to the outside of the housing 20; and a scotch yoke guide 54 detachably provided in the housing 20, and for guiding an axial movement of the scotch yoke shaft 45. The method comprises detachment of the lower cover from the housing 20, and extraction of the scotch yoke guide 54 to the outside of the housing 20 from the lower opening 21.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a method for disassembling a cryogenic refrigerator.

Background Art

[0002] There is known a cryogenic refrigerator including a drive motor, a Scotch yoke that converts the rotation of the drive motor into a linear reciprocating motion, a housing to which the drive motor is attached and that houses the Scotch yoke, and a guide provided in the housing to guide the linear reciprocating motion of the Scotch yoke and to regulate tilting about the rotation axis.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] During long-term use of a cryogenic refrigerator at a site, the guide may gradually wear due to sliding with the Scotch yoke. In particular, when the Scotch yoke is formed of a metal material and the guide is formed of a synthetic resin material, the guide is likely to wear. As the wear progresses, it becomes difficult for the guide to perform its role.

[0005] One exemplary object of an aspect of the present invention is to provide a method for disassembling a cryogenic refrigerator for replacing a Scotch yoke guide.

Means for Solving the Problems

[0006] According to one aspect of the present invention, a method for disassembling a cryogenic refrigerator is provided. The cryogenic refrigerator comprises a housing having a lower opening, a lower cover that closes the lower opening, a Scotch yoke shaft housed in the housing and extending out of the housing through the lower cover, and a Scotch yoke guide that is detachably provided in the housing and guides the axial movement of the Scotch yoke shaft. The method comprises removing the lower cover from the housing and removing the Scotch yoke guide out of the housing through the lower opening.

[0007] Furthermore, any combination of the above components, or any substitution of components or expressions of the present invention between methods, apparatus, systems, etc., is also valid as an embodiment of the present invention. [Effects of the Invention]

[0008] According to the present invention, a method for disassembling a cryogenic refrigerator to replace a Scotch yoke guide can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing a cryogenic refrigerator according to an embodiment. [Figure 2] This is a schematic diagram showing a cryogenic refrigerator according to an embodiment. [Figure 3] This is a schematic diagram showing a cryogenic refrigerator according to an embodiment. [Figure 4] This figure schematically shows an exploded perspective view of the cold head drive unit of a cryogenic refrigerator according to an embodiment. [Figure 5] This figure schematically shows an exploded perspective view of the main part of the motion conversion mechanism of the cold head according to the embodiment. [Figure 6] Figures 6(a) and 6(b) are schematic diagrams illustrating an embodiment of the Scotch yoke guide. [Figure 7] This figure schematically shows a method for disassembling a cryogenic refrigerator according to an embodiment. [Figure 8]This figure schematically shows a method for disassembling a cryogenic refrigerator according to an embodiment. [Modes for carrying out the invention]

[0010] The embodiments for carrying out the present invention will be described in detail below with reference to the drawings. In the description and drawings, identical or equivalent components, members, and processes are denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. The scale and shape of the illustrated parts are set for convenience to facilitate the explanation and are not to be interpreted restrictively unless otherwise specified. The embodiments are illustrative and do not limit the scope of the present invention in any way. Not all features or combinations thereof described in the embodiments are necessarily essential to the invention.

[0011] Figures 1 to 3 are schematic diagrams showing a cryogenic refrigerator 10 according to an embodiment. Figure 1 shows the external appearance of the cold head of the cryogenic refrigerator 10, and Figure 2 shows the internal structure of the low-temperature section of the cold head. Figure 3 shows the internal structure of the drive unit of the cold head. The cryogenic refrigerator 10 is typically installed in a vacuum vessel (not shown) such that the low-temperature section is located inside the vacuum vessel and the drive unit is located outside the vacuum vessel in the surrounding environment (e.g., room temperature and atmospheric pressure environment). As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator.

