Gas-driven cryogenic refrigerator

Abstract

To improve silence of a gas-driven cryogenic refrigerator.SOLUTION: A gas-driven cryocooler (10) capable of performing initial cooling for cooling from an initial temperature to a cryogenic temperature and a steady operation for maintaining the cryogenic temperature following the initial cooling is provided. The cryocooler 10 includes the compressor 12, the cold head 14, and the flow rate restrictor 100 that is connected between the compressor 12 and the cold head 14 and operates to restrict the flow rate of the working gas to the cold head 14 during the initial cooling as compared with the steady operation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas-driven cryogenic refrigerator. [Background technology]

[0002] GM (Gifford-McMahon) refrigerators, a typical example of cryogenic refrigerators, are broadly divided into two types depending on the drive source of the displacer: motor-driven and gas-driven. In the motor-driven type, the displacer is mechanically connected to a motor and driven by the motor. In the gas-driven type, the displacer is driven by gas pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 049936 Summary of the Invention [Problem to be solved by the invention]

[0004] Cryogenic refrigerators are used to cool various objects, such as superconducting devices, measuring instruments, and samples, that are used in cryogenic environments. To cool an object using a cryogenic refrigerator, the cryogenic refrigerator must first be started and cooled from an initial temperature, such as room temperature, to the desired cryogenic temperature. This initial cooling of the cryogenic refrigerator is also called cool-down. Following cool-down, the cryogenic refrigerator is operated to maintain the cryogenically cooled state. This steady-state operation allows the cryogenic refrigerator to cool the object.

[0005] In many cases, the amount of working gas charged into a cryogenic refrigerator is determined so that the cryogenic refrigerator can operate at its optimum operating pressure during steady-state operation, i.e., when cooled to a cryogenic temperature. The operating pressure of a cryogenic refrigerator at the start of cool-down tends to be high because the cryogenic refrigerator's initial temperature at that time is much higher than the cryogenic temperature during steady-state operation. As a result, the gas pressure driving the displacer can also be high during cool-down, especially at the beginning of the cool-down period. In a typical gas-driven cryogenic refrigerator, the gas pressure moves the displacer until it interferes with (e.g., impacts) the end of the cylinder. This interference can cause noise (e.g., a crashing sound). As the gas pressure increases, the noise can become more pronounced.

[0006] An exemplary object of an embodiment of the present invention is to improve the quietness of a gas-driven cryogenic refrigerator. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a gas-driven cryogenic refrigerator capable of performing initial cooling to cool from an initial temperature to a cryogenic temperature and steady operation to maintain the cryogenic temperature following the initial cooling. The gas-driven cryogenic refrigerator includes a compressor, a cold head, and a flow restrictor connected between the compressor and the cold head and operable to restrict the flow rate of a working gas to the cold head during the initial cooling compared to steady operation. [Effects of the Invention]

[0008] According to the present invention, the quietness of a gas-driven cryogenic refrigerator can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram schematically illustrating a cryogenic refrigerator according to an embodiment. [Figure 2] 1 is a diagram schematically illustrating a cryogenic refrigerator according to an embodiment. [Figure 3]FIG. 10 is a schematic diagram showing another example of a flow restrictor that can be applied to the cryogenic refrigerator according to the embodiment. [Figure 4] FIG. 4 is a schematic diagram illustrating another example of a cryogenic refrigerator according to an embodiment. [Figure 5] FIG. 10 is a schematic diagram showing another example of a flow restrictor that can be applied to the cryogenic refrigerator according to the embodiment. [Figure 6] FIG. 10 is a schematic diagram showing another example of a flow restrictor that can be applied to the cryogenic refrigerator according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description and drawings, identical or equivalent components, parts, and processes are designated by the same reference numerals, and redundant explanations will be omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience to facilitate explanation, and should not be interpreted as limiting unless otherwise specified. The embodiments are merely examples and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0011] 1 and 2 are schematic diagrams showing a cryogenic refrigerator 10 according to an embodiment. The cryogenic refrigerator 10 is, for example, a gas-driven GM refrigerator.

[0012] The cryogenic refrigerator 10 includes a compressor 12 that compresses a working gas (e.g., helium gas) 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, respectively, for the cryogenic refrigerator 10. The cold head 14 is also called an expander.

[0013] As will be described in detail later, 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 equipped with a regenerator 15 that pre-cools 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 as it passes through it. The compressor 12 compresses the recovered low-pressure (PL) working gas and supplies it to the cold head 14 again.

[0014] The illustrated coldhead 14 is a single stage, although the coldhead 14 may be multi-stage.

[0015] The cold head 14 includes an axially movable body 16 as a free piston driven by gas pressure, and an airtight cold head housing 18 that houses the axially movable body 16. The cold head housing 18 supports the axially movable body 16 so that it can reciprocate in the axial direction, and is configured as a pressure vessel for the working gas. Unlike a motor-driven GM refrigerator, the cold head 14 does not have a motor or a connecting mechanism (e.g., a Scotch yoke mechanism) that drives the axially movable body 16.

[0016] The axially movable body 16 extends in the axial direction (the vertical direction in FIG. 1 , indicated by arrow C) and includes a displacer 20 that can reciprocate in the axial direction, and a drive piston 22 that is coaxially connected to the displacer 20 so as to drive the displacer 20 in the axial direction. The drive piston 22 is rigidly connected to the displacer 20 so that the displacer 20 reciprocates in the axial direction together with the drive piston 22. The drive piston 22 has dimensions that are smaller than those of the displacer 20. The axial length of the drive piston 22 is shorter than that of the displacer 20, and the diameter of the drive piston 22 is also smaller than that of the displacer 20.

[0017] The cold head housing 18 includes a displacer cylinder 26 that accommodates the displacer 20 so that it can reciprocate in the axial direction, and a piston cylinder 28 that accommodates the drive piston 22 so that it can reciprocate in the axial direction. A drive chamber 29 that receives the drive piston 22 is formed within the piston cylinder 28. The piston cylinder 28 is disposed coaxially with and axially adjacent to the displacer cylinder 26. As will be described in detail later, the drive section of the gas-driven cold head 14 is composed of the drive piston 22 and the piston cylinder 28. The volume of the piston cylinder 28 is smaller than that of the displacer cylinder 26. The axial length of the piston cylinder 28 is shorter than that of the displacer cylinder 26, and the diameter of the piston cylinder 28 is also smaller than that of the displacer cylinder 26.

[0018] The axial reciprocating motion of the displacer 20 is guided by a displacer cylinder 26. Typically, the displacer 20 and the displacer cylinder 26 are each cylindrical members extending in the axial direction, and the inner diameter of the displacer cylinder 26 matches or is slightly larger than the outer diameter of the displacer 20. Similarly, the axial reciprocating motion of the drive piston 22 is guided by a piston cylinder 28. Typically, the drive piston 22 and the piston cylinder 28 are each cylindrical members extending in the axial direction, and the inner diameter of the piston cylinder 28 matches or is slightly larger than the outer diameter of the drive piston 22.

[0019] The displacer 20 and drive piston 22 are rigidly connected so that the axial stroke of the drive piston 22 is equal to the axial stroke of the displacer 20, and the two move together throughout the entire stroke. The position of the drive piston 22 relative to the displacer 20 remains unchanged during the axial reciprocation of the axially movable body 16.

