TWI460386B - Very low temperature freezer - Google Patents

Description

Extremely low temperature freezer

The present application claims priority from Japanese Patent Application No. 2011-059876, filed on March 17, 2011. The entire contents of the application are incorporated herein by reference.

The present invention relates to a cryogenic refrigerator, and more particularly to a cryogenic refrigerator for cooling a superconducting electromagnet.

A GM (Gifford McMahon) refrigerator having a Scotch yoke that converts a rotational motion of a motor into a linear reciprocating motion has been known (for example, refer to Patent Document 1).

The GM refrigerator is mainly composed of a compressor, a regenerator, an expander, and a switching valve. The refrigerant gas compressed by the compressor is supplied to the expander via a switching valve and a regenerator, and then the expander is used to expand the refrigerant cooled by the regenerator. Gas, thereby achieving extremely low temperatures.

The expander is mainly composed of a cylinder and a displacer that reciprocates in its cylinder, and the displacer reciprocates in the cylinder via a scotch yoke.

The scotch yoke is composed of a flat plate portion having two shafts projecting vertically, and a crank pin bearing rotatably disposed in a rounded rectangular window portion formed in the flat plate portion. Further, the crank pin bearing is configured to slidably support the crank pin eccentrically attached to the output shaft of the motor in the circumferential direction.

(previous technical literature) (Patent Literature)

Patent Document 1: Japanese Patent Laid-Open No. Hei 6-300378

However, crank pin bearings are usually formed of iron having excellent hardness. When a GM refrigerator including a crank pin bearing formed of such a ferromagnetic iron is used for cooling a superconducting electromagnet for generating a strong magnetic field, it is subjected to the configuration of the GM refrigerator. The external force of the superconducting magnet, so there is a fear of eccentric bending of the crank pin bearing.

In view of the above problems, it is an object of the present invention to provide a cryogenic refrigerator suitable for cooling a superconducting electromagnet.

In order to achieve the above object, an extremely low temperature freezer of an embodiment of the present invention is for cooling a superconducting electromagnet, characterized by having a crank pin bearing which is a crank pin bearing in a scotch yoke having a cylindrical inner wall And being formed of a cylindrical non-magnetic resin material, and slidably supporting a crank pin eccentrically mounted to the motor output shaft and an outer wall of the cylinder in a circumferential direction, which is attached to the window portion of the scotch yoke The inner wall is in contact.

According to the above means, the present invention can provide a cryogenic refrigerator suitable for cooling a superconducting electromagnet.

Fig. 1 is a cross-sectional view showing a configuration example of an extremely low temperature refrigerator according to an embodiment of the present invention. The cryogenic refrigerator 1, for example, a GM refrigerator, mainly includes a compressor 2 and a refrigerator 3.

The compressor 2 sucks the refrigerant gas (helium gas) from the low pressure side 2A, raises the pressure of the refrigerant gas, and discharges it to the high pressure side 2B and supplies it to the refrigerator 3.

The refrigerator 3 is composed of a casing 4, a cylinder 5, a motor 6, a crank member 7, a scotch yoke 8, a rotary valve 9, a displacer 10, a first cooling stage 11, and a second cooling stage 12.

The casing 4 has a refrigerant gas introduction port 13 connected to the high pressure side 2B of the compressor 2, and a refrigerant gas outlet port 14 connected to the low pressure side 2A of the compressor 2.

As shown in the figure, the cylinder 5 accommodates the two-stage displacer 10 in a reciprocating manner in the up-down direction, and a seal member is disposed on the sliding portion thereof.

The motor 6, for example, an electric motor, has an output shaft 24 coupled to the crank member 7.

Here, the crank member 7, the scotch yoke 8, and the rotary valve 9 in the casing 4 will be described in detail with reference to FIGS. 2 and 3. In addition, FIG. 2 is an exploded perspective view of the crank member 7, the scotch yoke 8, and the rotary valve 9 in the casing 4, and FIG. 3 is an exploded perspective view of the rotary valve 9.

