JP2001116379A - Cryogenic refrigerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress a decrease in capability according to a heat invasion. SOLUTION: In a two-stage GM refrigerator, a second cylinder 2b is constituted of a tubular member having a uniform predetermined thickness and formed in a predetermined length. A second displacer 22b is inserted into the cylinder 2b, and a second stage expansion chamber 31 is partitioned. A high pressure helium gas is introduced into the chamber 31, and a second heat station 42 is maintained at a cryogenic temperature by the Simon expansion of the gas. The cylinder 2b has a predetermined thickness to suppress its deformation due to an internal pressure. The cylinder 2b has a predetermined length to suppress a heat invasion according to a thermal conduction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic refrigerator in which a working gas such as helium is expanded by reciprocating a displacer (replacer) to generate cryogenic cooling.

[0002]

2. Description of the Related Art Conventionally, as a cryogenic refrigerator, as disclosed in JP-A-10-122682,
A GM (Gifford McMahon) refrigerator is known. In this type of GM refrigerator, a displacer is connected to a motor via a crankshaft, and a mechanical drive type in which the displacer is reciprocated by operation of the motor, or a piston is reciprocated together with the displacer by a pressure difference of a working gas. Gas pressure driven type (improved solvay type)
Are known.

As shown in FIG. 8, in the cryogenic refrigerator described above, a displacer (b) is inserted from the base end side of a cylinder (a) to partition an expansion chamber (c) in the cylinder (a). I have. A flange-shaped heat station (d) is provided at the tip of the cylinder (a). The displacer (b) reciprocates in the cylinder (a), and accordingly, a working gas such as helium is supplied and exhausted to the expansion chamber (c). The space between the displacer (b) and the cylinder (a) is sealed by a seal member (e) provided on the base end side of the displacer (b).

[0004] The displacer (b) is formed to be hollow, and a space inside the displacer (b) is filled with a regenerator material such as lead balls to constitute a regenerator (f). When the displacer (b) moves to the right in FIG. 8, a high-pressure (for example, 24 kgf / cm ² G) working gas is sent into the expansion chamber (c) through the inside of the displacer (b). At this time, the working gas flows into the expansion chamber (c) after being cooled by contact with the cold storage material. Thereafter, the working gas flows out of the expansion chamber (c) while expanding, whereby the cold occurs, and the heat station (d) is maintained at a predetermined extremely low temperature state. The working gas expanded to a low pressure (for example, 9 kgf / cm ² G) is completely discharged from the expansion chamber (c) by moving the displacer (b) to the left in FIG. At this time, the low-temperature working gas discharged from the expansion chamber (c) comes into contact with the cold storage material inside the displacer (b) and cools the cold storage material.

Here, in the cylinder (a), there is a temperature difference between the base end side and the front end side. For this reason, heat penetrates from the base end side toward the front end side due to heat conduction, which causes a reduction in cooling capacity. On the other hand, conventionally, the cylinder (a) has been formed to have a small thickness over substantially the entire length thereof, thereby reducing heat penetration due to heat conduction.

[0006]

As described above, in the prior art, the thickness of the cylinder (a) is reduced to reduce heat penetration. However, a working gas having a relatively high pressure exists in the cylinder (a). Therefore, when the thickness of the cylinder (a) is reduced, the deformation of the cylinder (a) becomes excessive, and there is a problem that the clearance between the cylinder (a) and the displacer (b) is widened.

As described above, when the clearance between them is widened, convection of the working gas occurs in the gap between the cylinder (a) and the displacer (b), and the convection causes heat to enter the tip side of the cylinder (a). Will happen. For this reason,
In the conventional device, heat penetration due to heat conduction can be suppressed, but on the other hand, heat penetration due to convection increases, and it is still not possible to prevent a decrease in performance due to heat penetration.

The present invention has been made in view of the foregoing, and an object of the present invention is to reliably suppress a decrease in performance of a cryogenic refrigerator due to heat intrusion.

