JP2871156B2 - Cryogenic refrigerator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic refrigerator for obtaining cryogenic cooling.

[0002]

2. Description of the Related Art As one type of this cryogenic refrigerator, conventionally,
For example, as disclosed in Japanese Patent Application Laid-Open No. 62-281375, a GM refrigerator (Gifford McMahon refrigerator) or an improved Solvay cycle refrigerator is used as a precooled refrigerator.
A working temperature such as helium cooled to a predetermined cryogenic level by this pre-cooling refrigerator is expanded by Joule-Thomson by a JT valve so that a refrigerating capacity of 4.2K level can be obtained. JT refrigerators are known.

[0003]

The JT refrigerator has the following features.
A refrigeration capacity of several watts has been obtained, and it has been put into practical use as a highly reliable system. However, the pre-cooling refrigeration circuit and JT
Since it is a binary cycle of the circuit, there is a disadvantage that the structure is complicated and the manufacturing cost is high.

On the other hand, today, GM refrigerators usually have two
The temperature level, which is a stage, is reduced to three stages, and the regenerator at the lowest temperature stage is made of a rare earth magnetic material, so that a JT circuit is not used while using a GM refrigerator with a simple structure and low manufacturing cost. However, it has been proposed to enable operation at a temperature level of 4.2K. However, on the other hand, the refrigerating capacity of the proposed refrigerator at 4.2K level is 1 unit.
Very low below watts, with low overall efficiency.

[0005] The present invention has been made in view of the above points, and an object thereof is to improve the efficiency of the lowest temperature stage by improving the structure of the GM refrigerator. Therefore, it is to secure a large refrigeration capacity.

[0006]

In order to achieve this object, according to the present invention, the displacer of the lowest temperature stage in the GM refrigerator is a so-called free displacer which moves by a gas pressure difference, The process was regulated so that a dead volume was generated in the expansion space at the lowest temperature stage.

More specifically, in the present invention, as shown in FIG. 1, a plurality of cylinder portions (1a) to (1c) whose diameters gradually decrease toward the tip end are arranged in series. Cylinder (1) and each of the cylinder portions (1
a) to (1c) are inserted into the cylinder (1) reciprocally so as to be reciprocally movable, and a plurality of expansion spaces (12) to (14) are defined in the cylinder (1) by seal members (8) to (10) arranged on the outer periphery. Displacers (5) to (7), and expansion spaces (12) to (1) housed in the displacers (5) to (7) and on both sides of the displacers (5) to (7).
4) A regenerator (2) that exchanges heat with the working gas flowing between
1) to (23), and a displacer (5)
The working gas is adiabatically expanded in the expansion spaces (12) to (14) by the reciprocating movements of (7) to (7), so that the temperature corresponding to each expansion space (12) to (14) in the cylinder (1) is increased. In a cryogenic refrigerator configured to generate cryogenic temperatures of different levels, the displacer (7) in the lowest temperature stage is separated from other displacers (5) and (6). Expansion space (13) on both sides of displacer (7) at lowest temperature stage, (1)
The regenerator (23) in the displacer (7) of the lowest temperature stage has a regenerator material made of a rare earth magnetic material and is reciprocated by the pressure difference of 4). A regulating means (29) for regulating the stroke of the displacer (7) so as to generate a predetermined dead volume in the expansion space (14) on the low temperature side is provided.

In the invention according to claim 2, the regulating means (2
9) is constituted by a rod-shaped member integrally projecting from the end of the displacer (7) at the lowest temperature stage and capable of contacting the bottom wall of the cylinder (1).

[0009]

According to the above construction, in the first aspect of the present invention, the displacer (7) at the lowest temperature stage is a free displacer that reciprocates due to the pressure difference between the expansion spaces (13) and (14) on both sides. The circulation amount of the working gas flowing in the free displacer (7) can be minimized, and the efficiency of the regenerator at the lowest temperature stage can be increased. Further, the stroke of the free displacer (7) is regulated by the regulating means (29), and a predetermined dead volume is generated in the expansion space (14) at the lowest temperature stage. Even when compression and expansion occur in the two-phase region, the liquefied working gas having a large specific heat does not flow out to the regenerator (23) in the free displacer (7), and the efficiency of the regenerator is reduced. The decrease can be suppressed. Therefore, a large refrigerating capacity of the refrigerator can be secured by a synergistic effect of these.