The crank member 7 is coupled to the output shaft 24 of the motor 6 by a key connection, and has a crank pin 25 that is eccentrically disposed from the output shaft 24 of the motor 6 and extends in parallel with the output shaft 24.

The scotch yoke 8 has a horizontally long flat portion 26, an upper shaft 27U, a lower shaft 27D, and a crank pin bearing 28, and the lower shaft 27D is fixed to the upper portion of the displacer 10, and the horizontally long flat portion 26 forms a circular rectangular window portion. A cylindrical crank pin bearing 28 is rotatably disposed on the inner side thereof.

Further, the scotch yoke 8 slidably receives the crank pin 25 on the inner wall of the crank pin bearing 28.

Further, the scotch yoke 8 is configured such that the rotation of the upper shaft 27U and the lower shaft 27D is restricted by the rotation preventing pin (not shown), and the sliding bearings 35U and 35D are respectively used as one of the sealing materials (refer to FIG. 1). ) to support the upper shaft 27U and the lower shaft 27D, and to reciprocate in the up and down direction.

So implemented, the scotch yoke 8 converts the rotational motion of the crank member 7 into the up and down reciprocating motion of the displacer 10.

Further, the crank pin bearing 28 is preferably formed of a non-magnetic resin material.

The rotary valve 9 has a valve plate 29, a valve main body 30, a compression spring 31, and a fixing pin 32, and accommodates a crank pin 25 in a crank pin engagement hole 33 formed in the valve plate 29.

The valve plate 29 has a low pressure side surface 29A on the crank member 7 side and a high pressure side surface 29B facing the valve body 30 on the opposite side of the low pressure side surface 29A.

Further, the valve plate 29 has an arc-shaped through hole 29C that communicates with the axial direction of the low pressure side surface 29A and the high pressure side surface 29B, and a radial long groove 29D formed on the surface of the high pressure side surface 29B.

The valve body 30 has a first side face 30A that closely contacts the high pressure side face 29B, and a second side face 30B that receives the refrigerant gas from the high pressure side 2B of the compressor 2 on the opposite side of the first side face 30A.

Further, the valve body 30 has a center through hole 30C that communicates with the first side face 30A and the second side face 30B, an arcuate groove 30D formed in the first side face 30A, and communicates with the arcuate groove 30D in the valve body 30. A rectangular hole 30E for communicating the outer peripheral surface opening and a fixing hole 30F for inserting the fixing pin 32.

Further, the communication rectangular hole 30E communicates with the first space 17 of the displacer 10 via the gas flow path 36 of the casing 4 (refer to FIG. 1).

Fig. 4 is a view of the contact surface (the high pressure side surface 29B and the first side surface 30A) of the valve plate 29 and the valve main body 30 as seen from the valve main body 30 side.

As shown in Fig. 4, the arc-shaped through hole 29C has a shape in which it is located at a radius from the center of the valve plate 29 to a radius equal to the distance between the center through hole 30C and the cylindrical groove 30D. The circular hole is expanded in a shape of a predetermined circumferential angular amount on the circumference of the same radius.

The radially elongated groove 29D having an elliptical shape in the valve plate 29 has a length from the center of the valve plate 29 to a length equal to the distance between the center through hole 30C and the arcuate groove 30D.

Further, the arc-shaped groove 30D located in the valve body 30 has the same shape as the arc-shaped through hole 29C, and has a position from the center of the valve body 30 to the center through hole 30C and the arcuate groove. The circular hole at the position of the radius of the distance between 30D is extended by a predetermined circumferential angular amount on the circumference of the same radius.

In this manner, the valve plate 29 has its central axis aligned with the central axis of the valve body 30, and the high pressure side surface 29B is slidably rotated while being in contact with the first side surface 30A, so that the center through hole 30C and the radial long groove 29D are always Connected state.

