JP2563275Y2 - Small 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 small refrigerator having a piston bearing suitable for being applied to a small refrigerator having a linear motor driven piston.

[0002]

2. Description of the Related Art Stirling refrigerators, Vermier refrigerators, Gifford McMahon refrigerators and the like are known as small refrigerators capable of generating a low temperature of about 100 K or less. Hereinafter, the Stirling refrigerator will be described without having a restrictive meaning.

A Stirling refrigerating machine is a refrigerating machine using an inverted Stirling cycle. Theoretically, the thermal efficiency is as high as that of a Carnot cycle, and the efficiency is high.

FIG. 3A schematically shows a Stirling cycle. In the figure, the horizontal axis indicates the volume, and the vertical axis indicates the pressure.
The Stirling cycle includes four steps of isothermal compression indicated by a curve PQ, isostatic transfer indicated by a curve QR, isothermal expansion indicated by a curve RS, and isostatic transfer indicated by a curve SP. The refrigeration cycle is realized when these four steps are performed in the direction of the arrow, and the heating cycle is realized when the steps are performed in the opposite directions.

In order to perform a Stirling cycle as shown in FIG. 3A, a Stirling refrigerator includes a compressor, an expander and piping between them. In FIG. 3 (B),
1 schematically illustrates the operation of a Stirling refrigerator. In the drawing, the expander (cold head) is shown on the left side, the compressor is shown on the right side, and piping is shown between them. The compressor includes a compression cylinder, and the working gas compressed by the compression cylinder is transferred to a cold head via piping. A displacer is provided in the cold head, and the working gas can move through the displacer. A regenerator is filled in the displacer.

In the compressor, the compression stroke is performed in the first to third stages in FIG. 3B, and the expansion stroke is performed while returning to the first stage through the third to fourth stages. It is.

[0007] In the cold head, the displacer reciprocates about 90 ° out of phase with the compression cylinder. From the first stage to the second stage, mainly equal volume transfer is performed, and from the second stage to the third stage, isothermal compression is mainly performed. From the third stage to the fourth stage, the isosteric transfer is mainly performed, and when returning from the fourth stage to the first stage, the isothermal expansion is mainly performed.

By such a Stirling cycle,
Freezing occurs at the tip of the cold head, and the object to be cooled, such as an infrared detection device, is cooled in a place requiring maintenance free, such as an artificial satellite, a radiation hazard area, or the like.

FIG. 4 shows an example of the configuration of a conventional Stirling refrigerator. FIG. 4A schematically shows the entire configuration of the Stirling refrigerator. The compressor 51 and the cold head 52 are connected by a pipe 53 to form a separated type structure.

In the compressor 51, a piston 57 is inserted into a cylinder 56, and a compression space 60 is defined therebetween. Outside the cylinder 56, a magnetic gap 58
A reciprocating coil 59 of a linear motor coupled to a piston 57 is inserted into a magnetic gap 58. In the compressor 51, two compression pistons are arranged to face each other, and a compressed gas is commonly connected to the pipe 53 from the middle.

In the displacer 52, a displacer 62 is disposed in a cylinder 61, and a regenerator 63 such as a lead particle or a copper wire mesh is disposed in the displacer 62. An expansion space 65 is defined between the displacer 62 and the cylinder 61 to generate refrigeration. A cooling target 70 is arranged adjacent to the expansion space 65.

FIG. 4B is an enlarged view of a configuration example of the compressor. The piston 57 inserted into the cylinder 56
It is held in a neutral position in the axial direction by two coil springs 74 and 75. The two springs 74 and 75 also serve as current supply terminals for the coil 59 of the linear motor.

A magnetic circuit having a magnetic gap 58 outside the cylinder 56 is connected. A coil 59 of a reciprocating linear motor is arranged in the magnetic gap 58 and connected to the piston 57. Numeral 72 indicates a pipe for charging the working gas.

