Cryocooler and method for operating a cryocooler

Abstract

An ultra-low temperature refrigerator (10) is provided with: an expander (14) capable of performing initial cooling from an initial temperature to an ultra-low temperature and steady operation for maintaining the ultra-low temperature after the initial cooling; a high-pressure line (63) connected to the expander (14) and through which working gas sucked by the expander (14) flows; a low-pressure line (64) connected to the expander (14) and through which working gas discharged from the expander (14) flows; a first pressure sensor (54) that measures the pressure of the high-pressure line (63); a buffer volume (70) that stores the working gas; a supply valve (72) that connects the buffer volume (70) to the low-pressure line (64); and a controller (110) that controls the supply valve (72) during the initial cooling based on the pressure of the high-pressure line (63) measured by the first pressure sensor (54) to keep the pressure of the high-pressure line (63) within a predetermined appropriate pressure range.

Description

Technical Field

[0001] This invention relates to an ultra-low temperature refrigerator and its operating method. Background Technology

[0002] Cryogenic refrigerators are used to cool various objects, such as superconducting equipment, measuring equipment, and samples, that operate in ultra-low temperature environments. When using a cryogenic refrigerator to cool an object, the refrigerator must first be started to cool it from an initial temperature, such as room temperature, to the target ultra-low temperature. This initial cooling process is also known as temperature reduction.

[0003] Previous technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 11-257768 Summary of the Invention

[0006] The technical problem to be solved by the invention

[0007] When using a cryogenic refrigerator to cool an object, the refrigerator must first be started to cool it from an initial temperature such as room temperature to the target cryogenic temperature. This initial cooling process is also known as temperature reduction. Initial cooling is merely a preparatory step before cooling the object; therefore, it is desirable that the time required for this process be as short as possible.

[0008] One of the exemplary objectives of one embodiment of the present invention is to shorten the initial cooling time of the cryogenic refrigerator.

[0009] means for solving technical problems

[0010] According to one embodiment of the present invention, an ultra-low temperature refrigerator is provided, comprising: an expander capable of performing initial cooling from an initial temperature to an ultra-low temperature and subsequent steady-state operation to maintain the ultra-low temperature; a high-pressure line connected to the expander and through which working gas drawn in by the expander flows; a low-pressure line connected to the expander and through which working gas discharged from the expander flows; a pressure sensor for measuring the pressure of the high-pressure line; a buffer volume for storing the working gas; a supply valve connecting the buffer volume to the low-pressure line; and a controller that, during initial cooling, controls the supply valve based on the pressure of the high-pressure line measured by the pressure sensor, so that the pressure of the high-pressure line is maintained within a predetermined appropriate pressure range.

[0011] According to one embodiment of the present invention, a method for operating an ultra-low temperature cryogenic refrigerator is provided. The ultra-low temperature cryogenic refrigerator includes: an expander; a high-pressure line connected to the expander and supplying working gas drawn into the expander; a low-pressure line connected to the expander and supplying working gas discharged from the expander; a pressure sensor for measuring the pressure of the high-pressure line; a buffer volume for storing the working gas; and a supply valve connecting the buffer volume to the low-pressure line. The method includes the following steps: performing initial cooling to cool the expander from an initial temperature to an ultra-low temperature; and, after the initial cooling, performing steady-state operation to maintain the expander at the ultra-low temperature. During the initial cooling, the supply valve is controlled based on the pressure of the high-pressure line measured by the pressure sensor to maintain the pressure of the high-pressure line within a predetermined appropriate pressure range.

[0012] Furthermore, any combination of the above-mentioned constituent elements, or embodiments in which the constituent elements or descriptions of the present invention are interchanged among methods, apparatuses, systems, etc., are also valid as embodiments of the present invention.

[0013] Invention Effects

[0014] According to the present invention, the initial cooling time of the cryogenic refrigerator can be shortened. Attached Figure Description

[0015] Figure 1 This is a diagram that roughly illustrates the cryogenic refrigerator involved in the implementation method.

[0016] Figure 2 This is a diagram that roughly illustrates the cryogenic refrigerator involved in the implementation method.

[0017] Figure 3 This is a flowchart illustrating the control method of the cryogenic refrigerator involved in the implementation method.

[0018] Figure 4 This is a flowchart illustrating the control method of the cryogenic refrigerator involved in the implementation method.

[0019] Figure 5 This is a graph illustrating an example of temperature and pressure changes during the operation of the cryogenic refrigerator involved in the embodiment.

[0020] Figure 6 Figures (A) and (B) are diagrams illustrating an example of pressure changes during operation of the cryogenic refrigerator according to the embodiment.

[0021] Figure 7 This is a graph illustrating an example of temperature and pressure changes during the operation of the cryogenic refrigerator involved in the embodiment.

[0022] Figure 8 This is a diagram that roughly illustrates the cryogenic refrigerator involved in the implementation method. Detailed Implementation

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same or equivalent constituent elements, components, and processes are labeled with the same symbols, and repeated descriptions are omitted where appropriate. For ease of explanation, scales or shapes of various parts are appropriately shown in the drawings, which are not intended to be limiting unless otherwise specified. The embodiments are illustrative and do not limit the scope of the invention in any way. All features or combinations thereof described in the embodiments are not necessarily essential to the invention.

[0024] Figure 1 and Figure 2 This is a schematic diagram illustrating the cryogenic refrigerator 10 involved in the embodiment. As an example, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator. Figure 1 The diagram schematically shows the cryogenic device 100 and the compressor 12 and expander 14 constituting the cryogenic refrigerator 10. Figure 2 The internal structure of the expander 14 of the cryogenic refrigerator 10 is shown.

[0025] 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 then supply it 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 also referred to as the cold head. The working gas is also referred to as the refrigerant gas, typically helium, but other suitable gases may also be used. For ease of understanding, in Figure 1 The arrows in the diagram indicate the direction of the working gas flow.

[0026] Furthermore, the pressure of the working gas supplied from compressor 12 to expander 14 and the pressure of the working gas returned from expander 14 to compressor 12 are typically much higher than atmospheric pressure, and 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 will also be simply 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, arrows are used to indicate the flow direction of the working gas.

[0027] The expander 14 includes a refrigerant cylinder 16 and a displacement assembly 18. The refrigerant cylinder 16 guides the displacement assembly 18 in a linear reciprocating motion, and forms expansion chambers 32 and 34 for the working gas between the refrigerant cylinder 16 and the displacement assembly 18. Furthermore, the expander 14 includes a pressure switching valve 40, which determines the start time of the intake of working gas into the expansion chambers and the start time of the exhaust of working gas from the expansion chambers.

[0028] In this specification, to illustrate the positional relationships between the components of the cryogenic refrigerator 10, for convenience, the side closer to the top dead center of the axial reciprocating movement of the displacement device is labeled "upper," and the side closer to the bottom dead center is labeled "lower." The top dead center is the position where the displacement device has the largest volume of the expansion space, and the bottom dead center is the position where the displacement device has the smallest volume of the expansion space. During operation of the cryogenic refrigerator 10, a temperature gradient is generated from the upper axial direction downwards; therefore, the upper side can also be referred to as the high-temperature side, and the lower side as the low-temperature side.