Further, when the radial long groove 29D is in communication with the arcuate groove 30D, the valve plate 29 is in a state in which the intake valve is "open" and the exhaust valve is "closed", and the arcuate through hole 29C is When the arcuate groove 30D is in communication, the intake valve is "closed" and the exhaust valve is "open".

Further, the valve plate 29 is supported by the bearing 37 (refer to Fig. 1) so as to be rotatable and unable to move in the axial direction. Further, the valve main body 30 is fixed by the fixing pin 32 so as not to be rotatable relative to the casing 4 and to slide relative to the valve plate 29.

The compression spring 31 is a member for preventing the deviation of the valve body 30 and presses the valve body 30 against the valve plate 29.

Here, the constitution of the refrigerator 3 in the cryogenic refrigerator 1 will be further described with reference to FIG. 1 again.

The displacer 10 is provided with the first regenerator 15 and the second regenerator 16 , and forms a first space 17 (room space), a second space 18 (first expansion space), and a third space with the cylinder 5 . In the 19th (second expansion space), the first communication hole 20, the second communication hole 21, the third communication hole 22, and the fourth communication hole 23 can communicate with each other through three spaces.

When the displacer 10 ascends, the volume of the first space 17 decreases, and conversely, the volume of the second space 18 and the third space 19 increases.

The first cooling stage 11 and the second cooling stage 12 are constituted by flanges extending outward from the cylinder 5, and are arranged to be capable of transmitting cold heat generated in the cylinder 5 to the object to be cooled.

Here, the normal cooling mode operation of the cryogenic refrigerator 1 will be described.

The high pressure helium gas discharged from the high pressure side 2B of the compressor 2 is introduced into the casing 4 through the refrigerant gas introduction port 13. At this time, the high pressure helium gas presses the valve body 30 against the valve plate 29 together with the compression spring 31.

Most of the helium gas is transmitted from the center through hole 30C of the valve body 30 to the radially long groove 29D of the valve plate 29.

The valve plate 29 is rotated counterclockwise as shown in FIG. 3 by the rotation of the motor 6, and the radial long groove 29D and the arcuate groove 30D are connected to supply the refrigerant gas to the first space 17. This state is the state in which the aforementioned intake valve is "on". The scotch yoke 8 and the displacer 10 start to rise simultaneously with the state in which the intake valve is "opened".

As the intake valve "opens" and the displacer 10 rises, the helium gas reaches the first space through the center through hole 30C, the radial long groove 29D, the arcuate groove 30D, the communication rectangular hole 30E, and the gas flow path 36. 17. The first cool storage material 15 is cooled and reaches the second space 18, and is cooled by the second cool storage material 16 and reaches the third space 19.

When the displacer 10 reaches the top dead center, the valve plate 29 releases the connection between the radial long groove 29D and the arcuate groove 30D, and connects the arcuate through hole 29C to the arcuate groove 30D.

As a result, the valve plate 29 blocks the flow of the high-pressure helium gas from the compressor 2 toward the cylinder 5, and builds the state in which the exhaust valve is "open", and simultaneously causes the second space 18 and the lowering of the displacer 10 The high pressure helium gas in the third space 19 expands.

The expanded helium gas cools the first regenerator material 15 and the second regenerator material 16 and passes through the gas flow path 36, the communication rectangular hole 30E, the arcuate groove 30D, and the arcuate through hole 29C, and passes through The vicinity of the scotch yoke 8 and the crank member 7 is then returned from the refrigerant gas outlet 14 to the low pressure side 2A of the compressor 2.

The cryogenic refrigerator 1 cools the first cooling stage 11 and the second cooling stage 12 by repeating such cooling mode operation.