In such a compressor or cold head of a refrigerator, the space between the cylinder and the piston must be kept airtight. For this reason, for example, a fluororesin is adhered to the piston surface and used as an airtight seal and sliding material. There is a gap of about 10 μm between the piston and the cylinder, forming a clearance seal.

[0015]

When the same member is used for both the sealing member for maintaining airtightness and the sliding member for moving the piston in the cylinder, the sealing member is required after a long operation. In addition, the sliding material is worn. Then, the gap between the piston and the cylinder is widened, and the sealing performance is reduced. A decrease in sealing performance causes deterioration of the performance of the refrigerator.

Further, abrasion powder is generated by the abrasion and scatters in the refrigerator, thereby impeding the flow of the working gas and impeding the movement of the moving member. This result also appears as a decrease in the performance of the refrigerator. Thus, the life of the refrigerator is limited by the wear of the sealing material.

An object of the present invention is to provide a small refrigerator capable of reducing the contact between a piston and a cylinder.

[0018]

The small refrigerator of the present invention is:
A cylinder (14) defining a hollow space with an inner wall, a piston (13) inserted into the cylinder, a gap sensor (5) for detecting a size of a gap between the inner wall of the cylinder and the piston, Magnetic circuit (9, 12, 15) coupled to the cylinder and having a magnetic gap (8)
A position control coil (7) coupled to the piston and inserted into the magnetic gap; and a controller (6) for supplying a current controlled based on a detection output of the gap sensor to the position control coil. ) And the piston
And inserted into the magnetic gap, in the circumferential direction
And a reciprocating coil (19) for supplying a current to the coil .

[0019]

The position control coil connected to the piston is disposed in the magnetic gap, and the position of the piston in the radial direction can be controlled. By detecting the gap between the cylinder and the piston by the gap sensor and supplying a controlled current from the controller to the position control coil, it is possible to always maintain an appropriate gap between the cylinder and the piston. In this way, contact between the cylinder and the piston is reduced.

[0020]

FIG. 1 shows a Stirling refrigerator according to an embodiment of the present invention. 1A schematically shows the entire configuration, FIG. 1B shows an enlarged view of a linear motor and a position control function, and FIG. 1C shows an operation concept in a magnetic circuit. Shown schematically.

In FIG. 1A, a compressor 1 and a cold head 3 are connected by a pipe 2. Compressor 1
, The piston 13 is arranged in the cylinder 14. The gap between the piston 13 and the inner wall of the cylinder 14 is about 10 μm.

At least two gap sensors 5 are embedded in the inner peripheral surface of the cylinder 14, detect a gap between the inner wall of the cylinder 14 and the piston 13, and send a detection signal to the controller 6. The cylinder 14 is formed of a magnetic material and is continuous with the base 12 which also serves as a magnetic yoke.

A permanent magnet 15 is connected to the base 12,
The other end of the permanent magnet 15 is connected to the pole piece 9. The pole piece 9 includes the cylinder 14 and the magnetic gap 8.
Face each other.

In the illustrated configuration, the permanent magnet 1
5 is magnetized in the axial direction, and the magnetic flux is bent in the pole piece 9 from the axial direction to the radial direction.
Generates a magnetic flux in the radial direction.

In the magnetic gap 8 a coil 19 of a linear motor connected to the piston 13 is arranged. The coil 19 is connected to an arm 20 extending from the piston 13.

Further, at least two position control coils 7 are arranged inside the linear motor coil 19,
It receives a drive signal from the controller 6. Preferably, four position control coils 7 are symmetrically arranged.

The rear end of the piston 13 is connected to two coil springs 18,23. These two coil springs 18 and 23 serve to hold the piston 13 at the neutral position and to supply current to the linear motor coil 19. In addition to these coils, a conducting wire (not shown) is arranged to supply current to the position control coil 7.

The other ends of the coil springs 18 and 23 are connected to the compressor 1
Is fixed to the inner case 16. The outer case 11 is arranged so as to cover the inner case 16. A current supply lead for the coil springs 18 and 23 is provided through these two cases.

Although only the right side of the compressor 1 is shown in FIG. 1, a symmetrical structure is arranged on the left side. These left and right parts constitute an opposed compressor.