[0009]

The first solution of the present invention is to provide a cylindrical cylinder (2a, 2b) and a cylinder (2a, 2b).
a, 2b), the expansion chambers (30, 31) are defined inside the cylinders (2a, 2b) and reciprocated in the cylinders (2a, 2b).
Displacer (22a, 2) that supplies and exhausts working gas to and from 1)
2b) and a regenerator (24, 27) for exchanging heat of the working gas supplied to and exhausted from the expansion chambers (30, 31) with a regenerator material, and the operation supplied to the expansion chambers (30, 31). It is intended for cryogenic refrigerators that generate cryogenic-level refrigeration by gas expansion. The cylinders (2a, 2b) have a predetermined uniform thickness such that the amount of deformation due to the pressure of the working gas is equal to or less than a predetermined value, and the amount of heat penetrated by heat conduction in the longitudinal direction is equal to or less than a predetermined value. It is formed in length.

A second solution taken by the present invention is to form a cylindrical cylinder (2a, 2b) and an expansion chamber (30, 31) inside the cylinder (2a, 2b). Cylinder (2a,
2b) A displacer (22a, 22b) that reciprocates inside and supplies and exhausts working gas to and from the expansion chambers (30 and 31), and a cold storage material that supplies and exhausts working gas to and from the expansion chambers (30 and 31). And a regenerator (24, 27) for exchanging heat with the cryogenic refrigerator that generates cryogenic-level refrigeration by expansion of the working gas supplied to the expansion chambers (30, 31). And
In the cylinders (2a, 2b), a plurality of thin portions (50) having a predetermined width and a small thickness over the entire circumference are formed intermittently in the longitudinal direction.

In the first and second solutions, the high-pressure working gas is introduced into the expansion chamber (30, 31) in the cylinder (2a, 2b) by the movement of the displacer (22a, 22b). . At this time, the working gas is cooled by exchanging heat with the cold storage material of the regenerators (24, 27), and the cooled working gas flows into the expansion chambers (30, 31). The working gas supplied to the expansion chambers (30, 31) expands to further lower the temperature, thereby generating cryogenic cooling. Thereafter, the working gas in the expansion chambers (30, 31) is discharged by the movement of the displacers (22a, 22b). At that time, the cryogenic working gas flows through the regenerator (24, 27) to cool the regenerator material. The cryogenic refrigerator performs the refrigeration operation by repeating the above operation.

In the first solution, the cylinders (2a, 2b) are formed with a predetermined uniform thickness and a predetermined length. Since the cylinders (2a, 2b) have a predetermined thickness, the cylinders (2a, 2b) are operated by the pressure of working gas.
The deformation of b) is suppressed. In addition, by setting the cylinders (2a, 2b) to a predetermined length, the amount of heat that enters due to heat conduction in the longitudinal direction of the cylinders (2a, 2b) is reduced.

On the other hand, in the second solution, a plurality of thin portions (50) are formed in the cylinders (2a, 2b). Therefore, the amount of heat that penetrates due to heat conduction in the longitudinal direction of the cylinder (2a, 2b) is reduced. In the cylinders (2a, 2b), the thin portion (50) is provided intermittently. That is,
Between the thin portions (50), there are portions where the thickness remains large. Therefore, the rigidity of the cylinders (2a, 2b) is ensured, and deformation of the cylinders (2a, 2b) due to the pressure of the working gas is suppressed.

[0014]

According to the above solution, the cylinder (2
The rigidity of a, 2b) can be secured to reduce the amount of heat entering by convection. In other words, by increasing the rigidity of the cylinder (2a, 2b), the cylinder (2
a, 2b) expansion can be suppressed. Therefore, the cylinder (2a, 2
The clearance between b) and the displacer (22a, 22b) can be kept constant. Therefore, the convection of the working gas in the gap between the cylinder (2a, 2b) and the displacer (22a, 22b) can be suppressed, and the amount of heat entering due to the convection can be reduced.

Further, with the above-described predetermined configuration, the amount of heat that enters due to heat conduction in the longitudinal direction of the cylinder (2a, 2b) can be reduced. As a result, as described above, both heat intrusion due to convection and heat intrusion due to heat conduction can be suppressed,
A sufficient refrigeration capacity can be exhibited by preventing a capacity reduction due to heat intrusion.

[0016]

Embodiment 1 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, “right” or “left” means “right” or “left” in each drawing unless otherwise specified.

As shown in FIG. 1, in the cryogenic refrigerator (R) according to the first embodiment, a displacer member (22) is inserted into a cylinder (2), and the displacer member (22) is connected to helium. Gas pressure driven GM that reciprocates by gas pressure to expand high pressure helium gas (working gas)
It consists of a cycle (Gifford McMahon Cycle) expander.