Next, the crank pin bearing 28 in the scotch yoke 8 will be described in detail with reference to FIG. In addition, Fig. 5 is a detailed view of the crank pin bearing 28, Fig. 5(A) is an enlarged view of a region surrounded by a broken circle in Fig. 1, and Fig. 5(B) is a fifth diagram (A) Cross section of the VB-VB line. Further, the VA-VA line cross-sectional view of Fig. 5(B) corresponds to Fig. 5(A).

The crank pin bearing 28 is formed of a cylindrical non-magnetic resin material and has a cylindrical inner wall that is in contact with the crank pin 25 and a circular rectangular window portion 34 formed in the flat plate portion 26. The outer wall of the cylinder that the inner wall contacts.

Further, the scotch yoke 8 is provided such that the contact frictional force between the cylindrical inner wall of the crank pin bearing 28 and the crank pin 25 is smaller than the contact friction between the cylindrical outer wall of the crank pin bearing 28 and the flat plate portion 26. The way the person is formed.

This is to enable the crank pin bearing 28 to slidably support the crank pin 25 on the inner wall of the cylinder, and to rotate on the inner wall of the window portion 34.

Therefore, the crank pin bearing 28 is integrally formed of, for example, a fluororesin material or the like which is hard and has excellent slidability.

Further, the crank pin bearing 28 formed of a non-magnetic resin material has an effect of preventing the crank pin 25 and the flat plate portion 26 formed of the non-magnetic stainless steel from being burnt.

Further, the crank pin bearing 28 is an outer peripheral surface of the crank pin 25 and the crank pin bearing 28 which is moved (revolved) along a circular orbit TR (refer to FIG. 5(B)) centered on the output shaft 24 of the motor 6. The inner wall of the cylinder slides.

Further, the crank pin bearing 28 is such that its outer cylindrical wall is frictionally contacted with the inner wall of the window portion 34 formed by the flat plate portion 26, and is rotated in the direction of the arrow AR (rotation) while being in the appearance side in the window portion. 34 moves (rotates) in the left direction toward the drawing.

In this manner, the crank pin bearing 28 rotates non-sliding on the inner wall of the window portion 34 while rotating the crank pin 25 on the crank pin 25, thereby rotating while rotating along the circular track TR. The appearance reciprocates in the window portion 34 in the left-right direction of the drawing.

According to the above configuration, the cryogenic refrigerator 1 having the crank pin bearing 28 can reciprocate the displacer 10 up and down by the scotch yoke 8 which is not affected by the strong magnetic field generated by the superconducting electromagnet. Cool the superconducting magnet.

Next, a crank pin bearing 28a as another embodiment of the crank pin bearing in the scotch yoke 8 will be described with reference to Fig. 6. 6 is a detailed view of the crank pin bearing 28a, and FIGS. 6(A) and 6(B) are views corresponding to FIGS. 5(A) and 5(B), respectively.

The crank pin bearing 28a is formed of two members, a cylindrical inner wall portion 28a1 and a cylindrical outer wall portion 28a2, which are each formed of a different non-magnetic resin material, which is different from the crank pin bearing 28. Further, the cylindrical inner wall portion 28a1 and the cylindrical outer wall portion 28a2 are combined by a known technique so as not to be relatively rotatable.

Further, the non-magnetic resin material forming the cylindrical inner wall portion 28a1 is selected to have a higher slidability than the non-magnetic resin material forming the cylindrical outer wall portion 28a2.

This is to allow the crank pin bearing 28a to slidably support the crank pin 25 on the cylindrical inner wall portion 28a1 while being rotatable on the inner wall of the window portion 34.

For example, in the crank pin bearing 28a, the cylindrical inner wall portion 28a1 is formed of a high-hardness resin material (for example, PTFE, PPS, or the like) having a high slidability such as a fluororesin material, and the cylindrical outer wall portion 28a2 is made of hardness. A low-hardness resin material (for example, polyethylene, polypropylene, polyamide, etc.) is formed.

Thereby, the crank pin bearing 28a can reduce the manufacturing cost as compared with the case where the crank pin bearing 28 is integrally formed of a fluororesin material.

