Gas-driven cryogenic refrigerator

Abstract

The present invention addresses the problem of improving the quietness of a gas-driven cryogenic refrigerator. Provided is a gas-driven cryogenic refrigerator (10) capable of performing initial cooling for cooling from an initial temperature to an ultra-low temperature, and steady-state operation for continuing to maintain the ultra-low temperature after the initial cooling. A cryogenic refrigerator (10) is provided with: a compressor (12); a cold head (14); and a flow restrictor (100) connected between the compressor (12) and the cold head (14) and configured to restrict a flow of the working gas flowing to the cold head (14) during initial cooling compared to during steady-state operation.

Description

[0001] This application claims priority based on Japanese Patent Application No. 2024-115601 filed on July 19, 2024. The entire contents of the Japanese application are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to a gas-driven ultra-low temperature refrigerator. BACKGROUND

[0003] A GM (Gifford-McMahon) refrigerator, which is one of representative examples of an ultra-low temperature refrigerator, is broadly classified into a motor-driven type and a gas-driven type according to a driving source of a displacer. In the motor-driven type, the displacer is mechanically coupled to a motor, and is driven by the motor. In the gas-driven type, the displacer is driven by gas pressure.

[0004] Patent Literature 1: International Publication No. 2020 / 049936

[0005] An ultra-low temperature refrigerator is used for cooling various objects, such as superconducting devices, measuring devices, samples, and the like, which are used in an ultra-low temperature environment. When an object is cooled with an ultra-low temperature refrigerator, it is necessary to first start the ultra-low temperature refrigerator and cool the ultra-low temperature refrigerator from an initial temperature, such as room temperature, to a target ultra-low temperature. This initial cooling of the ultra-low temperature refrigerator is also referred to as a temperature drop. After the temperature drop, the ultra-low temperature refrigerator is operated in a manner to maintain a state of being cooled to the ultra-low temperature. Through this steady-state operation, the ultra-low temperature refrigerator is able to cool the object.

[0006] In many cases, the amount of working gas enclosed in the ultra-low temperature refrigerator is set to be able to operate the ultra-low temperature refrigerator at an optimum operating pressure in a steady-state operation, that is, in a state of being cooled to the ultra-low temperature. At the stage of starting the temperature drop, the operating pressure of the ultra-low temperature refrigerator tends to be high because the temperature of the ultra-low temperature refrigerator at this time is an initial temperature that is much higher than the ultra-low temperature in the steady-state operation. Due to this, the gas pressure that drives the displacer can also become high during the temperature drop, particularly at the initial stage of the temperature drop. In a typical gas-driven ultra-low temperature refrigerator, the displacer moves by the gas pressure until it interferes with (for example, collides with) the end portion of the cylinder. The interference can generate noise (for example, a collision sound). If the gas pressure is increased, the noise can also become noticeable. SUMMARY

[0007] One of the exemplary objects of an embodiment of the present application is to improve the quietness of a gas-driven ultra-low temperature refrigerator.

[0008] According to one embodiment of the present application, there is provided a gas-driven ultra-low temperature refrigerator capable of performing initial cooling from an initial temperature to an ultra-low temperature and steady operation for continuously maintaining the ultra-low temperature after the initial cooling. The gas-driven ultra-low temperature refrigerator includes a compressor, a cold head, and a flow restrictor connected between the compressor and the cold head, the flow restrictor being configured to restrict a flow rate of working gas flowing to the cold head during the initial cooling as compared to the steady operation.

[0009] Effects of Invention

[0010] According to the present application, it is possible to improve the quietness of a gas-driven ultra-low temperature refrigerator. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a diagram schematically showing an ultra-low temperature refrigerator according to an embodiment.

[0012] Figure 2 is a diagram schematically showing an ultra-low temperature refrigerator according to an embodiment.

[0013] Figure 3 is a diagram schematically showing another example of a flow restrictor applicable to an ultra-low temperature refrigerator according to an embodiment.

[0014] Figure 4 is a diagram schematically showing another example of an ultra-low temperature refrigerator according to an embodiment.

[0015] Figure 5 is a diagram schematically showing another example of a flow restrictor applicable to an ultra-low temperature refrigerator according to an embodiment.

[0016] Figure 6 is a diagram schematically showing another example of a flow restrictor applicable to an ultra-low temperature refrigerator according to an embodiment.

[0017] In the drawings: 10 - ultra-low temperature refrigerator, 12 - compressor, 14 - cold head, 20 - displacer, 22 - drive piston, 26 - displacer cylinder, 29 - drive chamber, 34 - expansion chamber, 60 - main pressure switching valve, 62 - sub pressure switching valve, 100 - flow restrictor, 102 - flow control valve, 104 - gas volume, 106 - gas pressure actuator, 108 - valve body, 110b - pressure chamber, 116 - valve body stopper. DETAILED DESCRIPTION

[0018] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings. In the following description and drawings, like or equivalent components, members and processes are designated by like reference numerals, and repeated description is omitted. In order to facilitate the description, the proportions or shapes of the parts are appropriately set in each drawing, and unless otherwise specified, they are not to be construed as limiting interpretations. The embodiments are exemplary, and do not limit the scope of the present application in any way. All features described in the embodiments and combinations thereof do not necessarily constitute the essential nature of the present application.

[0019] Figure 1 and Figure 2 is a schematic view showing a super- cryogenic refrigerator 10 to which the embodiments are applied. The super-cryogenic refrigerator 10 is, for example, a gas-driven GM refrigerator.

[0020] The super-cryogenic refrigerator 10 is provided with a compressor 12 that compresses a working gas (for example, helium) and a cold head 14 that cools the working gas by adiabatic expansion. The compressor 12 has a compressor discharge port 12a and a compressor suction port 12b. The compressor discharge port 12a and the compressor suction port 12b function as a high-pressure source and a low-pressure source of the super-cryogenic refrigerator 10, respectively. The cold head 14 is also referred to as an expander.

[0021] As will be described later in detail, the compressor 12 supplies high-pressure (PH) working gas from the compressor discharge port 12a to the cold head 14. The cold head 14 is provided with a regenerator 15 for pre-cooling the working gas. The pre-cooled working gas is further cooled by expansion within the cold head 14. The working gas is recovered to the compressor suction port 12b through the regenerator 15. The working gas cools the regenerator 15 when passing therethrough. The compressor 12 compresses the recovered low-pressure (PL) working gas and supplies it again to the cold head 14.

[0022] The illustrated cold head 14 is single-stage. However, the cold head 14 can also be multi-stage.

[0023] The cold head 14 is provided with an axial movable body 16 that is driven by gas pressure as a free piston and a cold head case 18 that is airtightly constructed and houses the axial movable body 16. The cold head case 18 supports the axial movable body 16 and enables it to reciprocate along the axial direction, while serving as a pressure container for the working gas. Unlike a motor-driven GM refrigerator, the cold head 14 does not have a motor and a linking mechanism (for example, a stopper yoke mechanism) that drive the axial movable body 16.

[0024] The axial movable body 16 is provided with a piston 16a that is airtightly fitted to the cold head case 18 and a piston rod 16b that is airtightly fitted to the piston 16a and extends in the axial direction (in the Figure 1The displacer 20 extends in the axial direction (indicated by the arrow C) and is capable of reciprocating movement in the axial direction, and the drive piston 22 is coaxially linked to the displacer 20 in such a manner as to drive the displacer 20 in the axial direction. The drive piston 22 is rigidly linked to the displacer 20 so as to integrally move the displacer 20 and the drive piston 22 in the axial direction. The drive piston 22 has a smaller size than the displacer 20. The axial length of the drive piston 22 is shorter than the axial length of the displacer 20, and the diameter of the drive piston 22 is also smaller than the diameter of the displacer 20.

