JPH0618111A - Cryogenic refrigerator - Google Patents

Abstract

PURPOSE:To separate a substance to be cooled and a valve motor assembly as much as possible, and to shorten the time required for cool-down and inhibit the increase of the temperature of the normal-temperature end of a cylinder assembly. CONSTITUTION:The gas supply and exhaust ports 5, 45 of a cylinder assembly 3 and a valve motor assembly 40 are communicated mutually by a long-sized flexible refrigerant piping 61. An expanded gas flow path 8a communicated only when gas pressure is low to the gas flow path 8 of the cylinder assembly 3 is communicated with the suction side of a compressor 1 through an expansion-gas piping 60.

Description

Detailed Description of the Invention

[0001]

This invention relates to a cryogenic refrigerator,
More specifically, the present invention relates to a cryogenic refrigerator in which a displacer is reciprocated by gas pressure in a cylinder of an expander, and adiabatic expansion of a refrigerant gas accompanying the reciprocating motion of the displacer generates cryogenic refrigeration. .

[0002]

2. Description of the Related Art A gas pressure drive type GM refrigerator having a GM (Gifford-McMahon) cycle refrigerant cycle has been known as a cryogenic refrigerator of this type. The expander of this refrigerator comprises a cylinder, and a displacer and a slack piston that are reciprocally arranged in the cylinder. The displacer defines an expansion chamber at the tip of the cylinder. Through the regenerator of the above to communicate with the space on the base end side of the cylinder. The slack piston is arranged on the base end side of the cylinder so as to divide the base end side space into a gas supply / discharge chamber and an intermediate pressure chamber, and is engaged with the displacer at a predetermined stroke interval. The intermediate pressure chamber communicates with the surge volume, while the gas supply / discharge chamber communicates with a high pressure gas inlet and a low pressure gas outlet connected to the discharge side and the suction side of the compressor, respectively. Then, by periodically switching the supply / discharge of the refrigerant gas to / from the gas supply / discharge chamber or the expansion chamber, the slack piston is moved by the pressure difference between the gas supply / discharge chamber and the intermediate pressure chamber to reciprocate the displacer. The refrigerant gas expands in the expansion chamber due to the reciprocal movement of the cylinder, causing cold to be generated in the cylinder around the expansion chamber.

When switching the supply and discharge of the gas, it is roughly classified into one using an electric actuator such as a motor and a solenoid valve, and the gas pressure in the expander as disclosed in JP-A-58-190665. It can be divided into those that use fluctuations. By the way, in recent years, as one of superconducting devices, a superconducting quantum interference device utilizing the Josephson effect (Superconductive Quantum Interference Dev
Ice: hereinafter abbreviated as SQUID) is drawing attention.
By connecting a magnetic flux input circuit such as a gradiometer composed of a superconducting coil to this SQUID, it is possible to measure an extremely weak magnetic flux such as a magnetic field accompanying a minute current flowing in the living body or a magnetic field from a minute magnet in the body. You can get a total.

However, when a gas pressure drive type GM refrigerator having the above-mentioned electric actuator is used to cool the SQUID to an operating temperature level, a magnetic flux is generated in the refrigerator, such as a motor or a solenoid valve. Since the actuator is provided, there is a disadvantage that the magnetic flux from the actuator is detected as harmful noise and the measurement accuracy is reduced.

Therefore, conventionally, in order to reduce the influence of the valve motor, the valve and the valve motor in the expander are separated from the cylinder portion, and the valve motor assembly and the cylinder assembly are connected by a pipe, so that the valve motor is SQUID, that is, a separate type is proposed in which the harmful noise due to the magnetic flux from the valve motor is reduced away from the tip of the cylinder (for example, the paper “Gifford-Mcmahon Refrigerator With” published in “NASA Conference Publication 2287”). Split Co
ld Head "and the paper" Development of A Hybrid Gifford-Mcmahon Jo "at the conference" 5th International Cryocooler Conference "held from August 18, 1988 to August 19, 1988.
ule-Thompson Based Neuromagnetometer, Cryosquid ”).