In this case, the respective amounts of the high-hardness resin material and the low-hardness resin material, that is, the thickness of each of the cylindrical inner wall portion 28a1 and the cylindrical outer wall portion 28a2 are appropriately determined in consideration of the functional surface and the cost surface.

Further, the crank pin bearing 28a may be formed substantially of a high-hardness resin material, and the surface of the outer wall of the cylinder may be coated with a low-hardness resin material. This is to further improve the characteristics of the crank pin bearing 28a, that is, the crank pin bearing 28a is rotatably supported on the inner wall of the window portion 34 while slidably supporting the crank pin 25 on the inner wall of the cylinder.

Conversely, the crank pin bearing 28a may also be formed substantially of a low-hardness resin material, and the surface of the inner wall of the cylinder may be coated with a high-hardness resin material. This is because the above-described characteristics of the crank pin bearing 28a can be maintained while reducing the amount of use of the high-priced high-hardness resin material to reduce the manufacturing cost.

Fig. 7 is a view showing the relationship between the width W1 of the cylindrical inner wall portion 28a1 of the crank pin bearing 28a and the width W2 of the cylindrical outer wall portion 28a2, and Figs. 7(A) to 7(C) are respectively A diagram corresponding to Fig. 5(A).

Further, Fig. 7(A) shows a case where the width W1 is equal to the width W2, Fig. 7(B) shows a case where the width W2 is expanded to the width W21, and Fig. 7(C) shows a case where the width W1 is reduced to the width W11. .

As shown in FIG. 7(B), when the width W2 of the cylindrical outer wall portion 28a2 is increased to the width W21, the rotation of the crank pin bearing 28a in the window portion 34 is stabilized.

Further, as shown in Fig. 7(C), when the width W1 of the cylindrical inner wall portion 28a1 is reduced to the width W11, there is an effect of lowering the amount of use of the expensive high-hardness resin material.

In this manner, the crank pin bearing 28a is configured such that the width W1 of the cylindrical inner wall portion 28a1 and the width W2 of the cylindrical outer wall portion 28a2 can be set by the two members, and the desired effect including the above effects can be obtained. The width W1 and the width W2 can be selected more flexibly.

Further, the width W1 of the cylindrical inner wall portion 28a1 and the width W2 of the cylindrical outer wall portion 28a2 may each be larger than the width W3 of the flat plate portion 26, or may be smaller than the width W3 of the flat plate portion 26. Further, the width W1 of the cylindrical inner wall portion 28a1 may be larger than the width W2 of the cylindrical outer wall portion 28a2.

According to the above configuration, the cryogenic refrigerator 1 having the crank pin bearing 28a can reciprocate the displacer 10 up and down by the scotch yoke 8 which is not affected by the strong magnetic field generated by the superconducting electromagnet, and can be appropriately Cool the superconducting magnet.

Further, the crank pin bearing 28a uses a high-hardness resin material for the cylindrical inner wall portion 28a1 which is relatively easy to wear, and a low-hardness resin material for the cylindrical outer wall portion 28a2 which is hard to wear, thereby maintaining the same The required wear resistance can reduce the manufacturing cost as compared with the case of using a high hardness resin material as a whole.

Next, a crank pin bearing 28b as another embodiment of the crank pin bearing in the scotch yoke 8 will be described with reference to FIG. In addition, Fig. 8 is a detailed view of the crank pin bearing 28b, and Figs. 8(A) to 8(C) are views corresponding to Fig. 5(A), respectively.

Specifically, Fig. 8(A) shows a state in which the axis of the crank pin 25 is orthogonal to the axis of the scotch yoke 8 (the axes of the upper shaft 27U and the lower shaft 27D).

Further, Fig. 8(B) shows a state in which the axis of the crank pin 25 is inclined by an angle α with respect to the horizontal line and not orthogonal to the axis of the scotch yoke 8, and Fig. 8(C) shows the axis of the scotch yoke 8 with respect to the vertical line. A state in which an angle β is inclined without being orthogonal to the axis of the crank pin 25.