In the cold head 3, the cylinder 3
Displacer 34 is arranged in 7, and displacer 34 includes a regenerator 36 such as a copper wire mesh, a lead ball or the like therein.
An expansion space 35 is defined between the cylinder 37 and the displacer 34.

The rear end of the displacer 34 is connected to the housing 31 by a coil spring 38. In addition,
A seal member 33 is provided to maintain airtightness between the displacer 34 and the cylinder 37.

When the compressor 1 and the cold head 3 having such a configuration operate with a phase shift of about 90 °, refrigeration occurs in the expansion space 35 of the cold head. By this freezing, the cooling target 40 is cooled.

FIG. 1B is an enlarged view of the pole piece 9, the linear motor coil 19, and the position control coil 7. As shown in FIG. The pole piece 9 defines a cylindrical space, and accommodates the linear motor coil 19 and the position control coil 7 therein.

A magnetic flux is generated from the pole piece 9 in the radial direction. The linear motor coil 19 is wound in the circumferential direction. The position control coil 7 has a saddle shape and can generate a magnetic flux in the radial direction.

FIG. 1C shows a linear motor coil 19.
FIG. 4 is a conceptual diagram showing what kind of force acts on the position control coil 7. A magnetic flux B1 in the radial direction is generated from the pole piece 9. The linear motor coil 19 is arranged in the magnetic flux B1, and a current flows in the circumferential direction.
Since the electric charge moves almost at right angles to the magnetic flux, Lorentz force is generated, and the linear motor coil 19 receives an axial force.

On the other hand, in the position control coil 7, a coil is formed so as to surround a part of the circumferential surface, and generates a magnetic flux B2a or B2b in the radial direction. If the direction of the magnetic flux B2 is opposite to the direction of the magnetic flux B1 generated from the pole piece 9, a repulsive force is generated, and if the direction is the same, an attractive force is generated. These forces are generated in the same direction as the magnetic flux B1, that is, in the radial direction.

When a current is applied to the linear motor coil 19, an axial force is generated to drive the piston 13 in the axial direction. When a current flows through the position control coil 7, a magnetic flux B2 is generated in the radial direction, and the piston 13 is driven in the radial direction. Since the radial force and the axial force are arranged at substantially right angles, mutual interference is small. For example, the magnetic flux density B1 generated from the pole piece is about 5000 gauss, and the magnetic flux density generated by the position control coil 7 is negligible compared to B1.

In order to fix the position of the piston 13 in the radial direction, it is necessary to perform control in at least two axial directions, and it is necessary to use at least two position control coils. If three or more position control coils 7 are used, the position of the piston 13 can be controlled only by repulsion without using attraction. If four position control coils are used, it is possible to control the position of the piston 13 by repulsion using only orthogonal components.

FIG. 2 is a diagram for explaining the control of the radial position of the piston. FIG. 2A shows a schematic cross-sectional view in the radial direction of the compressor. A piston 13 is arranged at the center, and a cylinder 14 is arranged around the piston 13.

The gap sensor 5x in the x direction and the gap sensor 5y in the y direction are located on the inner peripheral surface of the cylinder 14 at positions orthogonal to each other.
Is embedded. The pole piece 9 is disposed outside the cylinder 14 via a magnetic gap.

Inside the magnetic gap, a linear motor coil 19 having windings wound in the circumferential direction on the outside, and four saddle-shaped position control coils 7xa, 7xy,
7ya and 7yb are arranged. Coils 7xa and 7x
b faces in the x direction, and the coils 7ya and 7yb face in the y direction.

FIG. 2B shows the electrical connection between the gap sensor 5 and the position control coil 7. The gap sensors 5x and 5y detect the gap between the cylinder 14 and the piston 13 in the x direction and the y direction.

An electric signal representing the detected gap is sent to the controller 6 to generate a position correcting electric signal.
These electric signals for position control include the position control coils 7x,
7y. Although only the position control coils 7xa and 7xb in the x direction are shown in FIG.
ya, 7yb are also arranged.