[0029] The refrigeration unit cylinder block 16 includes a first cylinder block 16a and a second cylinder block 16b. As an example, the first cylinder block 16a and the second cylinder block 16b are cylindrical components, with the diameter of the second cylinder block 16b being smaller than the diameter of the first cylinder block 16a. The first cylinder block 16a and the second cylinder block 16b are coaxially arranged, and the lower end of the first cylinder block 16a is rigidly connected to the upper end of the second cylinder block 16b.

[0030] The displacement assembly 18 includes a first displacement 18a and a second displacement 18b connected together, which move integrally. As an example, the first displacement 18a and the second displacement 18b are cylindrical components, with the diameter of the second displacement 18b being smaller than the diameter of the first displacement 18a. The first displacement 18a and the second displacement 18b are coaxially arranged.

[0031] The first displacement device 18a is housed in the first cylinder block 16a, and the second displacement device 18b is housed in the second cylinder block 16b. The first displacement device 18a is capable of axial reciprocating along the first cylinder block 16a, and the second displacement device 18b is capable of axial reciprocating along the second cylinder block 16b.

[0032] like Figure 2 As shown, the first displacement device 18a houses the first cold storage device 26. The first cold storage device 26 is formed by filling the cylindrical main body of the first displacement device 18a with a metal wire mesh, such as copper, or other suitable first cold storage material. The upper and lower cover portions of the first displacement device 18a can be components different from the main body of the first displacement device 18a. The upper and lower cover portions of the first displacement device 18a can be fixed to the main body by appropriate methods such as fastening or welding, thereby accommodating the first cold storage material within the first displacement device 18a.

[0033] Similarly, the second displacement device 18b houses the second cold storage device 28. The second cold storage device 28 is formed by filling the cylindrical main body of the second displacement device 18b with, for example, a non-magnetic cold storage material such as bismuth, a magnetic cold storage material such as HoCu2, or other suitable second cold storage material. The second cold storage material can be formed in granular form. The upper and lower cover portions of the second displacement device 18b can be components different from the main body of the second displacement device 18b. The upper and lower cover portions of the second displacement device 18b can be fixed to the main body by appropriate methods such as fastening or welding, thereby accommodating the second cold storage material within the second displacement device 18b.

[0034] The displacement assembly 18 forms a chamber 30, a first expansion chamber 32, and a second expansion chamber 34 inside the cryogenic cylinder 16. For heat exchange with the desired object or medium to be cooled by the cryogenic cryo-engine 10, the expander 14 includes a first cooling platform 33 and a second cooling platform 35. The chamber 30 is formed between the upper cover of the first displacement assembly 18a and the upper part of the first cylinder 16a. The first expansion chamber 32 is formed between the lower cover of the first displacement assembly 18a and the first cooling platform 33. The second expansion chamber 34 is formed between the lower cover of the second displacement assembly 18b and the second cooling platform 35. The first cooling platform 33 is fixed to the lower part of the first cylinder 16a surrounding the first expansion chamber 32, and the second cooling platform 35 is fixed to the lower part of the second cylinder 16b surrounding the second expansion chamber 34.

[0035] The first cold accumulator 26 is connected to the chamber 30 via a working gas flow path 36a formed on the upper cover of the first displacement device 18a, and is connected to the first expansion chamber 32 via a working gas flow path 36b formed on the lower cover of the first displacement device 18a. The second cold accumulator 28 is connected to the first cold accumulator 26 via a working gas flow path 36c formed from the lower cover of the first displacement device 18a to the upper cover of the second displacement device 18b. Furthermore, the second cold accumulator 28 is connected to the second expansion chamber 34 via a working gas flow path 36d formed on the lower cover of the second displacement device 18b.

[0036] To prevent the working airflow between the first expansion chamber 32, the second expansion chamber 34, and the chamber temperature 30 from entering the gap between the refrigeration cylinder 16 and the displacement assembly 18 and thus into the first accumulator 26 and the second accumulator 28, a first seal 38a and a second seal 38b can be provided. The first seal 38a can be installed on the upper cover of the first displacement assembly 18a, positioned between the first displacement assembly 18a and the first cylinder 16a. The second seal 38b can be installed on the upper cover of the second displacement assembly 18b, positioned between the second displacement assembly 18b and the second cylinder 16b.

[0037] like Figure 1As shown, the expander 14 has a refrigerator housing 20 that houses the pressure switching valve 40. The refrigerator housing 20 is combined with the refrigerator cylinder 16, thereby forming an airtight container that houses the pressure switching valve 40 and the displacement assembly 18.

[0038] like Figure 2 As shown, the pressure switching valve 40 is configured to have a high-pressure valve 40a and a low-pressure valve 40b, and to generate periodic pressure fluctuations within the refrigeration unit cylinder 16. The working gas outlet of the compressor 12 is connected to the chamber 30 via the high-pressure valve 40a, and the working gas inlet of the compressor 12 is connected to the chamber 30 via the low-pressure valve 40b. The high-pressure valve 40a and the low-pressure valve 40b are configured to selectively alternately open and close (i.e., while one valve is open, the other valve is closed).

[0039] The pressure switching valve 40 can also be a rotary valve. That is, the pressure switching valve 40 can also be configured to alternately open and close the high-pressure valve 40a and the low-pressure valve 40b by rotating and sliding the valve disc relative to the stationary valve body. In this case, the expander motor 42 can be connected to the pressure switching valve 40 in a way that rotates the valve disc of the pressure switching valve 40. For example, the pressure switching valve 40 can be configured such that the valve rotation axis is coaxial with the rotation axis of the expander motor 42.

[0040] Alternatively, the high-pressure valve 40a and the low-pressure valve 40b can be valves that can be controlled separately. In this case, the pressure switching valve 40 may not be connected to the expander motor 42.

[0041] The expander motor 42 is connected to the displacement drive shaft 44 via a motion conversion mechanism 43, such as an anti-rotation yoke mechanism. The expander motor 42 is mounted in the refrigerator housing 20. Similar to the pressure switching valve 40, the motion conversion mechanism 43 is also housed within the refrigerator housing 20. The motion conversion mechanism 43 converts the rotational motion output by the expander motor 42 into the linear reciprocating motion of the displacement drive shaft 44. The displacement drive shaft 44 extends from the motion conversion mechanism 43 toward the chamber 30 and is fixed to the upper cover of the first displacement device 18a. The rotation of the expander motor 42 is converted by the motion conversion mechanism 43 into the axial reciprocating motion of the displacement drive shaft 44, thereby causing the displacement assembly 18 to reciprocate axially within the refrigerator cylinder 16.

[0042] Furthermore, the expander 14 may also be equipped with a temperature sensor 46, which measures the temperature of the second cooling stage 35 (and / or the first cooling stage 33) and outputs a measured temperature signal representing the measured temperature.