[0006]

However, in an integral type expander in which a valve motor is integrated with a cylinder portion, high and low pressure gas circulates between the compressor and the low temperature end (tip end) of the cylinder. ), The heat of compression taken by the gas is released while the gas returns to the compressor, so there is no problem, but in the separate expander as described above, the amount of refrigerant gas circulating between the compressor and Therefore, the heat of compression taken by the gas at the low temperature end (tip) of the cylinder is not sufficiently released, and accumulates in the room temperature portion (base end portion) of the cylinder. This heat retention heats the surge volume located at the base end of the cylinder, increasing the gas pressure inside it, reducing the differential pressure between the intermediate and high pressures of the gas, and smoothing the slack piston and displacer. There are disadvantages that the movement is hindered, the cooldown time becomes long, and the refrigerating capacity at the time of steady suspension after the cooldown decreases.

In order to eliminate such inconvenience, a cooling fin is provided on the base end side of the cylinder, a water cooling pipe is provided, and low-pressure gas from the valve motor is guided to a heat exchanger provided in the cylinder portion. Return to compressor (CR
Paper "Interfacing s" published in YOGENICS.APRIL 1984
mall closed-cycle refrigerators to liquid heliumcr
yostats "), etc. However, if any configuration is adopted, the configuration will be considerably complicated and
When the first and third configurations are adopted, there is a disadvantage that sufficient cooling efficiency cannot be achieved.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an extremely low temperature that can reduce the cooldown time and can significantly suppress the temperature rise in the room temperature portion of the cylinder, while having a simple structure. The purpose is to provide a refrigerator.

[0009]

To achieve the above object, a cryogenic refrigerator according to claim 1 is a compressor for compressing a refrigerant gas to generate a high pressure gas, and a high pressure supplied from the compressor. A cryogenic refrigerator composed of an expander that adiabatically expands gas to generate a cryogenic level of cold, wherein the expander supplies and discharges gas into and from a cylinder through a gas supply / discharge port. A cylinder assembly that reciprocates the displacer to expand the gas in the expansion chamber of the cylinder, and a switching valve is driven by a valve motor, and a high pressure gas inlet and a low pressure gas that are respectively connected to the discharge side and the suction side of the compressor are connected. The cylinder motor is separated into a valve motor assembly that selectively communicates the outlet and the gas supply / exhaust port, and the cylinder assembly exposes the expansion gas outlet that communicates with the gas flow passage only when the gas pressure is low. Together we have further comprises an inflation gas flow path inlet side communicating with the compressor inflation gas discharge openings.

[0010]

In the cryogenic refrigerator of claim 1, the switching valve is driven by the valve motor of the valve motor assembly to supply / discharge gas into / from the cylinder through the gas supply / discharge port to reciprocate the displacer. In this case, when the gas is discharged from the inside of the cylinder, the expansion gas is returned to the suction side of the compressor through the expansion gas flow path and exchanges heat, so that compression heat retention at the room temperature end of the cylinder assembly can be significantly suppressed. As a result, the pressure loss of gas in the refrigerant pipe may reduce the refrigeration capacity or the load on the compressor may increase, and the reciprocating motion of the displacer may be adversely affected by the retention of compression heat at the room temperature end of the cylinder. It can be avoided. In addition, it is possible to prevent adverse effects on the resin material housed in the cylinder assembly. Furthermore, since it is only necessary to add an expansion gas flow path that connects the cylinder and the suction side of the compressor, it is possible to significantly suppress the complication of the configuration.

[0011]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 2 is a vertical sectional view showing the overall configuration of a gas pressure drive type GM type cryogenic refrigerator as one embodiment of the present invention. This refrigerator utilizes Joule-Thomson expansion of helium gas (refrigerant gas). It is used as a pre-cooling refrigerator of the JT refrigerator described above, and the SQUID (not shown) is cooled by this JT refrigerator to a cryogenic level.
In FIG. 2, 1 is a compressor that compresses helium gas as a refrigerant gas to generate high-pressure gas, and 2 is an expansion that adiabatically expands the high-pressure gas supplied from the compressor 1 to generate cryogenic level cold. It is a machine. The expander 2 includes the cylinder assembly 3 and the valve motor assembly 40.
It consists of and.