In the invention according to claim 2, the regulating means (29)
Is a rod-shaped member integrally protruding from the end of the displacer (7) at the lowest temperature stage and capable of abutting against the bottom wall of the cylinder (1), so that the regulating means (29) can be easily constructed with a simple structure. Thus, the cryogenic refrigerator can be realized at low cost.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a GM refrigerator (R) according to an embodiment of the present invention.
This refrigerator (R) comprises a compressor (C) for compressing helium gas (working gas) and a gas pipe (P).
And functions as an expander for expanding the helium gas compressed by the compressor (C).

The refrigerator (R) has a cylinder (1), and the cylinder (1) has three cylinder portions (first to third stages) whose diameters gradually decrease toward the front end. 1
a) to (1c) are connected in series in an airtight manner. At the lower end of the large-diameter first-stage cylinder portion (1a), for example, 55
A first heat station (2) maintained at a temperature level of ６０60 K, and a lower end of the middle diameter second-stage cylinder portion (1b), for example, 10-20 K lower than the first heat station (2). A second heat station (3) maintained at a temperature level is provided at the lower end of the third cylinder portion (1c) having a smaller diameter.
Third heat stations (4) are formed, each maintained at a lower temperature level of approximately 4K.

In the cylinder (1), first to third stages are provided.
The three displacers (5) to (7) (replacers) of the stage are reciprocally fitted. That is, the first-stage cylinder portion (1a) has a first-stage displacer (5), and the second-stage cylinder portion (1b) has a second-stage displacer (6) having a smaller diameter than the first-stage displacer (5). )But,
Further, a third-stage displacer (7) smaller in diameter than the second-stage displacer (6) is fitted into the third-stage cylinder portion (1c), and the first-stage displacer (5) has a lower end at the second-stage displacer. The displacers (5) and (6) are joined to the upper end of (6) and are integrally formed. Each of the above displacers (5)-
At predetermined positions on the outer periphery of (7), seal rings (8) to (10) that are in sliding contact with the inner peripheral surface of the cylinder (1) are attached. The seal rings (8) to (10) and the displacer (5) are provided. (7), the space (11) located above the first stage displacer (5) in the cylinder (1), and the heat stations (2) to (4).
And three expansion spaces (12) to (14) of the first to third stages located at positions corresponding to
1) is connected to the compressor (C).

Each of the displacers (5) to (7) is a bottomed cylinder having a hollow inside.
The outer periphery of the upper end of the first stage displacer (5) has a communication hole (1) communicating the space inside the displacer (5) with the space (11).
5), and a communication hole (16) for communicating the inside of the displacer (5) with the first-stage expansion space (12) is formed on the outer periphery of the lower end. A communication hole (17) communicating with the first-stage expansion space (12) in the displacer (6) is provided on the outer periphery of the upper end of the second-stage displacer (6), and the inside of the displacer (6) is provided on the outer periphery of the lower end. A communication hole (18) communicating with the two-stage expansion space (13) is formed. Further, a second-stage expansion space (1) is formed inside the displacer (7) around the upper end of the third-stage displacer (7).
A communication hole (19) communicating with 3) and a communication hole (20) communicating with the third-stage expansion space (14) at the lower end of the cylinder (1) in the displacer (7) are formed on the outer periphery of the lower end. I have. That is, the space (11) and the expansion space (1
Each of 2) to (14) is a displacer (5) to (7)
They are communicated with each other so that gas can flow through the internal space.