[0020] A first seal 32 is provided between the drive piston 22 and the piston cylinder 28. The first seal 32 is attached to either the drive piston 22 or the piston cylinder 28 and slides against the other of the drive piston 22 and the piston cylinder 28. The first seal 32 is formed of a sealing member such as a slipper seal or an O-ring. The first seal 32 makes the piston cylinder 28 airtight with respect to the displacer cylinder 26. Because the first seal 32 is provided, no direct gas communication occurs between the piston cylinder 28 and the displacer cylinder 26 (i.e., the drive chamber 29 and the room temperature chamber 36). The internal pressure of the piston cylinder 28 and the internal pressure of the displacer cylinder 26 can be different magnitudes.

[0021] The displacer cylinder 26 is divided by the displacer 20 into an expansion chamber 34 and a room-temperature chamber 36. The displacer 20 forms the expansion chamber 34 between itself and the displacer cylinder 26 at one axial end, and the room-temperature chamber 36 between itself and the displacer cylinder 26 at the other axial end. The room-temperature chamber 36 can also be called a compression chamber. The drive piston 22 extends from the displacer 20 on the axially opposite side of the expansion chamber 34, i.e., toward the room-temperature chamber 36. The cold head 14 also includes a cooling stage 38 fixed to the displacer cylinder 26 so as to enclose the expansion chamber 34.

[0022] The regenerator 15 is built into the displacer 20. The displacer 20 has an inlet passage 40 in its upper lid that connects the regenerator 15 to the room-temperature chamber 36. The displacer 20 also has an outlet passage 42 in its cylindrical portion that connects the regenerator 15 to the expansion chamber 34. Alternatively, the outlet passage 42 may be provided in the lower lid of the displacer 20. In addition, the regenerator 15 has an inlet retainer 41 inscribed in the upper lid and an outlet retainer 43 inscribed in the lower lid. The inlet retainer 41 and the outlet retainer 43 act as flow straighteners for the working gas. The regenerator material may be, for example, a copper wire mesh. The retainer may be a wire mesh that is coarser than the regenerator material.

[0023] A second seal 44 is provided between the displacer 20 and the displacer cylinder 26. The second seal 44 is, for example, a slipper seal, and is attached to the cylindrical portion or the upper cover portion of the displacer 20. Since the clearance between the displacer 20 and the displacer cylinder 26 is sealed by the second seal 44, there is no direct gas flow between the room temperature chamber 36 and the expansion chamber 34 (i.e., no gas flow bypassing the regenerator 15).

[0024] The working gas flows from the room-temperature chamber 36 into the regenerator 15 through the inlet passage 40. More precisely, the working gas flows from the inlet passage 40 through the inlet retainer 41 into the regenerator 15. The working gas flows from the regenerator 15 into the expansion chamber 34 via the outlet retainer 43 and the outlet passage 42. When the working gas returns from the expansion chamber 34 to the room-temperature chamber 36, it follows the reverse path. That is, the working gas returns from the expansion chamber 34 to the room-temperature chamber 36 through the outlet passage 42, the regenerator 15, and the inlet passage 40. Any working gas that attempts to bypass the regenerator 15 and flow through the clearance is blocked by the second seal portion 44.

[0025] The cold head 14 is installed in the orientation shown in the figure at the site where it will be used. That is, the cold head 14 is installed vertically with the displacer cylinder 26 facing vertically downward and the piston cylinder 28 facing vertically upward. In this manner, the cryocooler 10 achieves the highest cooling capacity when installed with the cooling stage 38 facing vertically downward. However, the orientation of the cryocooler 10 is not limited to this. Conversely, the cold head 14 may be installed with the cooling stage 38 facing vertically upward. Alternatively, the cold head 14 may be installed horizontally or in another orientation. The cold head 14 is capable of cooling operation regardless of the installation orientation.

[0026] The end of the reciprocating stroke of the displacer 20 on the expansion chamber 34 side is referred to as the bottom dead center of the displacer 20, and the end of the reciprocating stroke of the displacer 20 on the room temperature chamber 36 side is referred to as the top dead center of the displacer 20. Movement of the displacer 20 toward the top dead center may be referred to as an upward movement, and movement of the displacer 20 toward the bottom dead center may be referred to as a downward movement. However, these terms do not limit the orientation of the cold head 14.

[0027] When the displacer 20 moves axially, the expansion chamber 34 and the room temperature chamber 36 increase or decrease their volumes in a complementary manner. That is, when the displacer 20 moves downward, the expansion chamber 34 narrows and the room temperature chamber 36 widens. Conversely, the volume of the expansion chamber 34 is minimum (the volume of the room temperature chamber 36 is maximum) when the displacer 20 is located at bottom dead center. The volume of the expansion chamber 34 is maximum (the volume of the room temperature chamber 36 is minimum) when the displacer 20 is located at top dead center. Because the drive piston 22 moves integrally with the displacer 20, the volume of the drive chamber 29 is maximum when the displacer 20 is located at bottom dead center, and minimum when the displacer 20 is located at top dead center.

[0028] The cryogenic refrigerator 10 further includes a working gas circuit 52 connecting the compressor 12 to the cold head 14. The working gas circuit 52 is configured to generate a pressure difference between the piston cylinder 28 and the displacer cylinder 26 (i.e., the drive chamber 29 and the expansion chamber 34). This pressure difference causes the axially movable body 16 to move axially. If the pressure in the displacer cylinder 26 is lower than that of the piston cylinder 28, the drive piston 22 moves downward, and the displacer 20 also moves downward accordingly. Conversely, if the pressure in the displacer cylinder 26 is higher than that of the piston cylinder 28, the drive piston 22 moves upward, and the displacer 20 also moves upward accordingly.

[0029] The working gas circuit 52 includes a valve unit 54. The valve unit 54 may be disposed adjacent to the piston cylinder 28 so as to be integral with the cold head housing 18 and connected to the compressor 12 by piping. The valve unit 54 may also be disposed outside the cold head housing 18 and connected to the compressor 12 and the cold head 14 by piping.

[0030] The valve section 54 includes 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 opening / closing valve V1 and a main exhaust opening / closing valve V2. The sub-pressure switching valve 62 has a sub-intake opening / closing valve V3 and a sub-exhaust opening / closing valve V4.

[0031] The working gas circuit 52 includes a high-pressure line 13a and a low-pressure line 13b that connect the compressor 12 to the valve unit 54. The high-pressure line 13a extends from the compressor discharge port 12a, branches midway, and is connected to a main intake on-off valve V1 and a sub-intake on-off valve V3. The low-pressure line 13b extends from the compressor suction port 12b, branches midway, and is connected to a main exhaust on-off valve V2 and a sub-exhaust on-off valve V4.

[0032] The working gas circuit 52 also includes a main communication passage 64 and an auxiliary communication passage 66 that connect the cold head 14 to the valve unit 54. The main communication passage 64 connects the displacer cylinder 26 to the main pressure switching valve 60. The main communication passage 64 extends from the room temperature chamber 36 and branches midway to be connected to the main intake on-off valve V1 and the main exhaust on-off valve V2. The auxiliary communication passage 66 connects the piston cylinder 28 to the auxiliary pressure switching valve 62. The auxiliary communication passage 66 extends from the drive chamber 29 and branches midway to be connected to the auxiliary intake on-off valve V3 and the auxiliary exhaust on-off valve V4.

