Displacer devices and refrigerators

Abstract

The present invention provides a displacer device and refrigerator that, when adding a magnetic refrigeration function to achieve high-efficiency refrigerator performance, ensure a constant amplitude reciprocating motion by the displacer, thereby enabling the refrigerator to exhibit the high-efficiency refrigeration capacity as designed. [Solution] A magnetic refrigerant 15 is placed on the low-temperature end side of the displacer 11, and a magnetic circuit 40 that changes the magnetic state of the magnetic refrigerant 15 is provided outside the storage container 50 corresponding to the magnetic refrigerant 15. The magnetic circuit 40 increases and decreases the magnetization of the magnetic refrigerant 15 depending on the position of the displacer 11. A magnetic material 115 with a shape that allows working fluid to pass through is placed on the high-temperature end side of the displacer 11, and another magnetic circuit 140 that changes the magnetic state of the magnetic material 115 is provided outside the storage container 50 corresponding to the magnetic material 115. The electromagnetic force F1 acting on the magnetic refrigerant 15 and the electromagnetic force F2 acting on the magnetic material 115 are in different directions.

Description

[[Technical Field]]

[0001] The present invention relates to a displacer device and a refrigerator capable of ensuring reciprocating motion with a constant amplitude by the displacer and exhibiting high refrigeration efficiency as designed when a magnetic refrigeration function is added to achieve high-efficiency refrigerator performance. [[Background Art]]

[0002] Generally, as refrigerators, Stirling refrigerators including an expander that generates cryogenic-level cold by reciprocating motion of a displacer and a compressor that generates oscillating flow are well known. This Stirling refrigerator is configured such that the displacer operating in the cylinder of the expander and the piston operating in the cylinder of the compressor reciprocate within their respective cylinders.

[0003] On the other hand, Patent Document 1 describes a cooling device (3) which is a magnetic refrigeration device. That is, an active magnetic heat recovery device (18) is provided between the cold storage means (17) and the outlet of the storage conduit (14). The active magnetic heat recovery device (18) includes a superconducting magnet (19) disposed outside the cooling device (3) for generating a magnetic field inside the cooling device (3), and a magnetic material (20) disposed inside the cooling device (3), the magnetic material preferably has the shape of a piston, and the piston is slidably supported inside the cooling device (3) parallel to the longitudinal direction of the cooling device. [[Prior Art Literature]] [[Patent Literature]]

[0004] [[Patent Document 1]] Japanese Patent Application Laid-Open No. 62-182557 [[Non-Patent Literature]]

[0005] [[Non-Patent Document 1]] Akiko Saito et al., Magnetic Refrigeration Materials for Hydrogen Liquefaction by Active Anti-Rotating Recharge (AMRR), Cryogenic Engineering 58 (2023), pp. 51-57. [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, Patent Document 1 describes a cooling device (3) which is a magnetic refrigeration device. For pre-cooling of this cooling device (3), a GM refrigerator is used because it has a valve (4) at the high-pressure inlet (5) and a valve (6) at the low-pressure outlet (7), and it is cooled to 77K. When it is then cooled to 20K by an active magnetic heat recovery device (18), the entire cooling device (magnetic refrigeration device) (3) is in a temperature range from 77K to 20K. The gas inside the device (usually helium gas) is also at a similar temperature.

[0007] As a result, in the cooling device (3) of Patent Document 1, the volume of gas at low temperature becomes considerably large, and all of it becomes a load on the pre-cooling GM chiller, which degrades the performance of the GM chiller.

[0008] Furthermore, the discharge piston (11) and the push-pull rod (21) need to be driven back and forth by an external drive mechanism, requiring a separate power source.

[0009] Furthermore, power is required to excite the superconducting magnets. In other words, the performance of the base GM refrigerator is reduced, and the cooling device (3), which is a magnetic refrigerator, also requires additional power or electricity, so the total efficiency of the refrigerator cannot necessarily be high.

[0010] Therefore, despite its large configuration, the cooling system described in Patent Document 1 cannot be expected to be highly efficient in terms of overall refrigeration performance.

[0011] Therefore, in order to realize a compact and highly efficient refrigerator, it is conceivable to add a magnetic refrigeration function to a Stirling refrigerator. However, the static magnetic field generated to demagnetize and magnetize the magnetic refrigeration material generates an electromagnetic force on the magnetic refrigeration material. Since this electromagnetic force acts only in one direction, the direction of the reciprocating motion of the displacer, it hinders the constant amplitude reciprocating motion of the displacer, and the refrigerator will not be able to perform as designed.