Heat is transferred between the displacers (5) to (7) and the helium gas flowing between the expansion spaces (12) to (14) on both sides of the displacers (5) to (7). Regenerators (21) to (23) are accommodated. Each of the regenerators (21) to (23) is specifically formed by laminating a regenerator material composed of a mesh in multiple stages or filling a regenerator material composed of a large number of spheres. The gap serves as a gas flow path. And the first
The regenerator material in the stage and second stage displacers (5) and (6) is made of copper or the like, and the regenerator material in the third stage displacer (7) is made of a rare earth magnetic material.

Further, a gas pipe (P) between the space (11) at the upper end of the cylinder (1) and the compressor (C) is a high-pressure gas pipe (PH) connected to the discharge side of the compressor (C). And a low-pressure gas pipe (PL) connected to the suction side. The high-pressure gas pipe (PH) has a high-pressure valve (24) composed of an on-off valve, and the low-pressure gas pipe (PL) has a similar low-pressure valve. (25) are respectively disposed, and both valves (24) and (25) are displacers (5) to
The opening and closing of the valve (2) is controlled in synchronization with a motor (28) to be described later that reciprocates the valve (7) at a predetermined timing.
By switching between opening and closing of (4) and (25), the high-pressure helium gas discharged from the compressor (C) is supplied to the expansion spaces (12) to (14) in the cylinder (1) or the expansion space (1).
The low-pressure helium gas expanded in 2) to (14) is discharged from the cylinder (1) and returned to the compressor (C).

The displacers (5) to (7)
The upper end of the motor (28) is connected to the output shaft of a motor (28) via a Scotch yoke mechanism (27) having a rod (26) penetrating the upper wall of the cylinder (1) in an airtight manner. The first and second stage displacers (5) and (6) are reciprocated by changing the rotational motion into linear motion by the scotch yoke mechanism (27), and the reciprocating motion of the displacers (5) and (6) causes the expansion space ( 12) to (1)
By adiabatically expanding the helium gas in 4), the heat stations (2) to (4) corresponding to the expansion spaces (12) to (14) in the cylinder (1) have cryogenic levels having different temperature levels. I try to generate cold.

The third-stage displacer (7), which is the lowest temperature stage, is separated from the other first-stage and second-stage displacers (5) and (6), and the third-stage displacer (7) is separated. ) 2nd and 3rd stage expansion spaces (1
The free displacer is configured to reciprocate with a pressure difference of 3) and (14).

As shown in detail in FIG. 2, a rod-shaped stopper (29) having a predetermined length extending in the center line direction is provided at the lower end of the third stage (lowest temperature stage) displacer (7). This stopper (2
The third stage expansion space (14) is provided with a stopper (29) whose tip is in contact with the bottom wall of the cylinder (1) and which is located on the low temperature side of the third stage displacer (7).
A restricting means for restricting the stroke of the displacer (7) so that a predetermined dead volume occurs.

Next, in the above embodiment, the movement of each of the displacers (5) to (7) and the third stage expansion space (1)
The effect of the temperature decrease in 4) will be described. FIG. 3 shows the displacer (5) in one cycle of the refrigerator (R).
7 shows the movement of (7). FIG. 4 shows the first stage expansion space (12).
FIG. 5 is a PV diagram of the helium gas in the second-stage expansion space (13), and FIG.
Shows PV diagrams of the helium gas in the third-stage expansion space (14), respectively. The numbers in FIGS. 4 to 6 indicate the steps of one cycle of the displacers (5) to (7) described below.

(Step) In this step, as shown in FIG. 3 (a), the first and second stage displacers (5) and (6) driven by the motor (28) are on the low temperature side (the lower side in the figure). Side). On the other hand, the third stage displacer (7) is on the high temperature side (upper side in the figure), and in this state, the high pressure valve (2)
4) opens.