[0025] The cold head housing 18 is provided with a displacer cylinder 26 that houses the displacer 20 and enables the displacer 20 to reciprocate in the axial direction, and a piston cylinder 28 that houses the drive piston 22 and enables the drive piston 22 to reciprocate in the axial direction. A drive chamber 29 that houses the drive piston 22 is formed in the piston cylinder 28. The piston cylinder 28 is coaxially arranged with the displacer cylinder 26 and is arranged adjacent to the displacer cylinder 26 in the axial direction. Details will be described later, but the drive section of the gas-driven cold head 14 is configured to include the drive piston 22 and the piston cylinder 28. The volume of the piston cylinder 28 is smaller than the volume of the displacer cylinder 26. The axial length of the piston cylinder 28 is shorter than the axial length of the displacer cylinder 26, and the diameter of the piston cylinder 28 is also smaller than the diameter of the displacer cylinder 26.

[0026] The axial reciprocating movement of the displacer 20 is guided by the displacer cylinder 26. Typically, the displacer 20 and the displacer cylinder 26 are each a cylindrical member that extends in the axial direction, and the inner diameter of the displacer cylinder 26 is identical to or slightly larger than the outer diameter of the displacer 20. Similarly, the axial reciprocating movement of the drive piston 22 is guided by the piston cylinder 28. Typically, the drive piston 22 and the piston cylinder 28 are each a cylindrical member that extends in the axial direction, and the inner diameter of the piston cylinder 28 is identical to or slightly larger than the outer diameter of the drive piston 22.

[0027] The displacer 20 and the drive piston 22 are rigidly linked, so the axial stroke of the drive piston 22 is equal to the axial stroke of the displacer 20, and the two integrally move throughout the stroke range. The position of the drive piston 22 relative to the displacer 20 remains unchanged during the axial reciprocating movement of the axial movable body 16.

[0028] A first seal portion 32 is provided between the drive piston 22 and the piston cylinder 28. The first seal portion 32 is attached to either one of the drive piston 22 or the piston cylinder 28, and slides with the other one of the drive piston 22 or the piston cylinder 28. The first seal portion 32 is made of, for example, a sliding seal or an O-ring, or the like. The piston cylinder 28 is airtightly configured with respect to the displacer cylinder 26 by the first seal portion 32. Since the first seal portion 32 is provided, direct gas flow between the piston cylinder 28 and the displacer cylinder 26 (i.e., between the drive chamber 29 and the room temperature chamber 36) does not occur. The internal pressure of the piston cylinder 28 and the internal pressure of the displacer cylinder 26 can have different magnitudes.

[0029] The displacer cylinder 26 is partitioned by the displacer 20 into the expansion chamber 34 and the room temperature chamber 36. The displacer 20 forms the expansion chamber 34 between one end in the axial direction and the displacer cylinder 26, and forms the room temperature chamber 36 between the other end in the axial direction and the displacer cylinder 26. The room temperature chamber 36 can also be referred to as a compression chamber. The drive piston 22 extends from the displacer 20 on the side opposite to the expansion chamber 34 in the axial direction, i.e., on the side of the room temperature chamber 36. Further, a cooling section 38 that surrounds the expansion chamber 34 and is fastened to the displacer cylinder 26 is provided in the cold head 14.

[0030] The regenerator 15 is built into the displacer 20. The displacer 20 has an inlet flow path 40 that communicates the regenerator 15 with the room temperature chamber 36 in the upper cover portion thereof. Further, the displacer 20 has an outlet flow path 42 that communicates the regenerator 15 with the expansion chamber 34 in the barrel portion thereof. Alternatively, the outlet flow path 42 can also be provided in the lower cover portion of the displacer 20. In addition, the regenerator 15 is provided with an inlet retainer 41 that is fitted in the upper cover portion, and an outlet retainer 43 that is fitted in the lower cover portion. The inlet retainer 41 and the outlet retainer 43 function as flow straighteners for the working gas. The regenerative material can be, for example, a copper-made wire mesh. The retainers can be wire meshes that are coarser than the regenerative material.

[0031] A second seal portion 44 is provided between the displacer 20 and the displacer cylinder 26. The second seal portion 44 is, for example, a sliding seal, and is attached to the barrel portion or the upper cover portion of the displacer 20. The gap between the displacer 20 and the displacer cylinder 26 is sealed by the second seal portion 44, and thus there is no direct gas flow between the room temperature chamber 36 and the expansion chamber 34 (i.e., gas flow that bypasses the regenerator 15).

[0032] The working gas flows from the room temperature chamber 36 into the regenerator 15 via the inlet flow path 40. More precisely, the working gas flows from the inlet flow path 40 into the regenerator 15 via the inlet holder 41. The working gas flows from the regenerator 15 into the expansion chamber 34 via the outlet holder 43 and the outlet flow path 42. The working gas returns from the expansion chamber 34 to the room temperature chamber 36 by the reverse path. That is, the working gas returns from the expansion chamber 34 to the room temperature chamber 36 via the outlet flow path 42, the regenerator 15 and the inlet flow path 40. The working gas that is intended to flow through the gap while bypassing the regenerator 15 is blocked by the second seal portion 44.

[0033] The cold head 14 is set in the illustrated orientation at the site of use. That is, the displacer cylinder 26 is disposed below in the vertical direction and the piston cylinder 28 is disposed above in the vertical direction so that the cold head 14 is set longitudinally. Thus, the cooling capacity of the cryogenic refrigerator 10 becomes highest when the cooling stage 38 is set in a posture facing below in the vertical direction. However, the configuration of the cryogenic refrigerator 10 is not limited to this. Instead, the cold head 14 can also be set in a posture facing above in the vertical direction. Alternatively, the cold head 14 can also be set in a lateral or other orientation. The cold head 14 is able to perform a cooling operation regardless of the posture in which it is set.

[0034] The end of the reciprocating movement stroke of the displacer 20 on the expansion chamber 34 side is referred to as the lower dead point of the displacer 20, and the end of the reciprocating movement stroke of the displacer 20 on the room temperature chamber 36 side is referred to as the upper dead point of the displacer 20. The movement of the displacer 20 toward the upper dead point can also be referred to as upward movement, and the movement of the displacer 20 toward the lower dead point can also be referred to as downward movement. However, these terms do not limit the posture of the cold head 14.

[0035] The expansion chamber 34 and the room temperature chamber 36 complementarily increase and decrease in volume as the displacer 20 moves along the axial direction. That is, the expansion chamber 34 narrows and the room temperature chamber 36 widens as the displacer 20 moves downward. The reverse is also true. Therefore, the volume of the expansion chamber 34 becomes smallest (the volume of the room temperature chamber 36 becomes largest) when the displacer 20 is at the lower dead point. The volume of the expansion chamber 34 becomes largest (the volume of the room temperature chamber 36 becomes smallest) when the displacer 20 is at the upper dead point. The drive piston 22 moves integrally with the displacer 20, and therefore, the volume of the drive chamber 29 becomes largest when the displacer 20 is at the lower dead point, and the volume of the drive chamber 29 becomes smallest when the displacer 20 is at the upper dead point.

[0036] Further, the ultra-low temperature refrigerator 10 has a working gas flow path 52 connecting the compressor 12 and the cold head 14. The working gas flow path 52 is configured to generate a pressure difference between the piston cylinder 28 and the displacer cylinder 26 (i.e., between the drive chamber 29 and the expansion chamber 34). The axial movable body 16 moves in the axial direction by the pressure difference. If the pressure of the displacer cylinder 26 is lower than the pressure of the piston cylinder 28, the drive piston 22 moves downward, and in turn, the displacer 20 also moves downward. Conversely, if the pressure of the displacer cylinder 26 is higher than the pressure of the piston cylinder 28, the drive piston 22 moves upward, and in turn, the displacer 20 also moves upward.

[0037] The working gas flow path 52 has a valve section 54. The valve section 54 can also be provided adjacent to the piston cylinder 28 in an integrated manner with the cold head housing 18 and connected to the compressor 12 through a pipe. The valve section 54 can also be provided outside the cold head housing 18 and connected to the compressor 12 and the cold head 14 through pipes, respectively.