The above cryogenic refrigerator (R) includes a motor head (1) and a cylinder section (2). The cylinder portion (2) has a large-small two-stage structure in which a large-diameter first cylinder (2a) and a small-diameter second cylinder (2b) are coaxially arranged.

The first cylinder (2a) is at the right end (base end).
And is hermetically attached to the motor head (1). A first heat station (41) having a flange shape is provided at the left end (tip) of the first cylinder (2a). During the operation of the refrigerator (R), the temperature of the first heat station (41) is about 40K.

The second cylinder (2b) is at the right end (base end)
And is hermetically attached to the tip of the first cylinder (2a). A second heat station (42) having a flange shape is provided at the left end (tip) of the second cylinder (2b). The tip of the second cylinder (2b) is closed by the second heat station (42). And
During operation of the refrigerator (R), the second heat station (4
The temperature of 2) becomes about 4.2K.

As shown in FIG. 2, the second cylinder (2b)
Is formed of a tubular member having a uniform predetermined thickness and a predetermined length.

Specifically, the thickness t of the second cylinder (2b)
Is related to the inner radius a of the second cylinder (2b),^Two/
It is set so as to satisfy t ≦ 210 mm. Like this
By setting the wall thickness t, it depends on the pressure of the working gas.
The amount of deformation of the second cylinder (2b) is suppressed to a predetermined value or less.
You. The pressure of the working gas is set during operation of the refrigerator (R).
Is 24kgf / cm at high pressure^TwoAbout G, 9kgf / cm at low pressure^TwoAbout G
Available, 19 kgf / cm when stopped ^TwoIt is about G.

The length L of the second cylinder (2b) is 1
It is set to 50 mm or more. As described above, the first heat station (41) is about 40K, while the second heat station (41) is
The heat station (42) is about 4.2K.
That is, a temperature difference exists between both ends of the second cylinder (2b). Therefore, the length L of the second cylinder (2b) is set as described above, and the second heat station (4
2) Reduces the amount of heat that enters.

As shown in FIG. 1, the motor head (1) is formed in a closed container shape. On the lower surface of the motor head (1), a high-pressure gas inlet (4) and a low-pressure gas outlet (5) located on the left side thereof are formed. The high pressure gas inlet (4) is connected to the high pressure pipe (4
a) is connected through. In addition, low pressure gas outlet (5)
Is connected to the suction side of a compressor (not shown) via a low-pressure pipe (5a).

A motor chamber (6), a mounting hole (7), and an intermediate pressure chamber (8) are formed inside the motor head (1). The motor chamber (6) communicates with the high-pressure gas inlet (4). The mounting hole (7) is formed on the left side of the motor chamber (6), and is formed by a through hole in the left-right direction whose internal space communicates with the motor chamber (6) at the right end. Intermediate pressure chamber (8)
Is constituted by a substantially annular space located around the mounting hole (7).

A valve stem (9) constituting a closing member at the right end (base end) of the cylinder portion (2) is fitted into a boundary portion between the motor head (1) and the cylinder portion (2).
The valve stem (9) includes a valve seat (9a), a piston support (9b), and a flange (9c). The valve seat (9a) is fitted airtightly into the mounting hole (7). The piston support portion (9b) is formed to have a smaller diameter than the inner diameter of the first cylinder (2a) of the cylinder portion (2), and protrudes concentrically into the first cylinder (2a). The flange portion (9c) forms a left side wall of the intermediate pressure chamber (8). The space enclosed by the right side of the valve seat (9a) and the wall of the mounting hole (7) forms a valve chamber (10) that communicates with the high-pressure gas inlet (4) via the motor chamber (6). Have been.

As shown in FIGS. 4 and 5, a first gas flow path (12) and a second gas flow path (14) are formed through the valve stem (9). The first gas flow path (1
In the case of 2), the right half is bifurcated and the valve chamber (1
0) communicates with the cylinder (2). In addition, the first gas flow path (12) is provided with a capillary passage (1
It is always in communication with the intermediate pressure chamber (8) via 5).
One end of the second gas flow path (14) is connected to the first gas flow path (1).
2) The low pressure port (3
The other end is connected to the low-pressure gas outlet (5) via the low-pressure passage (13) of the motor head (1). The two gas flow paths (12, 14) are provided on the right side of the valve seat (9a) of the valve stem (9) facing the valve chamber (10). (9) In the central portion, the branched first gas flow paths (12, 12) are respectively opened at symmetrical positions with respect to the second gas flow paths (14).

