JP2000292022A - Gas cycle engine refrigerating machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive improvement of heat efficiency by raising an overall heat transfer coefficient holding a dead volume and pressure loss down at a cold head of a gas cycle engine refrigerating machine of a Stirling refrigerating machine or a pulse pipe refrigerating machine. SOLUTION: In a structure assembled integrally by a method wherein a cold storage device 2 is contained in a cylinder 4a of a displacer 4 or between a pulse pipe and an outside tube 7 and covered by a cold head 5 forming a gas flow channel 5a stretching across a low temperature side end of the cold storage device 2 and a cylinder opening end of the displacer 4 on the inside of the top, the cold head 5 is formed into a cap body and forms a screw groove 5b for the gas flow channel on the inside circumferential surface. A start end part and a terminal part of the screw groove 5b are opened, and a ring plug member is packed into the inside of the cold head, and then a working gas is allowed to flow through the cold head via the screw groove.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverse Stirling cycle refrigerator (hereinafter referred to as "Sterling refrigerator") or a gas cycle engine refrigerator intended for a pulse tube refrigerator, and more particularly, to a low-temperature refrigerator. It relates to the structure of the heat transfer section.

[0002]

2. Description of the Related Art Gas cycle engine refrigerators such as a Stirling refrigerator and a pulse tube refrigerator have been known as refrigerators which are applied to a cryocooler or the like to obtain low-temperature (about 80 K absolute) cold.

Here, the configuration and operation of a conventional Stirling refrigerator will be described with reference to FIG. 4, taking a Stirling refrigerator as an example. In the figure, reference numeral 1 denotes a gas compressor which reciprocates a compression piston 1b housed in a cylinder 1a with a radiation fin by a drive motor (not shown) such as a linear motor.
2 is a gas conduit 3 at the discharge port of the cylinder 1a of the gas compressor 1.
A regenerator 4 is connected via a disperser (expansion device) composed of an expansion cylinder 4a and an expansion piston 4b. A disk-shaped cold head (low-temperature heat transfer member) having a gas flow path 5a communicating between the regenerator 2 and the expansion cylinder 4a of the displacer 4 with its inner surface being a concave surface; It is a board.

Here, the regenerator 3 is mounted in an annular space between the cylinder 4a of the displacer 4 and an outer cylinder 7 fixed on an assembly base plate 6 around the cylinder 4a, and is assembled integrally with the cold head 5. ing. A working space (helium gas) is sealed in the closed space between the gas compressor 1 and the displacer 4, and the gas compressor 1 and the displacer 4 are relatively 90 ° apart. It is reciprocated by a motor (not shown) due to the phase difference. The cold head 5 has a top outer surface A
As a cold generating unit, a cooling target (for example, a photoelectric element of an infrared sensor) W is mounted thereon and thermally coupled to each other, and a cooling cycle is generated by a refrigeration cycle (reverse Stirling cycle) described below to generate a cooling target. Cool W to cryogenic temperature.

As is well known, the reverse Stirling cycle is
Cold is generated in the cold head in four steps of isothermal compression, equal volume transfer, isothermal expansion, and equal volume transfer. That is, in the normal operation of the refrigerator, the working gas is compressed by the gas compressor 1 in the isothermal compression step, and the working gas is cooled by the regenerator 2 and sent to the expansion space in the subsequent equal volume transfer step. In the next isothermal expansion step, the working gas generates cold, transfers heat to the cold head 5 and removes heat from the cooled body 8. In the subsequent equal volume transfer step, the low-temperature working gas cools the regenerator 2 and returns to the gas compressor 1. Then, by repeating this refrigeration cycle, the cooled object W mounted on the cold head 5 is cooled to an extremely low temperature.

[0006] Since the working gas in the low temperature section is at a normal temperature immediately after the start of the refrigerator, no heat is transferred between the gas and the cold head 5 in the first expansion process, and the working gas expands adiabatically. Gas temperature drops. Since the cooled gas cools the regenerator 2 in the process of returning to the gas compressor side with a change in volume, when the working gas is sent to the displacer in the next cycle, the temperature of the regenerator 2 is lower than in the previous cycle. Since the cooled gas undergoes further adiabatic expansion, the temperature further decreases, and the repetition of this refrigeration cycle causes a transition to a steady-state operation state to generate extremely low-temperature refrigeration.