[0033] The main pressure switching valve 60 is configured to selectively connect the compressor discharge port 12a or the compressor suction port 12b to the room-temperature chamber 36 of the displacer cylinder 26. In the main pressure switching valve 60, the main intake on-off valve V1 and the main exhaust on-off valve V2 are each opened exclusively. That is, the main intake on-off valve V1 and the main exhaust on-off valve V2 are prohibited from being opened simultaneously. However, the main intake on-off valve V1 and the main exhaust on-off valve V2 may both be closed temporarily.

[0034] When the main intake on-off valve V1 is open, the main exhaust on-off valve V2 is closed. Working gas flows from the compressor discharge port 12a through the high-pressure line 13a and the main communication passage 64 to the displacer cylinder 26. As described above, the working gas flows from the room-temperature chamber 36 through the regenerator 15 to the expansion chamber 34. In this way, high-pressure PH working gas is supplied from the compressor 12 to the expansion chamber 34, and the pressure in the expansion chamber 34 is increased. Conversely, when the main intake on-off valve V1 is closed, the supply of working gas from the compressor 12 to the expansion chamber 34 is stopped.

[0035] On the other hand, when the main exhaust on-off valve V2 is open, the main intake on-off valve V1 is closed. First, the high-pressure PH working gas expands and is reduced in pressure in the expansion chamber 34. The working gas flows from the expansion chamber 34 to the room-temperature chamber 36 through the regenerator 15. The working gas flows from the displacer cylinder 26 to the compressor suction port 12b through the main communicating passage 64 and the low-pressure line 13b. In this way, the low-pressure PL working gas is recovered from the cold head 14 to the compressor 12. When the main exhaust on-off valve V2 is closed, the recovery of the working gas from the expansion chamber 34 to the compressor 12 is stopped.

[0036] The auxiliary pressure switching valve 62 is configured to selectively connect the compressor discharge port 12a or the compressor suction port 12b to the piston cylinder 28. The auxiliary pressure switching valve 62 is configured to exclusively open the auxiliary intake on-off valve V3 and the auxiliary exhaust on-off valve V4. In other words, the auxiliary intake on-off valve V3 and the auxiliary exhaust on-off valve V4 are prohibited from being opened simultaneously. However, the auxiliary intake on-off valve V3 and the auxiliary exhaust on-off valve V4 may both be temporarily closed.

[0037] When the auxiliary intake on-off valve V3 is open, the auxiliary exhaust on-off valve V4 is closed. Working gas flows from the compressor discharge port 12a through the high-pressure line 13a and the auxiliary communication passage 66 to the piston cylinder 28. In this way, high-pressure working gas PH is supplied from the compressor 12 to the drive chamber 29, increasing the pressure in the drive chamber 29. When the auxiliary intake on-off valve V3 is closed, the supply of working gas from the compressor 12 to the piston cylinder 28 is stopped.

[0038] On the other hand, when the auxiliary exhaust on-off valve V4 is open, the auxiliary intake on-off valve V3 is closed. Working gas is returned from the piston cylinder 28 to the compressor suction port 12b through the auxiliary communication passage 66 and the low-pressure line 13b, and the pressure in the drive chamber 29 is reduced to low pressure PL. When the auxiliary exhaust on-off valve V4 is closed, the return of working gas from the piston cylinder 28 to the compressor 12 is stopped.

[0039] In this way, the main pressure switching valve 60 alternately connects the expansion chamber 34 to the compressor discharge port 12a and the compressor suction port 12b, generating periodic pressure fluctuations between the high pressure PH and the low pressure PL in the expansion chamber 34. The sub-pressure switching valve 62 alternately connects the drive chamber 29 to the compressor discharge port 12a and the compressor suction port 12b, generating periodic pressure fluctuations between the high pressure PH and the low pressure PL in the drive chamber 29.

[0040] The auxiliary pressure switching valve 62 alternately connects the drive chamber 29 to the compressor discharge port 12a and the compressor suction port 12b so as to generate a pressure difference between the expansion chamber 34 and the drive chamber 29, causing the drive piston 22 to reciprocate in the axial direction due to the pressure difference. Typically, pressure fluctuations in the drive chamber 29 are generated with the same period but approximately the opposite phase to the pressure fluctuations in the expansion chamber 34. When the expansion chamber 34 is at high pressure PH, the drive chamber 29 is at low pressure PL, allowing the drive piston 22 to move the displacer 20 upward. When the expansion chamber 34 is at low pressure PL, the drive chamber 29 is at high pressure PH, allowing the drive piston 22 to move the displacer 20 downward. In this way, the auxiliary pressure switching valve 62 controls the pressure in the drive chamber 29 so that the drive piston 22 drives the axial reciprocation of the displacer 20.

[0041] The valve unit 54 may take the form of a rotary valve. In this case, a group of valves (V1 to V4) are incorporated into the valve unit 54 and driven synchronously. The valve unit 54 is configured so that the valves (V1 to V4) are appropriately switched by the rotational sliding of a valve disc (or valve rotor) relative to a valve body (or valve stator). The group of valves (V1 to V4) are switched at the same cycle while the cryogenic refrigerator 10 is in operation, thereby periodically changing the open / closed state of the four on-off valves (V1 to V4). The four on-off valves (V1 to V4) are opened and closed at different phases.

[0042] The cryogenic refrigerator 10 may include a rotary drive source 56 connected to the valve unit 54 to rotate the valve unit 54. The rotary drive source 56 is mechanically connected to the valve unit 54. The rotary drive source 56 is, for example, a motor. However, the rotary drive source 56 is not mechanically connected to the axially movable body 16. The cryogenic refrigerator 10 may also include a controller 58 that controls the valve unit 54. The controller 58 may control the rotary drive source 56.

[0043] In one embodiment, the group of valves (V1-V4) may take the form of a plurality of individually controllable valves. Each of the valves (V1-V4) may be an electromagnetic on-off valve. In this case, instead of providing the rotary drive source 56, each of the valves (V1-V4) is electrically connected to a controller 58. The controller 58 may control the opening and closing of each of the valves (V1-V4).

[0044] The cold head 14 may also include a temperature sensor 68 that measures the temperature of a low-temperature portion thereof (e.g., the cooling stage 38) and outputs a measured temperature signal indicative of the measured temperature. The controller 58 may be electrically connected to the temperature sensor 68 so as to acquire the measured temperature signal from the temperature sensor 68.

[0045] FIG. 1 shows the displacer 20 at its bottom dead center, and FIG. 2 shows the displacer 20 at its top dead center.

[0046] In this embodiment, a design known as a "collar bumper" is employed to prevent interference between the displacer 20 and the end of the displacer cylinder 26 and reduce vibration and noise during operation of the cryogenic refrigerator 10. The cold head 14 includes a collar 70 and a collar chamber 72 divided by the collar 70 into an upper section 72a and a lower section 72b. The collar 70 is rigidly connected to the displacer 20 so as to reciprocate 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.

[0047] The displacer cylinder 26 includes 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 includes 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 unit 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.

[0048] The collar 70 includes a cylindrical body 70a and a collar upper end 70b. The body 70a has approximately the same outer diameter as the displacer 20 and extends upward from the room-temperature chamber 36 side of the displacer 20. The inner diameter of the body 70a is larger than the outer diameter of the piston cylinder 28. The collar upper end 70b is located outside the outer diameter of the displacer 20. The collar upper end 70b divides the collar chamber 72 into an upper section 72a and a lower section 72b. The collar chamber 72 is connected to the room-temperature chamber 36. When the displacer 20 reciprocates within the displacer cylinder 26, the collar 70 reciprocates within the collar chamber 72 without friction with the displacer cylinder 26 and the piston cylinder 28. The collar 70 also does not rub against the inner circumferential surface of the sleeve 73.

[0049] The cold head 14 also includes an upper bumper 74 provided in the upper section 72a to reduce interference between the displacer 20 and the displacer cylinder 26 when the displacer 20 is at top dead center. The upper bumper 74 is installed on the upper surface of the collar chamber 72 and has an upper cushioning material 74a and an upper retainer 74b. The upper bumper 74 is attached to, for example, a sleeve 73. The upper cushioning material 74a is an annular member made of resin, such as an O-ring, and is sandwiched between the upper surface of the collar chamber 72 and the upper retainer 74b. The upper retainer 74b is made of, for example, a resin material. Note that the upper retainer 74b does not necessarily have to be provided.

[0050] The upper bumper 74 comes into contact with the collar 70 when the displacer 20 is at the top dead center, preventing the displacer 20 from colliding with the displacer cylinder 26 on the room temperature chamber 36 side. When the displacer 20 moves upward, the collar upper end 70b engages with the upper bumper 74 inside the collar chamber 72 before the displacer 20 collides with the piston cylinder 28. At this time, the collar upper end 70b comes into contact with the upper retainer 74b, compressing the upper buffer material 74a and absorbing the impact.

[0051] The cold head 14 includes a lower bumper 76 provided in the lower section 72b to reduce interference between the displacer 20 and the displacer cylinder 26 when the displacer 20 is at bottom dead center. The lower bumper 76 is installed on the lower surface of the collar chamber 72 and has a lower cushioning material 76a and a lower retainer 76b. The lower bumper 76 is attached to, for example, the cylinder flange 26a. The lower bumper 76 may also be attached to the sleeve 73. The lower cushioning material 76a is an annular member made of resin, such as an O-ring, and is sandwiched between the lower surface of the collar chamber 72 and the lower retainer 76b. The lower retainer 76b is formed of, for example, a resin material. The lower retainer 76b does not necessarily have to be provided.

[0052] The lower bumper 76 comes into contact with the collar 70 when the displacer 20 is at 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 collar upper end 70b engages with the lower bumper 76 inside the collar chamber 72 before the displacer 20 collides with the displacer cylinder 26 on the expansion chamber 34 side. At this time, the collar upper end 70b comes into contact with the lower retainer 76b, compressing the lower buffer material 76a and absorbing the impact.

[0053] The upper section 72a communicates with the room 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 collar 70, and the working gas can flow between the room temperature chamber 36 and the upper section 72a through the first gap 78a.

[0054] The lower section 72b communicates with the upper section 72a. A second gap 78b is formed between the inner circumferential surface of the sleeve 73 and the outer circumferential surface of the collar upper end 70b, allowing working gas to flow between the upper section 72a and the lower section 72b through the second gap 78b. However, when the displacer 20 is positioned at bottom dead center, the collar upper end 70b contacts the lower bumper 76, blocking communication between the lower section 72b and the upper section 72a through the second gap 78b. When the displacer 20 is positioned at top dead center, the collar upper end 70b contacts the upper bumper 74, blocking communication between the lower section 72b and the upper section 72a through the second gap 78b. Therefore, when the displacer 20 is positioned between top dead center and bottom dead center, the lower section 72b communicates with the room-temperature chamber 36 through the upper section 72a, allowing working gas to flow between the room-temperature chamber 36 and the lower section 72b. Furthermore, the lower section 72b is sealed by the second seal portion 44 and is therefore not in communication with the expansion chamber 34.

[0055] The cold head 14 also includes a communication passage 80 that ensures communication between the upper section 72a and the lower section 72b when the displacer 20 is at bottom dead center. The communication passage 80 is formed in the collar 70 so that the upper section 72a communicates with the lower section 72b when the collar upper end 70b is in contact with the lower bumper 76. The communication passage 80 is formed to penetrate the collar 70 (e.g., the collar upper end 70b) from the upper section 72a to the lower section 72b, and at least one communication passage 80 may be formed in the circumferential direction. As shown in the figure, when the collar upper end 70b extends radially outward from the main body 70a of the collar 70, the communication passage 80 is formed in the collar upper end 70b at a position radially inward from the lower bumper 76. The communication passage 80 may also be formed to penetrate the main body 70a of the collar 70.

[0056] The first gap 78a, the second gap 78b, and the communication passage 80 act as flow resistances. Therefore, when the displacer 20 reciprocates, the upper section 72a and the lower section 72b can each generate a gas spring force. As the displacer 20 moves upward, the collar upper end 70b also moves upward, narrowing the upper section 72a. At this time, the gas in the upper section 72a is compressed, increasing its pressure. The pressure in the upper section 72a acts downward on the upper surface of the collar upper end 70b. Therefore, the upper section 72a generates a gas spring force that resists the upward movement of the collar 70 and the displacer 20. Similarly, when the displacer 20 moves downward, the lower section 72b generates a gas spring force that resists the downward movement of the collar 70 and the displacer 20. The upper section 72a and the lower section 72b may also be referred to as the upper gas spring chamber and the lower gas spring chamber, respectively. The gas spring force helps reduce vibrations and noise that may occur when collar 70 contacts upper bumper 74 and lower bumper 76 .

[0057] The cryocooler 10 can perform initial cooling and steady-state operation following the initial cooling. Initial cooling is an operating mode of the cold head 14 in which the cryocooler 10 is rapidly cooled from an initial temperature to a cryogenic temperature upon startup. Steady-state operation is an operating mode of the cold head 14 in which the cold head 14 maintains the cryogenically cooled state achieved by the initial cooling. As mentioned above, initial cooling can also be referred to as cool-down. The initial temperature may be ambient temperature (e.g., room temperature). The cold head 14 is cooled to a standard cooling temperature during initial cooling, and during steady-state operation, the cold head 14 is maintained within an allowable cryogenic temperature range that includes this standard cooling temperature. The standard cooling temperature may vary depending on the application and settings of the cryocooler 10, but may be, for example, approximately 10 K to 20 K, or below 10 K. The standard cooling temperature is typically approximately 4.2 K or below when used to cool superconducting devices.

[0058] The amount of working gas sealed in the cryogenic refrigerator 10 may be determined so that the cryogenic refrigerator 10 can be operated at an optimal operating pressure during steady-state operation, i.e., when cooled to a cryogenic temperature. During initial cooling, the density of the working gas in the cold head 14 increases as the temperature drops from the initial temperature to a cryogenic temperature. Accordingly, the amount of working gas accumulated in the cold head 14 increases, and, in other words, the working gas is absorbed into the cold head 14 from the working gas circuit 52. As a result, as the cold head 14 cools, the pressure of the working gas circulating in the working gas circuit 52 gradually decreases. As a result, the operating pressure of the cryogenic refrigerator 10 during steady-state operation is optimized.

[0059] From another perspective, the operating pressure of the cryogenic refrigerator 10 at the start of initial cooling tends to be high because the temperature of the cryogenic refrigerator 10 at that time is much higher than the cryogenic temperature during steady-state operation. Accordingly, the pressure difference between the drive chamber 29 and the expansion chamber 34, i.e., the gas pressure for driving the displacer 20, can also be high during initial cooling, especially at the beginning of the initial cooling. In a typical gas-driven cryogenic refrigerator, the gas pressure can move the displacer 20 until it interferes with (e.g., collides with) the end of the displacer cylinder 26. This interference can cause noise (e.g., a crashing sound). As the gas pressure increases, the noise can become more pronounced.

[0060] To address this issue, the cryogenic refrigerator 10 includes a flow restrictor 100 connected between the compressor 12 and the cold head 14. The flow restrictor 100 operates to restrict the flow rate of the working gas to the cold head 14 during initial cooling compared to steady operation. This reduces the flow rate of the working gas to the cold head 14 that occurs when the cryogenic refrigerator 10 switches between the intake stroke and the exhaust stroke during initial cooling, thereby delaying the rise in the gas pressure that drives the displacer 20. This improves the quietness of the cryogenic refrigerator 10. For example, the moving speed and therefore the kinetic energy of the displacer 20 can be reduced, thereby suppressing the sound of the displacer 20 hitting the displacer cylinder 26.

[0061] In this embodiment, the flow restrictor 100 is connected between the auxiliary pressure switching valve 62 and the drive chamber 29 and operates to restrict the flow rate of the working gas into the drive chamber 29 during initial cooling compared to steady operation. In this way, the flow rate of the working gas into the drive chamber 29 is reduced, and the pressure rise in the drive chamber 29 is delayed, thereby delaying the rise in the driving force of the drive piston 22 due to the gas pressure. This improves the quietness of the cryocooler 10.

[0062] The flow restrictor 100 includes a flow control valve 102 that opens at a smaller opening during initial cooling than during steady operation. In this way, the flow control valve 102 can restrict the flow rate of the working gas into the drive chamber 29 during initial cooling compared to steady operation. The flow control valve 102 is provided in the secondary communication passage 66 and is connected in series between the secondary pressure switching valve 62 and the drive chamber 29. The flow control valve 102 may be any flow control valve with a variable opening, such as a needle valve or a variable orifice.

[0063] To control the opening degree of the flow control valve 102, the flow restrictor 100 may include a controller 58. The controller 58 may obtain the operating state of the cryogenic refrigerator 10 (i.e., whether the cryogenic refrigerator 10 is performing initial cooling or steady operation) and control the flow control valve 102 based on the obtained operating state.

[0064] To obtain the operating state of the cryocooler 10, the controller 58 may use the temperature of the cryocooler 10. For example, the controller 58 may refer to the temperature measured by a temperature sensor 68 provided in a low-temperature portion of the cold head 14 (e.g., the cooling stage 38). When the measured temperature is higher than a predetermined target temperature for initial cooling (e.g., the standard cooling temperature described above), the controller 58 may determine that the cryocooler 10 is performing initial cooling. When the measured temperature is lower than the target temperature for initial cooling, the controller 58 may determine that the cryocooler 10 is performing steady-state operation.

[0065] To obtain the operating state of the cryogenic refrigerator 10, the controller 58 may use the pressure of the cryogenic refrigerator 10. For example, the controller 58 may refer to the pressure measured by a pressure sensor (not shown) that measures the high pressure of the cryogenic refrigerator 10 (e.g., the pressure at the compressor discharge port 12a) or the low pressure of the cryogenic refrigerator 10 (e.g., the pressure at the compressor suction port 12b). The differential pressure between the high pressure and the low pressure of the cryogenic refrigerator 10 may also be referenced. The measured pressure correlates with the cooling temperature of the cryogenic refrigerator 10. Therefore, when the measured pressure is higher than a predetermined pressure threshold, the controller 58 may determine that the cryogenic refrigerator 10 is performing initial cooling. When the measured pressure is lower than a predetermined pressure threshold, the controller 58 may determine that the cryogenic refrigerator 10 is performing steady operation.

[0066] Alternatively, the controller 58 may be configured to measure the elapsed time from the start of the initial cooling, and may acquire the operating state of the cryogenic refrigerator 10 based on the elapsed time. The time required for the initial cooling can be determined empirically or experimentally. Therefore, when the measured elapsed time is shorter than a predetermined time, the controller 58 may determine that the cryogenic refrigerator 10 is performing the initial cooling. When the measured elapsed time is longer than a predetermined time, the controller 58 may determine that the cryogenic refrigerator 10 is performing steady operation.

[0067] The controller 58 may set the flow control valve 102 to a first opening degree when the cryogenic refrigerator 10 is performing initial cooling, and may set the flow control valve 102 to a second opening degree when the cryogenic refrigerator 10 is performing steady 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 depending on the operating state of the cryogenic refrigerator 10.

[0068] The controller 58 may change the opening of the flow control valve 102 from a first opening to a second opening in a stepwise or continuous manner based on the measured temperature (or measured pressure). That is, the higher the measured temperature (or measured pressure), the smaller the opening of the flow control valve 102 may be. Similarly, the controller 58 may change the opening of the flow control valve 102 from the first opening to the second opening in a stepwise or continuous manner based on the elapsed time. That is, the shorter the elapsed time, the smaller the opening of the flow control valve 102 may be.

[0069] The opening degree of the flow control valve 102 may be manually controlled. The flow control valve 102 may be provided with an operating unit for adjusting the opening degree, and the opening degree may be changed by operating this operating unit. In this manner, the flow control valve 102 may operate to open at a smaller opening degree during initial cooling than during steady operation.

[0070] The operation of the cryogenic refrigerator 10 will now be described. When the displacer 20 is at or near bottom dead center, the intake stroke of the cryogenic refrigerator 10 begins. The main intake on-off valve V1 is opened, and the main exhaust on-off valve V2 is closed. Working gas is supplied from the compressor discharge port 12a through the main intake on-off valve V1 to the displacer cylinder 26 of the cold head 14, and the expansion chamber 34 and room temperature chamber 36 become high pressure PH. Simultaneously with the intake into the expansion chamber 34, the piston cylinder 28 is exhausted. The auxiliary intake on-off valve V3 is closed, and the auxiliary exhaust on-off valve V4 is opened. Working gas is discharged from the piston cylinder 28 through the auxiliary exhaust on-off valve V4 to the compressor suction port 12b, and the pressure in the drive chamber 29 is reduced to low pressure PL.

[0071] Therefore, during the intake stroke, an upward driving force due to the pressure difference (PH-PL) between the drive chamber 29 and the expansion chamber 34 acts on the drive piston 22. As a result, the displacer 20 moves from the bottom dead center toward the top dead center together with the drive piston 22. In this way, the volume of the expansion chamber 34 increases and is filled with high-pressure gas.

[0072] The collar 70 also moves upward together with the displacer 20. The collar 70 comes into contact with the upper bumper 74 before the displacer 20 collides with the high-temperature end of the displacer cylinder 26 (e.g., the piston cylinder 28). The upper buffer material 74a is compressed, absorbing the impact. While the collar 70 moves upward, the upper section 72a is in communication with the room-temperature chamber 36 through the first gap 78a, and the lower section 72b is in communication with the upper section 72a through the second gap 78b and the communication passage 80. Therefore, the upper section 72a and the lower section 72b are at high pressure PH, just like the room-temperature chamber 36.

[0073] When the displacer 20 is at or near the top dead center, the exhaust stroke of the cryogenic refrigerator 10 begins. The main exhaust on-off valve V2 is opened, and the main intake on-off valve V1 is closed. The high-pressure gas expands and is cooled in the expansion chamber 34. The expanded gas cools the regenerator 15 and passes through the room-temperature chamber 36 before being collected in the compressor intake port 12b. The expansion chamber 34 and the room-temperature chamber 36 become low-pressure PL. At the same time as exhaust from the expansion chamber 34, intake into the piston cylinder 28 is performed. The auxiliary exhaust on-off valve V4 is closed, and the auxiliary intake on-off valve V3 is opened. Working gas is supplied to the piston cylinder 28 from the compressor discharge port 12a through the auxiliary intake on-off valve V3, and the pressure in the drive chamber 29 is increased to high pressure PH.

[0074] Therefore, during the exhaust stroke, a driving force due to 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 displacer 20 moves from the top dead center toward the bottom dead center together with the drive piston 22. In this way, the volume of the expansion chamber 34 is reduced and the low-pressure gas is discharged.

[0075] The collar 70 also moves downward together with the displacer 20. The collar 70 comes into contact with the lower bumper 76 before the displacer 20 collides with the low-temperature end of the displacer cylinder 26. The lower cushioning material 76a is compressed, absorbing the impact. While the collar 70 is moving downward, the upper section 72a is in communication with the room-temperature chamber 36 through the first gap 78a, and the lower section 72b is in communication with the upper section 72a through the second gap 78b and the communication passage 80. Therefore, the upper section 72a and the lower section 72b are at the low pressure PL, just like the room-temperature chamber 36.

[0076] Unlike the above-described embodiment, a typical collar bumper-type gas-driven cryogenic refrigerator does not have the communication passage 80. In this case, when the collar 70 is positioned at the bottom dead center, the working gas at low pressure PL may be sealed in the lower section 72b. In this state, if the upper section 72a is pressurized to high pressure PH at the start of the intake stroke, the collar upper end 70b may be pressed against the lower bumper 76 by the differential pressure (PH-PL). This differential pressure may prevent the displacer 20 from moving upward.

[0077] However, the cryogenic refrigerator 10 according to the embodiment includes a communication passage 80 formed in the collar 70 to ensure communication between the upper section 72a and the lower section 72b when the displacer 20 is at the bottom dead center. Therefore, even when the collar 70 is at the bottom dead center and the collar upper end 70b is in contact with the lower bumper 76, the lower section 72b is in communication with the upper section 72a through the communication passage 80. The lower section 72b is not sealed. Any pressure difference that may occur between the upper section 72a and the lower section 72b is reduced or eliminated through the communication passage 80, so the upward movement of the displacer 20 is not impeded. Therefore, the displacer 20 can move from the bottom dead center toward the top dead center.

[0078] The cryogenic refrigerator 10 repeats this refrigeration cycle (i.e., the GM cycle) to cool the cooling stage 38. As a result, the cryogenic refrigerator 10 can cool an object to be cooled (not shown) that is thermally coupled to the cooling stage 38.

[0079] Since the cryogenic refrigerator 10 is of the collar bumper type, the contact between the collar 70 and the bumpers (74, 76) prevents interference (for example, collision) between the displacer 20 and the displacer cylinder 26, thereby reducing vibration and noise.

[0080] In this embodiment, as described above, the flow control valve 102 is provided between the auxiliary pressure switching valve 62 and the drive chamber 29, and the opening of the flow control valve 102 is smaller during initial cooling than during steady operation. This limits the flow of working gas from the drive chamber 29 to the compressor suction port 12b through the auxiliary exhaust valve V4 when the intake stroke begins, thereby delaying the pressure drop in the drive chamber 29 to low pressure PL. Because no such flow restriction is performed in the main communication passage 64, the increase in pressure in the expansion chamber 34 and the room temperature chamber 36 to high pressure PH is not delayed. This delay in the rise of the driving force acting on the drive piston 22 during initial cooling compared to steady operation. This reduces the moving speed and, therefore, the kinetic energy of the displacer 20, suppressing the impact noise of the displacer 20 at top dead center and improving the quietness of the cryogenic refrigerator 10 during initial cooling.

[0081] Furthermore, when the exhaust stroke begins, the flow rate of working gas from the compressor discharge port 12a to the drive chamber 29 through the auxiliary intake on-off valve V3 is restricted, delaying the rise in pressure of the drive chamber 29 to the high pressure PH. In the main communication passage 64, the pressure drop to the low pressure PL of the expansion chamber 34 and the room temperature chamber 36 is not delayed. Thus, during the initial cooling, the rise in the driving force acting on the drive piston 22 can be delayed compared to steady operation. The moving speed of the displacer 20, and therefore its kinetic energy, is reduced, suppressing the collision noise of the displacer 20 at bottom dead center, and improving the quietness of the cryogenic refrigerator 10 during the initial cooling.

[0082] On the other hand, during steady operation, the opening of the flow control valve 102 is increased and the flow rate restriction by the flow restrictor 100 is released. A sufficient flow rate of the working gas can be ensured in the sub-communication passage 66 so as to optimize the refrigeration capacity of the cryogenic refrigerator 10.

[0083] Fig. 3 is a schematic diagram showing another example of a flow restrictor 100 that can be applied to the cryogenic refrigerator 10 according to the embodiment. The flow restrictor 100 shown in Fig. 3 may be applied to the cryogenic refrigerator 10 shown in Figs. 1 and 2. Thus, similar to the above-described embodiment, the flow restrictor 100 may be connected between the compressor 12 and the cold head 14, for example, between the auxiliary pressure switching valve 62 and the driving chamber 29. The flow restrictor 100 may operate to restrict the flow rate of the working gas to the cold head 14 (e.g., the driving chamber 29) during initial cooling compared to steady operation.

[0084] 3, the flow restrictor 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 provided in the secondary communication passage 66. The first flow control valve 102a may be an on-off valve (e.g., a solenoid valve). The second flow control valve 102b may be an orifice, e.g., a fixed orifice.

[0085] The controller 58 may acquire the operating state of the cryogenic refrigerator 10 (i.e., whether the cryogenic refrigerator 10 is performing initial cooling or steady operation) and control the first flow control valve 102a based on the acquired operating state. The controller 58 may 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 operation.

[0086] In this way, during initial cooling, the first flow control valve 102a is closed, restricting the flow rate of the working gas in the auxiliary communication passage 66. That is, during initial cooling, the flow of working gas in the auxiliary communication passage 66 passes only through the second flow control valve 102b. During steady operation, the first flow control valve 102a is opened, and the flow rate restriction during initial cooling is lifted. The working gas can pass through both the first flow control valve 102a and the second flow control valve 102b.

[0087] Even in this way, the flow restrictor 100 can reduce the flow rate of the working gas into the driving chamber 29 during the initial cooling period compared to steady operation, and delay the pressure increase in the driving chamber 29. This can improve the quietness of the cryogenic refrigerator 10. Furthermore, compared to the aperture control of the flow rate control valve 102 described with reference to Figures 1 and 2, the on / off control of the first flow rate control valve 102a can be advantageous in that the controller 58 can be implemented with a simpler configuration.

[0088] The first flow control valve 102a may be a manually operable on / off valve.

[0089] Furthermore, the first flow control valve 102a may be a flow control valve whose opening degree is controllable. The second flow control valve 102b may be a flow control valve whose opening degree is controllable. If necessary, an additional orifice or a third flow control valve may be provided upstream and / or downstream of the first flow control valve 102a and / or the second flow control valve 102b.