[0012] The cryogenic refrigerator 10 comprises a compressor 12 and an expander 14. The compressor 12 is configured to recover the working gas of the cryogenic refrigerator 10 from the expander 14, pressurize the recovered working gas, and supply the working gas back to the expander 14. The compressor 12 and the expander 14 constitute the refrigeration cycle of the cryogenic refrigerator 10, thereby enabling the cryogenic refrigerator 10 to provide the desired cryogenic cooling. The expander 14 is often also referred to as the cold head. The working gas, also referred to as the refrigerant gas, is typically helium gas, but other suitable gases may be used. For understanding, the direction of flow of the working gas is indicated by arrows in Figure 1.

[0013] Generally, the pressure of the working gas supplied from the compressor 12 to the expander 14 and the pressure of the working gas recovered from the expander 14 to the compressor 12 are both considerably higher than atmospheric pressure and can be called the first high pressure and the second high pressure, respectively. For convenience of explanation, the first high pressure and the second high pressure are also simply called high pressure and low pressure, respectively. Typically, the high pressure is, for example, 2 to 3 MPa. The low pressure is, for example, 0.5 to 1.5 MPa, or approximately 0.8 MPa. For understanding, the direction of the working gas flow is indicated by arrows.

[0014] The expander 14 comprises a refrigerator cylinder 16, a displacer assembly (hereinafter sometimes simply referred to as a displacer) 18, and a refrigerator housing (hereinafter also simply referred to as a housing) 20. The refrigerator cylinder 16 guides the linear reciprocating motion of the displacer 18 and forms expansion chambers (32, 34) between itself and the displacer 18 as expansion spaces for the working gas. The refrigerator cylinder 16 is fixed to the refrigerator housing 20, thereby forming the enclosure of the expander 14, and an airtight space for housing the displacer 18 is formed inside the refrigerator cylinder 16.

[0015] In this book, for convenience, in order to explain the positional relationships between the components of the cryogenic refrigerator 10, the side of the displacer closer to the top dead center in its axial reciprocating motion will be referred to as "upper," and the side closer to the bottom dead center as "lower." The top dead center is the position of the displacer where the volume of the expansion space is maximum, and the bottom dead center is the position of the displacer where the volume of the expansion space is minimum. During operation of the cryogenic refrigerator 10, a temperature gradient occurs in which the temperature decreases from the upper axial direction downwards, so the upper side can also be called the high-temperature side and the lower side the low-temperature side.

[0016] The refrigeration cylinder 16 has a first cylinder 16a and a second cylinder 16b. The first cylinder 16a and the second cylinder 16b are, for example, cylindrical members, with the second cylinder 16b having a smaller diameter than the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are arranged coaxially, and the lower end of the first cylinder 16a is rigidly connected to the upper end of the second cylinder 16b.

[0017] The displacer assembly 18 includes a first displacer 18a and a second displacer 18b connected to each other, and they move integrally. The first displacer 18a and the second displacer 18b are, for example, members having a cylindrical shape, and the second displacer 18b has a smaller diameter than the first displacer 18a. The first displacer 18a and the second displacer 18b are coaxially arranged.

[0018] The first displacer 18a is accommodated in the first cylinder 16a, and the second displacer 18b is accommodated in the second cylinder 16b. The first displacer 18a is reciprocally movable in the axial direction along the first cylinder 16a, and the second displacer 18b is reciprocally movable in the axial direction along the second cylinder 16b.

[0019] As shown in FIG. 2, the first displacer 18a accommodates the first regenerator 26. The first regenerator 26 is formed by filling, for example, a wire mesh made of copper or other appropriate first regenerative material into the cylindrical main body portion of the first displacer 18a. The upper lid portion and the lower lid portion of the first displacer 18a may be provided as separate members from the main body portion of the first displacer 18a, and the upper lid portion and the lower lid portion of the first displacer 18a are fixed to the main body by appropriate means such as fastening or welding, whereby the first regenerative material may be accommodated in the first displacer 18a.