As a gas cycle engine refrigerator, there is also known a pulse tube refrigerator in which the displacer 4 in the Stirling refrigerator is replaced with a pulse tube, and the pulse tube is combined with an orifice and a reservoir.

[0008]

The conventional structure shown in FIG. 4 has the following problems. That is, with respect to the cold head 5, the inner surface of the disk is processed into a simple concave surface from the viewpoint of manufacturing and workability, and the gas flow path 5a is formed.
However, since this structure does not allow a large contact area with the working gas, the heat transfer rate between the working gas and the working gas flowing through the structure is low. Is difficult to obtain.

That is, the refrigerator is evaluated by the power consumption and the physique (external dimensions) with respect to the refrigeration capacity, and factors of the evaluation include the heat transfer rate of the cold head 5, the gas flow path volume (dead volume), and the pressure loss. Can be Here, the effects of the heat transfer rate of the cold head 5, the volume (dead volume) of the gas flow path, and the pressure loss on the refrigeration performance will be described.

(1) First, regarding the heat transfer rate, the cold head temperature between the cooling end temperature Ta of the cold head 5 and the gas temperature Tc of the low temperature gas flowing through the gas flow path 5a in the operation state of the refrigerator is determined. 5, a temperature difference ΔT corresponding to the heat transmission coefficient (also referred to as heat transmission coefficient) is generated. Therefore, the cooling end temperature T
In order to set “a” to the temperature required by the object 8 to be cooled, the low-temperature gas temperature Tc needs to be lower than the cooling end temperature Ta by a temperature difference ΔT (Tc = Ta−ΔT). On the other hand, the theoretical thermal efficiency of the Stirling refrigerator (coefficient of performance: COP)
Is the high temperature gas temperature as Th

[0011]

## EQU1 ## COP = Tc / (Th-Tc) = (Ta-.DELTA.)
T) / (Th−Ta + ΔT), and when the temperature difference ΔT increases, the coefficient of performance (C
OP) decreases, and the input (power consumption) of the refrigerator increases for the same heat load. When the low-temperature gas temperature Tc is lowered so as to compensate for the temperature difference ΔT with respect to the cooling end temperature Ta, the shuttle generated due to the heat loss in the regenerator 2 and the relative displacement between the piston 4 b and the cylinder 4 a of the displacer 4. The heat loss of the refrigerator itself, such as loss, also increases, and the heat load increases. As described above, when the heat transmission rate of the cold head 5 is low, the low-temperature gas temperature Tc must be reduced by the amount corresponding to the cooling end temperature Ta required by the object 8 to be cooled.
As a result, the coefficient of performance (COP) of the refrigerator decreases and the heat load to be cooled increases, so that the input increases and the efficiency of the refrigerator decreases.

In this respect, in the conventional cold head 5,
As shown in FIG. 4, the inner surface of the heat transfer member is a simple concave surface, and the gas flow path 5 a through which the working gas flows through the gap between the inner surface and the end surface of the regenerator 2 and the end surface of the cylinder opening of the expander 4. Due to the formation, the ratio of the heat transfer area (the inner peripheral surface of the hole) with which the working gas is in direct contact with the internal volume of the gas flow path 5a is small, and therefore, the heat transmission rate of the cold head 5 is reduced.

(2) When the volume (dead volume) of the gas passage 5a formed in the cold head 5 is large, the gas pressure with respect to the displacement (movement) of the piston 1b of the gas compressor 1 is increased. Change becomes small. For this reason, in order to obtain the necessary pressure amplitude between the isothermal compression step and the isothermal expansion step of the refrigeration cycle, it is necessary to increase the stroke of the piston 1a or increase the cross-sectional area of the piston 1a. In addition to increasing the size of the refrigerator, the amount of gas discharged from the gas compressor 1 required for the same change in gas pressure increases, so that the input of the refrigerator, that is, the power consumption increases.

(3) On the other hand, the gas flow path 5 of the cold head 5
The pressure loss at a increases the input of the gas compressor 1 and reduces the refrigeration output by reducing the gas pressure amplitude in the displacer 4, so that the cross-sectional area of the gas flow path (the volume of the flow path) is reduced. Therefore, it is necessary to keep it as small as possible. Further, the above-mentioned problems also apply to a pulse tube refrigerator as it is.