[0090] 4 is a schematic diagram showing another example of a cryogenic refrigerator 10 according to an 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 restrictor 100.

[0091] 4 has the same configuration as the cryogenic refrigerator 10 shown in FIGS. 1 and 2, except for the specific configuration of the flow restrictor 100 described below. Thus, similar to the above-described embodiment, the flow restrictor 100 may be connected between the compressor 12 and the cold head 14, for example, between the auxiliary pressure switching valve 62 and the driving chamber 29. The flow restrictor 100 operates to restrict the flow rate of the working gas to the cold head 14 (e.g., the driving chamber 29) during initial cooling compared to steady operation.

[0092] The flow restrictor 100 includes a flow control valve 102 and a gas volume 104. The flow control valve 102 includes a gas pressure actuator 106 that drives the flow control valve 102 so that the flow control valve 102 opens to a smaller degree during initial cooling compared to steady-state operation.

[0093] The flow control valve 102 includes a valve element 108 that determines the aperture of the flow control valve 102, and a valve housing 110 that accommodates the valve element 108. The valve element 108 includes a tip end 108a and a base end 108b that extends from the tip end 108a. The valve housing 110 includes an orifice 110a that is connected to and forms a part of the sub-communication passage 66, and a pressure chamber 110b that is isolated from the orifice 110a by an elastically deformable partition wall 112 (e.g., a bellows). The tip end 108a of the valve element 108 is accommodated in the orifice 110a, and the base end 108b of the valve element 108 is accommodated in the pressure chamber 110b. The aperture of the flow control valve 102 is determined by the tip end 108a of the valve element 108 at the orifice 110a. The valve element 108 is connected to a valve housing 110 by a partition wall 112 and is movable relative to the valve housing 110 by deformation of the partition wall 112. Movement of the valve element 108 relative to the valve housing 110 changes the opening degree of the flow control valve 102. The flow control valve 102 may be, for example, a needle valve as shown in the figure.

[0094] The gas volume 104 is thermally coupled to a low-temperature portion of the cold head 14 (e.g., the cooling stage 38). The gas volume 104 may be attached to a low-temperature portion of the cold head 14 so as to be cooled by the low-temperature portion of the cold head 14. The gas volume 104 is filled with a predetermined gas, such as nitrogen gas. The gas filling the gas volume 104 may be a gas that condenses (i.e., is 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 as to allow gas to flow between the gas volume 104 and the pressure chamber 110b. For example, the gas volume 104 may be connected to the pressure chamber 110b by a connecting flow path 105 such as a pipe.

[0095] The pressure chamber 110b of the valve housing 110 and the gas volume 104 constitute a part of a gas pressure actuator 106. The gas pressure actuator 106 drives a valve element 108 in response to the pressure in the pressure chamber 110b. The gas pressure actuator 106 is configured to open the flow control valve 102 to a first degree of opening during initial cooling and to open the flow control valve 102 to a second degree of opening during steady operation. The first degree of opening is smaller than the second degree of opening.

[0096] 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 when initial cooling begins is higher than the pressure in the orifice 110a (i.e., the working gas operating pressure of the cryogenic refrigerator 10 in the sub-communicating passage 66). In this way, the valve element 108 can be advanced from the pressure chamber 110b toward the orifice 110a so that the flow control valve 102 has the first opening.

[0097] During the initial cooling, the cold head 14 is cooled, and the cold head 14 also cools the gas volume 104. The volume of the gas in the gas volume 104 decreases as a result of the cooling, and the pressure in the pressure chamber 110b decreases accordingly. If the gas in the gas volume 104 condenses as a result of the cooling, the pressure in the pressure chamber 110b decreases further. As a result, the pressure in the pressure chamber 110b becomes lower than the pressure in the orifice 110a, and as shown schematically by arrow 114 in FIG. 4, the valve element 108 moves back from the orifice 110a toward the pressure chamber 110b while deforming the partition wall 112. As a result, the aperture of the flow control valve 102 increases from the first aperture to the second aperture.

[0098] In this way, the gas pressure actuator 106 can drive the valve element 108 to minimize the aperture of the flow control valve 102 at the beginning of the initial cooling, and then increase the aperture of the flow control valve 102 as the initial cooling progresses. Therefore, in this embodiment as well, the flow restrictor 100 operates to restrict the flow rate of the working gas into the drive chamber 29 during the initial cooling compared to steady operation. In this way, the flow rate of the working gas into the drive chamber 29 is reduced, and the pressure rise in the drive chamber 29 is delayed, thereby delaying the rise in the driving force of the drive piston 22 due to the gas pressure. This can improve the quietness of the cryocooler 10, as in the above-described embodiment.

[0099] The flow restrictor 100 described with reference to Figure 4 can be operated passively by utilizing the temperature drop of the cold head 14 during initial cooling, which can be advantageous in that it does not require control using the controller 58, unlike the flow restrictor 100 described with reference to Figures 1 and 2.

[0100] 5 is a schematic diagram showing another example of a flow restrictor 100 that can be applied to the cryogenic refrigerator 10 according to the embodiment. As shown in FIG. 5, the flow control valve 102 may be provided with a valve body stopper 116 that determines the maximum opening of the flow control valve 102 by the gas pressure actuator 106. In this way, the opening of the flow control valve 102 can be kept constant during steady operation. This can lead to stabilization of the refrigeration capacity of the cryogenic refrigerator 10 during steady operation.

[0101] The valve disc stopper 116 may be provided on the valve housing 110 so as to contact the valve disc 108 and hold the valve disc 108 when the flow control valve 102 is at the second opening. As shown, the valve disc stopper 116 may be provided in the pressure chamber 110b. When the flow control valve 102 is at the first opening, the valve disc 108 moves forward from the pressure chamber 110b toward the orifice 110a, thereby moving away from the valve disc stopper 116.

[0102] The position of the valve body stopper 116 relative to the valve housing 110 may be adjustable so that the maximum opening of the flow control valve 102 can be adjusted as needed.

[0103] 6 is a schematic diagram showing another example of a flow restrictor 100 that can be applied to the cryogenic refrigerator 10 according to the embodiment. As in the above-described embodiment, the flow restrictor 100 may be connected between the compressor 12 and the cold head 14, for example, between the auxiliary pressure switching valve 62 and the driving chamber 29. The flow restrictor 100 operates to restrict the flow rate of the working gas to the cold head 14 (for example, the driving chamber 29) during initial cooling compared to steady operation.

[0104] The flow restrictor 100 includes a flow control valve 102. The flow control valve 102 includes a gas pressure actuator 106 that drives the flow control valve 102 so that the flow control valve 102 opens to a smaller degree during initial cooling compared to normal operation.

[0105] The flow control valve 102 includes a valve element 108 that determines the aperture of the flow control valve 102, and a valve housing 110 that accommodates the valve element 108. The valve element 108 includes a tip end 108a and a base end 108b that extends from the tip end 108a. The valve housing 110 includes an orifice 110a that is connected to and forms a part of the sub-communication passage 66, and a pressure chamber 110b that is isolated from the orifice 110a. The tip end 108a of the valve element 108 is accommodated in the orifice 110a, and the base end 108b of the valve element 108 is accommodated in the pressure chamber 110b. The aperture of the flow control valve 102 is determined by the tip end 108a of the valve element 108 at the orifice 110a. The valve element 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. Movement of the valve element 108 relative to the valve housing 110 changes the opening of the flow control valve 102. The flow control valve 102 may be, for example, a needle valve as shown.