The crank pin bearing 28b is different from the crank pin bearings 28, 28a in that the outline 28b1 of the cylindrical outer wall is convex when viewed from a direction perpendicular to the axial direction thereof (when the drawing is viewed from the front).

Further, for clarification, the outline 28b1 is indicated by a thick solid line, specifically, an arc forming a part of a circle having a predetermined radius.

Even in the case where the axis of the crank pin 25 is not orthogonal to the axis of the scotch yoke 8, the shape of the profile 28b1 has the effect of not exerting excessive force on the crank pin bearing 28b when the scotch yoke 8 is actuated.

For example, even in the case shown in each of Figs. 8(B) and 8(C), the crank pin bearing 28b can also be on the inner wall of the window portion 34 by making the contour 28b1 convex. The center in the width direction is in contact with the inner wall thereof, and the rounded up and down reciprocating motion of the scotch yoke 8 can be continuously performed without excessive force.

The term "excessive force" as used herein includes, for example, when the shape of the contour 28b1 such as the crank pin bearings 28, 28a is linear, the crank pin bearing 28b is opposed to the window portion 34 due to the surface of the outer wall of the cylinder. The inner wall surface is inclined and in contact with one side, and thus withstands excessive force from the window portion 34.

Further, the "excessive force" includes, for example, when the shape of the contour 28b1 is linear, the crank pin bearing 28b is inclined with respect to the outer surface of the crank pin 25 due to the surface of the inner wall of the cylinder, and is thus subjected to contact. Excessive force from the crank pin 25.

Further, in Fig. 8, although the width W4 of the crank pin bearing 28b is larger than the width W3 of the flat plate portion 26, the width W4 may be equal to the width W3 or may be smaller than the width W3.

According to the above configuration, the cryogenic refrigerator 1 including the crank pin bearing 28b can appropriately reciprocate the displacer 10 by reciprocating the displacer 10 by the scotch yoke 8 which is not affected by the strong magnetic field generated by the superconducting magnet. Superconducting magnet.

Further, the crank pin bearing 28b can continuously perform the smooth up and down reciprocating motion of the scotch yoke 8 without excessive force, and can suppress or eliminate the abnormal sound caused by the excessive force.

Further, the crank pin bearing 28b is set to be formed of a non-magnetic resin material similarly to the crank pin bearings 28 and 28a, and the cryogenic refrigerator 1 including the crank pin bearing 28b is used for cooling of the superconducting electromagnet. However, the feature of the profile 28b1 of the crank pin bearing 28b can also be advantageously applied to the use of the cryogenic refrigerator 1 provided with the crank pin bearing 28b for applications other than the cooling of the superconducting magnet. In this case, the crank pin bearing 28b may also be formed of a magnetic material.

Next, the crank pin bearings 28c to 28e which are still another embodiment of the crank pin bearing in the scotch yoke 8 will be described with reference to Fig. 9. Further, Fig. 9 is a cross-sectional view of each of the crank pin bearings 28b to 28e.

Fig. 9(A) is a cross-sectional view showing the crank pin bearing 28b illustrated in Fig. 8 as a comparison object.

As described above, the outline 28b1 of the crank pin bearing 28b is represented by an arc which constitutes a part of a circle having a predetermined radius.

The contour 28b1 is such a range that the cylindrical outer wall of the crank pin bearing 28b can always be in contact with the center in the width direction of the inner wall of the window portion 34, and the inclination radius can be increased as the radius of curvature becomes smaller. Further, the inclination angle means an inclination angle of the axis of the crank pin 25 with respect to the horizontal line or an inclination angle of the axis of the Scottish yoke 8 with respect to the vertical line.