The present invention has been made in view of the above points, and has as its object to reduce the dead volume and pressure loss in the cold head of the Stirling refrigerator and the pulse tube refrigerator described above. It is an object of the present invention to provide a gas cycle engine refrigerator having a small size and high thermal efficiency by improving the heat transmission rate.

[0016]

In order to achieve the above object, according to the present invention, a Stirling refrigerator or a pulse tube refrigerator is constituted as follows. (1) A gas cycle engine refrigerator intended for a Stirling refrigerator composed of a gas compressor, a regenerator, a displacer, and a cold head whose top is a cold-generating unit. The expansion cylinder of the displacer has an inner cylinder. A regenerator is built in the space between the outer cylinder surrounding it and a cold head that has a gas flow path formed on the inner surface of the top at the lower end of the regenerator and the open end of the cylinder of the displacer. In a device in which a container, a displacer, and a cold head are integrally assembled, the cold head is formed into a cap-like body to form a spiral groove on an inner peripheral surface thereof, and a surface area excluding a start end and a terminal end of the spiral groove is formed. A plug-like member is mounted between the inner peripheral surface of the cold head and the outer peripheral surface of the expansion cylinder to cover the working gas through the spiral groove. To flow to the cold head (claim 1).

(2) A gas cycle engine refrigerator intended for a pulse tube refrigerator configured by combining a gas compressor, a regenerator, a pulse tube, and a cold head having a cold generation section at the top. A cold head with a built-in regenerator in the space between the outer cylinder surrounding it as an inner cylinder, and a cold head with a gas flow path formed on the inner surface of the top covering the low-temperature end of the regenerator and the open end of the pulse tube And the regenerator, pulse tube, and cold head are assembled together,
The cold head is formed into a cap-like body, and a spiral groove is formed on the inner peripheral surface thereof. The inner peripheral surface of the cold head and the outer peripheral surface of the expansion cylinder are covered by covering a surface area excluding the start and end of the spiral groove. A plug-like member is mounted between the cold head and the surface, and the working gas is caused to flow to the cold head via the spiral groove (claim 2).

According to the constitutions of (1) and (2), the working gas flowing through the cold head in the refrigeration cycle passes through the spiral groove having a long path, and turns and flows on the inner peripheral surface of the cold head. During the flow, the low-temperature working gas flushes the groove surface, and the cold heat is transferred to the cold head. Accordingly, a large contact area between the working gas and the cold head can be obtained, and an appropriate gas flow rate can be obtained, so that the heat flow between the working gas and the cold head increases, and the heat transmission rate between the two increases. Further, the dead volume of the gas flow path is reduced by loading the plug-shaped member inside the cold head. As a result, a gas cycle engine refrigerator having a small size and high thermal efficiency can be obtained. Further, according to the present invention, the configuration of the preceding paragraphs (1) and (2)
It can be configured in the following specific modes.

(3) The spiral groove formed on the inner peripheral surface of the cold head is formed into a triangular groove in cross section so as to increase the contact area with the working gas. (4) A plurality of spiral grooves are formed on the inner peripheral surface of the cold head to further increase the contact area with the working gas. (5) The gas flow path formed on the inner surface of the top of the cold head is
A concave gas collecting portion formed at the center thereof and a gas flow channel groove radially extending from the gas collecting portion are formed to increase the contact area with the working gas. ).

(6) Gases formed on both end surfaces of the plug-like member, between the beginning of the spiral groove formed on the inner peripheral surface of the cold head and the regenerator, and at the end of the cold spiral groove and on the inner surface of the top of the cold head. A helical groove is formed by forming a groove communicating with the flow path and suppressing the pressure loss of the working gas flowing out of the regenerator or the working gas returning from the displacer or pulse tube through the gas flow path of the cold head. (Claim 6).

(7) The plug-shaped member is made of a material having a larger coefficient of thermal expansion than the expansion cylinder and the pulse tube of the displacer, and becomes a ring-shaped plug using a difference in thermal expansion when the refrigerator operates at a low temperature. The member is tightly fitted to the expansion cylinder of the displacer or the outer periphery of the pulse tube (the same principle as shrink fitting), and the working gas does not flow through the gas flow path of the cold head and the gap on the inner peripheral surface side of the plug-like member Specifically, the material of the expansion cylinder and pulse tube of the displacer is made of stainless steel or a titanium alloy, and the material of the plug-shaped member has a small specific heat and a thermal expansion coefficient. Is made of aluminum or aluminum alloy larger than stainless steel and titanium alloy, and the plug-like member is made of a displacer syringe by utilizing the difference in thermal expansion as described above. The pull-down time from the start of the refrigerator to the transition to the steady operation is shortened while being tightly and tightly fitted to the outer periphery of the pulse tube or the pulse tube.