The valve chamber (10) of the motor head (1)
Inside, a rotary valve (35) is provided. The rotary valve (35) is rotatably driven by a valve motor (39) disposed in the motor chamber (6), and is configured to alternately switch between a high-pressure valve opening state and a low-pressure valve opening state.

Specifically, the output shaft (39) of the valve motor (39) is provided at the center on the right side of the rotary valve (35).
a) is rotationally engaged. The valve (35)
A spring (not shown) is contracted between the right side of the motor and the motor (39). The left side of the rotary valve (35) is pressed against the right side of the valve seat (9a) with a constant pressing force by the spring force of the spring and the pressure of the high-pressure helium gas in the valve chamber (10). ing.

As shown in FIG. 3, a high pressure port (36, 36) and a low pressure port (37) are formed on the left side of the rotary valve (35). High pressure port (36,36)
Is formed by cutting a predetermined length from the outer peripheral edge of the rotary valve (35) facing in the radial direction toward the center. The low pressure port (37) is disposed at an angle of about 90 ° in the rotation direction of the rotary valve (35) (direction indicated by an arrow in the figure) with respect to the high pressure port (36, 36). ) It is notched in the diametrical direction from the center of the left side surface toward the vicinity of the outer peripheral edge, and is formed in an end groove shape.

Then, as shown in FIG. 4, the rotary valve (35) is rotated, and the high pressure ports (36, 36) on the left side thereof are rotated.
When the inner ends of the first gas passages (12) coincide with the two open ends of the first gas flow path (12) that open to the right side of the valve seat (9a) of the valve stem (9), the valve is in a high pressure open state. In the high-pressure valve open state, the first gas flow path (12) and the valve chamber (10) are in communication with each other, and the high-pressure helium gas introduced from the high-pressure gas inlet (4) is supplied to the first gas flow path (12). Flows into.

On the other hand, as shown in FIG. 5, both outer ends of a low-pressure port (37) constantly communicating with the second gas flow path (14) opened at the right side of the valve seat part (9a) at the center are formed. When they correspond to both open ends of the first gas flow path (12),
The low pressure valve is opened. In this low-pressure valve open state, the first gas flow path (12) and the low-pressure passage (13) are in communication with each other, and helium gas flows from the first gas flow path (12) through the low-pressure passage (13) to the low-pressure gas outlet. Guided to (5).

As described above, the intermediate pressure chamber (8) communicates with the first gas flow path (12) via the capillary passage (15). The capillary passage (15) is narrow and elongated. The first gas flow path (12) is alternately connected to a high-pressure gas inlet (4) and a low-pressure gas outlet (5) via a rotary valve (35). That is, the first gas flow path (12) is alternately switched between a state in which high-pressure helium gas is present and a state in which low-pressure helium gas is present. When the pressure of the first gas passage (12) becomes high, the pressure of the high-pressure helium gas is reduced while flowing through the capillary passage (15), and flows into the intermediate pressure chamber (8).
When the pressure in 2) becomes low, the helium gas in the intermediate pressure chamber (8) is reduced in pressure while passing through the capillary passage (15) and flows out to the first gas passage (12). Therefore, the pressure in the intermediate pressure chamber (8) is
It is maintained at a value between high and low pressure.

A slack piston (17) and a displacer member (22) are provided inside the cylinder (2).

The slack piston (17) is formed in a cup shape having a bottom wall. The slack piston (17) is provided at the right end in the first cylinder (2a) of the cylinder section (2). The slack piston (17) has its inner surface facing the piston support (9b) of the valve stem (9).
Are externally fitted so as to be able to reciprocate while being slid and guided. Although not shown, seals for preventing the flow of the working gas are provided at sliding contact portions between the slack piston (17), the cylinder portion (2), and the piston support portion (9b). A large-diameter central hole (18) is formed in the center of the bottom wall of the slack piston (17), and a plurality of communication holes (19, 19) for communicating the inside and the outside of the slack piston (17) are formed in the peripheral corner. , ...) are formed.