[0038] The valve section 54 has an expansion chamber pressure switching valve (hereinafter, also referred to as a main pressure switching valve) 60 and a drive chamber pressure switching valve (hereinafter, also referred to as a sub pressure switching valve) 62. The main pressure switching valve 60 has a main intake on-off valve V1 and a main exhaust on-off valve V2. The sub pressure switching valve 62 has a sub intake on-off valve V3 and a sub exhaust on-off valve V4.

[0039] The working gas flow path 52 has a high-pressure line 13a and a low-pressure line 13b connecting the compressor 12 and the valve section 54. The high-pressure line 13a extends from the compressor discharge port 12a and branched in the middle to be connected to the main intake on-off valve V1 and the sub intake on-off valve V3. The low-pressure line 13b extends from the compressor suction port 12b and branched in the middle to be connected to the main exhaust on-off valve V2 and the sub exhaust on-off valve V4.

[0040] Further, the working gas flow path 52 has a main communication passage 64 and a sub communication passage 66 connecting the cold head 14 and the valve section 54. The main communication passage 64 connects the displacer cylinder 26 and the main pressure switching valve 60. The main communication passage 64 extends from the room temperature chamber 36 and branched in the middle to be connected to the main intake on-off valve V1 and the main exhaust on-off valve V2. The sub communication passage 66 connects the piston cylinder 28 and the sub pressure switching valve 62. The sub communication passage 66 extends from the drive chamber 29 and branched in the middle to be connected to the sub intake on-off valve V3 and the sub exhaust on-off valve V4.

[0041] The main pressure switching valve 60 is configured to selectively communicate the compressor discharge port 12a or the compressor suction port 12b with the chamber room 36 of the displacer cylinder 26. In the main pressure switching valve 60, the main intake opening and closing valve VI and the main discharge opening and closing valve V2 are opened in an exclusive manner. That is, the main intake opening and closing valve VI and the main discharge opening and closing valve V2 are prohibited from being opened at the same time. In addition, the main intake opening and closing valve VI and the main discharge opening and closing valve V2 can be temporarily closed at the same time.

[0042] When the main intake opening and closing valve VI is opened, the main discharge opening and closing valve V2 is closed. The working gas flows from the compressor discharge port 12a to the displacer cylinder 26 via the high-pressure line 13a and the main communication passage 64. As described above, the working gas flows from the chamber room 36 to the expansion chamber 34 via the cold head 14. Thus, the high-pressure PH working gas is supplied from the compressor 12 to the expansion chamber 34, and the expansion chamber 34 is boosted in pressure. On the contrary, when the main intake opening and closing valve VI is closed, the supply of the working gas from the compressor 12 to the expansion chamber 34 is stopped.

[0043] On the other hand, when the main discharge opening and closing valve V2 is opened, the main intake opening and closing valve VI is closed. First, the high-pressure PH working gas is expanded and reduced in pressure in the expansion chamber 34. The working gas flows from the expansion chamber 34 to the chamber room 36 via the cold head 14. The working gas flows from the displacer cylinder 26 to the compressor suction port 12b via the main communication passage 64 and the low-pressure line 13b. Thus, the low-pressure PL working gas is recovered from the cold head 14 to the compressor 12. When the main discharge opening and closing valve V2 is closed, the recovery of the working gas from the expansion chamber 34 to the compressor 12 is stopped.

[0044] The sub pressure switching valve 62 is configured to selectively communicate the compressor discharge port 12a or the compressor suction port 12b with the piston cylinder 28. The sub pressure switching valve 62 is configured such that the sub intake opening and closing valve V3 and the sub discharge opening and closing valve V4 are opened in an exclusive manner. That is, the sub intake opening and closing valve V3 and the sub discharge opening and closing valve V4 are prohibited from being opened at the same time. In addition, the sub intake opening and closing valve V3 and the sub discharge opening and closing valve V4 can be temporarily closed at the same time.

[0045] When the sub intake opening and closing valve V3 is opened, the sub discharge opening and closing valve V4 is closed. The working gas flows from the compressor discharge port 12a to the piston cylinder 28 via the high-pressure line 13a and the sub communication passage 66. Thus, the high-pressure PH working gas is supplied from the compressor 12 to the drive chamber 29, and the drive chamber 29 is boosted in pressure. When the sub intake opening and closing valve V3 is closed, the supply of the working gas from the compressor 12 to the piston cylinder 28 is stopped.

[0046] On the other hand, when the sub-exhaust on-off valve V4 is open, the sub- intake on-off valve V3 is closed. Working gas is recovered from the piston cylinder 28 to the compressor suction port 12b via the sub-communication passage 66 and the low-pressure line 13b, and the driving chamber 29 is depressurized to the low pressure PL. When the sub-exhaust on-off valve V4 is closed, the recovery of working gas from the piston cylinder 28 to the compressor 12 is stopped.

[0047] Thus, the main pressure switching valve 60 alternately communicates the expansion chamber 34 with the compressor discharge port 12a and the compressor suction port 12b, thereby generating a periodic pressure variation of the high pressure PH and the low pressure PL in the expansion chamber 34. Also, the sub-pressure switching valve 62 alternately communicates the driving chamber 29 with the compressor discharge port 12a and the compressor suction port 12b, thereby generating a periodic pressure variation of the high pressure PH and the low pressure PL in the driving chamber 29.

[0048] The sub-pressure switching valve 62 alternately communicates the driving chamber 29 with the compressor discharge port 12a and the compressor suction port 12b to generate a pressure difference between the expansion chamber 34 and the driving chamber 29 and to move the driving piston 22 along the axial direction by the pressure difference. Typically, the pressure variation in the driving chamber 29 is generated with the same period as the pressure variation in the expansion chamber 34, but the phase is substantially opposite. When the expansion chamber 34 is at the high pressure PH, the driving chamber 29 becomes the low pressure PL, and the driving piston 22 can move the displacer 20 upward. When the expansion chamber 34 is at the low pressure PL, the driving chamber 29 becomes the high pressure PH, and the driving piston 22 can move the displacer 20 downward. Thus, the sub-pressure switching valve 62 controls the pressure of the driving chamber 29 to move the displacer 20 by the driving piston 22 along the axial direction.

[0049] The valve section 54 can also be in the form of a rotary valve. At this time, a set of valves (V1 to V4) is assembled in the valve section 54 and is synchronously driven. The valve section 54 is configured to accurately switch the valves (V1 to V4) by the rotational sliding of a valve disc (or a valve rotor) with respect to a valve main body (or a valve stator). The set of valves (V1 to V4) is switched with the same period in the operation of the ultra-low temperature refrigerator 10, whereby the four on-off valves (V1 to V4) periodically change the on-off state. The four on-off valves (V1 to V4) are opened and closed (opened and closed) with different phases, respectively.

[0050] The ultra-low temperature refrigerator 10 can also be provided with a rotational driving source 56 linked to the valve section 54 to rotate the valve section 54. The rotational driving source 56 is mechanically linked to the valve section 54. The rotational driving source 56 is, for example, a motor. However, the rotational driving source 56 is not mechanically connected to the axial movable body 16. Also, the ultra-low temperature refrigerator 10 can be provided with a controller 58 for controlling the valve section 54. The controller 58 can also control the rotational driving source 56.

[0051] In one embodiment, the set of valves (V1-V4) can also be in the form of a plurality of individually controllable valves. Each valve (V1-V4) can also be an electromagnetic on-off valve. In this case, each valve (V1-V4) is electrically connected to the controller 58 instead of the rotary drive source 56. The controller 58 can control the opening and closing of each valve V1-V4.

[0052] Also, the cold head 14 can be provided with a temperature sensor 68 that measures the temperature of the low-temperature portion (e.g., the cooling section 38) and outputs a measured temperature signal indicative of the measured temperature. Also, the controller 58 can be electrically connected to the temperature sensor 68 to acquire the measured temperature signal from the temperature sensor 68.