[0020] Similarly, the second displacer 18b accommodates the second regenerator 28. The second regenerator 28 is formed by filling, for example, a non-magnetic regenerative material such as bismuth, a magnetic regenerative material such as HoCu2, or other appropriate second regenerative material into the cylindrical main body portion of the second displacer 18b. The second regenerative material may be formed into a granular shape. The upper lid portion and the lower lid portion of the second displacer 18b may be provided as separate members from the main body portion of the second displacer 18b, and the lower lid portion of the upper lid portion of the second displacer 18b is fixed to the main body by appropriate means such as fastening or welding, whereby the second regenerative material may be accommodated in the second displacer 18b.

[0021] The displacer 18 forms an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the refrigerator cylinder 16. For heat exchange with the desired object or medium to be cooled by the cryogenic refrigerator 10, the expander 14 includes a first cooling stage 33 and a second cooling stage 35. The upper chamber 30 is formed between the upper lid of the first displacer 18a and the upper part of the first cylinder 16a. The first expansion chamber 32 is formed between the lower lid of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is formed between the lower lid of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fixed to the lower part of the first cylinder 16a so as to surround the first expansion chamber 32, and the second cooling stage 35 is fixed to the lower part of the second cylinder 16b so as to surround the second expansion chamber 34.

[0022] The first regenerator 26 is connected to the upper chamber 30 through an operating gas passage 36a formed in the upper lid of the first displacer 18a, and to the first expansion chamber 32 through an operating gas passage 36b formed in the lower lid of the first displacer 18a. The second regenerator 28 is connected to the first regenerator 26 through an operating gas passage 36c formed from the lower lid of the first displacer 18a to the upper lid of the second displacer 18b. The second regenerator 28 is also connected to the second expansion chamber 34 through an operating gas passage 36d formed in the lower lid of the second displacer 18b.

[0023] A first seal 38a and a second seal 38b may be provided to ensure that the working gas flow between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 is directed to the first regenerator 26 and the second regenerator 28, rather than to the clearance between the chiller cylinder 16 and the displacer 18. The first seal 38a may be mounted on the top cover of the first displacer 18a so as to be positioned between the first displacer 18a and the first cylinder 16a. The second seal 38b may be mounted on the top cover of the second displacer 18b so as to be positioned between the second displacer 18b and the second cylinder 16b.

[0024] As shown in Figure 3, the refrigeration housing 20 comprises a housing body 22 having a lower opening 21 and a lower cover 24 that closes the lower opening 21. The lower opening 21 is formed on the lower surface of the housing body 22. The internal housing volume 20a formed by the housing body 22 and the lower cover 24 may be connected to the low-pressure side of the compressor 12 and maintained at a low pressure, as shown in the figure.

[0025] The lower cover 24 separates the internal volume 20a of the housing from the displacer housing space (upper chamber 30) within the refrigeration cylinder 16. The lower cover 24 has a disc-like shape overall, and more specifically, it has a large-diameter upper portion and a small-diameter lower portion. A first sealing member 25a is provided between the lower cover 24 and the refrigeration cylinder 16 to maintain airtightness of the internal volume of the refrigeration cylinder 16, and a second sealing member 25b is provided between the lower cover 24 and the housing body 22 to maintain airtightness of the internal volume 20a of the housing. As shown in the figure, the first sealing member 25a may be attached to the small-diameter portion of the lower cover 24, and the second sealing member 25b may be attached to the large-diameter portion of the lower cover 24.

[0026] The lower cover 24 is removably fitted into the lower opening 21, and the upper flange portion of the refrigeration cylinder 16 is fastened to the housing body 22 by fastening members such as bolts. In this way, the lower cover 24 is sandwiched between the housing body 22 and the upper flange portion of the refrigeration cylinder 16. The lower cover 24 is not fixed to the housing body 22 by fastening. However, a structure in which the housing body 22 and the lower cover 24 are fastened together by fastening members such as bolts may be adopted.

[0027] The expander 14 also includes an expander motor 40, a rotary valve 42, and a motion conversion mechanism 43. The expander motor 40 is mounted to the refrigerator housing 20, more specifically to the side of the housing body 22. To maintain the airtightness of the internal volume 20a of the housing, a sealing member (not shown) may be provided on the mounting surface between the expander motor 40 and the housing body 22. The rotary valve 42 and the motion conversion mechanism 43 are housed in the refrigerator housing 20.