(9) In the pulse tube refrigerator according to the above (2),
A rectifying portion is arranged at the open end of the pulse tube communicating with the gas flow path of the low-temperature heat transfer portion member, and the rectifying portion is housed in a cylindrical holder, and a flange-like flange projecting outward from the top of the holder. Between the end surface of the plug-shaped member and the support plate fastened to the end surface of the member (Claim 9), and further, a tapered surface that expands toward the inside of the pulse tube is formed at the tip of the rectifying portion holder (Claim 9). According to the tenth aspect, turbulence of the working gas flowing through the pulse tube is suppressed to reduce the pressure loss.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention corresponding to the above-mentioned items will be described below with reference to the embodiments shown in FIGS. In the drawings of each embodiment, the same members corresponding to those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1 shows a second embodiment of the present invention.
1 shows an assembly structure of a regenerator, a displacer, and a cold head for a Stirling refrigerator as an embodiment corresponding to 1 to 8 except for the above. In this embodiment, a cold head 5 attached between the low-temperature end of the regenerator 2 and the open end of the expansion cylinder of the displacer 4 is formed as a cap and attached to the outer cylinder 7 by welding. Further, a ring-shaped plug-shaped member 8 is loaded in the inside thereof.

Here, in the inner peripheral surface area of the cold head 5, one or a plurality of spiral grooves 5b serving as gas flow paths are formed. As shown in FIG. 1 (b), a gas flow path 5a formed on the inner surface of the top of the cold head 5 has a concave gas collecting part 5a-1 having substantially the same diameter as the displacer 4 formed at the center thereof. A plurality of gas flow grooves 5 radially extending from the gas collecting portion 5a-1 toward the inner peripheral surface of the cold head 5.
a-2.

On the other hand, the inner diameter and outer diameter of the ring-shaped plug-shaped member 8 are set corresponding to the outer diameter of the expansion cylinder 4a of the displacer 4 and the inner diameter of the cap-shaped cold head 5, respectively. As shown in the figure, the plug-like member 8 closes the end face of the spiral groove 5a formed on the inner peripheral surface of the cold head 5 from the inner peripheral side. A peripheral groove 8 formed along the inner and outer peripheral edges of the plug-shaped member 8 as a gas flow path is provided on the bottom end face facing the regenerator 2 as shown in FIG.
a, 8b, and the peripheral groove 8a through the central rib projection 8c.
And a radial groove 8d is formed on the upper surface of the cold head 5 facing the gas flow path 5a along the outer peripheral edge.
Are notched. Then, the aforementioned circumferential grooves 8a, 8
e communicates with the beginning and end of the spiral groove 5b described above at the assembly position, and the peripheral groove 8e on the upper surface communicates with the gas channel groove 5a-1 of the cold head 5 described above.

In this configuration, during operation of the Stirling refrigerator, the working gas flowing out of the regenerator 2 is transferred to the inner peripheral surface of the cold head 5 through the grooves 8a, 8b, 8d formed on the bottom surface of the plug-shaped member 8. After flowing through the formed spiral groove 5b and exiting from the end thereof, the gas flow groove 5a-2 of the gas flow path 5a formed on the inner surface of the top of the cold head 5 through the peripheral groove 8e formed on the upper surface of the plug-shaped member 8. Gas collecting part 5
It flows through a-1 and is sent to the expansion cylinder 4a of the displacer 4. Therefore, in this gas flow process, the working gas is supplied to the spiral groove 5b having a large ratio of the heat transfer area to the passage volume.
After flowing while turning on the inner peripheral surface side of the cold head 5 along the flow path, the gas further flows through the gas flow channel 5a-1 on the top side, and the cold heat of the working gas is transferred to the cold head 5 in the flowing process. .

Therefore, while keeping the volume (dead volume) of the gas flow channel low, the heat transfer area between the cold head 5 and the working gas can be increased, thereby increasing the heat transmission rate of the cold head 5. In addition, cold generated in the refrigeration cycle is efficiently transferred to the cold head 5. If the spiral groove 5b is formed as a multiple groove, the heat transfer area with the working gas is further increased.