[0106] In the flow restrictor 100 shown in FIG. 6, a pressure chamber 110b of a valve housing 110 is connected to the compressor 12 instead of the gas volume 104 shown in FIG. 4. More specifically, the pressure chamber 110b includes a first chamber 118 and a second chamber 120 that are isolated from each other. The second chamber 120 has a lower pressure than the first chamber 118. For example, the first chamber 118 is connected to the compressor discharge port 12a, and the second chamber 120 is connected to the compressor suction port 12b. The second chamber 120 is located intermediate the first chamber 118 and the orifice 110a. The second chamber 120 is isolated from the orifice 110a.

[0107] The valve element 108 is driven in response to the differential pressure between the first chamber 118 and the second chamber 120. When the temperature of the cryogenic refrigerator 10 is relatively high, such as at the beginning of initial cooling, the differential pressure between the pressure at the compressor discharge port 12a (high pressure PH) and the pressure at the compressor suction port 12b (low pressure PL) is relatively large. Therefore, the differential pressure between the first chamber 118 and the second chamber 120 acts to compress the elastic member 113, thereby moving the valve element 108 forward from the pressure chamber 110b toward the orifice 110a so that the flow control valve 102 has the first opening.

[0108] During the initial cooling, as described above, the operating pressure of the cryogenic refrigerator 10 gradually decreases. As a result, the pressure difference between the first chamber 118 and the second chamber 120 also decreases, and with the addition of the restoring force of the elastic member 113, the valve element 108 moves back from the orifice 110a toward the pressure chamber 110b. As a result, the opening of the flow control valve 102 increases from the first opening to the second opening.

[0109] In this way, the gas pressure actuator 106 can drive the valve element 108 to minimize the aperture of the flow control valve 102 at the beginning of the initial cooling, and then increase the aperture of the flow control valve 102 as the initial cooling progresses. Therefore, in this embodiment as well, the flow restrictor 100 operates to restrict the flow rate of the working gas into the drive chamber 29 during the initial cooling compared to steady operation. In this way, the flow rate of the working gas into the drive chamber 29 is reduced, and the pressure rise in the drive chamber 29 is delayed, thereby delaying the rise in the driving force of the drive piston 22 due to the gas pressure. This can improve the quietness of the cryocooler 10, as in the above-described embodiment.

[0110] Similar to the flow restrictor 100 shown in Figure 4, the flow restrictor 100 described with reference to Figure 6 can also be operated passively by utilizing the temperature drop of the cold head 14 during initial cooling. Unlike the flow restrictor 100 described with reference to Figures 1 and 2, this can be advantageous in that it does not require control using the controller 58.

[0111] Instead of connecting the second chamber 120 to the compressor intake port 12b, the second chamber 120 may be open to the atmosphere. Even in this case, the first chamber 118 is connected to the compressor discharge port 12a, so that the pressure difference between the first chamber 118 and the second chamber 120 can be ensured.

[0112] The valve element stopper 116 described with reference to Fig. 5 may also be applied to the flow control valve 102 shown in Fig. 6. In this case, the valve element stopper 116 may be provided in the first chamber 118 of the pressure chamber 110b.

[0113] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and that various design changes and modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment created by combining embodiments will have the combined effects of the respective combined embodiments.

[0114] In the above embodiment, the flow restrictor 100 is connected between the auxiliary pressure switching valve 62 and the drive chamber 29, but the present invention is not limited to this. The flow restrictor 100 may be connected between the main pressure switching valve 60 and the cold head 14 (e.g., the room temperature chamber 36). Even in this case, the flow rate of the working gas to the cold head 14 can be restricted compared to that during steady operation during initial cooling, thereby delaying the rise in the gas pressure that drives the displacer 20. This improves the quietness of the cryocooler 10.

[0115] Although the above-described embodiment has been described with reference to an example in which the cryogenic refrigerator 10 is of the collar bumper type, the present invention is not limited to this. That is, the cryogenic refrigerator 10 does not have to include the collar 70, the upper bumper 74, and the lower bumper 76, and the flow restrictor 100 according to the embodiment may be applied to such a cryogenic refrigerator 10.

[0116] Although the above-described embodiment has been described with reference to an example in which the cryocooler 10 is a gas-driven GM refrigerator, the present invention is not limited to this. The flow restrictor 100 according to the embodiment can also be applied to other gas-driven cryocoolers, such as a Solvay refrigerator.

[0117] The present invention has been described using specific terms based on the embodiments, but the embodiments merely illustrate one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments as long as they do not deviate from the concept of the present invention as defined in the claims. [Explanation of symbols]

[0118] 10 cryogenic 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.

Claims

1. A gas-driven cryogenic refrigerator capable of performing initial cooling to cool from an initial temperature to a cryogenic temperature and steady operation to maintain the cryogenic temperature following the initial cooling, A compressor; Cold head and a flow restrictor connected between the compressor and the cold head and operating to restrict the flow rate of the working gas to the cold head during the initial cooling compared to the steady operation.

2. the compressor has a discharge port and a suction port for the working gas, The cold head comprises: an axially extending displacer; a displacer cylinder that accommodates the displacer so as to be reciprocable in the axial direction and forms an expansion chamber between the displacer and a displacer cylinder; a main pressure switching valve that alternately connects the expansion chamber to the discharge port and the suction port; a drive piston extending from the displacer axially opposite the expansion chamber; a drive chamber that accommodates the drive piston so that the drive piston can reciprocate in the axial direction; a sub-pressure switching valve that alternately connects the drive chamber to the discharge port and the suction port so as to generate a pressure difference between the expansion chamber and the drive chamber, thereby causing the drive piston to reciprocate in the axial direction by the pressure difference, 2. The gas-driven cryogenic refrigerator according to claim 1, wherein the flow restrictor is connected between the auxiliary pressure switching valve and the drive chamber and operates to restrict the flow rate of the working gas into the drive chamber during the initial cooling period compared to the steady operation.

3. 3. The gas-driven cryogenic refrigerator according to claim 1, wherein the flow restrictor comprises a flow control valve that opens at a smaller opening during the initial cooling period than during the steady-state operation.

4. 4. The gas-driven cryogenic refrigerator according to claim 3, wherein the flow control valve comprises a gas pressure actuator that drives the flow control valve so that the flow control valve opens to a smaller degree during the initial cooling compared to the steady operation.

5. the flow restrictor comprises a gas volume thermally coupled to a cryogenic section of the cold head; the flow control valve includes a valve body that determines the opening degree of the flow control valve, 5. The gas-driven cryogenic refrigerator according to claim 4, wherein the gas pressure actuator includes a pressure chamber connected to the gas volume, and drives the valve body in response to pressure in the pressure chamber.

6. the flow control valve includes a valve body that determines the opening degree of the flow control valve, 5. The gas-driven cryogenic refrigerator according to claim 4, wherein the gas pressure actuator includes a pressure chamber connected to the compressor, and drives the valve body in response to pressure in the pressure chamber.

7. 5. The gas-driven cryogenic refrigerator according to claim 4, wherein the flow control valve includes a valve body stopper that determines the maximum opening of the flow control valve by the gas pressure actuator.

Images