The cylinder assembly 3 has a cylinder 10 having a bottomed cylindrical shape that is opened upward, and a valve stem 4 that hermetically closes an opening on the upper end side (base end side) of the cylinder 10. The valve stem 4 has, in the cylinder 10, a columnar protrusion 4a that protrudes concentrically from the inner wall of the cylinder 10 with a predetermined gap. Also, the valve stem 4 has
Gas supply / discharge port 5 opening on the cylinder center line on the upper surface
And a surge volume 7 having a relatively small capacity, and a gas flow path 8 that connects the gas supply / discharge port 5 to the inside of the cylinder 10. Further, the gas flow passage 8 is always in communication with the surge volume 7 via a communication passage 9 having a small passage cross-sectional area, and the communication passage 9 sets the intermediate pressure in the surge volume 7 to an appropriate value.

The cylinder 10 is formed in a two-stage structure with a large diameter portion 10a on the upper end side (base end side) and a small diameter portion 10b continuous to the lower end (tip) of the large diameter portion 10a. 1
At the lower end of 0a is a first-stage heat station 11 which is maintained at a temperature level of 55 to 60K, and at the lower end of the small diameter portion 10b is at a lower temperature level of, for example, 15 to 20K than the first-stage heat station 11. The second stage heat station 12 is provided for holding the helium gas in the JT refrigerator (not shown) to be pre-cooled.

Inside the upper end of the large-diameter portion 10a of the cylinder 10, a slack piston 15 for partitioning and forming an intermediate pressure chamber 13 is arranged inside the large-diameter portion 10a, and the intermediate pressure chamber 13 has a surge volume inside the valve stem 4. 7 through the orifice 14 at all times. The slack piston 15 is of a substantially cup shape having a bottom wall, and the upper end of the inner circumference is the outer circumference of the protruding portion 4a of the valve stem 4, and the lower end of the outer circumference is the cylinder 1.
The inner diameter of the large diameter portion 10a of 0 is slidably contacted with each other. Further, a center hole 15a is formed at the center of the bottom wall of the slack piston 15, and a plurality of communication holes 15b, 15b, ... Which communicate the inside and outside of the piston 15 are formed at the corners of the bottom wall.

A displacer 16 is reciprocally fitted in the cylinder 10. The displacer 16 is continuous with a large-diameter portion 16a which is arranged so as to be airtightly slidable in the large-diameter portion 10a of the cylinder 10 and a lower end (tip) of the large-diameter portion 16a, and is airtight with the small-diameter portion 10b of the cylinder 10. It has a two-stage structure composed of a slidably arranged small-diameter portion 16b, and a sealed space is formed inside each of the large-diameter portion 16a and the small-diameter portion 16b. The space is surrounded by the gas supply / discharge chamber 17 surrounded by the upper end of the displacer 16 and the slack piston 15, the large diameter portion 16a of the displacer 16 and the large diameter portion 10a of the cylinder 10, and corresponds to the first-stage heat station 11. The second-stage heat station is surrounded by the first-stage expansion chamber 18, the small-diameter portion 16b of the displacer 16 and the small-diameter portion 10b of the cylinder 10. Is partitioned into a second stage expansion chamber 19 that corresponds to 2.

The large diameter portion 16a of the displacer 16 is also provided.
Communication holes 20, 20 are formed at the lower end so that the sealed space in the large diameter portion 16a is always communicated with the first-stage expansion chamber 18. Further, at the upper end of the small diameter portion 16b, the communication holes 21 and 21 for constantly communicating the space inside the small diameter portion 16b with the first stage expansion chamber 18.
However, at the lower end thereof, communication holes 22 and 22 for constantly communicating the closed space with the second expansion chamber 19 are formed.

Further, at the upper end of the large diameter portion 16a of the displacer 16, a tubular locking piece 23 for communicating the space inside the large diameter portion 16a with the gas supply / discharge chamber 17 is integrally projected, and the locking piece 23 is formed. Is the central hole 15 in the bottom wall of the slack piston 15
A flange-shaped engaging portion 23a that engages with the bottom wall of the piston 15 is integrally formed at the upper end of the slack piston 15 when the slack piston 15 moves upward. When the piston 15 is lifted by a predetermined stroke, the displacer 16 is driven by the piston 15 to start rising by engagement of the bottom wall of the piston 15 with the locking portion 23a of the locking piece 23, that is, the displacer 16 is moved by a predetermined stroke. With a delay of 15
It is designed to move following.