[0043] The compressor 12 includes a high-pressure gas outlet 50, a low-pressure gas inlet 51, a high-pressure flow path 52, a low-pressure flow path 53, a first pressure sensor 54, a second pressure sensor 55, a bypass pipe 56, a compressor body 57, and a compressor frame 58. The high-pressure gas outlet 50 is located in the compressor frame 58 as the working gas discharge port of the compressor 12, and the low-pressure gas inlet 51 is located in the compressor frame 58 as the working gas intake port of the compressor 12. The high-pressure flow path 52 connects the discharge port of the compressor body 57 to the high-pressure gas outlet 50, and the low-pressure flow path 53 connects the low-pressure gas inlet 51 to the intake port of the compressor body 57. The compressor frame 58 houses the high-pressure flow path 52, the low-pressure flow path 53, the first pressure sensor 54, the second pressure sensor 55, the bypass pipe 56, and the compressor body 57. The compressor 12 is also referred to as a compressor unit.

[0044] The compressor body 57 is configured to internally compress the working gas drawn in from its inlet and discharge it from its outlet. The compressor body 57 can be, for example, a scroll pump, a rotary pump, or other pump that pressurizes the working gas. In this embodiment, the compressor body 57 is configured to discharge a constant flow rate of working gas. Alternatively, the compressor body 57 may be configured to allow a variable flow rate of the discharged working gas. The compressor body 57 is sometimes also referred to as a compression chamber.

[0045] The first pressure sensor 54 is disposed on the high-pressure flow path 52 to measure the pressure of the working gas flowing through the high-pressure flow path 52. The first pressure sensor 54 is configured to output a first measured pressure signal PH indicating the measured pressure. The second pressure sensor 55 is disposed on the low-pressure flow path 53 to measure the pressure of the working gas flowing through the low-pressure flow path 53. The second pressure sensor 55 is configured to output a second measured pressure signal PL indicating the measured pressure. Therefore, the first pressure sensor 54 and the second pressure sensor 55 can also be referred to as a high-pressure sensor and a low-pressure sensor, respectively. Furthermore, in this specification, either the first pressure sensor 54 or the second pressure sensor 55, or both, are sometimes referred to as "pressure sensors".

[0046] A bypass line 56 connects the high-pressure flow path 52 and the low-pressure flow path 53, allowing the working gas to bypass the expander 14 and return from the high-pressure flow path 52 to the low-pressure flow path 53. A safety valve 60 is provided on the bypass line 56 for opening and closing the bypass line 56 or controlling the flow rate of the working gas flowing through the bypass line 56. The safety valve 60 is configured to open when a pressure difference exceeding a set pressure acts between its inlet and outlet. The safety valve 60 can be an on / off valve or a flow control valve, for example, a solenoid valve. The set pressure can be appropriately set based on the designer's experience, experiments, or simulations. This prevents the pressure difference between the high-pressure line 63 and the low-pressure line 64 from exceeding the set pressure. Furthermore, it prevents the pressure in the high-pressure line 63 from becoming excessive.

[0047] Safety valve 60 can be configured to operate as a so-called safety valve, that is, to mechanically open when a pressure difference above a set pressure acts between the inlet and outlet. Alternatively, safety valve 60 can also be opened and closed under the control of control device 100. Control device 100 can control safety valve 60 by comparing the measured pressure difference between high-pressure line 63 and low-pressure line 64 with a set pressure, and opening safety valve 60 when the measured pressure difference is above the set pressure, and closing safety valve 60 when the measured pressure difference is below the set pressure. Control device 100 can obtain the measured pressure difference between high-pressure line 63 and low-pressure line 64 based on a first measured pressure signal PH from first pressure sensor 54 and a second measured pressure signal PL from second pressure sensor 55. As another example, control device 100 can also control safety valve 60 by comparing the measured pressure of high-pressure line 63 with an upper limit pressure based on the first measured pressure signal PH, and opening safety valve 60 when the measured pressure is above the upper limit pressure, and closing safety valve 60 when the measured pressure is below the upper limit pressure.

[0048] In addition, the compressor 12 may have various other components. For example, an oil separator, an adsorber, etc., may be provided on the high-pressure flow path 52. A storage tank and other components may be provided on the low-pressure flow path 53. Furthermore, an oil circulation system that uses oil to cool the compressor body 57 and a cooling system for cooling the oil may be provided on the compressor 12.

[0049] Furthermore, the cryogenic refrigerator 10 includes a gas pipeline 62 that circulates the working gas between the compressor 12 and the expander 14. The gas pipeline 62 includes a high-pressure pipeline 63 connecting the compressor 12 and the expander 14 to supply working gas from the compressor 12 to the expander 14, and a low-pressure pipeline 64 connecting the compressor 12 and the expander 14 to recover working gas from the expander 14 back to the compressor 12. A high-pressure gas inlet 22 and a low-pressure gas outlet 24 are provided on the refrigerator housing 20 of the expander 14. The high-pressure gas inlet 22 is connected to the high-pressure gas outlet 50 via a high-pressure piping 65, and the low-pressure gas outlet 24 is connected to the low-pressure gas inlet 51 via a low-pressure piping 66. The high-pressure pipeline 63 consists of the high-pressure piping 65 and the high-pressure flow path 52, and the low-pressure pipeline 64 consists of the low-pressure piping 66 and the low-pressure flow path 53. The bypass pipeline 56 can be considered part of the gas pipeline 62. The bypass line 56 connects the high-pressure line 63 and the low-pressure line 64 so that the working gas bypasses the expander 14 and flows back from the high-pressure line 63 to the low-pressure line 64.

[0050] Therefore, the working gas recovered from expander 14 to compressor 12 enters the low-pressure gas inlet 51 of compressor 12 from the low-pressure gas outlet 24 of expander 14 through low-pressure piping 66, and then returns to compressor body 57 via low-pressure flow path 53, where it is compressed and pressurized. The working gas supplied from compressor 12 to expander 14 exits from compressor body 57 through high-pressure flow path 52 and is discharged from high-pressure gas outlet 50 of compressor 12, and then is further supplied to expander 14 via high-pressure piping 65 and high-pressure gas inlet 22 of expander 14.

[0051] Furthermore, the cryogenic refrigerator 10 includes a buffer volume 70, a supply valve 72, and a recovery valve 74. The buffer volume 70 is a volume used to store the working gas; for example, it can be a buffer tank. The supply valve 72 connects the buffer volume 70 to the low-pressure line 64, and the recovery valve 74 connects the buffer volume 70 to the high-pressure line 63. The supply valve 72 and the recovery valve 74 can be on / off valves or flow control valves; for example, they can be solenoid valves.

[0052] During periods when the cryogenic refrigerator 10 is not in operation, the pressure of the buffer volume 70 becomes the sealing pressure of the working gas sealed in the cryogenic refrigerator 10. During periods when the cryogenic refrigerator 10 is in operation (e.g., during initial cooling or steady-state operation), the pressure of the buffer volume 70 becomes the intermediate pressure between the pressure of the high-pressure line 63 and the pressure of the low-pressure line 64 (e.g., the average pressure of the high and low pressures).