(Stroke) As shown in FIG. 3B, with the opening of the high-pressure valve (24), normal-temperature high-pressure helium gas discharged from the compressor (C) is displaced at each stage. It enters the expansion spaces (12) to (14) while being cooled by the regenerators (21) to (23) in (7). In this state, the first and second stage displacers (5), (6)
Is still stopped, but the third-stage displacer (7) comprises second-stage and third-stage expansion spaces (13), (14).
The gas in the third-stage expansion space (14) is pushed downward by the pressure difference in the figure to descend while adiabatically compressing the gas in the third-stage expansion space (14).

(Stroke) As shown in FIG. 3 (c), the high-pressure gas continues to flow in by opening the high-pressure valve (24), and the lower end of the stopper (29) hits the bottom wall of the cylinder (1). In contact therewith, the movement of the third stage displacer (7) is further restricted and a dead space is formed in the third stage expansion space (14), and the pressure inside the cylinder (1) becomes high due to the subsequent pressure rise. Further, the first and second stage displacers (5) and (6) start rising to the normal temperature side (upward in the figure).

(Stroke) As shown in FIG. 3D, the first-stage and second-stage displacers (5) and (6) move to the rising end positions and are stopped and held. Third-stage expansion space (1
The pressure in 4) is at a maximum.

(Stroke) As shown in FIG.
The stage and second stage displacers (5), (6) are stopped and held at the raised end position. Displacer for each stage (5)
With (7) stopped at each of the above positions, the high pressure valve (24) is closed, and instead the low pressure valve (25)
Opens.

(Stroke) As shown in FIG. 3 (f), the first-stage and second-stage displacers (5) and (6) are stopped, but with the opening of the low-pressure valve (25), the space (11) is opened. )
Communicates with the suction side of the compressor (C), and the gas in the cylinder (1) flows out. For this reason, the third-stage displacer (7) is accelerated to the high-temperature side (upward) by the instantaneous pressure difference on both sides, and the gas in the low-temperature dead volume of the third-stage expansion space (14) expands adiabatically, Its temperature drops.

(Stroke) As shown in FIG. 3 (g), the first and second stage displacers (5) and (6) start descending to the low temperature side (downward in the figure). Also, the low pressure valve (25) is opened, and the helium gas in the cylinder (1) continuously flows out, and the third stage displacer (7)
Continues to rise until its upper end abuts on the lower end of the second stage displacer (6), stops rising after that abutment,
It is depressed by the first and second stage displacers (5), (6). At this time, the helium gas in the third-stage expansion space (14) passes through the regenerator (23) inside the third-stage displacer (7) due to the stop of the upward movement of the third displacer (7). (13).

(Stroke) As shown in FIG.
The stage and the second stage displacers (5) and (6) are stopped and held at the lower end position, and the third stage displacer (7) is moved to the third stage displacer (6) with its upper end in contact with the lower end of the second stage displacer (6). It is stopped and held at the upper end of the cylinder part (1c).
At this time, the whole inside of the cylinder (1) is in a low pressure condition.
Then, after this step, the process returns to the above-described step, and thereafter, the steps 1 to 5 are repeated in the same manner as described above.

Therefore, in this embodiment, the third stage displacer (7), which is the lowest temperature stage, is a free displacer that reciprocates due to the pressure difference between the expansion spaces (13) and (14) on both sides thereof. The amount of helium gas circulating in the third stage displacer (7) can be minimized, and the efficiency of the regenerator (23) can be increased. Moreover, the third stage displacer (7)
Is restricted by the stopper (29), and a predetermined dead volume is generated in the third-stage expansion space (14). Therefore, the compression and expansion of the helium gas in the two-phase region are performed in the expansion space (14) due to the pressure condition. Does not flow out into the regenerator (23) in the third-stage displacer (7), thereby suppressing a decrease in the efficiency of the regenerator (23). be able to. Due to these synergistic effects, a large refrigerating capacity of the refrigerator (R) can be secured.

In this embodiment, a rod-shaped stopper (29) protruding from the lower end of the third stage displacer (7) is used.
Since the movement of the displacer (7) is restricted, the means for restricting the movement can be easily obtained with a simple structure.