The first-stage regenerator 24 (regenerator) is placed in the closed space inside the large-diameter portion 16a of the displacer 16, and the second-stage regenerator 25 is placed in the closed space inside the small-diameter portion 16b. It has been inserted. Each of these regenerators 24 and 25 is composed of a cold storage type heat exchanger. Specifically, the first stage regenerator 24
Is a stack of a large number of disk-shaped copper meshes as a cold storage material in a closed space, while the second stage regenerator 25 has a large number of lead balls (lead Shot) is filled and enclosed, and the mesh of these meshes and the gap between the lead balls serve as a gas passage. The cold heat of the helium gas flowing through this gas passage is stored in the mesh and each lead ball. That is, when the displacer 16 is in the intake stroke in which it rises in the cylinder 10, the mesh and lead balls that have dropped to the cryogenic temperature level in the previous exhaust stroke are transferred from the gas supply / discharge chamber 17 to the first and second expansion chambers 18, 19. It is brought into contact with the helium gas at room temperature, and the heat exchange between the two cools the gas to near the cryogenic level. On the other hand, when the displacer 16 is in the descending exhaust stroke, the helium gas whose temperature has dropped to an extremely low temperature level due to expansion in the expansion chambers 18 and 19 is brought into contact with the mesh and the lead ball while being discharged to the outside of the cylinder 10, It is configured to re-cool the mesh and the lead ball to near the cryogenic level by the heat exchange of.

On the other hand, the valve motor assembly 40 has a closed cylinder having a bottomed cylindrical valve housing 41 with its upper end closed, and a valve stem 42 for hermetically closing the lower opening of the housing 41. In the side wall of the valve housing 41, a high pressure gas inlet 43 connected to the discharge side of the compressor 1 and a low pressure gas outlet 44 connected to the suction side of the compressor 1 are opened. A gas supply / discharge port 45 having the same diameter as the gas supply / discharge port 5 of the cylinder assembly 3 is opened at the lower end of the valve stem 42.
Inside the valve housing 41, a valve chamber 46 communicating with the high pressure gas inlet 43 is formed, and the valve chamber 46 faces the upper surface of the valve stem 42.

The valve stem 42 has a first gas passage 48 whose upper half is branched into two and communicates the valve chamber 46 with the gas supply / discharge port 45, and one end of which is described later in the first gas passage 48. A second gas flow path 49, which communicates with the low pressure port 53 of the valve disc 51 and has the other end communicating with the low pressure gas outlet 44 through a communication passage 50 formed in the valve housing 41, is formed. . Both gas channels 48,
As shown in FIG. 3, the reference numeral 49 designates a valve chamber 46 on the upper surface of the valve stem 42, a central portion of the valve stem 42 in the second gas passage 49, and two branch portions of the first gas passage 48. In that case, the second gas flow paths 49 are opened at symmetrical positions with respect to the openings.

Further, in the valve chamber 46, the valve motor 5
4 is provided with a valve disc 51 as a switching valve which is rotationally driven at a predetermined cycle.
By this switching operation, the valve chamber 46 communicating with the high pressure gas inlet 43 and the communication passage 50 communicating with the low pressure gas outlet 44 are alternately communicated with the gas supply / discharge port 45.

More specifically, the valve disc 51 is slidably connected to the output shaft 54a of the valve motor 54. A spring 55 is compressed between the upper surface of the valve disk 51 and the motor 54. The spring force of the spring 55 and the pressure of the high pressure helium gas introduced into the valve chamber 46 cause the lower surface of the valve disk 51 to move toward the valve stem. 42 is pressed against the upper surface with a constant pressing force. Further, as shown in FIG. 4, a pair of high-pressure ports 52, 5 are formed on the lower surface of the valve disc 51 by cutting a predetermined length in the center direction from the outer peripheral edges facing each other in the radial direction.
2 and the valve disk 51 for the high pressure ports 52, 52
Are arranged at angular intervals of about 90 ° in the rotation direction of
A low-pressure port 53 is formed by notching in the diameter direction from the center of the lower surface of the valve disk 51 toward the vicinity of the outer peripheral edge. When the valve disk 51 is rotated by the drive of the valve motor 54 while pressing its lower surface against the upper surface of the valve stem 42 to perform a switching operation, the high pressure gas inlet 43 or the low pressure gas outlet 44 is operated in accordance with the switching operation of the valve disk 51. Are alternately communicated with the gas supply / discharge port 45 at a predetermined timing.