[0053] Therefore, during the operation of the cryogenic refrigerator 10, if the supply valve 72 is opened, the working gas is supplied from the buffer volume 70 to the low-pressure line 64 after passing through the supply valve 72. If the supply valve 72 is closed, the supply of working gas from the buffer volume 70 to the low-pressure line 64 is stopped. Furthermore, if the recovery valve 74 is opened, the working gas is recovered from the high-pressure line 63 to the buffer volume 70 after passing through the recovery valve 74. If the recovery valve 74 is closed, the recovery of working gas from the high-pressure line 63 to the buffer volume 70 is stopped. Thus, by opening and closing the supply valve 72 and the recovery valve 74, the amount of working gas circulating in the gas line 62 can be adjusted, and consequently, the pressures of the high-pressure line 63 and the low-pressure line 64 can also be controlled.

[0054] like Figure 1As shown, the control device 100 for controlling the cryogenic refrigerator 10 includes a controller 110 that controls the supply valve 72 and the recovery valve 74. The controller 110 is electrically connected to a first pressure sensor 54 and a second pressure sensor 55 to acquire a first measured pressure signal PH and a second measured pressure signal PL. As explained later, the controller 110 is configured to receive the first measured pressure signal PH from the first pressure sensor 54 and open / close the supply valve 72 and the recovery valve 74 based on the measured pressure of the high-pressure line 63 represented by the first measured pressure signal PH. Furthermore, the controller 110 is electrically connected to a temperature sensor 46 to acquire a measured temperature signal from the temperature sensor 46.

[0055] In the illustrated example, the control device 100 is separately installed and connected to the compressor 12 and expander 14, but it is not limited to this. The control device 100 may also be mounted on the compressor 12. The control device 100 may also be mounted on the expander motor 42, etc. (i.e., mounted on the expander 14). The controller 110 may also be mounted on the supply valve 72 or the recovery valve 74, or may be mounted on the supply valve 72 and the recovery valve 74 respectively.

[0056] The control device 100 is implemented in terms of hardware structure through components or circuits, such as a computer's CPU or memory, and in terms of software structure through computer programs, etc. Figure 1 The functional blocks that are realized through their cooperation are appropriately depicted. Those skilled in the art will understand that these functional blocks can be implemented in various forms through a combination of hardware and software.

[0057] During the operation of compressor 12 and expander motor 42, the cryogenic refrigerator 10 generates periodic volume changes and synchronous pressure changes of the working gas in the first expansion chamber 32 and the second expansion chamber 34. Typically, in the intake process, by closing the low-pressure valve 40b and opening the high-pressure valve 40a, high-pressure working gas flows from compressor 12 through high-pressure valve 40a into chamber 30, and is supplied to the first expansion chamber 32 via the first accumulator 26, and then to the second expansion chamber 34 via the second accumulator 28. As a result, the first expansion chamber 32 and the second expansion chamber 34 are pressurized from low pressure to high pressure. At this time, the displacement assembly 18 moves from bottom dead center to top dead center, and the volume of the first expansion chamber 32 and the second expansion chamber 34 increases. If the high-pressure valve 40a is closed, the intake process ends.

[0058] During the exhaust process, by closing the high-pressure valve 40a and opening the low-pressure valve 40b, the high-pressure first expansion chamber 32 and second expansion chamber 34 are connected to the low-pressure working gas inlet of the compressor 12. Therefore, the working gas expands in the first expansion chamber 32 and second expansion chamber 34, resulting in the low-pressure working gas being discharged from the first expansion chamber 32 and second expansion chamber 34 through the first accumulator 26 and second accumulator 28 towards the chamber temperature 30. At this time, the displacement assembly 18 moves from top dead center to bottom dead center, and the volume of the first expansion chamber 32 and second expansion chamber 34 decreases. The working gas is recovered from the expander 14 to the compressor 12 after passing through the low-pressure valve 40b. If the low-pressure valve 40b is closed, the exhaust process ends.

[0059] This forms a refrigeration cycle (e.g., a GM cycle), whereby the first cooling stage 33 and the second cooling stage 35 are cooled to the desired ultra-low temperature. The first cooling stage 33 can be cooled to a first cooling temperature (e.g., in the range of about 20K to about 40K). The second cooling stage 35 can be cooled to a second cooling temperature lower than the first cooling temperature (e.g., about 1K to about 4K).

[0060] The cryogenic refrigerator 10 is capable of performing initial cooling and steady-state operation following initial cooling. Initial cooling is the operating mode of the expander 14, which rapidly cools from an initial temperature to a cryogenic state when the cryogenic refrigerator 10 is started. Steady-state operation is the operating mode of the expander 14, which maintains the cryogenic state achieved through initial cooling. The initial temperature can be the ambient temperature (e.g., room temperature). The expander 14 is cooled to a standard cooling temperature based on the initial cooling and maintained within the permissible temperature range of the cryogenic state, including this standard cooling temperature, during steady-state operation. The standard cooling temperature varies depending on the application and settings of the cryogenic refrigerator 10. For example, in applications involving cooling superconducting devices, a typical standard cooling temperature is below approximately 4.2 K. In other cooling applications, the standard cooling temperature may be, for example, approximately 10 K to 20 K, or below 10 K. As mentioned above, initial cooling can also be referred to as temperature reduction.

[0061] However, during initial cooling, as the temperature drops from the initial temperature to the cryogenic temperature, the density of the working gas within the expander 14 increases. Consequently, the amount of working gas stored within the expander 14 increases, meaning that working gas is drawn into the expander 14 from the gas line 62. As a result, as the expander 14 cools, the pressure of the working gas circulating within the gas line 62 gradually decreases. This pressure drop in the working gas leads to a reduction in the cooling capacity of the cryogenic refrigerator 10, and therefore may contribute to a longer initial cooling time. Initial cooling is merely a preparation for beginning the cooling of the object using the cryogenic refrigerator; therefore, it is desirable that the required time be as short as possible.

[0062] To address this issue, in this embodiment, the controller 110 controls the supply valve 72 during the initial cooling period based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, so that the pressure of the high-pressure line 63 is maintained within a preset appropriate pressure range. More specifically, the controller 110 may compare the measured pressure of the high-pressure line 63 during the initial cooling period with a lower limit Pc of the appropriate pressure range and actuate the supply valve 72 to repeatedly open and close it, so as to prevent the pressure of the high-pressure line 63 from falling below the lower limit Pc.

[0063] Furthermore, in this embodiment, the controller 110 controls the recovery valve 74 during the initial cooling period based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, so as to maintain the pressure of the high-pressure line 63 within an appropriate pressure range. More specifically, the controller 110 may compare the measured pressure of the high-pressure line 63 during the initial cooling period with an upper limit value Pd of the appropriate pressure range and actuate the recovery valve 74 to repeatedly open and close it, so as to prevent the pressure of the high-pressure line 63 from exceeding the upper limit value Pd.