By the slack piston (17), the second pressure chamber (29) and the first pressure chamber (2) are provided in the cylinder portion (2).
0) are respectively formed. That is, the second pressure chamber (29) is formed on the left side of the slack piston (17), and the first pressure chamber (20) is formed on the right side thereof.
The first pressure chamber (20) is always in communication with the intermediate pressure chamber (8) in the motor head (1) via an orifice (21). Therefore, the first pressure chamber (20) is set at an intermediate pressure between high pressure and low pressure helium gas, and the pressure difference between the gas pressures of the first pressure chamber (20) and the second pressure chamber (29) is determined. The slack piston (17) reciprocates with the displacer member (22).

The displacer member (22) is reciprocally fitted to the cylinder (2). The displacer member (22) is provided to the left of the second pressure chamber (29). The displacer member (22) is configured by integrally connecting the first displacer (22a) and the second displacer (22b).

The first displacer (22a) is formed into a cylindrical container having a diameter corresponding to the inner diameter of the first cylinder (2a), and reciprocates in the first cylinder (2a). By the first displacer (22a), a first-stage expansion chamber (30) is defined at the left end (tip) in the first cylinder (2a). Although not shown, the first displacer (22a) and the first displacer (22a) are connected to the right end (base end) of the first displacer (22a).
A first seal member for sealing between the cylinders (2a) is provided.

The internal space of the first displacer (22a) is always in communication with the first-stage expansion chamber (30) via a communication hole (23). Also, the first displacer (22a)
The inner space is filled with a large number of small spherical regenerative materials made of lead or reticulated reticulated material made of copper, and is configured as a first-stage regenerator (24).

The second displacer (22b) is formed in a cylindrical container having a diameter corresponding to the inner diameter of the second cylinder (2b). That is, the second displacer (22b)
The diameter is smaller than the displacer (22a).
The second displacer (22b) is coaxially connected to the left end of the first displacer (22a), and is connected to the second cylinder (2b).
Reciprocate in b).

Specifically, the second displacer (22b)
The first displacer (22a) through the protruding piece (46)
Is combined with The right end of the projecting piece (46) is first.
It is embedded in the distal end of the displacer (22a), and the left end is inserted into the proximal end of the second displacer (22b). The projecting piece (46) is fitted in the second displacer (22b) in a state where there is play, and a gap is formed between the projecting piece (46) and the second displacer (22b). An elongated pin (47) is provided through the protruding piece (46) and the second displacer (22b). The pin (47) connects the protruding piece (46) to the second displacer (22b). I have.

At the right end (base end) of the second displacer (22b), there is provided a second seal member (45) for sealing between the second displacer (22b) and the second cylinder (2b). . In FIG. 1, the illustration of the second seal member (45) is omitted.

The second displacer (22b) defines a second-stage expansion chamber (31) at the left end (tip) in the second cylinder (2b). The internal space of the second displacer (22b) is always in communication with the second-stage expansion chamber (31) via a communication hole (26). The inner space of the second displacer (22b) is formed by the projecting piece (46) and the second displacer (22b).
It is always in communication with the first-stage expansion chamber (30) through a gap formed between the displacers (22b).

The interior space of the second displacer (22b) is filled with a large number of small spherical regenerators made of a so-called magnetic regenerator, and is configured as a second stage regenerator (27). Materials such as holmium copper (HoCu ₂ ), holmium 2 aluminum (Ho ₂ Al), erbium 3 nickel (Er ₃ Ni), and erbium cobalt (Er ₃ Co) are known as magnetic regenerative materials of this kind.

An engaging piece (33) is integrally provided at the right end of the first displacer (22a) of the displacer member (22) so as to protrude therefrom. The locking piece (33) is formed in a tubular shape, and connects the internal space of the first displacer (22a) to the second pressure chamber (29). The locking piece (33)
The right side portion is shaped to extend through the center hole (18) of the bottom wall of the slack piston (17) into the slack piston (17) by a predetermined dimension. Further, a flange-shaped locking portion (33a) that engages with the bottom wall of the slack piston (17) is formed integrally with the right end of the locking piece (33).

When the slack piston (17) moves to the left, when the slack piston (17) moves by a predetermined stroke, its bottom wall comes into contact with the displacer member (22), and the displacer member (22) ) Is pushed by the slack piston (17) and starts moving to the left. On the other hand, when the slack piston (17) moves to the right, the bottom wall engages with the locking portion (33a) of the locking piece (33) when the slack piston (17) moves by a predetermined stroke. The displacer member (22) is configured to be pulled by the slack piston (17) and start moving to the right. That is, the displacer member (2
2) is configured to follow the slack piston (17) with a delay of a predetermined stroke.