An electric signal corresponding to the gap in the x direction detected by the gap sensor 5x is supplied to one of the position control coils 7xa and 7xb for the x direction to correct the position of the piston 13 in the x direction.

Similarly, a control current based on the electric signal detected by the gap sensor 5i is sent to one of the y-direction position control coils 7ya and 7yb, and the piston 1
3 is corrected in the y direction.

With such a configuration, the radial position of the piston 13 is constantly monitored by the gap sensor, and the radial position of the piston 13 is corrected by the force generated by the position control coil 7. By always arranging the piston 13 near the center of the cylindrical space defined by the inner wall of the cylinder 14, collision between the piston and the cylinder is avoided.

A strong disturbance from the outside such as an impact cannot be completely opposed only by the force generated by the position control coil, but a contact between the piston and the cylinder due to the fluctuation of the position of the piston 13 cannot be prevented. In addition, the force generated by the position control coil exerts a sufficient force, and the collision is greatly reduced. For this reason, the durability of the refrigerator can be significantly improved.

Although a case has been described in which a magnetic circuit is formed using permanent magnets magnetized in the axial direction, a similar structure can be realized using permanent magnets magnetized in the radial direction. Instead of permanent magnets, it is also possible to use electromagnets.

Although the configuration in which four position control coils are arranged is shown, it is obvious to those skilled in the art that the in-plane position of the cylinder can be controlled by using three or more position control coils. Would. The number of gap sensors is not limited to two, and three or more gap sensors can be used.

The same configuration is effective for controlling the position of the piston reciprocating in the cylinder in the radial direction, and can be used not only for the compressor but also for the cold head. Although the present invention has been described with reference to the embodiments, the present invention is not limited to these embodiments. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0051]

Advantages of the Invention Since the collision between the piston and the cylinder is reduced, the life of the small refrigerator can be greatly improved.

[Brief description of the drawings]

FIG. 1 shows a Stirling refrigerator according to an embodiment of the present invention. 1A is a sectional view, FIG. 1B is a partially cutaway perspective view, and FIG. 1C is a conceptual view.

FIG. 2 is a view for explaining control of a radial position of a piston in the compressor of FIG. 1; 2A is a sectional view in the radial direction, and FIG. 2B is a circuit block diagram.

FIG. 3 is a diagram for explaining a Stirling cycle. FIG. 3A is a graph showing a relationship between pressure and volume in a Stirling cycle, and FIG. 3B is a conceptual diagram showing a relative relationship between an expander and a compressor in a Stirling refrigerator.

FIG. 4 shows a configuration example of a Stirling refrigerator according to a conventional technique. FIG. 4A is a cross-sectional view schematically showing the entire structure.
(B) is an enlarged sectional view showing a part of the compressor.

[Description of Signs] 1 Compressor 2 Piping 3 Expander (cold head) 5 Gap sensor 6 Controller 7 Position control coil 8 Magnetic gap 9 Pole piece 12 Base (yoke) 13 Piston 14 Cylinder 15 Permanent magnet 19 Linear motor coil

Claims (2)

(57) [Scope of request for utility model registration] 1. A cylinder (14) defining a hollow space with an inner wall, a piston (13) inserted into the cylinder, and a gap sensor for detecting a size of a gap between the inner wall of the cylinder and the piston. (5) a magnetic circuit (9, 12, 15) coupled to the cylinder and having a magnetic gap (8); and a position control coil (7) coupled to the piston and inserted into the magnetic gap. And a controller (6) for supplying a current controlled based on a detection output of the gap sensor to the position control coil.
When coupled to the piston, it is inserted into the magnetic gap
And a reciprocating coil (19) for flowing current in a circumferential direction . 2. The magnetic circuit includes a permanent magnet (15) for generating magnetic flux in the magnetic gap in a radial direction with respect to a drive shaft of a piston, wherein the position control coil controls at least two independently in the radial direction. The small refrigerator according to claim 1, which can generate a magnetic flux that can be generated.