Fig. 9(B) is a cross-sectional view showing the crank pin bearing 28c, and the outline 28c1 of the crank pin bearing 28c includes a straight portion at its center, and includes curved portions on both sides thereof.

The contour 28c1 is more than the contour 28b1 of Fig. 9(A). When the axis of the crank pin 25 is orthogonal to the axis of the scotch yoke 8, the cylindrical outer wall and the flat plate of the crank pin bearing 28c can be more enlarged by the straight portion thereof. The contact area between the portions 26 can further stabilize the rotation of the crank pin bearing 28c.

Further, even if the axis of the crank pin 25 is not orthogonal to the axis of the scotch yoke 8, the contour 28c1 can make the scotch yoke 8 sleek up and down without excessive force by the curved portion of the crank pin bearing 28c. The reciprocating motion continues.

Further, the contact between the flat plate portion 26 and the crank pin bearing 28c in this case can be made closer to the edge of the inner wall of the window portion 34 than the contour 28b1 of Fig. 9(A).

Fig. 9(C) is a cross-sectional view showing the crank pin bearing 28d mainly composed of a main body portion 28d1 having a convex wheel portion having the same contour as the contour 28b1 of Fig. 9(A). Made of non-magnetic resin material. Further, the non-magnetic resin material is preferably a low-hardness resin material.

Further, the cylindrical inner wall of the main body portion 28d1 is coated with other non-magnetic resin material. Further, the coating layer 28d2 coated with the other non-magnetic resin material is preferably formed of a high-hardness resin material such as a fluororesin material.

Fig. 9(D) is a cross-sectional view showing the crank pin bearing 28e which is composed of a cylindrical outer wall portion 28e1 and a cylindrical inner wall portion 28e2 which is composed of the ninth outer wall portion 28e1. The outline 28b1 of Fig. (A) is made of a non-magnetic resin material having the same convex profile; the cylindrical inner wall portion 28e2 is made of a non-magnetic resin material different from the cylindrical outer wall portion 28e1.

Further, the cylindrical outer wall portion 28e1 is preferably made of a low-hardness resin material, and the cylindrical inner wall portion 28e2 is preferably made of a high-hardness resin material such as a fluororesin material.

With the above configuration, the crank pin bearings 28d, 28e can achieve the effect produced by the crank pin bearing 28b (the effect produced by the contour shape including the curve), and can also achieve the effect produced by the crank pin bearing 28a. (Based on the effect produced by using two kinds of resin materials separately).

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the invention.

For example, in the above-described embodiment, the crank pin bearings 28a, 28d, and 28e are formed of two kinds of resins, but they may be formed of three or more kinds of resin materials.

In this case, the crank pin bearings 28a, 28d, and 28e may be made of a low-hardness resin material in a portion not in contact with other members, and different high-hardness resin materials may be used in two portions in contact with other members.

Further, the crank pin bearings 28a, 28d, and 28e may each have the same high-hardness resin material in two portions that are in contact with other members.

Further, the cryogenic refrigerator of the embodiment of the present invention is particularly preferable for MRI use since it does not generate magnetic noise.