As described above, the rotary valve (35)
It rotates to switch between a high-pressure valve opening state and a low-pressure valve opening state.
When the rotary valve (35) is in the high pressure open state and the first gas flow path (12) communicates with the high pressure gas inlet (4), the second pressure chamber (29), the first and second stage expansion chambers ( High pressure helium gas is supplied to (30, 31). On the other hand, the rotary valve (3
When the first gas flow path (12) communicates with the low-pressure gas outlet (5) when the state (5) is in the low-pressure valve opening state, the second pressure chamber (29)
Helium gas in the stage and the second stage expansion chamber (30, 31) is exhausted. The switching operation of the rotary valve (35) generates a pressure difference between the second pressure chamber (29) and the intermediate pressure chamber (8).
7) and the displacer member (22) reciprocates.

-Operation-The operation of the cryogenic refrigerator (R) will be described. The pressure in the cylinder (2) of the refrigerator (R) is low (about 9kg)
f / cm ² G), and the operation will be described from the state where the slack piston (17) and the displacer member (22) are at the left end position. The rotary valve (35) is driven and rotated by the valve motor (39) to be in a high pressure open state (FIG. 4).
reference).

In this state, the valve chamber (10) communicates with the first gas flow path (12) via the rotary valve (35). Therefore, the high-pressure helium gas (about 24 kgf / cm ² G) introduced from the high-pressure gas inlet (4) into the motor chamber (6) is supplied to the valve chamber (10) and the high-pressure ports (36,3) of the rotary valve (35).
6) and the second pressure chamber (2) through the first gas passage (12).
9) will be introduced. The high-pressure helium gas introduced into the second pressure chamber (29) sequentially passes through each regenerator (24, 27) of the displacer member (22) and fills each expansion chamber (30, 31). The high-pressure helium gas radiates heat to the regenerator material while passing through the regenerators (24, 27), and its temperature decreases.

After that, when the gas pressure in the second pressure chamber (29) becomes higher than the first pressure chamber (20) communicating with the intermediate pressure chamber (8), the pressure between the two pressure chambers (20, 29) becomes larger. The slack piston (17) moves to the right due to the pressure difference. When the amount of movement of the slack piston (17) reaches a predetermined value, the bottom wall of the slack piston (17) and the locking portion (33a) of the locking piece (33) connected to the displacer member (22) Engage. Therefore, the displacer member (22) is pulled to the right by the slack piston (17) with a delay with respect to the pressure change. By the movement of the displacer member (22), the high-pressure gas further flows into the expansion chambers (30, 31).

Subsequently, when the rotary valve (35) is closed, the displacer member (22) continues to move due to the inertial force thereafter, and the helium gas in the second pressure chamber (29) is expanded by the expansion chambers (30, 31). Go to

After the displacer member (22) reaches the right end position, the rotary valve (35) is opened to a low pressure (see FIG. 5). That is, via the rotary valve (35),
The first gas passage (12) communicates with the low-pressure passage (13).

In this state, the helium gas in each of the expansion chambers (30, 31) undergoes Simon expansion, and the temperature of each of the heat stations (41, 42) is set to a predetermined temperature level due to a temperature drop accompanying the expansion of the gas.

The helium gas, which has been brought to a low temperature in the expansion chambers (30, 31), passes through the regenerators (24, 27) in the displacer member (22) in reverse to the time of the introduction of the gas.
Return to the pressure chamber (29). At this time, the helium gas absorbs heat from the regenerator material while passing through the regenerators (24, 27), and is almost at room temperature when flowing into the second pressure chamber (29). The helium gas at normal temperature flows from the second pressure chamber (29) through the first gas flow path (12), the low-pressure port (37) of the valve (35), and the low-pressure passage (13) in that order, and the low-pressure gas outlet (5) From the refrigerator (R). Thereafter, the discharged helium gas is sucked into a compressor (not shown).

As the gas is discharged, the gas pressure in the second pressure chamber (29) decreases, and the second pressure chamber (29) and the intermediate pressure chamber (8)
The slack piston (17) moves to the left due to the pressure difference between the first pressure chamber (20) and the first pressure chamber (20). When the bottom wall abuts on the displacer member (22) due to the movement of the slack piston (17), the displacer member (22) is thereafter pressed and moved by the slack piston (17). Helium gas is discharged from the expansion chambers (30, 31) by the movement of the displacer member (22).