[0053] In Figure 1 the state in which the displacer 20 is at the upper dead center is shown in FIG. 6B. Figure 2

[0054] In the present embodiment, in order to prevent interference between the displacer 20 and the end portion of the displacer cylinder 26 and to reduce vibrations and noise during operation of the ultra-low temperature refrigerator 10, a design called a "collar bumper" is employed. The cold head 14 is provided with a collar 70 and a collar chamber 72 that is divided by the collar 70 into an upper section 72a and a lower section 72b. The collar 70 is rigidly linked to the displacer 20 so as to move reciprocally together with the displacer 20 and constitutes a part of the axially movable body 16. As will be described later, the reciprocating stroke of the collar 70 in the collar chamber 72 determines the reciprocating stroke of the displacer 20.

[0055] The displacer cylinder 26 is provided with a cylinder flange 26a that defines an upper opening of the cylinder. The cylinder flange 26a extends radially outward from the axial upper end of the displacer cylinder 26. The cold head housing 18 is provided with a top plate 30 and a sleeve 73. The piston cylinder 28 and the sleeve 73 are fixed to the top plate 30, and the valve portion 54 is mounted on the top plate 30. The cylinder flange 26a is connected to the top plate 30 via the sleeve 73. The sleeve 73 is disposed outside the piston cylinder 28 so as to surround the piston cylinder 28.

[0056] ​The gasket 70 has a cylindrical main body 70a and a gasket upper end 70b. The main body 70a has substantially the same outer diameter as the displacer 20 and extends upward from the side of the room temperature chamber 36 of the displacer 20. The inner diameter of the main body 70a is larger than the outer diameter of the piston cylinder 28. The gasket upper end 70b is present at a position further outward than the outer diameter of the displacer 20. The gasket chamber 72 is divided into an upper section 72a and a lower section 72b by the gasket upper end 70b. The gasket chamber 72 communicates with the room temperature chamber 36. When the displacer 20 reciprocates within the displacer cylinder 26, the gasket 70 reciprocates within the gasket chamber 72 without coming into friction with the displacer cylinder 26 and the piston cylinder 28. The gasket 70 also does not come into friction with the inner peripheral surface of the sleeve 73.

[0057] Further, the cold head 14 has an upper buffer 74 provided to the upper section 72a to moderate interference between the displacer 20 and the displacer cylinder 26 when the displacer 20 is at the top dead center. The upper buffer 74 is provided to the upper surface of the gasket chamber 72 and has an upper buffer material 74a and an upper holder 74b. The upper buffer 74 is mounted to the sleeve 73, for example. The upper buffer material 74a is a ring-shaped member made of resin such as an O-ring, for example, and is sandwiched between the upper surface of the gasket chamber 72 and the upper holder 74b. The upper holder 74b is formed of a resin material, for example. Alternatively, the upper holder 74b can not be provided.

[0058] When the displacer 20 is at the top dead center, the upper buffer 74 comes into contact with the gasket 70, preventing the displacer 20 from colliding with the displacer cylinder 26 on the side of the room temperature chamber 36. When the displacer 20 moves upward, the gasket upper end 70b engages with the upper buffer 74 within the gasket chamber 72 before the displacer 20 collides with the piston cylinder 28. At this time, the gasket upper end 70b comes into contact with the upper holder 74b, and the upper buffer material 74a is compressed, absorbing the impact.

[0059] The cold head 14 has a lower buffer 76 provided to the lower section 72b to moderate interference between the displacer 20 and the displacer cylinder 26 when the displacer 20 is at the bottom dead center. The lower buffer 76 is provided to the lower surface of the gasket chamber 72 and has a lower buffer material 76a and a lower holder 76b. The lower buffer 76 is mounted to the cylinder flange 26a, for example. The lower buffer 76 can also be mounted to the sleeve 73. The lower buffer material 76a is a ring-shaped member made of resin such as an O-ring, for example, and is sandwiched between the lower surface of the gasket chamber 72 and the lower holder 76b. The lower holder 76b is formed of a resin material, for example. Alternatively, the lower holder 76b can not be provided.

[0060] The lower buffer 76 contacts the gasket 70 when the displacer 20 is at the bottom dead center, preventing the displacer 20 from colliding with the displacer cylinder 26 on the expansion chamber 34 side. When the displacer 20 moves downward, the gasket upper end 70b engages with the lower buffer 76 in the gasket chamber 72 before the displacer 20 collides with the displacer cylinder 26 on the expansion chamber 34 side. At this time, the gasket upper end 70b contacts the lower retainer 76b, and the lower buffer material 76a is compressed, absorbing the impact.

[0061] The upper section 72a communicates with the chamber temperature chamber 36. A first gap 78a is formed between the outer peripheral surface of the piston cylinder 28 and the inner peripheral surface of the gasket 70, and the working gas is able to flow between the chamber temperature chamber 36 and the upper section 72a via the first gap 78a.

[0062] The lower section 72b communicates with the upper section 72a. A second gap 78b is formed between the inner peripheral surface of the sleeve 73 and the outer peripheral surface of the gasket upper end 70b, and the working gas is able to flow between the upper section 72a and the lower section 72b via the second gap 78b. However, when the displacer 20 is at the bottom dead center, the gasket upper end 70b contacts the lower buffer 76, and the communication between the lower section 72b and the upper section 72a via the second gap 78b is blocked. When the displacer 20 is at the top dead center, the gasket upper end 70b contacts the upper buffer 74, and the communication between the lower section 72b and the upper section 72a via the second gap 78b is blocked. Therefore, when the displacer 20 is at an intermediate position between the top dead center and the bottom dead center, the lower section 72b communicates with the chamber temperature chamber 36 via the upper section 72a, and the working gas is able to flow between the chamber temperature chamber 36 and the lower section 72b. Also, the lower section 72b is sealed by the second seal portion 44, and thus does not communicate with the expansion chamber 34.

[0063] Also, the cold head 14 is provided with a communication passage 80 that ensures the communication between the upper section 72a and the lower section 72b when the displacer 20 is at the bottom dead center. The communication passage 80 is formed in the gasket 70 to communicate the upper section 72a and the lower section 72b in a state where the gasket upper end 70b contacts the lower buffer 76. The communication passage 80 is formed to penetrate the gasket 70 (e.g., the gasket upper end 70b) from the upper section 72a to the lower section 72b, and at least one in the circumferential direction is sufficient. As shown in the drawing, in the case where the gasket upper end 70b extends to the radially outer side from the main body 70a of the gasket 70, the communication passage 80 is formed in the gasket upper end 70b at a position radially inside the lower buffer 76. The communication passage 80 can also be formed to penetrate the main body 70a of the gasket 70.

[0064] The first gap 78a, the second gap 78b, and the connecting channel 80 function as flow path resistance. Therefore, when the displacement device 20 reciprocates, the upper section 72a and the lower section 72b can generate gas spring forces respectively. As the displacement device 20 moves upward, the upper end 70b of the washer also moves upward, and the upper section 72a narrows. At this time, the gas in the upper section 72a is compressed, and the pressure increases. The pressure of the upper section 72a acts downward on the upper surface of the upper end 70b of the washer. Therefore, the upper section 72a generates a gas spring force that resists the upward movement of the washer 70 and the displacement device 20. Similarly, when the displacement device 20 moves downward, the lower section 72b generates a gas spring force that resists the downward movement of the washer 70 and the displacement device 20. The upper section 72a and the lower section 72b can also be referred to as the upper gas spring chamber and the lower gas spring chamber, respectively. The gas spring force helps to reduce vibration and noise that may occur when the washer 70 contacts the upper buffer 74 and the lower buffer 76.

[0065] However, the cryogenic refrigerator 10 is capable of performing initial cooling and subsequent steady-state operation. Initial cooling is the operating mode in which the cold head 14 is rapidly cooled from an initial temperature to a cryogenic temperature when the cryogenic refrigerator 10 is started. Steady-state operation is the operating mode in which the cold head 14 maintains its cryogenic state after initial cooling. As mentioned above, initial cooling can also be referred to as temperature reduction. The initial temperature can also be the ambient temperature (e.g., room temperature). The cold head 14 is cooled to a standard cooling temperature through initial cooling and maintained within the permissible temperature range of cryogenicity, including this standard cooling temperature, during steady-state operation. The standard cooling temperature may vary depending on the application and settings of the cryogenic refrigerator 10, but may, for example, be approximately 10K to 20K or below 10K. For example, in applications involving the cooling of superconducting devices, a typical standard cooling temperature is below approximately 4.2K.