1. . . Extremely low temperature freezer

2. . . compressor

2A. . . Low pressure side of compressor 2

2B. . . High pressure side of compressor 2

3. . . freezer

4. . . case

5. . . Cylinder

6. . . motor

7. . . Crank member

8. . . Scotch yoke

9. . . Rotary valve

10. . . Displacer

11. . . 1st cooling station

12. . . 2nd cooling station

13. . . Refrigerant gas inlet

14. . . Refrigerant gas outlet

15. . . First cold storage material

16. . . Second cold storage material

17. . . First space

18. . . Second space

19. . . Third space

20. . . First communication hole

twenty one. . . Second communication hole

twenty two. . . Third communication hole

twenty three. . . 4th communication hole

twenty four. . . Motor output shaft

25. . . Crank pin

26. . . Flat section

27U. . . Upper axis

27D. . . Lower axis

28, 28a ~ 28e. . . Crank pin bearing

28a1. . . Cylinder inner wall portion of crank pin bearing 28a

28a2. . . Cylinder outer wall portion of crank pin bearing 28a

28b1. . . Outline of the outer wall of the cylinder of the crank pin bearing 28b

28c1. . . Outline of the outer wall of the cylinder of the crank pin bearing 28c

28d1. . . Main body of crank pin bearing 28d

28d2. . . Coating

28e1. . . Cylinder outer wall portion of crank pin bearing 28e

28e2. . . Cylinder inner wall portion of crank pin bearing 28e

29. . . Valve plate

29A. . . Low pressure side of valve plate 29

29B. . . High pressure side of valve plate 29

29C. . . Arc-shaped through hole of valve plate 29

29D. . . Radial long groove of valve plate 29

30. . . Valve body

30A. . . The first side of the valve body 30

30B. . . The second side of the valve body 30

30C. . . Center through hole of valve body 30

30D. . . Arc-shaped groove of valve body 30

30E. . . Rectangular hole for communication of the valve body 30

30F. . . Fixing hole of valve body 30

31. . . compressed spring

32. . . Fixed pin

33. . . Crank pin snap hole

34. . . Window

35U, 35D. . . Sliding bearing

36. . . Gas flow path

37. . . Bearing

Fig. 1 is a cross-sectional view showing a configuration example of an extremely low temperature refrigerator according to an embodiment of the present invention.

Fig. 2 is an exploded perspective view of the crank member, the scotch yoke, and the rotary valve in the casing.

Fig. 3 is an exploded perspective view of the rotary valve.

Figure 4 is a diagram showing the relative relationship between the valve plate and the valve body.

Figure 5 is a detailed view of the crank pin bearing (1).

Figure 6 is a detailed view of the crank pin bearing (2).

Fig. 7 is a view showing the relationship between the width of the inner wall portion of the cylinder of the crank pin bearing and the width of the outer wall portion of the cylinder.

Figure 8 is a detailed view of the crank pin bearing (3).

Figure 9 is a detailed view of the crank pin bearing (4).

27U‧‧‧Upper axis

25‧‧‧ crank pin

28‧‧‧Crank pin bearing

26‧‧‧ Flat section

27D‧‧‧lower shaft

25‧‧‧ crank pin

28‧‧‧Crank pin bearing

26‧‧‧ Flat section

34‧‧‧ Window Department

TR‧‧‧ circular orbit

VA‧‧‧ centerline that cuts the scotch yoke in the lateral direction

VB‧‧‧ centerline that cuts the scotch yoke in the front direction

Rotation (rotation) direction of AR‧‧‧ crank pin bearing

Claims (6)

A cryogenic refrigerator for cooling a superconducting electromagnet, characterized by comprising a crank pin bearing, which is a crank pin bearing in a scotch yoke, having: an inner wall of a cylinder, which is non-magnetic by a cylindrical shape The resin material is formed to slidably support the crank pin eccentrically mounted to the motor output shaft and the outer wall of the cylinder in a circumferential direction, which is in contact with the inner wall of the window portion in the scotch yoke. The cryogenic refrigerator according to claim 1, wherein the inner wall of the cylinder is formed of a different non-magnetic resin material different from the non-magnetic resin material forming the outer wall of the cylinder. The cryogenic refrigerator according to claim 2, wherein the hardness of the inner wall of the cylinder is higher than the hardness of the outer wall of the cylinder. The cryogenic refrigerator according to any one of claims 1 to 3, wherein the outer cylindrical outer wall of the crank pin bearing is convex when viewed from the side. The cryogenic refrigerator according to claim 4, wherein the outer wall of the cylinder when the crank pin bearing is viewed from the side is shown as an arc. The cryogenic refrigerator according to claim 4, wherein the outer contour of the cylindrical outer wall when the crank pin bearing is viewed from the side includes a straight portion.