Thereafter, the rotary valve (35) closes, but thereafter, the displacer member (22) moves to the left end position. Thereby, the helium gas in the expansion chambers (30, 31) is almost completely exhausted, and returns to the initial state. Thus, one cycle of the operation of the displacer member (22) is completed, and thereafter, the same operation as described above is repeated, and the temperature of each heat station (41, 42) is maintained at a predetermined cryogenic temperature level. Specifically, the first heat station (41) is maintained at about 40K, and the second heat station (42) is maintained at about 4.2K.

-Effects of First Embodiment- In the first embodiment, the second cylinder (2b) is formed of a tubular member having a uniform and predetermined thickness. For this reason,
The rigidity of the second cylinder (2b) can be increased and the second cylinder (2b) due to the pressure of helium gas can be increased as compared with the conventional case where the thickness of the second cylinder (2b) is reduced over almost the entire length. ) Can be suppressed.

Specifically, assuming that the second cylinder (2b) is a cylinder having both ends open, the increment Δa of the inner radius of the second cylinder (2b) is expressed by the following equation (1).

[0059]

(Equation 1)

Here, the inner radius a = 20 mm, the inner pressure P = 19
kgf / cm ² G (corresponding to internal pressure at stop), Young's modulus E = 196
Consider the case of 00 kgf / mm ² . In this case, if the thickness of the second cylinder (2b) is reduced to t = 1 mm as in the prior art, the increase amount of the inner radius becomes Δa = 4 μm. On the other hand, when the thickness t is 2 mm over the entire second cylinder (2b) as in the present embodiment, the increase amount Δa of the inner radius is 2 μm.
m, and the radius increase amount is reduced.

Accordingly, the clearance between the second cylinder (2b) and the second displacer (22b) can be maintained at a predetermined value. Therefore, convection of the working gas in the gap between the second cylinder (2b) and the second displacer (22b) can be suppressed, and the amount of heat entering due to this convection can be reduced. That is, as described above, the second cylinder (2
Since there is a temperature difference between the base end side (right end side) and the front end side (left end side) of b), if convection occurs in the gap between the second cylinder (2b) and the second displacer (22b), Due to the movement of the helium gas, heat enters the tip side of the second cylinder (2b). As shown by the solid line in FIG. 6, as the thickness t of the second cylinder (2b) increases, the second cylinder (2b) increases.
The clearance between b) and the second displacer (22b) is reduced, and the amount of heat entering by convection is reduced.

On the other hand, the amount of heat penetrated by the heat conduction in the longitudinal direction of the second cylinder (2b) is expressed by the following equation (2).

[0063]

(Equation 2)

That is, the amount of heat Qi that enters the second cylinder (2
It is proportional to the cross-sectional area A of b). Therefore, simply increasing the thickness t of the second cylinder (2b) results in an increase in the amount of heat that penetrates due to heat conduction, as shown by a broken line or a dashed line in FIG.

However, the amount of invading heat Qi is inversely proportional to the length L of the second cylinder (2b). Therefore, the first embodiment
In the above, members constituting the second cylinder (2b) have not only a predetermined thickness but also a predetermined length. For this reason, as shown in FIG. 6, by increasing the length L of the second cylinder (2b), the amount of heat that enters the second cylinder (2b) due to heat conduction can be reduced.

As a result, as described above, both heat intrusion due to convection and heat infiltration due to heat conduction can be suppressed, and a reduction in performance due to heat intrusion can be prevented, and sufficient refrigeration performance can be exhibited. .

[0067]

Second Embodiment A second embodiment of the present invention is a modification of the first embodiment, except that the configuration of the second cylinder (2b) is changed.

As shown in FIG. 7, a plurality of thin portions (50) are formed intermittently in the second cylinder (2b). The thickness of each thin portion (50) is reduced over the entire circumference of the second cylinder (2b) and over a predetermined length. Therefore, thick portions and thin portions are formed alternately in the second cylinder (2b) in the longitudinal direction.

For this reason, according to the second embodiment, the rigidity of the second cylinder (2b) is increased as compared with the conventional case where the thickness of the second cylinder (2b) is reduced over almost the entire length. Therefore, the expansion amount of the second cylinder (2b) due to the pressure of the helium gas can be suppressed. For this reason, the clearance between the second cylinder (2b) and the second displacer (22b) can be kept small, and the amount of heat entering due to convection can be reduced.