Further, as a feature of the present invention, as shown in FIG. 1, the gas supply / discharge port 5 of the cylinder assembly 3 and the gas supply / discharge port 45 of the valve motor assembly 40 are connected by a flexible refrigerant pipe 61 having a long length. The expansion gas flow path 8a is branched from a predetermined position of the gas flow path 8 communicating with the flexible refrigerant pipe 61. The branch portion has a valve body 8b that closes the branch to the expansion gas passage 8a by the pressure of the high-pressure gas supplied from the valve motor assembly 40, and the low-pressure gas is returned to the valve motor assembly 40. In this case, there is a spring member 8c that operates the valve body 8b to release the branch to the expansion gas flow path 8a. The expansion gas flow path 8a and the suction side of the compressor 1 are connected to the expansion gas pipe 60.
Are in communication with each other.

The operation of the GM type cryogenic refrigerator having the above construction is as follows. If the valve motor assembly 40 is operated so that the high pressure gas generated by the compressor 1 can be supplied to the cylinder assembly 3, the high pressure gas can be supplied to the cylinder assembly 3 through the high and low pressure gas pipe 61. Then, by switching the valve disk 51 in the valve motor assembly 40, the high pressure gas from the high pressure gas inlet 43 or the low pressure gas from the low pressure gas outlet 44 is alternately acted on the gas supply / discharge port 5 of the cylinder assembly 3 to slack piston. As shown in FIG. 3A, the inner ends of the high pressure ports 52, 52 on the lower surface of the valve disk 51 are respectively the first gas flow path 4 on the upper surface of the valve stem 42.
8 is met, the valve chamber 46 is set to the high pressure port 5
2, 52, the first gas passage 48 and the flexible refrigerant pipe 61, the gas supply / discharge chamber 17 in the cylinder 10, the first
The second stage expansion chambers 18 and 19 are communicated with each other, and high pressure helium gas is introduced into and filled in each of the chambers 17 to 19 to raise the slack piston 15 and the displacer 16 driven by the piston 15.
The valve body 8b is moved against the spring 8c by the pressure of the high-pressure gas supplied to the gas flow path 8, and the expansion gas flow path 8a
Block the branch to {see FIG. 1 (A)}.

On the other hand, as shown in FIG. 3B, the outer end of the low-pressure port 53, which is always in communication with the second gas passage 49 opening on the upper surface of the valve stem 42 at the center, is the first gas passage 48.
If the chambers 17 to 19 in the cylinder 10
The flexible refrigerant pipe 61, the first gas flow paths 48, 4
8, low pressure port 53, second gas passage 49 and communication passage 5
0 to communicate with the low pressure gas outlet 44, and each chamber 17 to
The helium gas filled in 19 is supplied to the low pressure gas outlet 44
The slack piston 15 and the displacer 16 are lowered by discharging them to the displacer 16
The helium gas in the expansion chambers 18 and 19 is expanded by the downward movement of the heat stations 11 and 12 to generate cold in the heat stations 11 and 12. In this case,
Since the gas pressure in the gas passage 8 is low, the valve body 8
b is moved by the spring 8c to open the branch to the expansion gas passage 8a {see FIG. 1 (B)}. Therefore, a considerable amount of the expansion gas can be directly supplied to the suction side of the compressor 1 through the expansion gas pipe 60 without passing through the valve motor assembly 40.

The operation of the cryogenic refrigerator having the above structure is as follows. At the time of cool down, the SQUID is gradually cooled to a low temperature level as the GM refrigerator and the JT refrigerator are operated, and the temperature of the SQUID is kept at an extremely low temperature level (about 4 ° C).
After descending to K), the refrigerator shifts to a steady operation state, and the SQUID operates in that state.