[0064] Figure 3 This is a flowchart illustrating the control method of the cryogenic refrigerator 10 according to the embodiment. During the initial cooling of the cryogenic refrigerator 10, the controller 110 repeatedly executes this method according to a predetermined cycle. Furthermore, this method can be executed not only during the initial cooling period but also during the steady-state operation of the cryogenic refrigerator 10.

[0065] First, the pressure of the high-pressure line 63 is measured (S10). The first pressure sensor 54 measures the pressure of the high-pressure line 63 and outputs a first measured pressure signal PH representing the measured pressure of the high-pressure line 63. The controller 110 receives the first measured pressure signal PH and acquires the measured pressure of the high-pressure line.

[0066] Next, the measured pressure of the high-pressure line 63 is compared with an appropriate pressure range (S12). The lower limit Pc of the appropriate pressure range is set to ensure that the cryogenic refrigerator 10 provides sufficient cooling capacity. The upper limit Pd of the appropriate pressure range is set to prevent excessive pressure from being generated in the high-pressure line 63. The upper limit Pd of the appropriate pressure range can be set to a pressure value lower than the aforementioned set pressure that opens the safety valve 60. The appropriate pressure range can be appropriately set based on the designer's experience, experiments, or simulations. The appropriate pressure range can be pre-stored in the controller 110 as the initial setting for the cryogenic refrigerator 10, or it can be set by the user in the controller 110 before the cryogenic refrigerator 10 is operated.

[0067] As an example, the upper limit Pd and lower limit Pc of the appropriate pressure range can be selected from the range of 2 MPa to 3 MPa or the range of 2.1 MPa to 2.7 MPa. The range of the appropriate pressure range (i.e., the difference between the upper limit Pd and the lower limit Pc) can be set to a value within 0.5 MPa, 0.3 MPa, or 0.1 MPa. For example, the appropriate pressure range can be set to 2.45 ± 0.05 MPa, in which case the range of the appropriate pressure range is 0.1 MPa, the upper limit Pd is 2.5 MPa, and the lower limit Pc is 2.4 MPa.

[0068] The controller 110 compares the measured pressure of the high-pressure line 63 with the lower limit Pc of the appropriate pressure range, and opens the supply valve 72 (S14) when the measured pressure of the high-pressure line 63 is lower than the lower limit Pc (PH < Pc). As a result, working gas is supplied from the buffer volume 70 to the low-pressure line 64 after passing through the supply valve 72. Because the amount of working gas circulating in the gas line 62 increases, the pressure in the high-pressure line 63 is restored.

[0069] The controller 110 closes the supply valve 72 (S16) when the measured pressure of the high-pressure line 63 returns to the appropriate pressure range. For example, the controller 110 can compare the measured pressure of the high-pressure line 63 with the lower limit Pc of the appropriate pressure range, and close the supply valve 72 when the measured pressure of the high-pressure line 63 becomes above the lower limit Pc (PH>Pc or Ph≥Pc). If the supply valve 72 is closed, the supply of working gas from the buffer volume 70 to the low-pressure line 64 is stopped. Thus, the method ends and is executed again in the next control cycle.

[0070] Furthermore, the pressure threshold for closing the supply valve 72 may differ from the lower limit Pc of the appropriate pressure range; for example, it may be greater than the lower limit Pc. This pressure threshold may be set to not exceed the upper limit Pd of the appropriate pressure range. For example, the pressure threshold may also be a value obtained by adding a predetermined proportion of the range of the appropriate pressure range (upper limit Pd - lower limit Pc) to the lower limit Pc. The predetermined proportion may be, for example, less than 50%, less than 30%, or less than 10%.

[0071] Figure 4 This is a flowchart illustrating the control method of the cryogenic refrigerator 10 according to the embodiment. During the initial cooling of the cryogenic refrigerator 10, the controller 110 repeatedly executes this method according to a predetermined cycle. This method can be combined with... Figure 3 The methods shown are executed together. In addition, this method can be executed not only during the initial cooling period, but also during the steady-state operation of the cryogenic refrigerator 10.

[0072] First, the pressure of the high-pressure line 63 is measured using the first pressure sensor 54 (S20). The controller 110 receives the first measured pressure signal PH from the first pressure sensor 54 and acquires the measured pressure of the high-pressure line.

[0073] Next, the measured pressure of the high-pressure line 63 is compared with an appropriate pressure range (S22). The controller 110 compares the measured pressure of the high-pressure line 63 with the upper limit Pd of the appropriate pressure range, and when the measured pressure of the high-pressure line 63 is greater than the upper limit Pd (PH > Pd), the recovery valve 74 is opened (S24). As a result, the working gas is recovered from the high-pressure line 63 to the buffer volume 70 after passing through the recovery valve 74, and the pressure of the high-pressure line 63 decreases.

[0074] When the measured pressure in the high-pressure line 63 returns to the appropriate pressure range, the controller 110 closes the recovery valve 74 (S26). For example, the controller 110 can compare the measured pressure in the high-pressure line 63 with the upper limit Pd of the appropriate pressure range, and close the recovery valve 74 when the measured pressure in the high-pressure line 63 falls below the upper limit Pd (PH < Pd or PH ≤ Pd). If the recovery valve 74 is closed, the recovery of working gas from the high-pressure line 63 to the buffer volume 70 is stopped. This ends the process and the process is repeated in the next control cycle.

[0075] Furthermore, the pressure threshold for closing the recovery valve 74 can differ from the upper limit Pd of the appropriate pressure range; for example, it can be less than the upper limit Pd. This pressure threshold can be selected from the appropriate pressure range, i.e., it can be greater than the lower limit Pc of the appropriate pressure range.

[0076] During the operation of the cryogenic refrigerator 10, the appropriate pressure range can be varied. For example, the appropriate pressure range during initial cooling can differ from the appropriate pressure range during steady-state operation; for instance, it can be higher than the appropriate pressure range during steady-state operation. For example, the lower limit Pc during initial cooling can be higher than the lower limit Pc during steady-state operation, and / or, the upper limit Pd during initial cooling can be higher than the upper limit Pd during steady-state operation.

[0077] At this time, the switching from initial cooling to steady-state operation and the change of the appropriate pressure range can be controlled by the control device 100. For example, the control device 100 can compare the measured temperature of the second cooling stage 35 (and / or the first cooling stage 33) with the aforementioned standard cooling temperature based on the measured temperature signal from the temperature sensor 46, and perform initial cooling when the measured temperature is higher than the standard cooling temperature, and switch from initial cooling to steady-state operation when the measured temperature is lower than the standard cooling temperature. The controller 110 can also change the appropriate pressure range in conjunction with the switching from initial cooling to steady-state operation.

[0078] Furthermore, as referenced Figure 7 and Figure 8 As will be explained later, the switching from initial cooling to steady-state operation and the change of appropriate pressure range can also be based on the pressure of the buffer volume 70 or the pressure difference between the high-pressure line 63 and the low-pressure line 64. In this way, the control device 100 can complete the initial cooling of the cryogenic refrigerator 10 without relying on the temperature sensor 46.