In the second embodiment, the thin portion (50) is formed intermittently in the second cylinder (2b). Therefore, it is possible to minimize an increase in the amount of invading heat due to an increase in the sectional area of the second cylinder (2b).

As a result, according to the second embodiment, as in the first embodiment, both heat intrusion due to convection and heat intrusion due to heat conduction can be suppressed, and a decrease in performance due to heat intrusion can be prevented. Sufficient refrigerating capacity can be exhibited.

[0072]

Other Embodiments In the first embodiment, the second cylinder (2b) is set to a predetermined thickness and a predetermined length, and the second cylinder (2b)
The heat intrusion into the second heat station (42) at the tip of the cylinder (2b) is suppressed. In contrast, the second
Not only the cylinder (2b) but also the first cylinder (2a) is set to a predetermined thickness and a predetermined length, and the first cylinder (2a)
You may make it suppress the heat invasion to the 1st heat station (41) of a front-end | tip. However, only the second displacer (22b) is inserted into the second cylinder (2b), while the first displacer (22) is inserted into the first cylinder (2a).
a) and the slack piston (17) are inserted. Therefore, the length of the first cylinder (2a) is set to be longer than the value obtained by adding the length of the slack piston (17) to 150 mm.

Similarly, in the second embodiment, the thin portion (50) is formed only in the second cylinder (2b). In addition, a plurality of thin portions (50) are formed in the first cylinder (2a). ) May be formed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a cryogenic refrigerator according to a first embodiment.

FIG. 2 is an essential part enlarged view showing a schematic cross section of the cryogenic refrigerator according to the first embodiment.

FIG. 3 is an enlarged perspective view of a rotary valve.

FIG. 4 is an enlarged view of a main part showing a high-pressure opening state of the rotary valve.

FIG. 5 is an enlarged view of a main part showing a low-pressure opening state of the rotary valve.

FIG. 6 is a relationship diagram showing a relationship between a cylinder thickness and a radius increase amount, and a relationship between a cylinder thickness and a penetrating heat amount.

FIG. 7 is an essential part enlarged view showing a schematic cross section of a cryogenic refrigerator according to a second embodiment.

FIG. 8 is an enlarged view of a main part showing a schematic cross section of a conventional cryogenic refrigerator.

[Explanation of symbols]

 (2a) 1st stage cylinder (2b) 2nd stage cylinder (22a) 1st displacer (22b) 2nd displacer (24) 1st stage regenerator (27) 2nd stage regenerator (30) 1st stage expansion chamber (31) Second-stage expansion chamber (50) Thin section

Claims (2)

[Claims] 1. A cylindrical cylinder (2a, 2b) and an expansion chamber (30, 31) defined inside the cylinder (2a, 2b), and reciprocating in the cylinder (2a, 2b). Displacers (22a, 22b) for supplying and exhausting working gas to and from the expansion chambers (30, 31), and a regenerator for exchanging heat with the cold storage material for the working gas supplied to and exhausted from the expansion chambers (30, 31). (24, 27), wherein the working gas supplied to the expansion chamber (30, 31) is expanded to generate cryogenic cooling at a cryogenic level. The cylinder (2a, 2b) A cryogenic temperature having a predetermined uniform thickness such that the amount of deformation due to the pressure of the working gas is equal to or less than a predetermined value, and having a predetermined length such that the amount of heat penetrated by heat conduction in the longitudinal direction is equal to or less than the predetermined value. refrigerator. 2. A cylindrical cylinder (2a, 2b) and an expansion chamber (30, 31) defined inside the cylinder (2a, 2b), and reciprocating in the cylinder (2a, 2b). Displacers (22a, 22b) for supplying and exhausting working gas to and from the expansion chambers (30, 31), and a regenerator for exchanging heat with the cold storage material for the working gas supplied to and exhausted from the expansion chambers (30, 31). (24, 27), wherein the cryogenic refrigerator generates a cryogenic level of cold by expansion of the working gas supplied to the expansion chamber (30, 31), wherein the cylinder (2a, 2b) Is a cryogenic refrigerator in which a plurality of thin portions (50) having a predetermined width and a small thickness over the entire circumference are formed intermittently in the longitudinal direction.