The operation of the GM refrigerator will be described in detail.
Cylinder 1 in cylinder assembly 3 of expander 2
When the pressure in 0 is low and the slack piston 15 and the displacer 16 are at the lower end position, the valve disk 54 is rotated by the drive of the valve motor 54 of the valve motor assembly 40, as shown in FIG. As shown, the high pressure ports 52, 52 coincide with the first gas passages 48, 48 on the upper surface of the valve stem 42 to open the valve disc 51 to the high pressure side. Accordingly, the high-pressure helium gas at room temperature supplied from the compressor 1 to the valve chamber 46 of the valve motor assembly 40 via the high-pressure gas inlet 43 is supplied to the high-pressure ports 52 and 52 of the valve disk 51 and the first gas flow. The gas is supplied to the gas supply / discharge port 45 via the passage 48, and the gas supply below the slack piston 15 is supplied from the gas supply / discharge port 45 via the flexible refrigerant pipe 61, the gas supply / discharge port 5 of the cylinder assembly 3 and the gas flow passage 8. It is introduced into the discharge chamber 17. Further, this gas is filled from the gas supply / discharge chamber 17 through the regenerators 24, 25 of the displacer 16 into the expansion chambers 18, 19 in order, and is cooled in the previous exhaust stroke while passing through the regenerators 24, 25. It is cooled by heat exchange with the copper mesh and the lead balls.

Since the intermediate pressure chamber 13 on the upper side of the slack piston 15 communicates with the surge volume 7 through the orifice 14, its pressure is maintained at a constant proper value. Therefore, when high-pressure helium gas is introduced into the gas supply / discharge chamber 17, the internal pressure thereof becomes higher than that of the intermediate pressure chamber 13, and the piston 15 rises due to the pressure difference between the chambers 13 and 17. Then, when the piston 15 moves upward by a predetermined stroke, the bottom wall of the piston 15 and the locking piece 23 at the upper end of the displacer 16 are engaged with each other, and the displacer 16 is delayed with respect to the pressure change.
By the upward movement of the displacer 16, the expansion chambers 18 and 19 below the displacer 16 are further filled with high-pressure gas (intake stroke).

After that, the valve disc 51 is rotated by 90 ° and closed, but the displacer 16 is also raised by the inertial force thereafter, and along with this, the helium gas in the gas supply / discharge chamber 17 above the displacer 16 becomes the first. And it moves to the second expansion chambers 18, 19. After the displacer 16 reaches the rising end position, the valve disc 51 is
Rotate 0 °, and as shown in FIG. 3 (B), the low pressure port 53
Corresponds to the first gas flow path 48 and the valve disc 51 opens to the low pressure side. With this valve opening, the helium gas in the expansion chambers 18 and 19 below the displacer 16 expands by Simon, and the helium gas Chilling occurs due to expansion (expansion stroke).

The helium gas in this cryogenic state is
Contrary to the above-described gas introduction, the gas flows through the regenerators 24 and 25 in the displacer 16 and returns into the gas supply / discharge chamber 17, while cooling the copper mesh and the lead balls in the regenerators 24 and 25 at room temperature. Can be warmed up to. The helium gas at room temperature is, together with the gas in the gas supply / discharge chamber 17, the gas flow path 8, the gas supply / discharge port 5, the expansion gas pipe 60, the valve motor assembly 40, in reverse to the above.
Through the gas supply / discharge port 45, the first gas flow path 48, the low pressure port 53 of the valve disc 51 and the communication passage 50, and is sucked into the compressor 1 from there. Further, since the pressure of the gas flowing through the gas flow path 8 is low, the valve body 8b is operated by the spring 8c to open the branch to the expansion gas flow path 8a, and a considerable amount of the expansion gas passes through the above path. Instead, the gas is sucked into the compressor 1 through the expansion gas pipe 60. After the gas pressure decreases and becomes lower than the intermediate pressure chamber 13, the slack piston 15 descends due to the pressure difference between the chambers 13 and 17, and the bottom wall of the piston 15 contacts the upper surface of the displacer 16. Is the displacer 16
Is pushed and descends, and by the downward movement of the displacer 16, the gas in the expansion chambers 18 and 19 is further discharged to the outside of the expander 2 (exhaust stroke).

Then, the valve disc 51 is rotated by 90 ° and closed, and after that, the displacer 16 descends to the descending end position, and the gas in the expansion chambers 18 and 19 is discharged to return to the initial state. With the above, one cycle of the operation of the expander 2 is completed, and thereafter, the same operation as described above is repeated. By repeating this, the two-stage heat stations 11 and 12 of the cylinder 10 are gradually cooled, and the helium gas of the JT refrigerator that has received the cold from the two-stage heat stations 11 and 12 is pre-cooled. Cooled to low temperature level.