[0079] Here, in order to reliably supply the working gas from the buffer volume 70, the conditions required for the buffer volume 70 are considered. According to the ideal gas law, during the period when the cryogenic refrigerator 10 is not operating (i.e., before initial cooling), the following equation holds.

[0080] PI(VH+VL+VB)=nRT(1)

[0081] Here, PI (MPa) represents the working gas sealing pressure of the cryogenic refrigerator 10 at temperature T (K), VH (L) represents the volume of the high-pressure pipeline 63, VL (L) represents the volume of the low-pressure pipeline 64, VB (L) represents the volume of the buffer volume 70, n (mol) represents the amount of working gas in the cryogenic refrigerator 10, and R represents the gas constant.

[0082] Similarly, during the steady-state operation of the cryogenic refrigerator 10, the following equation holds true.

[0083] PHVH+PLVL+PBVB=nRT(2)

[0084] Here, PH (MPa) represents the pressure of high-pressure pipeline 63 in steady-state operation at temperature T, PL (MPa) represents the pressure of low-pressure pipeline 64 in steady-state operation at temperature T, and PB (MPa) represents the pressure of buffer volume 70 in steady-state operation at temperature T.

[0085] According to equations (1) and (2), we can obtain PI(VH+VL+VB)=PHVH+PLVL+PBVB(3).

[0086] In order to supply working gas from buffer volume 70 to low-pressure pipeline 64 at any time during the operation of cryogenic refrigerator 10, the following formula should be satisfied at any temperature T within the temperature range from the initial temperature to the cryogenic temperature of cryogenic refrigerator 10.

[0087] PL≤PB(4)

[0088] If we solve equation (3) to obtain PB and substitute it into equation (4), we can obtain the following relationship.

[0089] VB≥VH(PH-PI) / (PI-PL)-VL(5)

[0090] Therefore, in order to reliably supply working gas from buffer volume 70 to low-pressure line 64, it is preferable that buffer volume 70 satisfies equation (5) at any temperature in the temperature range from initial temperature to ultra-low temperature.

[0091] Similarly, in order to reliably recover gas from the buffer volume 70, the conditions required for the buffer volume 70 must be considered. At this time, in order to supply working gas from the buffer volume 70 to the high-pressure pipeline 63 at any time during the operation of the cryogenic refrigerator 10, the following formula should be satisfied at any temperature T within the temperature range from the initial temperature to the cryogenic temperature of the cryogenic refrigerator 10.

[0092] PB≤PH(6)

[0093] If we solve equation (3) to obtain PB and substitute it into equation (6), we can obtain the following relationship.

[0094] VB≥-VH+VL(PI-PL) / (PH-PI) (7)

[0095] Therefore, in order to reliably recover working gas from high-pressure line 63 to buffer volume 70, it is preferable that buffer volume 70 satisfies equation (7) at any temperature in the temperature range from initial temperature to ultra-low temperature.

[0096] Figure 5 This is a graph illustrating, for example, the time-varying temperature and pressure changes during operation of the cryogenic refrigerator 10 according to the embodiment. The pressure changes shown are obtained experimentally. Figure 5 The upper part shows the pressure PH of the high-pressure line 63 measured by the first pressure sensor 54 and the pressure PL of the low-pressure line 64 measured by the second pressure sensor 55. Figure 5 The lower part shows the temperature T1 of the first cooling stage 33 and the temperature T2 of the second cooling stage 35. The horizontal axis represents time.

[0097] Before starting the cryogenic refrigerator 10 (time 0), the pressure PH of the high-pressure line 63 and the pressure PL of the low-pressure line 64 are both the sealing pressure PI, and the temperatures T1 of the first cooling platform 33 and T2 of the second cooling platform 35 are both room temperature (approximately 300K). If the cryogenic refrigerator 10 is started to begin initial cooling, the compressor 12 and expander 14 begin operation. The pressure PH of the high-pressure line 63 increases from the sealing pressure PI, and the pressure PL of the low-pressure line 64 decreases from the sealing pressure PI. Through initial cooling, the temperatures T1 of the first cooling platform 33 and T2 of the second cooling platform 35 continuously decrease. If the first cooling platform 33 and the second cooling platform 35 are cooled to the aforementioned standard cooling temperatures (e.g., T1 ≤ 30K, T2 ≤ 4K), the initial cooling ends and the system switches to steady-state operation.

[0098] Figure 6 The enlarged representation in (A) shows Figure 5 Part A shown, Figure 6 The middle (B) section enlarges the representation of Figure 5 Part B is shown. Figure 6 In diagram (A), the pressure PH of the high-pressure line 63 after initial cooling is shown along with the open / closed state of the recovery valve 74. Figure 6 In section (B), the pressure PH of the high-pressure line 63, which is further delayed than that in section A, is shown along with the opening and closing state of the supply valve 72.

[0099] like Figure 6 As shown in (A), if the pressure PH of the high-pressure line 63 exceeds the upper limit Pd of the appropriate pressure range, the recovery valve 74 is opened. The working gas is recovered from the high-pressure line 63 to the buffer volume 70 after passing through the recovery valve 74, thus lowering the pressure PH of the high-pressure line 63. If the pressure PH of the high-pressure line 63 falls below the upper limit pressure Pd, the recovery valve 74 is closed. This prevents excessive pressure build-up in the high-pressure line 63, reducing the risk of an emergency shutdown of the compressor 12. Furthermore, the buffer volume 70 is pressurized through the recovery of the working gas, thus enabling efficient supply of working gas from the buffer volume 70 to the low-pressure line 64.

[0100] like Figure 6 As shown in (B), if the pressure PH of the high-pressure line 63 falls below the lower limit Pc of the appropriate pressure range, the supply valve 72 is opened. Working gas is supplied from the buffer volume 70 to the low-pressure line 64 through the supply valve 72. As the amount of working gas circulating in the gas line 62 increases, the pressure in the high-pressure line 63 is restored. If the pressure PH of the high-pressure line 63 exceeds the lower limit Pc, the supply valve 72 is closed.

[0101] As described above, due to the temperature drop in the expander 14 during initial cooling, the density of the working gas inside the expander 14 increases, which causes the pressure PH in the high-pressure line 63 to decrease. Therefore, even if the pressure PH in the high-pressure line 63 temporarily recovers, it will again fall below the lower limit value Pc. At this time, the supply valve 72 is opened, and if the pressure in the high-pressure line 63 recovers, the supply valve 72 is closed. Thus, the supply valve 72 operates in a repeated opening and closing manner to maintain the pressure PH in the high-pressure line 63 within an appropriate pressure range.

[0102] Assuming that working gas is not supplied to gas line 62 during the initial cooling period, the pressure PH of high-pressure line 63 may decrease significantly due to the temperature drop in expander 14. The cooling capacity of cryogenic refrigerator 10 is related to the pressure PH of high-pressure line 63; therefore, the cooling capacity of cryogenic refrigerator 10 may decrease as initial cooling progresses. This would be a reason for the longer initial cooling time.

[0103] In contrast, according to the embodiment, by controlling the supply valve 72 during the initial cooling period, the pressure PH of the high-pressure line 63 can be maintained within an appropriate pressure range. Therefore, the cooling capacity of the cryogenic refrigerator 10 can be reliably maintained, and the increase in initial cooling time can be suppressed. Furthermore, by keeping the pressure PH of the high-pressure line 63 substantially constant, the cryogenic refrigerator 10 can provide stable cooling capacity.

[0104] In this embodiment, because a bypass line 56 and a safety valve 60 are provided, when the pressure PH of the high-pressure line 63 increases, the working gas can be released from the high-pressure line 63 to the low-pressure line 64 through the bypass line 56, thereby suppressing excessive pressure rise. However, this bypass flow reduces the flow rate of the working gas supplied from the compressor 12 to the expander 14, which may reduce the cooling capacity of the cryogenic refrigerator 10. However, in this embodiment, the pressure PH of the high-pressure line 63 can be maintained within an appropriate pressure range using the buffer volume 70, thus eliminating the need for a bypass flow, which is advantageous.

[0105] To maintain the pressure PH of the high-pressure line 63 within an appropriate pressure range, a method of controlling the supply valve 72 and the recovery valve 74 based on the pressure of the low-pressure line 64 can also be considered. The pressure of the low-pressure line 64 is affected by the cooling temperature of the expander 14 (it varies depending on the cooling temperature). Therefore, in practical applications, the appropriate pressure range of the low-pressure line 64 (i.e., the pressure threshold of the low-pressure line 64 used to open and close the supply valve 72 and the recovery valve 74) must be set to a value that varies depending on the cooling temperature, thus complicating the control design. Furthermore, even if the low-pressure line 64 is within an appropriate pressure range, the pressure of the high-pressure line 63 may become excessively high depending on the cooling temperature. Therefore, the method based on the pressure of the high-pressure line 63, as in the embodiment, is advantageous in mitigating or preventing such adverse conditions.

[0106] Figure 7 This is a graph illustrating an example of the time-varying temperature and pressure changes during operation of the cryogenic refrigerator 10 according to the embodiment. Figure 8 This is a diagram that schematically illustrates the cryogenic refrigerator 10 involved in the embodiment.

[0107] Similar to the embodiments described above, the cryogenic refrigerator 10 includes a compressor 12, an expander 14, a buffer volume 70, and a control device 100. During initial cooling, the controller 110 controls the supply valve 72 based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, thereby maintaining the pressure of the high-pressure line 63 within a preset appropriate pressure range. Furthermore, during initial cooling, the controller 110 controls the recovery valve 74 based on the pressure of the high-pressure line 63 measured by the first pressure sensor 54, thereby maintaining the pressure of the high-pressure line 63 within an appropriate pressure range.

[0108] The cryogenic refrigerator 10 includes a buffer pressure sensor 76 connected to a buffer volume 70 to measure the pressure of the buffer volume 70. The buffer pressure sensor 76 is configured to be electrically connected to the control device 100 and output a measured buffer pressure signal PB, representing the measured pressure, to the control device 100.

[0109] exist Figure 7 The upper part shows Figure 5 The pressure PH of the high-pressure line 63 and the pressure PL of the low-pressure line 64 are shown, and the pressure PB of the buffer volume 70 measured by the buffer pressure sensor 76 is also shown. Figure 7 The lower part shows the temperature T1 of the first cooling platform 33 and the temperature T2 of the second cooling platform 35. From Figure 7 It can be seen that if the cryogenic refrigerator 10 is sufficiently cooled after the initial cooling is completed and the temperatures of the first cooling platform 33 and the second cooling platform 35 become stable, then the pressure PH of the high-pressure pipeline 63 and the pressure PL of the low-pressure pipeline 64 will also become stable. At this time, both the supply valve 72 and the recovery valve 74 are closed, and the buffer volume 70 is disconnected from the gas pipeline 62. Therefore, the pressure PB of the buffer volume 70 will also become constant. Figure 7 The final buffer pressure PF is shown.

[0110] Therefore, by detecting when the pressure PB of buffer volume 70 stabilizes, the end of the initial cooling can be determined. If the working gas inlet pressure PI and operating conditions of the cryogenic refrigerator 10 are known (e.g., high pressure PH, low pressure PL, temperature T1, T2, etc.), the final pressure of buffer volume 70 at the end of the initial cooling can be predicted. At this time, the controller 110 can also compare the predicted final buffer pressure with the measured pressure PB of buffer volume 70, and determine whether the measured pressure PB of buffer volume 70 is equal to the predicted final buffer pressure based on the comparison result. The controller 110 can also terminate the initial cooling if the state where the measured pressure PB of buffer volume 70 is equal to the predicted final buffer pressure continues for a predetermined time (e.g., several minutes).

[0111] Alternatively, controller 110 can calculate the difference between the measured pressure PB of buffer volume 70 and the reference pressure during the initial cooling period and determine the end of the initial cooling period by detecting when the calculated pressure difference stabilizes. The reference pressure can be the previously measured pressure of buffer volume 70, for example, it can be the maximum pressure PM of buffer volume 70 measured during the initial cooling period. Figure 7 It can be seen that the pressure of the buffer volume 70 increases from the initial sealing pressure PI after the initial cooling and reaches the maximum value PM.

[0112] The controller 110 can compare the calculated pressure difference (i.e., the difference between the measured pressure PB of the buffer volume 70 and the reference pressure) with the target pressure difference value and determine whether the calculated pressure difference is equal to the target pressure difference value based on the comparison result. The controller 110 can end the initial cooling when the state in which the calculated pressure difference is equal to the target pressure difference value continues for a specified time. The specified time can be selected, for example, from more than 1 minute to less than 10 minutes. If the difference between the calculated pressure difference and the target pressure difference value is within a specified value (e.g., 0.05 MPa), the calculated pressure difference can be considered equal to the target pressure difference value. This target pressure difference value does not depend on the sealing pressure PI, therefore, even if the sealing pressure PI is unknown, the end of the initial cooling can be determined.

[0113] As another example of reference pressure, the pressure PH of the high-pressure line 63 (or the pressure PL of the low-pressure line 64) measured simultaneously with the measured pressure PB of the buffer volume 70 can also be used. The controller 110 can also calculate the difference between the measured pressure PB of the buffer volume 70 and the measured pressure PH of the high-pressure line 63 (or the measured pressure PL of the low-pressure line 64) and detect when the calculated pressure difference becomes stable to determine the end of the initial cooling. Similarly, as in the example above, the controller 110 can compare the calculated pressure difference with a target pressure difference value and end the initial cooling when the calculated pressure difference equals the target pressure difference value and remains so for a specified time.

[0114] As a further alternative, the controller 110 can also calculate the difference between the measured pressure PH of the high-pressure line 63 and the measured pressure PL of the low-pressure line 64, and detect when the calculated pressure difference becomes stable to determine the end of the initial cooling.

[0115] The present invention has been described above with reference to embodiments. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and various design changes and modifications are possible, 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. New embodiments resulting from combinations possess the effects of each of the combined embodiments.

[0116] In the above embodiment, the case where the expander motor 42 operates at a constant operating frequency (motor speed) (i.e., the expander motor 42 operates at the same operating frequency during initial cooling and steady-state operation) has been described as an example, but the present invention is not limited to this. The cryogenic refrigerator 10 may also include an expander motor 42 with a variable operating frequency, which can perform so-called accelerated cooling during the initial cooling period by operating the expander motor 42 at a frequency higher than that during steady-state operation. In this case, as described above... Figure 7 and Figure 8 As explained, the switching from initial cooling (accelerated cooling) to steady-state operation and the change in operating frequency can be made based on the pressure of buffer volume 70 or the pressure difference between high-pressure line 63 and low-pressure line 64. By performing accelerated cooling, the initial cooling time can be further shortened.

[0117] Pressure sensors such as the first pressure sensor 54 and the second pressure sensor 55 do not necessarily have to be installed on the compressor 12. They can also be installed at any location capable of measuring pressure, such as the gas line 62 or the expander 14. For example, the first pressure sensor 54 can be installed at any location on the high-pressure line 63, and the second pressure sensor 55 can be installed at any location on the low-pressure line 64.

[0118] In the above embodiment, the supply valve 72 and the recovery valve 74 are each provided as separate valves and are respectively connected to the buffer volume 70, but the present invention is not limited thereto. For example, the supply valve 72 and the recovery valve 74 can be integrated, for example, they can be a three-way valve connected to the buffer volume 70. The supply state of connecting the buffer volume 70 to the low-pressure line 64 and the recovery state of connecting the buffer volume 70 to the high-pressure line 63 can be switched by switching the three-way valve.

[0119] In the above embodiment, the buffer volume 70 is a single buffer tank, but in one embodiment, the buffer volume 70 may also be multiple buffer tanks. One buffer tank can be connected to the low-pressure line 64 via the supply valve 72, and the other buffer tanks can be connected to the high-pressure line 63 via the recovery valve 74. Furthermore, in the above embodiment, the buffer volume 70 is disposed outside the compressor 12 and the expander 14, but it is not limited to this. For example, the buffer volume 70 may also be disposed inside the compressor 12.

[0120] In the above embodiments, the case of a two-stage GM refrigerator 10 as the cryogenic refrigerator 10 was described as an example, but it is not limited to this. The cryogenic refrigerator 10 can also be a single-stage or multi-stage GM refrigerator, and it can also be other types of cryogenic refrigerators such as pulse tube refrigerators.

[0121] The present invention has been described above with reference to the embodiments. Those skilled in the art should understand that the present invention is not limited to the above-described embodiments, and various design changes and modifications are possible, and such modifications are also within the scope of the present invention.

[0122] Industrial availability

[0123] This invention can be applied to the field of cryogenic refrigerators and methods for operating cryogenic refrigerators.

[0124] Symbol Explanation

[0125] 10-Cryogenic refrigerator, 14-Expander, 63-High pressure pipeline, 64-Low pressure pipeline, 70-Buffer volume, 72-Supply valve, 74-Recovery valve, 76-Buffer pressure sensor, 110-Controller.

Claims

1. An ultra-low temperature refrigerator, characterized in that, have: An expander capable of performing initial cooling from an initial temperature to an ultra-low temperature and then maintaining steady-state operation at the ultra-low temperature following the initial cooling; A high-pressure pipeline is connected to the expander and through which the working gas drawn in by the expander flows; A low-pressure pipeline is connected to the expander and through which the working gas discharged from the expander flows; A pressure sensor measures the pressure in the high-pressure pipeline; Buffer volume for storing working gas; A supply valve connects the buffer volume to the low-pressure pipeline; The controller controls the supply valve based on the pressure of the high-pressure line measured by the pressure sensor during the initial cooling period, so as to keep the pressure of the high-pressure line within a preset appropriate pressure range; and A buffer pressure sensor measures the pressure in the buffer volume. The controller terminates the initial cooling based on the pressure of the buffer volume measured by the buffer pressure sensor.

2. The cryogenic refrigerator according to claim 1, characterized in that, The controller compares the measured pressure of the high-pressure line during the initial cooling period with the lower limit of the appropriate pressure range and causes the supply valve to operate in a repetitive opening and closing manner to prevent the pressure of the high-pressure line from falling below the lower limit.

3. The cryogenic refrigerator according to claim 1 or 2, characterized in that, When the buffer volume is denoted as VB, the volume of the high-pressure pipeline as VH, the volume of the low-pressure pipeline as VL, the working gas sealing pressure at a certain temperature as PI, the pressure of the high-pressure pipeline in steady-state operation at that temperature as PH, and the pressure of the low-pressure pipeline in steady-state operation at that temperature as PL, the buffer volume satisfies VB≥VH(PH-PI) / (PI-PL)-VL at any temperature within the temperature range from the initial temperature to the ultra-low temperature.

4. The cryogenic refrigerator according to claim 1 or 2, characterized in that, It also includes a recovery valve that connects the buffer volume to the high-pressure pipeline. The controller controls the recovery valve in a manner that maintains the pressure in the high-pressure pipeline within the appropriate pressure range.

5. The cryogenic refrigerator according to claim 4, characterized in that, When the buffer volume is denoted as VB, the volume of the high-pressure pipeline as VH, the volume of the low-pressure pipeline as VL, the working gas sealing pressure at a certain temperature as PI, the pressure of the high-pressure pipeline in steady-state operation at that temperature as PH, and the pressure of the low-pressure pipeline in steady-state operation at that temperature as PL, the buffer volume satisfies VB≥-VH+VL(PI-PL) / (PH-PI) at any temperature within the temperature range from the initial temperature to the ultra-low temperature.

6. A method for operating an ultra-low temperature refrigerator, the ultra-low temperature refrigerator comprising: an expander; a high-pressure pipeline connected to the expander and through which working gas drawn in by the expander flows; a low-pressure pipeline connected to the expander and through which working gas discharged from the expander flows; a pressure sensor for measuring the pressure of the high-pressure pipeline; a buffer volume; and a supply valve connecting the buffer volume to the low-pressure pipeline, characterized in that... The method includes the following steps: Perform initial cooling to cool the expander from its initial temperature to an ultra-low temperature; Following the initial cooling, the expander is then kept in a steady-state operation at the ultra-low temperature. During the initial cooling period, the supply valve is controlled based on the pressure of the high-pressure line measured by the pressure sensor, so that the pressure of the high-pressure line is maintained within a preset appropriate pressure range. The pressure in the buffer volume was measured during the initial cooling period; and The initial cooling is terminated based on the measured pressure of the buffer volume.

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