[0066] The amount of working gas sealed in the cryogenic refrigerator 10 can also be set to allow the cryogenic refrigerator 10 to operate at the optimal operating pressure under steady-state operation, i.e., cooling to cryogenic temperature. During initial cooling, as the temperature drops from the initial temperature to the cryogenic temperature, the density of the working gas in the cold head 14 increases. Consequently, the amount of working gas accumulated in the cold head 14 increases; in other words, working gas is drawn from the working gas flow path 52 into the cold head 14. As a result, as the cooling of the cold head 14 progresses, the pressure of the working gas circulating in the working gas flow path 52 gradually decreases. Consequently, the operating pressure of the cryogenic refrigerator 10 during steady-state operation is optimized.

[0067] From another perspective, during the initial cooling phase, the operating pressure of the cryogenic refrigerator 10 tends to be high because its temperature is significantly higher than the initial cryogenic temperature required for steady-state operation. Consequently, the pressure difference between the drive chamber 29 and the expansion chamber 34, i.e., the gas pressure used to drive the displacementr 20, may also increase during initial cooling, especially in the early stages. In a typical gas-driven cryogenic refrigerator, the displacementr 20 moves under gas pressure until it interferes (e.g., collides) with the end of the displacementr cylinder 26. This interference can generate noise (e.g., a knocking sound). The higher the gas pressure, the more noticeable the noise may become.

[0068] To address this issue, the cryogenic refrigerator 10 includes a flow limiter 100 connected between the compressor 12 and the cold head 14. The flow limiter 100 is configured to restrict the flow of working gas to the cold head 14 during initial cooling, compared to steady-state operation. This reduces the flow of working gas to the cold head 14 during the initial cooling process when the cryogenic refrigerator 10 switches between intake and exhaust phases, thereby delaying the rise in gas pressure driving the displacementr 20. This improves the quietness of the cryogenic refrigerator 10. For example, reducing the moving speed of the displacementr 20 reduces kinetic energy, thus suppressing the collision noise between the displacementr 20 and the displacementr cylinder 26.

[0069] In this embodiment, the flow limiter 100 is connected between the secondary pressure switching valve 62 and the drive chamber 29, and during the initial cooling period, it limits the flow rate of the working gas to the drive chamber 29 compared to steady-state operation. This reduces the flow rate of the working gas to the drive chamber 29, delaying the pressure rise in the drive chamber 29, and thus delaying the increase in the driving force of the gas pressure-driven piston 22. Consequently, the quietness of the cryogenic refrigerator 10 can be improved.

[0070] The flow limiter 100 includes a flow control valve 102 that opens with a smaller opening degree during initial cooling compared to steady-state operation. Thus, the flow control valve 102 can limit the flow rate of working gas to the drive chamber 29 during initial cooling compared to steady-state operation. The flow control valve 102 is located in the secondary communication passage 66 and is connected in series with the secondary pressure switching valve 62 and the drive chamber 29. The flow control valve 102 can also be, for example, a flow control valve of any structure with a variable opening degree, such as a needle valve or a variable orifice valve.

[0071] To control the opening degree of the flow control valve 102, the flow limiter 100 may also include a controller 58. The controller 58 can acquire the operating status of the cryogenic refrigerator 10 (i.e., whether the cryogenic refrigerator 10 is performing initial cooling or steady-state operation) and control the flow control valve 102 according to the acquired operating status.

[0072] To obtain the operating status of the cryogenic refrigerator 10, the controller 58 can use the temperature of the cryogenic refrigerator 10. For example, the controller 58 can refer to the measured temperature of the temperature sensor 68 installed on the cryogenic section (e.g., cooling section 38) of the cold head 14. When the measured temperature is higher than the preset target temperature for initial cooling (e.g., the standard cooling temperature mentioned above), the controller 58 can determine that the cryogenic refrigerator 10 is performing initial cooling. When the measured temperature is lower than the target temperature for initial cooling, the controller 58 can determine that the cryogenic refrigerator 10 is performing steady-state operation.

[0073] To obtain the operating status of the cryogenic refrigerator 10, the controller 58 can also use the pressure of the cryogenic refrigerator 10. For example, the controller 58 can refer to the measured pressure of a pressure sensor (not shown) used to measure the high pressure (e.g., the pressure at the compressor outlet 12a) or the low pressure (e.g., the pressure at the compressor inlet 12b) of the cryogenic refrigerator 10. The pressure difference between the high and low pressures of the cryogenic refrigerator 10 can also be referenced. The measured pressure is related to the cooling temperature of the cryogenic refrigerator 10. Therefore, when the measured pressure is higher than a predetermined pressure threshold, the controller 58 can determine that the cryogenic refrigerator 10 is performing initial cooling. When the measured pressure is lower than the predetermined pressure threshold, the controller 58 can determine that the cryogenic refrigerator 10 is performing steady-state operation.

[0074] Alternatively, the controller 58 can be configured to measure the elapsed time after the start of initial cooling and obtain the operating status of the cryogenic refrigerator 10 based on the elapsed time. The time required for initial cooling can be determined through experience or experimentation. Therefore, when the measured elapsed time is shorter than a predetermined time, the controller 58 can determine that the cryogenic refrigerator 10 is performing initial cooling. When the measured elapsed time is longer than a predetermined time, the controller 58 can also determine that the cryogenic refrigerator 10 is performing steady-state operation.

[0075] The controller 58 can set the flow control valve 102 to a first opening degree when the cryogenic refrigerator 10 is performing initial cooling, and set the flow control valve 102 to a second opening degree when the cryogenic refrigerator 10 is performing steady-state operation. The first opening degree is smaller than the second opening degree. In this way, the opening degree of the flow control valve 102 can be switched according to the operating state of the cryogenic refrigerator 10.

[0076] The controller 58 can change the opening degree of the flow control valve 102 from the first opening degree to the second opening degree in stages or continuously based on the measured temperature (or measured pressure). That is, the higher the measured temperature (or measured pressure), the smaller the opening degree of the flow control valve 102 can be. Similarly, the controller 58 can also change the opening degree of the flow control valve 102 from the first opening degree to the second opening degree in stages or continuously based on the elapsed time. That is, the shorter the elapsed time, the smaller the opening degree of the flow control valve 102 can be.

[0077] The opening degree of the flow control valve 102 can also be controlled manually. The flow control valve 102 may have an operating part for adjusting the opening degree, and the opening degree can be changed by operating the operating part. In this way, the flow control valve 102 can be opened at a smaller opening degree during the initial cooling period compared with steady-state operation.

[0078] The operation of the cryogenic refrigerator 10 is described below. When the displacement valve 20 is at or near the bottom dead center, the intake process of the cryogenic refrigerator 10 begins. The main intake valve V1 is opened, and the main exhaust valve V2 is closed. Working gas is supplied from the compressor outlet 12a to the displacement valve 26 of the cold head 14 via the main intake valve V1, causing the expansion chamber 34 and chamber temperature 36 to reach high pressure PH. Simultaneously with the intake of gas into the expansion chamber 34, exhaust gas is discharged from the piston cylinder 28. The auxiliary intake valve V3 is closed, and the auxiliary exhaust valve V4 is opened. Working gas is discharged from the piston cylinder 28 to the compressor suction port 12b via the auxiliary exhaust valve V4, causing the drive chamber 29 to drop to low pressure PL.

[0079] Therefore, during the intake process, the driving force generated by the pressure difference (PH-PL) between the drive chamber 29 and the expansion chamber 34 acts upward on the drive piston 22. As a result, the displacement device 20 and the drive piston 22 move together from the bottom dead center to the top dead center. In this way, the volume of the expansion chamber 34 increases and it is filled with high-pressure gas.