During this cooldown operation, since the temperature of the low temperature end of the cylinder 10 is high, the effect of compression heat retention at the room temperature end is greater than that after the cooldown, but the expansion gas expands not only in the flexible refrigerant pipe 61. Since it is sucked into the compressor 1 through the gas pipe 60, the compression heat taken at the low temperature end of the cylinder 10 is radiated favorably by heat exchange with the refrigerant gas. Therefore, even if the expander 2 is separated into the cylinder assembly 3 and the valve motor assembly 40, the temperature rise at the room temperature end of the cylinder 10 can be effectively suppressed,
The intermediate pressure by the surge volume 7 can be maintained in an appropriate range, and thus the reciprocating motion of the displacer 16 can be normally maintained and the cooldown by the refrigerator can be achieved in a short time.

In this way, after a lapse of a predetermined time from the start of the refrigerator or after the temperature of the SQUID has dropped to the predetermined temperature, the cool down operation is finished and the refrigerator is in a steady operation state. Even in this state, the same operation as in the cool down operation is performed. In this constant operation state, the gas supply / discharge ports 5 and 45 of the cylinder assembly 3 and the valve motor assembly 40 communicate with each other through the flexible refrigerant pipe 61 having a long length. The steady operation is performed with the cylinder assembly 3 and the valve motor assembly 40 separated from each other, and the influence of noise magnetic flux due to the valve motor assembly 40 on the SQUID can be significantly reduced.

The present invention is not limited to the above embodiment, and for example, instead of using the valve body 8b and the spring 8c, a valve body having a predetermined spring characteristic can be used. Various design changes can be made without changing the gist of the present invention.

[0035]

As described above, according to the invention of claim 1, when the gas is discharged from the inside of the cylinder, the expansion gas is returned to the suction side of the compressor through the expansion gas passage and exchanges heat, so that the temperature of the cylinder assembly is at room temperature. Retention of compression heat at the end can be greatly suppressed, refrigeration capacity is reduced due to gas pressure loss in the refrigerant pipe, or the load on the compressor is increased, and reciprocating motion of the displacer is caused by retention of compression heat at the room temperature end of the cylinder. Can be prevented from being adversely affected, and the resin material housed in the cylinder assembly can be prevented from being adversely affected. Furthermore, an expansion gas flow path that connects the cylinder and the suction side of the compressor can be provided. Since it only needs to be added, it has a unique effect that the complexity of the configuration can be significantly suppressed.

[Brief description of drawings]

FIG. 1 is a schematic enlarged vertical sectional view showing a main part of a cryogenic refrigerator of the present invention.

FIG. 2 is a gas pressure drive type G as one embodiment of the present invention.
It is a longitudinal section showing the whole M type cryogenic refrigerator composition.

FIG. 3 is a plan view of an upper surface of a valve stem facing a valve chamber.

FIG. 4 is a plan view of the lower surface of the valve disc.

[Explanation of symbols]

1 Compressor 2 Expander 3 Cylinder assembly 5 Gas supply / discharge port 8 Gas flow path 8a Expansion gas flow path 8b Valve body 8c Spring 10 Cylinder 16 Displacer 18, 19 Expansion chamber 40 Valve motor assembly 43 High pressure gas inlet 44 Low pressure gas outlet 45 Gas supply / discharge port 51 Valve disc 54 Valve motor 60 Expansion gas piping

Claims (1)

[Claims] 1. A compressor (1) for compressing a refrigerant gas to generate a high-pressure gas, and an expander (a) for adiabatically expanding the high-pressure gas supplied from the compressor (1) to generate cryogenic level cold. 2) A cryogenic refrigerator constituted by 2), wherein the expander (2) supplies / discharges gas into / from the cylinder (10) through the gas supply / discharge port (5) to displace the displacer (16). By reciprocating, the expansion chambers (18) (1) in the cylinder (10)
Cylinder assembly (3) for expanding gas in 9)
And a high pressure gas inlet (43) and a low pressure gas outlet (44) which communicate with the discharge side and the suction side of the compressor (1) by driving a switching valve (51) by a valve motor (54). Expansion in which the cylinder assembly (3) is separated into a valve motor assembly (40) that selectively communicates with the supply / discharge port (45), and the cylinder assembly (3) communicates with the gas flow path (8) only when the gas pressure is low. Gas outlet (8a)
And an expansion gas flow path (60) for communicating the expansion gas outlet (8a) with the suction side of the compressor (1).
A cryogenic refrigerator characterized by further comprising: