Cryogenic refrigerator, gas replacement method for expander of cryogenic refrigerator, and gas replacement piping

Abstract

The present invention addresses the problem of providing a gas replacement technique for an expansion machine of a cryogenic refrigerator for preventing electrical equipment in the expansion machine from coming into contact with combustible gas. The invention provides a gas replacement method for an expander (14) of a cryogenic refrigerator (10). An expander (14) is provided with: an expander cylinder (16); a pressure switching valve (42) for switching the pressure within the expander cylinder (16); a connection flow path (20b) from the pressure switching valve (42) to the expander cylinder (16); and an expander motor (40) for driving the pressure switching valve (42). The method is provided with: a step for connecting a non-combustible gas source to the connection flow path (20b) or the expander cylinder (16); and a step in which the remaining gas within the expander cylinder (16) is purged using the non-combustible gas from the non-combustible gas source during the shutdown of the expander motor (40).

Description

[0001] This application claims priority based on Japanese Patent Application No. 2023-100053 filed on Jun. 19, 2023. The entire contents of the Japanese Patent Application are incorporated herein by reference. Technical Field

[0002] The present invention relates to a gas replacement method for an expander of a cryogenic refrigerator and a cryogenic refrigerator, and also to a gas replacement pipe used in the gas replacement method. Background Art

[0003] For example, as one of the uses of a cryogenic refrigerator such as a Gifford-McMahon (GM) refrigerator, the refrigerator is sometimes mounted on a storage container of a liquefied gas to recondense the gas.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2001-241796

[0005] In the case where the gas recondensed by the cryogenic refrigerator includes a flammable gas such as hydrogen, the flammable gas may be contained in the surrounding environment of the cryogenic refrigerator. The inventors have found that flammable gas may enter the expander of the cryogenic refrigerator during maintenance work performed by interrupting the operation of the cryogenic refrigerator. The maintenance work involves disassembly and reassembly of the expander in order to inspect or replace internal components. Therefore, when maintenance work is performed at a site where the expander is installed, the surrounding gas (i.e., gas that may contain flammable gas) may enter the interior of the expander. As a result, electrical equipment in the expander such as a motor may come into contact with the flammable gas. If the electrical equipment is operated in a state where the electrical equipment is in contact with the flammable gas, there may be a risk of fire. Summary of the invention

[0006] One of the exemplary purposes of one embodiment of the present invention is to provide a gas replacement technology for an expander of a cryogenic refrigerator for preventing electrical equipment in the expander from coming into contact with flammable gas.

[0007] According to one embodiment of the present invention, a method for replacing gas in an expander of a cryogenic refrigerator is provided. The expander includes an expander cylinder, a pressure switching valve for switching the pressure in the expander cylinder, a connecting flow path from the pressure switching valve to the expander cylinder, and an expander motor for driving the pressure switching valve. The method includes the following steps: a connecting step of connecting a non-flammable gas source to the connecting flow path or the expander cylinder; and a cleaning step of cleaning the retained gas in the expander cylinder using the non-flammable gas from the non-flammable gas source while the expander motor is stopped.

[0008] According to one embodiment of the present invention, there is provided an ultra-low temperature refrigerator, which comprises: an expander cylinder; a pressure switching valve for switching the pressure in the expander cylinder; a high-pressure port and a low-pressure port connected to the expander cylinder via the pressure switching valve; a connecting flow path extending from the pressure switching valve to the expander cylinder; and a gas receiving port, which is different from the high-pressure port and the low-pressure port and is connected to the connecting flow path in a manner that allows gas to flow into the connecting flow path.

[0009] According to one embodiment of the present invention, a gas replacement piping for gas replacement of an expander of a cryogenic refrigerator is provided. The gas replacement piping comprises: a main piping, which can be connected to a non-flammable gas source; a first branch pipe, which branches from the main piping and can be connected to a gas receiving port of the expander; a second branch pipe, which branches from the main piping and can be connected to a high-pressure port of the expander; and a third branch pipe, which branches from the main piping and can be connected to a low-pressure port of the expander.

[0010] According to the present invention, it is possible to provide a gas replacement technology for an expander of a cryogenic refrigerator for preventing electrical equipment in the expander from coming into contact with flammable gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a diagram schematically showing a cryogenic refrigerator according to an embodiment.

[0012] Figure 2 It is a diagram schematically showing a cryogenic refrigerator according to an embodiment.

[0013] Figure 3 It is a diagram schematically showing a cryogenic refrigerator according to an embodiment.

[0014] Figure 4 It is an exploded perspective view schematically showing a main part of a motion conversion mechanism of a cold head according to an embodiment.

[0015] Figure 5 This is a flowchart showing a gas replacement method of an expander of a cryogenic refrigerator according to an embodiment.

[0016] Figure 6 It is a schematic diagram showing an expander of a cryogenic refrigerator in the gas replacement method according to the embodiment.

[0017] Figure 7 It is a schematic diagram showing an expander of a cryogenic refrigerator in the gas replacement method according to the embodiment.

[0018] Figure 8 It is a diagram schematically showing a cryogenic refrigerator according to an embodiment.

[0019] In the figure: 10-ultra-low temperature refrigerator, 13a-high pressure port, 13b-low pressure port, 14-expander, 16-expander cylinder, 20-expander housing, 20b-connecting flow path, 40-expander motor, 42-pressure switching valve, 54-gas receiving port, 56-gas replacement piping, 58-gas outlet port, 60-non-flammable gas source. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, identical or equivalent components, parts, and processes are marked with the same symbols, and repeated descriptions are appropriately omitted. For ease of explanation, in each of the accompanying drawings, the scale or shape of each part is appropriately set, and unless otherwise specifically stated, it is not interpreted as limiting. The embodiments are illustrative and do not limit the scope of the present invention in any way. All features or combinations thereof described in the embodiments are not necessarily the essence of the invention.

[0021] Figures 1 to 3 It is a diagram schematically showing a cryogenic refrigerator 10 according to the embodiment. Figure 1 FIG. 4 shows the appearance of the cold head of the cryogenic refrigerator 10. Figure 2 The internal structure of the low temperature part of the cold head is shown in FIG. Figure 3 , the internal structure of the driving part of the cold head is shown in FIG. Typically, the cryogenic refrigerator 10 is arranged on a vacuum container in such a manner that the low temperature part is arranged in a vacuum container (not shown) and the driving part is arranged in an ambient environment (e.g., room temperature atmospheric pressure environment) outside the vacuum container. As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator.

[0022] As an example of use, the cryogenic refrigerator 10 can be mounted on a cryogenic liquid storage tank storing a cryogenic liquid. The cryogenic refrigerator 10 can also be used to recondense the vaporized cryogenic liquid. In this embodiment, the cryogenic liquid can be a refrigerant having a boiling point lower than the boiling point of nitrogen (about 77K), for example, liquid hydrogen, liquid helium or liquid neon.

[0023] The cryogenic refrigerator 10 includes 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, increase the pressure of the recovered working gas, and then supply the working gas to the expander 14 again. The compressor 12 and the expander 14 constitute a refrigeration cycle of the cryogenic refrigerator 10, so that the cryogenic refrigerator 10 can provide the desired cryogenic cooling. The expander 14 is sometimes also called a cold head. The working gas is also called a refrigerant gas, which is usually helium, but other suitable gases can also be used. For ease of understanding, in Figure 1 The arrows in the figure indicate the flow direction of the working gas.

[0024] In addition, usually, 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 much higher than the atmospheric pressure, and they can be referred to as the first high pressure and the second high pressure, respectively. For ease of explanation, the first high pressure and the second high pressure can also be referred to as 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, for example, about 0.8 MPa. For ease of understanding, the flow direction of the working gas is indicated by an arrow.

[0025] The expander 14 includes an expander cylinder 16, a displacer assembly (hereinafter, sometimes simply referred to as a displacer) 18, and an expander casing (hereinafter, sometimes simply referred to as a casing) 20. The expander cylinder 16 guides the linear reciprocating motion of the displacer 18, and expansion chambers 32 and 34 are formed between the expander cylinder 16 and the displacer 18 as expansion spaces for the working gas. The expander cylinder 16 is fixed to the expander casing 20, thereby constituting a frame of the expander 14, and an airtight space for accommodating the displacer 18 is formed in the expander cylinder 16.

[0026] Furthermore, the expander 14 has a high-pressure port 13a and a low-pressure port 13b. The high-pressure port 13a is provided in the expander housing 20 as an inlet of the working gas of the expander 14, and the low-pressure port 13b is provided in the expander housing 20 as an outlet of the working gas of the expander 14. Therefore, the high-pressure port 13a is connected to the high-pressure side of the compressor 12 through the high-pressure side piping, and the low-pressure port 13b is connected to the low-pressure side of the compressor 12 through the low-pressure side piping. Thus, the high-pressure working gas is supplied from the high-pressure side of the compressor 12 to the expander 14 via the high-pressure port 13a. Furthermore, the low-pressure working gas is recovered from the expander 14 to the low-pressure side of the compressor 12 via the low-pressure port 13b.

[0027] In this specification, in order to explain the positional relationship between the components of the ultra-low temperature refrigerator 10, for convenience, the side close to the upper dead point of the axial reciprocating movement of the displacer is marked as "up", and the side close to the lower dead point is marked as "down". The upper dead point is the position of the displacer when the volume of the expansion space becomes the maximum, and the lower dead point is the position of the displacer when the volume of the expansion space becomes the minimum. When the ultra-low temperature refrigerator 10 is running, a temperature gradient is generated in which the temperature decreases from the upper side to the lower side in the axial direction, so the upper side can also be called the high temperature side, and the lower side can be called the low temperature side.

[0028] The expander cylinder 16 includes a first cylinder 16a and a second cylinder 16b. For example, the first cylinder 16a and the second cylinder 16b are cylindrical components, and the diameter of the second cylinder 16b is smaller than the diameter of the first cylinder 16a. The first cylinder 16a and the second cylinder 16b are coaxially arranged, and the lower end of the first cylinder 16a and the upper end of the second cylinder 16b are rigidly connected.

[0029] The displacer assembly 18 includes a first displacer 18a and a second displacer 18b connected to each other, and they move integrally. As an example, the first displacer 18a and the second displacer 18b are both cylindrical components, and the diameter of the second displacer 18b is smaller than the diameter of the first displacer 18a. The first displacer 18a and the second displacer 18b are coaxially arranged.

[0030] 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 reciprocable in the axial direction along the first cylinder 16a, and the second displacer 18b is reciprocable in the axial direction along the second cylinder 16b.