The displacer 4 is usually made of a material having a low thermal conductivity, such as stainless steel or a Ti alloy, in order to minimize heat penetration due to heat conduction from the tube wall. The plug-like member 8 is made of a material having a higher coefficient of thermal expansion than the displacer 4. As a result, the displacer 4 is kept at a low temperature during the operation of the refrigerator.
The plug-shaped member 8 is tightly fitted to the outer circumference of the expansion cylinder 4a of the displacer by utilizing the difference in the coefficient of thermal expansion between the plug-shaped member 8 and the plug-shaped member 8. Therefore, it is possible to effectively prevent the working gas from bypassing (short-circuiting) the gap between the inner peripheral surface of the plug-shaped member 8 and the expansion cylinder 4a without passing through the gas flow path 5a and the spiral groove 5b of the cold head 5. Can be prevented. In this case, if aluminum or an aluminum alloy having a small specific heat is adopted as the material of the plug-shaped member 8, the heat capacity of the plug-shaped member 8 becomes small. The effect of reducing the pull-down time can be expected.

[Embodiment 2] FIG. 2 shows an embodiment corresponding to claim 3 of the present invention. In this embodiment, the configuration is basically the same as that of the first embodiment.
The spiral groove 5b formed on the inner peripheral surface of the cold head 5 becomes a triangular groove in cross section.

As a result, the peripheral length / cross-sectional area ratio of the spiral groove becomes larger than that of the rectangular groove shown in FIG. 1. The contact area between them, that is, the heat transfer area can be further increased, thereby increasing the heat transmission rate of the cold head 5 and obtaining a large refrigeration output.

[Embodiment 3] FIG. 3 shows an embodiment corresponding to the second, ninth and tenth aspects of the present invention, which is applied to a pulse tube refrigerator. In this embodiment, a pulse tube 9 is provided in place of the displacer 4 of the Stirling refrigerator shown in FIGS. 1 and 2, and the pulse tube 9 and the regenerator 2, the cold head 5, and the plug member 8 are integrated. Is assembled.

Here, the cold head 5 is used in the first embodiment.
Similarly, a spiral groove 5b is formed on the inner peripheral surface of the cap-shaped body, and a ring-shaped plug-shaped member 8 is provided between the inner peripheral surface of the cold head 5 and the pulse tube 9. It is installed. At the open end of the pulse tube 9, a rectifying unit 10 made of a laminated metal mesh or the like is accommodated in a cylindrical holder 11 and held at this position. The cylindrical holder 11 has a Z-shaped cross section as shown in the figure, and has a flange-like flange 11a projecting from the top to the outer periphery of the end surface of the plug-shaped member 8 and a support plate 12 placed on the member. , And the support plate 12 is fastened to the plug-like member 8 with screws 13 and fixed in place. Further, a tapered surface 11b that expands toward the inside of the pulse tube 9 is formed at the tip of the cylindrical holder 11 that supports the rectifying unit 10 and protrudes inward of the pulse tube 9.

With this configuration, as in the case of the Stirling refrigerator of the first embodiment, the heat transfer rate of the cold head 5 is increased to improve the thermal efficiency of the pulse tube refrigerator, and when the working gas flows into and out of the pulse tube 9. In addition to the rectifying action of the rectifying section 10, the tapered surface 11b suppresses the generation of turbulence such as eddies and contributes to the improvement of the efficiency of the pulse tube refrigerator.

[0035]

As described above, according to the structure of the present invention, since the spiral groove is formed on the inner peripheral surface of the cold head, the area of heat exchange with the working gas flowing therethrough can be increased, and the appropriate area can be obtained. The gas flow velocity is obtained, and the heat transfer rate and the amount of heat exchange can be increased. Furthermore, by mounting a plug-like member in the cold head, the dead volume of the gas flow path can be reduced and the refrigerating output can be increased, thereby providing a gas cycle engine refrigerator having a small size and high thermal efficiency. Can be.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a cold head peripheral portion of a Stirling refrigerator corresponding to a first embodiment of the present invention, where (a) is a longitudinal sectional view, and (b) and (c) are arrows in FIG. Sight XX,
YY sectional view

FIG. 2 is a cross-sectional view of a configuration around a cold head of a Stirling refrigerator corresponding to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a configuration around a cold head of a pulse tube refrigerator corresponding to a third embodiment of the present invention.