In the above embodiment, the regulating means for regulating the stroke of the third stage displacer (7) is the rod-shaped stopper (29) attached to the lower end thereof, but the inner periphery of the third cylinder portion (1c). It can also be constituted by a projection or the like attached to the.

In the above-described embodiment, the refrigerator has a three-stage cryogenic temperature level. However, the present invention can be applied to a refrigerator having two or four or more temperature levels.

Further, in the above embodiment, the mechanically driven GM
The present invention relates to a gas cycle driven GM cycle and an improved Solvay cycle GM cycle.
It can also be applied to refrigerators.

[0034]

As described above, according to the first aspect of the present invention, the displacer at the lowest temperature stage in the GM refrigerator is a free displacer that reciprocates due to a difference in working gas pressure, and the regenerator inside the displacer. The cold storage material is made of a rare earth magnetic material, and the reciprocating motion of the free displacer is regulated to create a dead volume in the expansion space of the lowest temperature stage, thereby minimizing the amount of working gas circulation and minimizing the lowest stage. The liquefied working gas generated in the expansion space is prevented from flowing into the regenerator, and the refrigeration capacity is suppressed by suppressing the decrease in the efficiency of the GM refrigerator. The GM refrigeration using only a rare earth magnetic material as a regenerator material. Therefore, it is possible to realize a GM refrigerator having a simple structure, a low manufacturing cost, and a large refrigeration capacity.

According to the second aspect of the present invention, since the regulating means for regulating the reciprocating movement of the free displacer is formed in a rod-like shape integrally projecting with the displacer, the regulating means can be obtained with a simple structure. A cryogenic refrigerator having the above effects can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a GM refrigerator.

FIG. 2 is an enlarged sectional view showing a structure of a cylinder and a displacer at a lowest temperature stage.

FIG. 3 is an explanatory diagram showing the movement of a displacer.

FIG. 4 is a PV diagram of a first-stage expansion space.

FIG. 5 is a PV diagram of a second-stage expansion space.

FIG. 6 is a PV diagram of a third-stage expansion space.

[Explanation of symbols]

 (R) Refrigerator (1) Cylinder (1a) to (1c) Cylinder (5) to (7) Displacer (8) to (10) Seal ring (seal member) (12) to (14) ) ... Expansion space (21)-(23) ... Regenerator (29) ... Stopper (Regulator)

Claims (2)

(57) [Claims] A cylinder (1) in which a plurality of cylinders (1a) to (1c) each having a diameter decreasing stepwise toward the tip end are arranged in series, and each of the cylinders (1a).
To (1c), each of which is reciprocally movable and which defines a plurality of expansion spaces (12) to (14) in the cylinder (1) by seal members (8) to (10) arranged on the outer periphery. The stage displacers (5) to (7) and the expansion spaces (12) to (1) housed in the displacers (5) to (7) and on both sides of the displacers (5) to (7).
4) A regenerator (2) that exchanges heat with the working gas flowing between
1) to (23), and a displacer (5)
The working gas is adiabatically expanded in the expansion spaces (12) to (14) by the reciprocating movements of (7) to (7), so that the temperature corresponding to each expansion space (12) to (14) in the cylinder (1) is increased. A cryogenic refrigerator configured to generate cryogenic cold at different levels, wherein the displacer (7) at the lowest temperature stage is separated from other displacers (5) and (6). , Expansion spaces (13), (1) on both sides of the displacer (7) at the lowest temperature stage.
The regenerator (23) in the displacer (7) at the lowest temperature stage has a regenerator material made of a rare earth magnetic material, and reciprocates with the pressure difference of (4). The displacer (7) is used to create a predetermined dead volume in the expansion space (14) on the low temperature side.
A cryogenic refrigerator provided with a regulating means (29) for regulating the process of (1). 2. The regulating means (29) is formed as a rod-shaped member integrally projecting from an end of the displacer (7) at the lowest temperature stage and capable of abutting against the bottom wall of the cylinder (1). Item 7. The cryogenic refrigerator according to Item 1.