[0031] like Figure 2 As shown, the first displacer 18a accommodates the first cold storage device 26. The first cold storage device 26 is formed by filling a metal wire mesh such as copper or other appropriate first cold storage material in the cylindrical main body of the first displacer 18a. The upper cover and the lower cover of the first displacer 18a can be provided as components different from the main body of the first displacer 18a, and the upper cover and the lower cover of the first displacer 18a can be fixed to the main body by an appropriate method such as fastening and welding, so that the first cold storage material is accommodated in the first displacer 18a.

[0032] Similarly, the second displacer 18b accommodates the second cold storage device 28. The second cold storage device 28 is formed by filling the cylindrical main body of the second displacer 18b with a non-magnetic cold storage material such as bismuth, a magnetic cold storage material such as HoCu2, or other appropriate second cold storage material. The second cold storage material can be formed into a granular form. The upper cover and the lower cover of the second displacer 18b can be provided as components different from the main body of the second displacer 18b, and the upper cover and the lower cover of the second displacer 18b can also be fixed to the main body by an appropriate method such as fastening or welding, so that the second cold storage material is accommodated in the second displacer 18b.

[0033] The displacer 18 forms an upper chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the expander cylinder 16. In order to perform heat exchange with a desired object or medium to be cooled by the ultra-low temperature refrigerator 10, the expander 14 is provided with a first cooling stage 33 and a second cooling stage 35. The upper chamber 30 is formed between the upper cover portion of the first displacer 18a and the upper portion of the first cylinder 16a. The first expansion chamber 32 is formed between the lower cover portion of the first displacer 18a and the first cooling stage 33. The second expansion chamber 34 is formed between the lower cover portion of the second displacer 18b and the second cooling stage 35. The first cooling stage 33 is fastened to the lower portion of the first cylinder 16a in a manner surrounding the first expansion chamber 32, and the second cooling stage 35 is fastened to the lower portion of the second cylinder 16b in a manner surrounding the second expansion chamber 34.

[0034] The first regenerator 26 is communicated with the upper chamber 30 through a working gas flow path 36a formed on the upper cover portion of the first displacer 18a, and is communicated with the first expansion chamber 32 through a working gas flow path 36b formed on the lower cover portion of the first displacer 18a. The second regenerator 28 is communicated with the first regenerator 26 through a working gas flow path 36c formed from the lower cover portion of the first displacer 18a to the upper cover portion of the second displacer 18b. Furthermore, the second regenerator 28 is communicated with the second expansion chamber 34 through a working gas flow path 36d formed on the lower cover portion of the second displacer 18b.

[0035] In order to allow the working air flow between the first expansion chamber 32, the second expansion chamber 34 and the upper chamber 30 to be introduced into the first cold storage device 26 and the second cold storage device 28 instead of being introduced into the gap between the expander cylinder 16 and the displacer 18, a first seal 38a and a second seal 38b may be provided. The first seal 38a may be mounted on the upper cover of the first displacer 18a in a manner arranged between the first displacer 18a and the first cylinder 16a. The second seal 38b may be mounted on the upper cover of the second displacer 18b in a manner arranged between the second displacer 18b and the second cylinder 16b.

[0036] like Figure 3 As shown, the expander casing 20 includes: a casing 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 casing body 22. Figure 3 As shown, the housing inner volume 20 a formed by the housing body 22 and the lower cover 24 can be connected to the low-pressure side of the compressor 12 so as to be maintained at a low pressure.

[0037] The lower cover body 24 separates the internal volume 20a of the shell from the displacer accommodating space (upper chamber 30) in the expander cylinder 16. The lower cover body 24 is disc-shaped as a whole, and more specifically, has a large diameter portion on the upper side and a small diameter portion on the lower side. The first sealing component 25a is provided between the lower cover body 24 and the expander cylinder 16 to maintain the airtightness of the internal volume of the expander cylinder 16, and the second sealing component 25b is provided between the lower cover body 24 and the shell body 22 to maintain the airtightness of the internal volume 20a of the shell. As shown in the figure, the first sealing component 25a can be installed on the small diameter portion of the lower cover body 24, and the second sealing component 25b can be installed on the large diameter portion of the lower cover body 24.

[0038] The lower cover 24 is detachably embedded in the lower opening 21, and the upper flange portion of the expander cylinder 16 is fastened to the housing body 22 by fastening members such as bolts. In this way, the lower cover 24 is clamped between the housing body 22 and the upper flange portion of the expander cylinder 16. The lower cover 24 is not fastened to the housing body 22. However, a structure in which the housing body 22 and the lower cover 24 are fastened together by fastening members such as bolts may also be adopted.

[0039] Furthermore, the expander 14 includes an expander motor 40, a pressure switching valve 42, and a motion conversion mechanism 43. The expander motor 40 is mounted on the expander housing 20, more specifically, on the side of the housing body 22. In order to maintain the airtightness of the housing internal volume 20a, a sealing member (not shown) may be provided on the mounting surface between the expander motor 40 and the housing body 22. The pressure switching valve 42 and the motion conversion mechanism 43 are accommodated in the expander housing 20.

[0040] The expander motor 40 is provided in the expander 14 as a driving source for the displacer 18 and the pressure switching valve 42. The expander motor 40 may be an appropriate electric motor, and may be configured to rotate the motor rotating shaft 40a at a constant speed or to control the speed of the motor rotating shaft 40a to be variable.

[0041] The pressure switching valve 42 connects the high-pressure port 13a and the low-pressure port 13b to the expander cylinder 16 (i.e., the upper chamber 30, the first expansion chamber 32, and the second expansion chamber 34). The pressure switching valve 42 is configured to alternately connect the high-pressure port 13a and the low-pressure port 13b to the expander cylinder 16 and periodically switch the intake and exhaust of the expander cylinder 16.