[0028] The expander motor 40 is provided in the expander 14 as a drive source for the displacer 18 and the rotary valve 42. The expander motor 40 may be any suitable electric motor, and may be configured to rotate the motor shaft 40a at a constant rotational speed, or the rotational speed of the motor shaft 40a may be variably controlled.

[0029] The rotary valve 42 is configured to alternately connect the high-pressure and low-pressure sides of the compressor 12 to the refrigeration cylinder 16 (i.e., the upper chamber 30, the first expansion chamber 32, and the second expansion chamber 34), and to periodically switch between intake and exhaust of the refrigeration cylinder 16.

[0030] The rotary valve 42 comprises a valve rotor 42a and a valve stator 42b, with the valve rotor 42a in contact with the valve stator 42b so as to rotate while sliding relative to the valve stator 42b. The valve rotor 42a is rotatably supported relative to the housing body 22, and the valve stator 42b is non-rotatably supported relative to the housing body 22. An elastic body, such as a spring, may be interposed between the valve stator 42b and the housing body 22 to press the valve stator 42b toward the valve rotor 42a in the direction of the rotation axis of the valve rotor 42a.

[0031] The refrigeration unit housing 20 has an internal flow path 20b that connects the rotary valve 42 to the upper chamber 30. The valve rotor 42a and valve stator 42b of the rotary valve 42 have internal flow paths formed so that the internal flow path 20b alternately connects the high-pressure side of the compressor 12 to the internal volume 20a of the housing. Various known configurations can be used for the internal flow paths of the valves, which will not be described in detail here.

[0032] The motion conversion mechanism 43 is configured to connect the expander motor 40 to the rotary valve 42 and the displacer 18 so as to transmit the rotation of the motor shaft 40a to the rotary valve 42 and convert it into linear reciprocating motion of the displacer 18. An example of the motion conversion mechanism 43 will be described later. One rotation of the motor shaft 40a results in one reciprocating motion of the displacer 18 via the motion conversion mechanism 43, thereby causing a periodic change in the volume of the working gas expansion space. At the same time, one rotation of the motor shaft 40a results in one rotation of the rotary valve 42 via the motion conversion mechanism 43, thereby causing a periodic change in the pressure of the working gas expansion space.

[0033] In this way, synchronized volume and pressure fluctuations are introduced into the expansion space, forming a refrigeration cycle for the cryogenic refrigerator 10, thereby enabling the cryogenic refrigerator 10 to provide desired cryogenic cooling. The first cooling stage 33 can be cooled to a first cooling temperature, and the second cooling stage 35 can be cooled to a second cooling temperature lower than the first cooling temperature. The first cooling temperature may be, for example, in the range of about 10K to about 100K, or in the range of about 20K to about 40K. The second cooling temperature may be, for example, about 20K or less, or about 10K or less, or in the range of about 1K to about 4K.

[0034] Figure 4 is a schematic exploded perspective view of the cold head drive unit of the cryogenic refrigerator 10 according to an embodiment. Figure 5 is a schematic exploded perspective view of the main part of the cold head motion conversion mechanism 43 according to an embodiment. Exemplary forms of the motion conversion mechanism 43 will be described with reference to Figures 3 to 5.

[0035] In this embodiment, the motion conversion mechanism 43 is a Scotch yoke and comprises a crank 44 having a crankpin 44a, a Scotch yoke shaft 45, and a crankpin bearing 46. The Scotch yoke shaft 45 comprises a Scotch yoke plate 45a, an upper rod 45b, and a lower rod 45c. The Scotch yoke shaft 45 may be made of a metallic material such as stainless steel.

[0036] The crank 44 is fixed to the motor rotation shaft 40a. The crank pin 44a extends parallel to the motor rotation shaft 40a at an eccentric position from the motor rotation shaft 40a. The crank pin 44a extends from the crank 44 in the direction opposite to the motor rotation shaft 40a.

[0037] The Scotch yoke plate 45a is a rectangular plate-like member having a horizontal window 47. The horizontal window 47 extends in the axial direction and in a direction perpendicular to the motor rotation axis 40a. A crankpin bearing 46 is rotatably positioned in this horizontal window 47. The crankpin bearing 46 may be, for example, a roller bearing. An engagement hole 46a is formed in the center of the crankpin bearing 46, which engages with a crankpin 44a, and the crankpin 44a passes through the engagement hole 46a.

[0038] On the side of the Scotch yoke plate 45a opposite to the crank 44, the valve rotor 42a of the rotary valve 42 is positioned with its central axis aligned with the motor rotation axis 40a, and the tip of the crank pin 44a, which passes through the engagement hole 46a, is fixed to the valve rotor 42a.

[0039] The upper rod 45b extends upward from the center of the upper frame of the Scotch yoke plate 45a, and the lower rod 45c extends downward from the center of the lower frame of the Scotch yoke plate 45a; these rods are arranged coaxially. The Scotch yoke plate 45a and the upper rod 45b are housed in the refrigeration housing 20, while the lower rod 45c extends outside the refrigeration housing 20 through the lower cover 24. The tip of the lower rod 45c is connected to the displacer 18 within the refrigeration cylinder 16.

[0040] A first sliding bearing 48a is provided between the upper rod 45b and the housing body 22, and a second sliding bearing 48b is provided between the lower rod 45c and the lower cover 24. The housing body 22 has a recess at its upper part to receive the upper rod 45b, and the first sliding bearing 48a is positioned in this recess to support the upper rod 45b so that it can slide in the axial direction. The lower cover 24 has a through hole in its center, and the second sliding bearing 48b is positioned in this through hole to support the lower rod 45c so that it can slide in the axial direction. The second sliding bearing 48b is provided with a sealing part, such as a slipper seal or a clearance seal, and is configured to be airtight, so that the internal volume 20a of the housing is isolated from the upper chamber 30. There is no direct gas flow between the internal volume 20a of the housing and the upper chamber 30.

[0041] A collar portion 50 is fixed to the tip of the lower rod 45c, which is connected to the displacer 18, by a fixing pin 49. The collar portion 50 is a short cylindrical member into which the tip of the displacer assembly 18 is inserted. Through holes are formed in the tip of the lower rod 45c and the collar portion 50 in a direction perpendicular to the axial direction, and the collar portion 50 is fixed to the lower rod 45c by fitting the fixing pin 49 into these through holes.

[0042] The first displayer 18a has a lid portion 52a and a body portion 52b. The lid portion 52a is the top lid of the first displayer 18a and has a disc shape. The lid portion 52a is made of a metal material or other material, such as an anodized aluminum alloy. The body portion 52b has a cylindrical shape and has a regenerator inside. The body portion 52b is made of a synthetic resin material or other material, and may be made of a phenolic resin such as bakelite. The above-mentioned working gas passage 36a is formed by passing through the upper ends of the lid portion 52a and the body portion 52b in the axial direction. The above-mentioned first seal 38a may be sandwiched between the outermost periphery of the lid portion 52a and the body portion 52b, respectively. The lid portion 52a and the body portion 52b are fixed to each other, for example, using fastening members such as bolts, or by other methods such as adhesive.

[0043] A through hole is formed in the center of the lid portion 52a to receive the tip of the lower rod 45c and the collar portion 50. The collar portion 50 has a flange that extends radially outward at its lower end, and this flange is sandwiched between the lid portion 52a and the main body portion 52b of the first displacer 18a, thereby connecting the lower rod 45c and the collar portion 50 to the first displacer 18a. In this way, the displacer 18 is attached to the Scotch yoke shaft 45.

[0044] Therefore, when the expander motor 40 is driven and the motor rotation shaft 40a rotates, the crankpin bearing 46, which is engaged with the crankpin 44a, rotates in a circular motion. At this time, the crankpin bearing 46 reciprocates along the horizontal window 47 of the Scotch yoke plate 45a, and together with it, the Scotch yoke shaft 45 and the displacer 18 reciprocate in the axial direction. In this way, the expander motor 40 drives the axial movement of the Scotch yoke shaft 45.

[0045] Figures 6(a) and 6(b) schematically show the Scotch yoke guide 54 according to an embodiment. Figure 6(a) schematically shows a cross-section of the housing body 22 according to the AA cross-section shown in Figure 3, and Figure 3(b) schematically shows a part of the BB cross-section shown in Figure 6(a).

[0046] In this embodiment, as shown in the figure, a Scotch yoke guide 54 is provided. The Scotch yoke guide 54 is configured to guide the axial movement of the Scotch yoke shaft 45 and to restrict the rotation of the Scotch yoke shaft 45 about its axis.

[0047] The Scotch yoke guide 54 comprises a plurality (two in this example) of pins 54a, 54b, each pin 54a extending axially along the Scotch yoke shaft 45. The pins 54a, 54b have a cylindrical shape and may be made of a wear-resistant synthetic resin material such as a fluororesin or other material. The housing body 22 has a plurality (two in this example) of pin insertion holes 56 into which the plurality of pins 54a, 54b are each removably inserted. Thus, the Scotch yoke guide 54 is removably provided within the housing 20. As will be described later, the Scotch yoke shaft 45 and the Scotch yoke guide 54 can be removed from the housing body 22 through the lower opening 21 of the housing body 22.

[0048] The Scotch yoke guide 54 is positioned differently from the lower rod 45c with respect to the direction of the motor rotation shaft 40a that drives the axial movement of the Scotch yoke shaft 45, and is adjacent to the Scotch yoke plate 45a. In this embodiment, the Scotch yoke guide 54 is positioned offset toward the motor rotation shaft 40a side relative to the Scotch yoke plate 45a and the lower rod 45c, but it may also be positioned toward the rotary valve 42 side.

[0049] The cylindrical sides of each pin 54a of the Scotch yoke guide 54 are in contact with the side surface 58 of the Scotch yoke plate 45a, which has a horizontally elongated window 47 formed therein. One pin 54a is in contact with the side surface 58 at the right frame portion of the Scotch yoke plate 45a, and the other pin 54a is in contact with the side surface 58 at the left frame portion of the Scotch yoke plate 45a.

[0050] Therefore, the Scotch yoke guide 54 can guide the axial movement of the Scotch yoke plate 45a on the side of each pin 54a. In addition, the Scotch yoke guide 54 can restrict the rotation of the Scotch yoke shaft 45 about its axis by the pins 54a.

[0051] Figures 7 and 8 schematically show the disassembly method of the cryogenic refrigerator 10 according to the embodiment. First, as shown in Figure 7, the expander motor 40 is removed from the refrigerator housing 20 (S10). The fastening members that fix the expander motor 40 to the refrigerator housing 20 are removed, and the expander motor 40 is removed from the side of the housing body 22. The crank 44 may also be removed together with the expander motor 40. At the same time, the high-pressure piping and low-pressure piping attached to the refrigerator housing 20 are also removed.

[0052] Next, the fixing between the refrigeration housing 20 and the refrigeration cylinder 16 is released (S11). As described above, the housing body 22 is attached to the refrigeration cylinder 16 by fastening members, and by removing the fastening members, the refrigeration housing 20 is removed from the refrigeration cylinder 16. After that, the refrigeration housing 20 is lifted up from the refrigeration cylinder 16. As a result, the displacer 18 can be pulled out from the refrigeration cylinder 16 together with the refrigeration housing 20.

[0053] Next, the displacer 18 is removed from the Scotch yoke shaft 45 (S12). The lid 52a and the main body 52b of the first displacer 18a are released, and the main body 52b is removed from the lid 52a. Furthermore, the fixing pin 49 and the collar 50 are removed from the lower rod 45c of the Scotch yoke shaft 45, and the lid 52a is also removed (S13). In this way, the displacer 18 is removed from the Scotch yoke shaft 45 before the lower cover 24 is removed from the refrigerator housing 20. Then, the lower cover 24 is removed from the refrigerator housing 20 (S13).

[0054] As shown in Figure 8, the second sealing member 25b is removed from the housing body 22 (S14). For ease of understanding, Figure 8 is shown upside down (i.e., with the lower opening 21 facing upwards). As described above, the second sealing member 25b is sandwiched between the lower cover 24 and the housing body 22 and positioned inside the lower opening 21. The second sealing member 25b is removed from the lower opening 21, which is opened again when the lower cover 24 is removed from the housing body 22.

[0055] Next, the Scotch yoke shaft 45 is pulled out of the refrigerator housing 20 through the lower opening 21 (S15). By removing the Scotch yoke shaft 45 before removing the Scotch yoke guide 54, a larger workspace can be created within the refrigerator housing 20 for removing the Scotch yoke guide 54.

[0056] Then, the Scotch yoke guide 54 is removed from the refrigerator housing 20 through the lower opening 21. First, one pin 54a is removed from the refrigerator housing 20 through the lower opening 21 (S16), and then the other pin 54b is also removed from the refrigerator housing 20 through the lower opening 21 (S17).

[0057] After removing pins 54a and 54b, new pins 54a and 54b are installed. Then, the expander 14 is reassembled in the reverse order described above. In this way, the worn Scotch yoke guide 54 can be replaced with a new one. This ensures that the rotation of the Scotch yoke shaft 45 around its axis is prevented.

[0058] Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate one aspect of the principle and application of the present invention, and many modifications and changes in arrangement are permitted in the embodiments, as long as they do not depart from the spirit of the present invention as defined in the claims. [Explanation of symbols]

[0059] 10 Cryogenic refrigerator, 21 Lower opening, 24 Lower cover, 40a Motor rotating shaft, 45 Scotch yoke shaft, 45a Scotch yoke plate, 54 Scotch yoke guide, 54a Pin, 56 Pin insertion hole.

Claims

1. A method for disassembling a cryogenic refrigerator, wherein the cryogenic refrigerator comprises a housing having a lower opening, a lower cover that closes the lower opening, a Scotch yoke shaft housed in the housing and extending outside the housing through the lower cover, and a Scotch yoke guide that is removably provided inside the housing and guides the axial movement of the Scotch yoke shaft, and the method is as follows: Removing the lower cover from the housing, The Scotch yoke guide is removed from the lower opening to the outside of the housing, The Scotch yoke shaft comprises a Scotch yoke plate housed in the housing and a rod extending from the Scotch yoke plate through the lower cover and out of the housing. The method is characterized in that the Scotch yoke guide is positioned at a different location from the rod with respect to the direction of the motor rotation shaft that drives the axial movement of the Scotch yoke shaft, and is adjacent to the Scotch yoke plate.

2. The method according to claim 1, characterized in that the Scotch yoke guide is configured to restrict rotation of the Scotch yoke shaft around its axis.

3. The method according to 1 or 2, characterized in that the Scotch yoke guide comprises a plurality of pins extending in the axial direction of the Scotch yoke shaft, and the housing has a plurality of pin insertion holes into which each of the plurality of pins is removably inserted.

4. A method for disassembling a cryogenic refrigerator, wherein the cryogenic refrigerator comprises a housing having a lower opening, a lower cover that closes the lower opening, a Scotch yoke shaft housed in the housing and extending outside the housing through the lower cover, and a Scotch yoke guide that is removably provided inside the housing and guides the axial movement of the Scotch yoke shaft, and the method is Removing the lower cover from the housing, The Scotch yoke guide is removed from the lower opening to the outside of the housing, The method further comprises pulling the Scotch yoke shaft out of the housing through the lower opening before removing the Scotch yoke guide.

5. The cryogenic refrigerator is equipped with a displacer attached to the Scotch yoke shaft, The method according to any one of 1 to 4, further comprising removing the displacer from the Scotch yoke shaft before removing the lower cover from the housing.

6. The cryogenic refrigerator is fixed to the housing and includes a cylinder that houses the displacer, Releasing the fixing of the housing and the cylinder, The method according to the 5th, further comprising withdrawing the displacer from the cylinder together with the housing.

7. The cryogenic refrigerator is mounted on the housing and includes a motor that drives the axial movement of the Scotch yoke shaft, The method according to any one of 1 to 6, further comprising removing the motor from the housing.

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