[0080] The gasket 70 also moves upwards along with the displacement device 20. The gasket 70 contacts the upper buffer 74 before the displacement device 20 collides with the high-temperature end of the displacement device cylinder 26 (e.g., piston cylinder 28). The upper buffer material 74a is compressed, and the impact is absorbed. During the upward movement of the gasket 70, the upper section 72a communicates with the chamber temperature 36 via the first gap 78a, and the lower section 72b communicates with the upper section 72a via the second gap 78b and the connecting channel 80. Therefore, both the upper section 72a and the lower section 72b, along with the chamber temperature 36, become high-pressure pH.

[0081] When the displacement device 20 is at or near top dead center, the venting process of the cryogenic refrigerator 10 begins. The main exhaust valve V2 is opened, and the main intake valve V1 is closed. High-pressure gas expands and cools in the expansion chamber 34. The expanded gas is recovered to the compressor suction port 12b via the chamber temperature 36 while cooling the accumulator 15. The expansion chamber 34 and the chamber temperature 36 become low pressure PL. Simultaneously with the venting from the expansion chamber 34, air is introduced into the piston cylinder 28. The auxiliary exhaust valve V4 is closed, and the auxiliary intake valve V3 is opened. Working gas is supplied from the compressor discharge port 12a to the piston cylinder 28 via the auxiliary intake valve V3, driving the chamber 29 to pressurize to high pressure PH.

[0082] Therefore, during the exhaust process, the driving force generated by the pressure difference (PH-PL) between the drive chamber 29 and the expansion chamber 34 acts downward on the drive piston 22. As a result, the displacement device 20 moves together with the drive piston 22 from top dead center to bottom dead center. Thus, the volume of the expansion chamber 34 decreases and low-pressure gas is discharged.

[0083] The gasket 70 also moves downwards along with the displacement device 20. The gasket 70 contacts the lower buffer 76 before the displacement device 20 collides with the low-temperature end of the displacement device cylinder 26. The lower buffer material 76a is compressed, and the impact is absorbed. During the downward movement of the gasket body 70, the upper section 72a communicates with the chamber temperature 36 via the first gap 78a, and the lower section 72b communicates with the upper section 72a via the second gap 78b and the connecting channel 80. Therefore, both the upper section 72a and the lower section 72b, along with the chamber temperature 36, become low-pressure zones (PL).

[0084] However, typical gas-driven cryogenic refrigerators using a gasket-buffer configuration, unlike the embodiments described above, do not have a connecting passage 80. In this case, when the gasket 70 is at the bottom dead center, the low-pressure PL working gas may be trapped in the lower section 72b. In this state, if the upper section 72a is pressurized to the high-pressure PH at the start of the gas intake process, the upper end 70b of the gasket may be pressed against the lower buffer 76 due to the pressure difference (PH-PL). This pressure difference may hinder the upward movement of the displacement device 20.

[0085] However, the cryogenic refrigerator 10 according to this embodiment includes a communication channel 80 formed in the gasket 70 to ensure communication between the upper section 72a and the lower section 72b when the displacementr 20 is at the bottom dead center. Therefore, even when the gasket 70 is at the bottom dead center and the upper end 70b of the gasket is in contact with the lower buffer 76, the lower section 72b is connected to the upper section 72a via the communication channel 80. The lower section 72b is not closed. The communication channel 80 reduces or eliminates the pressure difference that may be generated between the upper section 72a and the lower section 72b, thus not hindering the upward movement of the displacementr 20. Therefore, the displacementr 20 can move from the bottom dead center toward the top dead center.

[0086] The cryogenic refrigerator 10 cools the cooling section 38 by repeating this refrigeration cycle (i.e., the GM cycle). Thus, the cryogenic refrigerator 10 is able to cool the object being cooled (not shown) that is thermally connected to the cooling section 38.

[0087] The cryogenic refrigerator 10 uses a gasket damper. Therefore, through the contact between the gasket 70 and the damper (74, 76), interference (e.g., collision) between the displacement device 20 and the displacement device cylinder 26 can be prevented, thereby reducing vibration and noise.

[0088] In this embodiment, as described above, the flow control valve 102 is disposed between the secondary pressure switching valve 62 and the drive chamber 29, and the opening degree of the flow control valve 102 is smaller during initial cooling compared to steady-state operation. Therefore, at the start of the intake process, the flow rate of the working gas from the drive chamber 29 to the compressor suction port 12b via the secondary exhaust valve V4 is restricted, thereby delaying the pressure drop of the drive chamber 29 to the low-pressure PL. This flow restriction is not performed in the main communication channel 64, therefore, the pressure rise of the expansion chamber 34 and the chamber temperature 36 to the high-pressure PH is not delayed. Thus, during initial cooling, the rise of the driving force acting on the drive piston 22 can be delayed compared to steady-state operation. By reducing the moving speed of the displacementr 20, and thus reducing kinetic energy, the impact noise of the displacementr 20 at top dead center can be suppressed, thereby improving the quietness of the cryogenic refrigerator 10 during initial cooling.

[0089] Furthermore, at the start of the exhaust process, the flow rate of working gas from the compressor outlet 12a to the drive chamber 29 via the auxiliary intake valve V3 is restricted, thereby delaying the pressure rise of the drive chamber 29 to the high pressure PH. In the main connecting passage 64, the pressure reduction of the expansion chamber 34 and the chamber temperature 36 to the low pressure PL is not delayed. Thus, during initial cooling, the rise of the driving force acting on the drive piston 22 can be delayed compared to steady-state operation. By reducing the moving speed of the displacementr 20, and thus reducing kinetic energy, the impact noise of the displacementr 20 at bottom dead center can be suppressed, thereby improving the quietness of the cryogenic refrigerator 10 during initial cooling.

[0090] On the other hand, during steady-state operation, the opening of the flow control valve 102 increases, and the flow restriction imposed by the flow limiter 100 is lifted. This ensures sufficient working gas flow in the secondary communication channel 66 to optimize the cooling capacity of the cryogenic refrigerator 10.

[0091] Figure 3 This is a schematic diagram showing another example of a flow limiter 100 that can be applied to the cryogenic refrigerator 10 involved in the embodiment. Figure 3 The flow limiter 100 shown can also be applied to Figure 1and Figure 2 In the cryogenic refrigerator 10 shown, similarly to the embodiment described above, the flow limiter 100 can also be connected between the compressor 12 and the cold head 14, for example, between the secondary pressure switching valve 62 and the drive chamber 29. The flow limiter 100 can also limit the flow rate of working gas to the cold head 14 (e.g., drive chamber 29) during initial cooling compared to steady-state operation.

[0092] like Figure 3 As shown, the flow limiter 100 may include a first flow control valve 102a and a second flow control valve 102b connected in parallel. Both the first flow control valve 102a and the second flow control valve 102b are located in the secondary communication channel 66. The first flow control valve 102a may be a switching valve (e.g., a solenoid valve). The second flow control valve 102b may be a throttling orifice, such as a fixed throttling orifice.

[0093] The controller 58 can acquire the operating status of the cryogenic refrigerator 10 (i.e., whether the cryogenic refrigerator 10 is performing initial cooling or steady-state operation), and control the first flow control valve 102a according to the acquired operating status. The controller 58 can close the first flow control valve 102a when the cryogenic refrigerator 10 is performing initial cooling, and open the first flow control valve 102a when the cryogenic refrigerator 10 is performing steady-state operation.

[0094] Thus, during initial cooling, the first flow control valve 102a is closed, thereby restricting the flow rate of the working gas in the secondary connection channel 66. That is, during initial cooling, the working gas flow in the secondary connection channel 66 only passes through the second flow control valve 102b. During steady-state operation, the first flow control valve 102a is opened, and the flow restriction during initial cooling is lifted. The working gas can then pass through both the first flow control valve 102a and the second flow control valve 102b.

[0095] Even so, the flow limiter 100 can reduce the flow rate of working gas to the drive chamber 29 during the initial cooling period compared to steady-state operation, thereby delaying the pressure rise in the drive chamber 29. This improves the quietness of the cryogenic refrigerator 10. Furthermore, compared to the reference... Figure 1 and Figure 2 Compared to the opening control of the flow control valve 102 described herein, the on / off control of the first flow control valve 102a can be implemented with a simpler structure to realize the controller 58, which is an advantage.

[0096] Alternatively, the first flow control valve 102a can also be a switch valve that can be operated manually.

[0097] Furthermore, the first flow control valve 102a can also be a flow control valve capable of controlling its opening degree. The second flow control valve 102b can also be a flow control valve capable of controlling its opening degree. If necessary, additional throttling orifices or a third flow control valve can also be provided upstream and / or downstream of the first flow control valve 102a and / or the second flow control valve 102b.

[0098] Figure 4 This is a schematic diagram illustrating another example of the cryogenic refrigerator 10 according to the embodiment. The cryogenic refrigerator 10 is, for example, a gas-driven GM refrigerator. The cryogenic refrigerator 10 includes a compressor 12, a cold head 14, and a flow limiter 100.

[0099] Figure 4 The cryogenic refrigerator 10 shown, except for the specific structure of the flow limiter 100 described below, has the same... Figure 1 and Figure 2 The cryogenic refrigerator 10 shown has the same structure. Therefore, similarly to the embodiment described above, the flow limiter 100 can also be connected between the compressor 12 and the cold head 14, for example, between the secondary pressure switching valve 62 and the drive chamber 29. During initial cooling, the flow limiter 100 restricts the flow of working gas to the cold head 14 (e.g., the drive chamber 29) compared to steady-state operation.

[0100] The flow limiter 100 includes a flow control valve 102 and a gas volume 104. The flow control valve 102 includes a gas pressure actuator 106 for driving the flow control valve 102 to open the flow control valve 102 at a smaller opening degree compared to steady-state operation during initial cooling.

[0101] The flow control valve 102 includes a valve body 108 that determines the opening degree of the flow control valve 102 and a valve housing 110 that houses the valve body 108. The valve body 108 has a front end portion 108a and a base end portion 108b extending from the front end portion 108a. Inside the valve housing 110, there is a throttling orifice 110a that is connected to and forms part of a secondary communication channel 66, and a pressure chamber 110b that is separated from the throttling orifice 110a by an elastically deformable partition 112 (e.g., a bellows). The front end portion 108a of the valve body 108 is housed in the throttling orifice 110a, and the base end portion 108b of the valve body 108 is housed in the pressure chamber 110b. The opening degree of the flow control valve 102 is determined by the front end portion 108a of the valve body 108 in the throttling orifice 110a. The valve body 108 is connected to the valve housing 110 by the partition 112, which is movable relative to the valve housing 110 by deformation of the partition 112. The opening degree of the flow control valve 102 changes as the valve body 108 moves relative to the valve housing 110. As shown in the figure, the flow control valve 102 can also be, for example, a needle valve.

[0102] The gas volume 104 is thermally connected to the cryogenic section (e.g., cooling section 38) of the cold head 14. The gas volume 104 can also be installed to the cryogenic section of the cold head 14 for cooling. The gas volume 104 is filled with a predetermined gas, such as nitrogen. The gas filling the gas volume 104 can be a gas that has condensed (i.e., liquefied or solidified) at the cooling temperature of the cryogenic refrigerator 10 (e.g., the standard cooling temperature described above). The gas volume 104 is connected to the pressure chamber 110b so that gas can flow between it and the pressure chamber 110b. For example, the gas volume 104 can be connected to the pressure chamber 110b via a flow path 105 connected by piping or the like.

[0103] The pressure chamber 110b and gas volume 104 of the valve housing 110 constitute part of the gas pressure actuator 106. The gas pressure actuator 106 drives the valve body 108 according to the pressure in the pressure chamber 110b. The gas pressure actuator 106 is configured to open the flow control valve 102 at a first opening degree during initial cooling and at a second opening degree during steady-state operation. The first opening degree is smaller than the second opening degree.

[0104] Therefore, the gas volume 104 and the pressure chamber 110b are pre-filled with gas so that the pressure in the pressure chamber 110b at the initial temperature at the start of initial cooling is higher than the pressure in the orifice 110a (i.e., the operating pressure of the cryogenic refrigerator 10 in the secondary connecting channel 66). In this way, the valve body 108 can be moved from the pressure chamber 110b toward the orifice 110a so that the flow control valve 102 is in the first opening degree.

[0105] During the initial cooling period, the cold head 14 is cooled, and the gas volume 104 is also cooled by the cold head 14. The gas within the gas volume 104 decreases in volume due to cooling, thereby reducing the pressure in the pressure chamber 110b. As the gas within the gas volume 104 condenses due to cooling, the pressure in the pressure chamber 110b decreases further. Consequently, the pressure in the pressure chamber 110b becomes lower than the pressure in the throttling orifice 110a, such as... Figure 4 As indicated by arrow 114, the valve body 108 deforms the diaphragm 112 while retracting from the throttling orifice 110a toward the pressure chamber 110b. As a result, the opening degree of the flow control valve 102 increases from the first opening degree to the second opening degree.

[0106] Thus, the gas pressure actuator 106 can drive the valve body 108 to minimize the opening of the flow control valve 102 during the initial cooling phase, and increase the opening of the flow control valve 102 as the initial cooling progresses. Therefore, in this embodiment, the flow limiter 100 restricts the flow of working gas to the drive chamber 29 during the initial cooling period compared to steady-state operation. This reduces the flow of working gas to the drive chamber 29, delaying the pressure rise in the drive chamber 29, and consequently delaying the increase in the driving force of the gas pressure-driven piston 22. Consequently, similar to the embodiment described above, the quietness of the cryogenic refrigerator 10 can be improved.

[0107] refer to Figure 4 The flow limiter 100, as described, can passively operate by utilizing the temperature drop of the cold head 14 during initial cooling. (Refer to the reference...) Figure 1 and Figure 2 The flow limiter 100 described is different, and its advantage is that it does not require the control of controller 58.

[0108] Figure 5 This is a schematic diagram illustrating another example of a flow limiter 100 that can be applied to the cryogenic refrigerator 10 involved in the embodiment. Figure 5 As shown, the flow control valve 102 may include a valve body stop 116 for limiting the maximum opening degree of the flow control valve 102 of the gas pressure actuator 106. This allows the opening degree of the flow control valve 102 to be kept constant during steady-state operation. This helps to stabilize the cooling capacity of the cryogenic refrigerator 10 during steady-state operation.

[0109] A valve body stop 116 can be disposed on the valve housing 110 to contact the valve body 108 and hold the valve body 108 in place when the flow control valve 102 is in the second opening position. As shown, the valve body stop 116 can be disposed on the pressure chamber 110b. When the flow control valve 102 is in the first opening position, the valve body 108 separates from the valve body stop 116 by moving forward from the pressure chamber 110b toward the throttle orifice 110a.

[0110] Alternatively, the position of the valve body stop 116 relative to the valve housing 110 can be adjusted so that the maximum opening of the flow control valve 102 can be adjusted as needed.

[0111] Figure 6 This is a schematic diagram illustrating another example of a flow limiter 100 that can be applied to the cryogenic refrigerator 10 according to the embodiments described above. Similar to the embodiments described above, the flow limiter 100 can be connected between the compressor 12 and the cold head 14, for example, between the secondary pressure switching valve 62 and the drive chamber 29. During initial cooling, the flow limiter 100 restricts the flow of working gas to the cold head 14 (e.g., the drive chamber 29) compared to steady-state operation.

[0112] The flow limiter 100 includes a flow control valve 102. The flow control valve 102 includes a gas pressure actuator 106 for actuating the flow control valve 102 to open the flow control valve 102 at a smaller opening degree during initial cooling compared to steady-state operation.