FIG. 4 is an overall configuration diagram of a conventional Stirling refrigerator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas compressor 2 Regenerator 4 Displacer 4a Expansion cylinder 5 Cold head 5a Gas flow path 5a-1 Gas collecting part 5a-2 Gas flow path groove 5b Spiral groove 7 Outer cylinder 8 Plug member 8a, 8b, 8d, 8e Groove (gas flow path) 9 Pulse tube 10 Rectifier 11 Holder 11a Flange 11b Tapered surface 12 Support plate

Claims (10)

[Claims] 1. A gas cycle engine refrigerator intended for a Stirling refrigerator comprising a gas compressor, a regenerator, a displacer, and a cold head having a cold-generating section at the top, wherein an expansion cylinder of the displacer has an internal cylinder. A regenerator is built in the space between the outer cylinder surrounding it as a cylinder, and a cold head with a gas flow path formed on the inner surface of the top is attached to the low-temperature end of the regenerator and the cylinder opening end of the displacer. A regenerator, a displacer, and a cold head, which are integrally assembled, wherein the cold head is formed into a cap-like body to form a spiral groove on an inner peripheral surface thereof, and a surface excluding a start end and an end of the spiral groove. A plug-like member is attached between the inner peripheral surface of the cold head and the outer peripheral surface of the expansion cylinder so as to cover the region, and is formed via the spiral groove. Gas cycle engine refrigerator is characterized in that so as to flow the gas into the cold head. 2. A gas cycle engine refrigerator intended for a pulse tube refrigerator comprising a gas compressor, a regenerator, a pulse tube, and a cold head having a cold generation section at the top. A cold head with a built-in regenerator in the space between the outer cylinder surrounding it as a cylinder and a gas head formed on the inner surface of the top covering the low-temperature side end of the regenerator and the open end of the pulse tube is attached. A regenerator, a pulse tube, and a cold head, which are integrally assembled, wherein the cold head is formed into a cap-like body to form a spiral groove on an inner peripheral surface thereof, and excluding a start end and an end of the spiral groove. A plug-like member is mounted between the inner peripheral surface of the cold head and the outer peripheral surface of the expansion cylinder so as to cover the surface area, and the working gas flows to the cold head via the spiral groove. That gas cycle institutions refrigerator. 3. The gas cycle engine refrigerator according to claim 1, wherein the spiral groove formed on the inner peripheral surface of the cold head is a V-shaped groove having a triangular cross section. 4. The gas cycle engine refrigerator according to claim 1, wherein a plurality of spiral grooves are formed on an inner peripheral surface of the cold head. 5. The refrigerator according to claim 1, wherein the gas flow path formed on the inner surface of the top of the cold head comprises:
A gas cycle engine refrigerator comprising: a concave gas collecting portion formed to face an opening end of an inner cylinder; and a gas passage groove radially extending from the gas collecting portion. 6. The refrigerating machine according to claim 1, wherein both ends of the plug-like member are provided between a start end of a spiral groove formed on an inner peripheral surface of the cold head and the regenerator, and a low-temperature spiral groove. A gas cycle engine refrigerator characterized in that a groove is formed to communicate between an end of the cold head and a gas flow path formed on the inner surface of the top of the cold head. 7. The refrigerator according to claim 1, wherein the plug-shaped member is made of a material having a larger coefficient of thermal expansion than the expansion cylinder and the pulse tube of the displacer. Gas cycle engine refrigerator. 8. The gas refrigerator according to claim 7, wherein the material of the expansion cylinder and the pulse tube of the displacer is stainless steel or a titanium alloy, and the material of the plug-like member is aluminum or an aluminum alloy. Cycle engine refrigerator. 9. The refrigerator according to claim 2, wherein a rectifying section is provided at an open end of the pulse tube communicating with the gas flow path of the cold head, and the rectifying section is housed and held in a cylindrical holder. A gas cycle engine refrigerator, wherein a flange-like flange extending outward from the top of the holder is sandwiched between an end surface of the plug-like member and a support plate fastened to the end surface of the member. 10. The gas cycle engine refrigerator according to claim 9, wherein a tapered surface expanding toward the inside of the pulse tube is formed at the tip of the rectifying portion holder.