[0042] Furthermore, the pressure switching valve 42 may be configured to temporarily disconnect both the high-pressure port 13a and the low-pressure port 13b from the expander cylinder 16 when switching the connection between the high-pressure port 13a and the low-pressure port 13b. At this time, the pressure switching valve 42 does not instantly switch the connection between the high-pressure port 13a and the low-pressure port 13b, but has a period during which the expander cylinder 16 is not connected to either the high-pressure port 13a or the low-pressure port 13b.

[0043] In this embodiment, the pressure switching valve 42 is in the form of a rotary valve. Therefore, the pressure switching valve 42 includes a valve rotor 42a and a valve stator 42b, and the valve rotor 42a contacts the valve stator 42b in a manner that the valve rotor 42a slides relative to the valve stator 42b and rotates. The valve rotor 42a is supported to be rotatable relative to the housing body 22, and the valve stator 42b is supported to be non-rotatable relative to the housing body 22. An elastic body such as a spring for pressing the valve stator 42b toward the valve rotor 42a in the direction of the rotation axis of the valve rotor 42a may be present between the valve stator 42b and the housing body 22.

[0044] A connecting flow path 20b is formed on the expander housing 20 from the pressure switching valve 42 to the expander cylinder 16. The connecting flow path 20b connects the pressure switching valve 42 to the upper chamber 30. A valve internal flow path is formed on the valve rotor 42a and the valve stator 42b of the pressure switching valve 42 in such a manner that the connecting flow path 20b is alternately connected to the high-pressure port 13a and the housing internal volume 20a (i.e., the low-pressure port 13b). The valve internal flow path can be formed in various well-known ways, which will not be described in detail here.

[0045] The motion conversion mechanism 43 is configured to connect the expander motor 40 to the pressure switching valve 42 and the displacer 18 in such a manner that the rotation of the motor rotating shaft 40a is transmitted to the pressure switching valve 42 and converted into a linear reciprocating movement of the displacer 18. An example of the motion conversion mechanism 43 will be described later. One rotation of the motor rotating shaft 40a realizes one reciprocation of the displacer 18 via the motion conversion mechanism 43, whereby the volume of the expansion space of the working gas changes periodically. At the same time, one rotation of the motor rotating shaft 40a realizes one rotation of the pressure switching valve 42 via the motion conversion mechanism 43, whereby the high-pressure port 13a and the low-pressure port 13b are alternately connected to the expander cylinder 16 via the pressure switching valve 42, and the pressure of the expansion space of the working gas changes periodically.

[0046] As a result, synchronous volume changes and pressure changes are generated in the expansion space, forming a refrigeration cycle of the ultra-low temperature refrigerator 10, so that the ultra-low temperature refrigerator 10 can provide the desired ultra-low temperature 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 can 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 can be, for example, below about 20K or below about 10K, or in the range of about 1K to about 4K. In the case where the ultra-low temperature refrigerator 10 is used to recondense the vaporized ultra-low temperature liquid, the cooling temperature (for example, the second cooling temperature) of the ultra-low temperature refrigerator 10 can be a temperature below the boiling point of the ultra-low temperature liquid.

[0047] like Figure 1 As shown, the expander 14 of the ultra-low temperature refrigerator 10 can be arranged on the airtight container 11. The airtight container 11 can be, for example, a vacuum container such as a cryostat. In the case where the ultra-low temperature refrigerator 10 is used to recondense the vaporized ultra-low temperature liquid, the airtight container 11 can constitute an ultra-low temperature liquid storage tank for storing the ultra-low temperature liquid. The expander 14 can be inserted into the airtight container 11 from an opening on the wall of the airtight container 11, and the expander casing 20 can be fixed to the airtight container 11 at the opening. The expander casing 20 is exposed to the surrounding environment of the airtight container 11 (for example, room temperature and atmospheric pressure environment), and the first cooling stage 33 and the second cooling stage 35 are arranged in the airtight container 11. The expander 14 can be longitudinally arranged on the airtight container 11 in a manner that the expander casing 20 faces upward and the first cooling stage 33 and the second cooling stage 35 face downward.

[0048] Figure 4 FIG. 4 is an exploded perspective view schematically showing a main part of the motion conversion mechanism 43 of the cold head according to the embodiment. Figure 3 and Figure 4 , an exemplary method of the motion conversion mechanism 43 is described.

[0049] In this embodiment, the motion conversion mechanism 43 is a scotch yoke, and includes a crank 44 having a crank pin 44a, a scotch yoke shaft 45, and a crank pin bearing 46. The scotch yoke shaft 45 includes a scotch yoke plate 45a, an upper rod 45b, and a lower rod 45c. The scotch yoke shaft 45 can be made of a metal material such as stainless steel.

[0050] The crank 44 is fixed to the motor rotating shaft 40a. The crank pin 44a extends parallel to the motor rotating shaft 40a at a position eccentric from the motor rotating shaft 40a. The crank pin 44a extends from the crank 44 toward the side opposite to the motor rotating shaft 40a.

[0051] The scotch yoke plate 45a is a rectangular plate-shaped member having a transverse window 47. The transverse window 47 extends in a direction perpendicular to the axial direction and the motor rotating shaft 40a. The transverse window 47 is rotatably provided with a crank pin bearing 46. The crank pin bearing 46 may be, for example, a roller bearing. An engaging hole 46a engaging with the crank pin 44a is formed at the center of the crank pin bearing 46, and the crank pin 44a passes through the engaging hole 46a.

[0052] On the side of the scotch yoke plate 45a opposite to the crank 44, the valve rotor 42a of the pressure switching valve 42 is arranged, and its central axis is arranged to be consistent with the motor rotating shaft 40a, and the distal end of the crank pin 44a passing through the engaging hole 46a is fixed to the valve rotor 42a.

[0053] 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, and these rods are coaxially arranged. The scotch yoke plate 45a and the upper rod 45b are accommodated in the expander casing 20, and the lower rod 45c passes through the lower cover 24 and extends to the outside of the expander casing 20. The end of the lower rod 45c is connected to the displacer 18 in the expander cylinder 16.

[0054] The first sliding bearing 48a is provided between the upper rod 45b and the housing body 22, and the second sliding bearing 48b is provided between the lower rod 45c and the lower cover body 24. The housing body 22 has a recessed portion at its upper portion for receiving the upper rod 45b, and the first sliding bearing 48a is arranged in the recessed portion and supports the upper rod 45b so as to be able to slide in the axial direction. The lower cover body 24 has a through hole at the center portion, and the second sliding bearing 48b is arranged in the through hole and supports the lower rod 45c so as to be able to slide in the axial direction. The second sliding bearing 48b is provided with a sealing portion such as a sliding seal or a gap seal so as to be airtight, thereby isolating the housing internal volume 20a from the upper chamber 30. There is no direct gas flow between the housing internal volume 20a and the upper chamber 30.

[0055] A collar 50 is fixed to the end of the lower rod 45c connected to the displacer 18 by a fixing pin 49. The collar 50 is a short cylindrical member into which the end of the lower rod 45c is inserted. A through hole is formed in the end of the lower rod 45c and the collar 50 in a direction orthogonal to the axial direction, and the collar 50 is fixed to the lower rod 45c by inserting the fixing pin 49 into the through hole.

[0056] The first displacer 18a has a cover 52a and a main body 52b. The cover 52a is an upper cover of the first displacer 18a and has a disc-like shape. The cover 52a is made of a metal material such as an anodized aluminum alloy or other materials. The main body 52b has a cylindrical shape and has a cold storage device inside. The main body 52b is made of a synthetic resin material or other materials, for example, it can be made of a phenolic resin such as phenolic plastic. The working gas flow path 36a is formed by axially penetrating the upper end of the cover 52a and the main body 52b. The first seal 38a can be sandwiched between the cover 52a and the main body 52b at their respective outermost peripheries. The cover 52a and the main body 52b are fixed to each other using a fastening member such as a bolt, or are fixed to each other by other methods such as bonding.

[0057] A through hole is formed at the center of the cover 52a to receive the end of the lower rod 45c and the collar 50. The collar 50 has a flange portion extending radially outward at the lower end thereof, and the lower rod 45c and the collar 50 are connected to the first displacer 18a by sandwiching the flange portion between the cover 52a and the main body 52b of the first displacer 18a. In this way, the displacer 18 is mounted on the scotch yoke shaft 45.

[0058] Therefore, when the expander motor 40 is driven to rotate the motor rotating shaft 40a, the crankpin bearing 46 engaged with the crankpin 44a rotates in a circular manner. At this time, the crankpin bearing 46 reciprocates in the transverse window 47 of the scotch yoke plate 45a, and at the same time, the scotch yoke shaft 45 and the displacer 18 reciprocate in the axial direction. In this way, the expander motor 40 drives the scotch yoke shaft 45 to move in the axial direction.

[0059] In this embodiment, if Figure 1 and Figure 3 As shown, the expander 14 has a gas receiving port 54 different from the high-pressure port 13a and the low-pressure port 13b. The gas receiving port 54 is provided on the expander housing 20 and is connected to the connecting flow path 20b so that the gas can flow into the connecting flow path 20b. Therefore, the gas receiving port 54 is not provided on the compressor 12 side (that is, the high-pressure port 13a and the low-pressure port 13b side) relative to the pressure switching valve 42, but is provided on the expander cylinder 16 side.

[0060] The gas receiving port 54 is not used and is closed during the normal operation of the cryogenic refrigerator 10 for cryogenic cooling. As described later, the gas receiving port 54 is opened and used in the gas replacement method of the expander 14 for restoring the cryogenic refrigerator 10 from maintenance work to normal operation.

[0061] The gas receiving port 54 is provided on the expander housing 20 and is therefore arranged outside the airtight container 11. Therefore, when the expander 14 is installed on the airtight container 11, the operator can approach the gas receiving port 54 from the outside of the airtight container 11, thereby making it easy to open and close the gas receiving port 54.

[0062] Similar to the high-pressure port 13a and the low-pressure port 13b, the gas receiving port 54 may be a detachable joint such as a self-sealing coupling, so that the pipe can be easily attached and detached from the gas receiving port 54 for gas replacement operation of the expander 14 .

[0063] The gas receiving port 54 may have a size different from that of the high pressure port 13a and the low pressure port 13b, for example, a size smaller than that of the high pressure port 13a and the low pressure port 13b. For example, the gas receiving port 54 may be a joint having a size (e.g., a nominal diameter) smaller than that of the joint constituting the high pressure port 13a (or the low pressure port 13b). In this way, by setting the size of the gas receiving port 54 to be different from that of the other ports, the gas receiving port 54 can be easily identified. This helps prevent the wrong connection of the piping between the gas receiving port 54 and the other ports.