[0113] The flow control valve 102 includes a valve body 108 that determines the opening degree of the flow control valve 102 and a valve housing 110 that accommodates the valve body 108. The valve body 108 has a front end portion 108a and a base end portion 108b extending from the front end portion 108a. Inside the valve housing 110, there is a throttling orifice 110a connected to and forming part of a secondary communication channel 66, and a pressure chamber 110b spaced apart from the throttling orifice 110a. The front end portion 108a of the valve body 108 is accommodated in the throttling orifice 110a, and the base end portion 108b of the valve body 108 is accommodated in the pressure chamber 110b. The opening degree of the flow control valve 102 is determined by the front end portion 108a of the valve body 108 in the throttling orifice 110a. The valve body 108 is connected to the valve housing 110 by an elastic member 113 such as a spring, and is movable relative to the valve housing 110. The opening degree of the flow control valve 102 changes as the valve body 108 moves relative to the valve housing 110. As shown in the figure, the flow control valve 102 can be, for example, a needle valve.

[0114] exist Figure 6 In the flow limiter 100 shown, the pressure chamber 110b of the valve housing 110 is connected to the compressor 12, replacing... Figure 4 The gas volume 104 is shown. More specifically, the pressure chamber 110b includes a first chamber 118 and a second chamber 120 spaced apart from each other. The second chamber 120 has a lower pressure than the first chamber 118. Thus, for example, the first chamber 118 is connected to the compressor outlet 12a, and the second chamber 120 is connected to the compressor inlet 12b. The second chamber 120 is disposed between the first chamber 118 and the orifice 110a. The second chamber 120 is spaced apart from the orifice 110a.

[0115] The valve body 108 is driven by the pressure difference between the first chamber 118 and the second chamber 120. For example, during the initial cooling phase, when the temperature of the cryogenic refrigerator 10 is relatively high, the pressure difference between the compressor outlet 12a (high pressure PH) and the compressor inlet 12b (low pressure PL) is relatively large. Therefore, the pressure difference between the first chamber 118 and the second chamber 120 causes the elastic member 113 to compress, thereby allowing the valve body 108 to advance from the pressure chamber 110b toward the throttle orifice 110a, so that the flow control valve 102 is at its first opening.

[0116] During the initial cooling period, as described above, the operating pressure of the cryogenic refrigerator 10 gradually decreases. Consequently, the pressure difference between chamber 118 and chamber 120 also decreases, and combined with the restoring force of the elastic member 113, the valve body 108 retracts from the throttling orifice 110a toward the pressure chamber 110b. As a result, the opening degree of the flow control valve 102 increases from the first opening degree to the second opening degree.

[0117] Thus, the gas pressure actuator 106 can drive the valve body 108 to minimize the opening of the flow control valve 102 during the initial cooling phase, and increase the opening of the flow control valve 102 as the initial cooling progresses. Therefore, in this embodiment, the flow limiter 100 restricts the flow of working gas to the drive chamber 29 during the initial cooling period compared to steady-state operation. This reduces the flow of working gas to the drive chamber 29, delaying the pressure rise in the drive chamber 29, and consequently delaying the increase in the driving force of the gas pressure-driven piston 22. Consequently, similar to the embodiment described above, the quietness of the cryogenic refrigerator 10 can be improved.

[0118] refer to Figure 6 The flow limiter 100 described also relates to... Figure 4 Similarly, the flow limiter 100 shown can also operate passively by utilizing the temperature drop of the cold head 14 during initial cooling. (Refer to reference...) Figure 1 and Figure 2 The flow limiter 100 described is different, and its advantage is that it does not require the control of controller 58.

[0119] Alternatively, the second chamber 120 can be opened to the atmosphere instead of being connected to the compressor inlet 12b. Even so, since the first chamber 118 is connected to the compressor outlet 12a, the pressure difference between the first chamber 118 and the second chamber 120 can be ensured.

[0120] Furthermore, refer to Figure 5 The valve body stop 116 described herein can also be applied to Figure 6 In the flow control valve 102 shown. At this time, the valve body stop 116 can also be provided in the first chamber 118 of the pressure chamber 110b.

[0121] 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.

[0122] The above embodiment has been described using the case where the flow limiter 100 is connected between the secondary pressure switching valve 62 and the drive chamber 29 as an example, but the present invention is not limited thereto. The flow limiter 100 may also be connected between the main pressure switching valve 60 and the cold head 14 (e.g., chamber temperature 36). Even so, during the initial cooling period, the flow rate of the working gas to the cold head 14 can be limited compared to steady-state operation, thereby delaying the rise in gas pressure driving the displacement device 20. As a result, the quietness of the cryogenic refrigerator 10 can be improved.

[0123] The above embodiments are described using the case where the cryogenic refrigerator 10 uses a gasket buffer as an example, but the present invention is not limited to this. That is, the cryogenic refrigerator 10 may not have the gasket 70, the upper buffer 74, and the lower buffer 76, and the flow limiter 100 involved in the embodiments may also be applied to such a cryogenic refrigerator 10.

[0124] The above embodiments are described using the case where the cryogenic refrigerator 10 is a gas-driven GM refrigerator as an example, but the present invention is not limited thereto. The flow limiter 100 involved in the embodiments can also be applied to other gas-driven cryogenic refrigerators, such as Solvay refrigerators.

[0125] According to the embodiments, the present invention has been described using specific terms, but the embodiments only show one aspect of the principle and application of the present invention. There are many variations and configuration changes in the embodiments without departing from the scope of the inventive spirit defined in the claims.

Claims

1. A gas-driven cryogenic refrigerator, capable of performing initial cooling from an initial temperature to a cryogenic temperature and then maintaining steady-state operation at the cryogenic temperature after the initial cooling, characterized in that it comprises: compressor; Cold head; and A flow limiter is connected between the compressor and the cold head and is configured to limit the flow of working gas to the cold head during the initial cooling period compared to the steady-state operation.

2. The gas-driven cryogenic refrigerator according to claim 1, characterized in that, The compressor has an outlet and an inlet for the working gas. The cold head has the following features: Displacement device, extending along the axial direction; Displacement cylinder housing the displacement device and enabling it to reciprocate axially, and forming an expansion chamber between the displacement cylinder and the displacement device; The main pressure switching valve alternately connects the expansion chamber to the discharge port and the suction port; The drive piston extends from the displacement device on the side opposite to the expansion chamber in the axial direction; A drive chamber that houses the drive piston and enables it to reciprocate axially. and A secondary pressure switching valve alternately connects the drive chamber to the discharge port and the suction port to generate a pressure difference between the expansion chamber and the drive chamber, thereby causing the drive piston to reciprocate axially through the pressure difference; The flow limiter is connected between the secondary pressure switching valve and the drive chamber, and is configured to limit the flow rate of the working gas to the drive chamber during the initial cooling period, compared to the steady-state operation.

3. The gas-driven cryogenic refrigerator according to claim 1 or 2, characterized in that, The flow limiter includes a flow control valve that opens at a smaller degree during the initial cooling period compared to the steady-state operation.

4. The gas-driven cryogenic refrigerator according to claim 3, characterized in that, The flow control valve includes a gas pressure actuator that drives the flow control valve to open at a smaller opening degree during the initial cooling period compared to the steady-state operation.

5. The gas-driven cryogenic refrigerator according to claim 4, characterized in that, The flow limiter has a gas volume that is thermally connected to the low-temperature section of the cold head. The flow control valve includes a valve body for determining the opening degree of the flow control valve. The gas pressure actuator has a pressure chamber connected to the gas volume, and drives the valve body according to the pressure in the pressure chamber.

6. The gas-driven cryogenic refrigerator according to claim 4, characterized in that, The flow control valve includes a valve body for determining the opening degree of the flow control valve. The gas pressure actuator has a pressure chamber connected to the compressor and drives the valve body according to the pressure in the pressure chamber.

7. The gas-driven cryogenic refrigerator according to claim 4, characterized in that, The flow control valve includes a valve body stop that limits the maximum opening of the flow control valve that can be achieved by the gas pressure actuator.

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