[0064] The flow path cross-sectional area of ​​the gas receiving port 54 may be smaller than the flow path cross-sectional area of ​​the connecting flow path 20b. Here, the flow path cross-sectional area represents the flow path cross-sectional area in the direction perpendicular to the flow direction of the working gas. The gas receiving port 54 (and the flow path volume from the gas receiving port 54 to the connecting flow path 20b) is not used during the normal operation of the ultra-low temperature refrigerator 10, and therefore may become a dead volume (dead volume) that reduces the refrigeration capacity of the ultra-low temperature refrigerator 10. Therefore, by setting the flow path cross-sectional area of ​​the gas receiving port 54 to be smaller than the flow path cross-sectional area of ​​the connecting flow path 20b, this dead volume can be reduced, thereby reducing the adverse effects on the refrigeration capacity of the ultra-low temperature refrigerator 10.

[0065] Figure 5 1 is a flowchart showing a gas replacement method of the expander 14 of the cryogenic refrigerator 10 according to the embodiment. Figure 6 It is a schematic diagram showing the expander 14 of the cryogenic refrigerator 10 in the gas replacement method according to the embodiment.

[0066] The gas replacement method can be performed during the period when the ultra-low temperature refrigerator 10 is stopped (for example, maintenance work is performed on the ultra-low temperature refrigerator 10 and before the normal operation of the ultra-low temperature refrigerator 10 is restarted thereafter). During the maintenance work, the expander 14 is sometimes disassembled and reassembled, for example, in order to check or replace the internal components of the expander 14 such as the displacer assembly 18. In the case where the ultra-low temperature refrigerator 10 is mounted on a storage container of an ultra-low temperature liquid and is used for recondensation of vaporized ultra-low temperature liquid, if maintenance work is performed on the site, the vaporized ultra-low temperature liquid may be included in the surrounding atmosphere of the ultra-low temperature refrigerator 10. The gas may enter the interior of the expander 14 along with the maintenance work. In the case where the ultra-low temperature liquid is liquid hydrogen, since hydrogen is a flammable gas, the retained gas entering the expander 14 may contain flammable gas. If the operation of the ultra-low temperature refrigerator 10 is restarted in this state (i.e., the driving of the expander motor 40 is started), it is difficult to say that the contact between the electrical equipment in the expander 14 (i.e., the expander motor 40) and the combustible gas is avoided because it cannot be ensured that the internal volume of the expander 14 is filled only with non-flammable gas.

[0067] The gas replacement method of the expander 14 according to the embodiment includes the following steps: a step (S10) of connecting the incombustible gas source 60 to the connecting flow path 20b, and a step (S20) of purging the stagnant gas in the expander cylinder 16 with the incombustible gas from the incombustible gas source 60 during the stop period of the expander motor 40 (i.e., in a state where the expander motor 40 is de-energized). In addition, in the present method, when the purging of the stagnant gas is completed, the connection between the incombustible gas source 60 and the connecting flow path 20b is released, and the operation of the cryogenic refrigerator 10 is restarted.

[0068] Here, the inflammable gas is preferably the working gas of the cryogenic refrigerator 10, such as helium, so that after the removal of the trapped gas is completed, the internal volume of the expander cylinder 16 is filled with the working gas of the cryogenic refrigerator 10, so that the operation of the cryogenic refrigerator 10 can be immediately restarted.

[0069] In S10, the non-combustible gas source 60 is connected to the gas receiving port 54 of the connection flow path 20b by the gas replacement pipe 56. Figure 6 An example of connection between the expander 14 of the cryogenic refrigerator 10 and the non-flammable gas source 60 is shown in FIG.

[0070] The gas replacement piping 56 is provided with a gas supply valve 57. The gas supply valve 57 is provided on the main piping 56a of the gas replacement piping 56. An incombustible gas source 60 is connected to one end of the main piping 56a, and a joint that can be attached and detached to the gas receiving port 54 of the expander 14 is provided at the other end of the main piping 56a, and the main piping 56a is connected to the gas receiving port 54 through the joint. By opening the gas supply valve 57, incombustible gas is supplied from the incombustible gas source 60 to the gas receiving port 54, and by closing the gas supply valve 57, the supply of incombustible gas is stopped. The incombustible gas source 60 may be, for example, a gas cylinder filled with incombustible gas (for example, an inert gas such as helium) under high pressure.

[0071] Furthermore, the gas replacement piping 56 includes a gas outlet port 58 branching from the main piping 56a. The gas outlet port 58 may be, for example, an on-off valve. By opening the gas outlet port 58, the gas can be discharged from the gas replacement piping 56 to the outside, and by closing the gas outlet port 58, the gas discharge from the gas replacement piping 56 is stopped.

[0072] In S20, the incombustible gas from the incombustible gas source 60 is supplied from the gas replacement pipe 56 to the expander cylinder 16 through the gas receiving port 54. And the stagnant gas in the expander cylinder 16 is discharged from the gas outlet port 58 of the gas replacement pipe 56. In other words, the stagnant gas in the expander cylinder 16 is diluted by the supply of the incombustible gas, and the diluted gas is discharged from the expander cylinder 16. The supply of the incombustible gas and the discharge of the stagnant gas are performed during the stop period of the expander motor 40.

[0073] The supply of the incombustible gas and the discharge of the stagnant gas may be performed simultaneously. In this case, the gas supply valve 57 and the gas outlet port 58 are opened simultaneously. Alternatively, the supply of the incombustible gas and the discharge of the stagnant gas may be performed alternately. In this case, the supply state in which the gas supply valve 57 is opened and the gas outlet port 58 is closed and the discharge state in which the gas supply valve 57 is closed and the gas outlet port 58 is opened may be repeated alternately.

[0074] If the cryogenic refrigerator 10 stops operating, the pressure switching valve 42 will be in any of the following three states: the first state in which the high-pressure port 13a is connected to the expander cylinder 16, the second state in which the low-pressure port 13b is connected to the expander cylinder 16, or the third state in which neither the high-pressure port 13a nor the low-pressure port 13b is connected to the expander cylinder 16. Therefore, in a conventional cryogenic refrigerator that is not provided with a gas receiving port 54, even if a non-flammable gas source is connected to the high-pressure port 13a or the low-pressure port 13b and non-flammable gas is supplied from this portion, it is not guaranteed that the stagnant gas in the expander cylinder 16 will be purged. For example, in the third state, both the high-pressure port 13a and the low-pressure port 13b are cut off from the expander cylinder 16 by the pressure switching valve 42, so that the non-flammable gas is not supplied to the expander cylinder 16.

[0075] In contrast, according to the embodiment, since the gas receiving port 54 is connected to the connection flow path 20b from the pressure switching valve 42 to the expander cylinder 16, the incombustible gas source 60 can be connected to the expander cylinder 16 by the gas replacement pipe 56 in parallel with the pressure switching valve 42. Therefore, regardless of the state of the pressure switching valve 42, the stagnant gas in the expander cylinder 16 can be purged using the incombustible gas from the incombustible gas source 60, so that the internal volume of the expander cylinder 16 can be reliably replaced with the incombustible gas (for example, helium). When the operation of the cryogenic refrigerator 10 is resumed, the stagnant gas that may include flammable gas will not exist in the expander 14, and it can be ensured that the expander 14 is filled with incombustible gas. Therefore, the cryogenic refrigerator 10 can be restored from maintenance work to normal operation in a state where the electrical equipment in the expander 14 is prevented from contacting the flammable gas.

[0076] Furthermore, in S20, incombustible gas may also be supplied to the expander 14 from the high-pressure port 13a and the low-pressure port 13b. This may be performed simultaneously with the supply of incombustible gas to the expander cylinder 16 from the gas receiving port 54. Alternatively, the supply from the gas receiving port 54, the supply from the high-pressure port 13a, and the supply from the low-pressure port 13b may be performed in sequence (the order of the three is not limited). In order to supply incombustible gas to the expander 14 from the high-pressure port 13a, the incombustible gas source 60 may be connected to the high-pressure port 13a using the above-mentioned gas replacement piping 56. Similarly, in order to supply incombustible gas to the expander 14 from the low-pressure port 13b, the incombustible gas source 60 may be connected to the low-pressure port 13b using the above-mentioned gas replacement piping 56. In this way, incombustible gas may also be used to replace the stagnant gas in the internal volume of the expander 14 connected to the high-pressure port 13a and the low-pressure port 13b.

[0077] Figure 7FIG. 1 is a schematic diagram showing an expander 14 of a cryogenic refrigerator 10 in a gas replacement method according to an embodiment. Figure 7 As shown, a three-way gas replacement piping 56 can be used. The gas replacement piping 56 can include: a main piping 56a that can be connected to the incombustible gas source 60; a first branch pipe 56b that branches from the main piping 56a and can be connected to the gas receiving port 54 of the expander 14; a second branch pipe 56c that branches from the main piping 56a and can be connected to the high-pressure port 13a of the expander 14; and a third branch pipe 56d that branches from the main piping 56a and can be connected to the low-pressure port 13b of the expander 14. By using such a gas replacement piping 56, incombustible gas can be supplied to the expander 14 from the three ports (gas receiving port 54, high-pressure port 13a and low-pressure port 13b) of the expander 14 at the same time to purge the stagnant gas, so it is preferred.

[0078] In addition, similarly to the above-mentioned embodiment, the gas replacement piping 56 may also include a gas supply valve 57 on the main piping 56a. The gas replacement piping 56 may also include a gas outlet port 58 branched from the main piping 56a. Instead of the gas outlet port 58 branched from the main piping 56a, a gas outlet port 59 may be provided on the expander 14 (for example, the expander casing 20), or the gas outlet port 58 branched from the main piping 56a may be provided while also providing the gas outlet port 59 on the expander 14 (for example, the expander casing 20). In addition, the gas replacement piping 56 may also include a pressure sensor 62 for measuring the pressure of the gas supplied from the incombustible gas source 60.

[0079] Figure 8 It is a diagram schematically showing a cryogenic refrigerator 10 according to the embodiment. Figure 8 The internal structure of the driving part of the cold head is shown in FIG. Figure 8 As shown, there is known a so-called gas-assisted ultra-low temperature refrigerator 10, in which an airtight space (i.e., a gas-assisted chamber 64) is formed between the upper rod 45b of the stop rod yoke shaft 45 and the expander housing 20. Similar to the expander cylinder 16, the gas-assisted chamber 64 is also connected to the high-pressure port 13a and the low-pressure port 13b via the pressure switching valve 42. Therefore, a second connecting flow path 20c is formed in the expander housing 20 to connect the pressure switching valve 42 to the gas-assisted chamber 64. The pressure switching valve 42 is configured to alternately connect the high-pressure port 13a and the low-pressure port 13b to the gas-assisted chamber 64. As a result, the pressure difference periodically acting between the gas-assisted chamber 64 and the internal volume of the expander housing 20 can assist the stop rod yoke shaft 45 (i.e., the displacer 18) to reciprocate in the axial direction.

[0080] The expander 14 having such a gas assist chamber 64 may further include a second gas receiving port 55 connected to the second connecting flow path 20c in addition to the first gas receiving port 54 connected to the first connecting flow path 20b. The gas replacement method according to the embodiment may be applied to the gas assist chamber 64 through the second gas receiving port 55. In this way, the stagnant gas in the gas assist chamber 64 may be purged using the non-flammable gas. In the gas replacement of the expander 14 having the gas assist chamber 64, the gas assist port 55 may be used. Figure 7 The gas replacement pipe 56 shown in the figure is provided with a four-way gas replacement pipe having a fourth branch pipe branched from the main pipe 56 a and connectable to the gas assist chamber 64 of the expander 14 .

[0081] The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that the present invention is not limited to the above-mentioned embodiments, and various design changes can be made, and various modifications can exist, and such modifications are also within the scope of the present invention. Various features described in one embodiment can also be applied to another embodiment. The new embodiment generated by the combination has the effects of each of the combined embodiments.

[0082] In the above embodiment, an example is given in which the non-combustible gas source 60 uses the gas replacement piping 56 and is connected to the connecting flow path 20b through the gas receiving port 54, but other connection structures may also be used. In one embodiment, the non-combustible gas source 60 may also be connected to the expander cylinder 16 instead of being connected to the connecting flow path 20b. In this case, the gas receiving port 54 may be provided on the expander cylinder 16. The gas replacement piping 56 may be provided through the airtight container 11 in order to connect the gas receiving port 54 disposed in the airtight container 11 to the non-combustible gas source 60 disposed outside the airtight container 11.

[0083] In the above embodiment, the case where the cryogenic refrigerator 10 is a two-stage GM refrigerator is exemplified, but the cryogenic refrigerator 10 involved in the embodiment may also be, for example, a single-stage GM refrigerator (for example, providing cryogenic cooling from 20K to 80K) or other cryogenic refrigerators whose expansion machines are equipped with a pressure switching valve. In this case, the gas replacement method involved in the embodiment can also be applied in the same manner.

[0084] The present invention has been described above based on the embodiments. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various design changes and variations are possible, and such variations are also within the scope of the present invention.

Claims

1. A method, which is a gas replacement method for an expander of a cryogenic refrigerator, The expander has: Expander cylinder; A pressure switching valve for switching the pressure in the expander cylinder; a connecting flow path extending from the pressure switching valve to the expander cylinder; and an expander motor, driving the pressure switching valve, The method is characterized by comprising the following steps: A connecting step of connecting a non-combustible gas source to the connecting flow path or the expander cylinder; and A purging step of purging the gas retained in the expander cylinder using the incombustible gas from the incombustible gas source while the expander motor is stopped.

2. The method according to claim 1, characterized in that The connecting step includes connecting the non-combustible gas source to the gas receiving port of the connecting flow path by using a gas replacement pipe. The purging step includes supplying the incombustible gas from the incombustible gas source from the gas replacement pipe to the expander cylinder via the gas receiving port and discharging the stagnant gas from the gas replacement pipe or the gas outlet port of the expander.

3. The method according to claim 2, characterized in that The expander includes a high-pressure port and a low-pressure port connected to the expander cylinder via the pressure switching valve. The purging step includes the step of supplying an incombustible gas to the expander from the high-pressure port and the low-pressure port.

4. The method according to any one of claims 1 to 3, characterized in that The non-flammable gas is the working gas of the ultra-low temperature refrigerator.

5. A cryogenic refrigerator, characterized in that: have: Expander cylinder; A pressure switching valve for switching the pressure in the expander cylinder; a high-pressure port and a low-pressure port connected to the expander cylinder via the pressure switching valve; a connecting flow path extending from the pressure switching valve to the expander cylinder; and A gas receiving port is a port different from the high-pressure port and the low-pressure port and is connected to the connecting flow path so that gas can flow into the connecting flow path.

6. The ultra-low temperature refrigerator according to claim 5, characterized in that: The ultra-low temperature refrigerator further comprises an expander housing coupled to the expander cylinder and accommodating the pressure switching valve. The gas receiving port is disposed on the expander housing.

7. The ultra-low temperature refrigerator according to claim 6, characterized in that: In addition to the high-pressure port, the low-pressure port and the gas receiving port, the expander housing is also provided with a gas outlet port.

8. The ultra-low temperature refrigerator according to claim 5, characterized in that: The gas receiving port has a size different from sizes of the high pressure port and the low pressure port.

9. The ultra-low temperature refrigerator according to any one of claims 5 to 8, characterized in that: A flow path cross-sectional area of ​​the gas receiving port is smaller than a flow path cross-sectional area of ​​the connecting flow path.

10. A gas replacement piping used for gas replacement of an expander of a cryogenic refrigerator, characterized in that: have: A main pipe capable of being connected to a non-combustible gas source; a first branch pipe branched from the main pipe and connectable to a gas receiving port of the expander; a second branch pipe branched from the main pipe and connectable to a high-pressure port of the expander; and The third branch pipe branches from the main pipe and can be connected to the low-pressure port of the expander.

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