[0012] The present invention has been made in view of the above, and aims to provide a displacer device and a refrigerator that can achieve high-efficiency refrigerator performance as designed by ensuring a constant amplitude reciprocating motion by the displacer when adding a magnetic refrigeration function. [Means for solving the problem]

[0013] To solve the above-mentioned problems and achieve the objective, the displacer device according to the present invention is a displacer device in which a displacer having a cold storage material inside is arranged, and the displacer reciprocates within a storage container to expand the working fluid compressed within the storage container and generate cold, wherein a magnetic refrigeration material is arranged on the low-temperature end side of the displacer, a magnetic circuit is provided outside the storage container corresponding to the magnetic refrigeration material to change the magnetic state of the magnetic refrigeration material, the magnetic circuit increases and decreases the magnetization of the magnetic refrigeration material depending on the position of the displacer, a magnetic material with a shape through which the working fluid can pass is arranged on the high-temperature end side of the displacer, another magnetic circuit is provided outside the storage container corresponding to the magnetic material to change the magnetic state of the magnetic material, and the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material are in different directions.

[0014] Furthermore, the present invention is characterized in that, in the above invention, a spring is provided that provides a restoring force to the axial reciprocating motion of the displacer, and the restoring force is assisted by the difference between the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material.

[0015] Furthermore, in the above invention, the present invention is characterized in that the difference between the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material serves as a restoring force for the axial reciprocating movement of the displacer.

[0016] Furthermore, in the above invention, the present invention is characterized in that a plurality of said magnetic refrigeration materials are arranged with a cold storage material interposed therebetween from the low temperature end side of said displacer.

[0017] Furthermore, in the above invention, the present invention is characterized in that a plurality of said magnetic materials are arranged with a cold storage material interposed therebetween on the high temperature end side of said displacer.

[0018] Furthermore, in the above invention, the present invention is characterized in that said magnetic material is a magnetic refrigeration material.

[0019] Furthermore, in the above invention, the present invention is characterized in that a plurality of different magnetic refrigeration materials are arranged on said displacer from the low temperature end side.

[0020] Furthermore, in the above invention, the present invention is characterized by comprising a drive device that controls the position of said displacer, and adjusting the position of said displacer.

[0021] Furthermore, in the above invention, the present invention is characterized in that said magnetic circuit and said other magnetic circuit each generate a magnetic field having directivity with respect to the magnetization regions of said magnetic refrigeration material and said magnetic material, respectively.

[0022] Furthermore, in the above invention, the present invention is characterized in that said magnetic refrigeration material is arranged with the end face on the low temperature end side of said magnetic circuit as a neutral position, is demagnetized when said magnetic refrigeration material moves from said neutral position to the low temperature end side, and is magnetized when it moves from said neutral position to the high temperature end side.

[0023] Furthermore, the refrigerator according to the present invention comprises: a compressor that generates pressure amplitude in a working fluid by reciprocating motion of a compression piston; and a displacer device, wherein in a storage container connected to the compressor and forming a working fluid space filled with the working fluid having the pressure amplitude generated by the compressor, a displacer that reciprocates with a phase difference relative to the reciprocating motion of the compression piston and has a regenerator material therein is disposed, and the displacer device has a mechanism for supporting the displacer in the storage container, wherein a magnetic refrigeration material is disposed on a low-temperature end side of the displacer, a magnetic circuit that changes a magnetic state of the magnetic refrigeration material is provided outside the storage container corresponding to the magnetic refrigeration material, the magnetic circuit magnetizes and demagnetizes the magnetic refrigeration material depending on a position of the displacer, a magnetic material shaped to allow the working fluid to pass through is disposed on a high-temperature end side of the displacer, another magnetic circuit that changes a magnetic state of the magnetic material is provided outside the storage container corresponding to the magnetic material, and directions of an electromagnetic force acting on the magnetic refrigeration material and an electromagnetic force acting on the magnetic material are different from each other.

[0024] Furthermore, in the above invention, the present invention is characterized by comprising a spring that applies a restoring force to the reciprocating motion of the displacer in an axial direction, and assists the restoring force by a difference between the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material.

[0025] Furthermore, in the above invention, the present invention is characterized in that the difference between the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material serves as a restoring force for the reciprocating motion of the displacer in the axial direction.

[0026] Furthermore, in the above invention, the present invention is characterized in that a plurality of the magnetic refrigeration materials are arranged with a regenerator material interposed therebetween from the low-temperature end side of the displacer.

[0027] Furthermore, in the above invention, the present invention is characterized in that a plurality of the magnetic materials are arranged with a regenerator material interposed therebetween on the high-temperature end side of the displacer.

[0028] Furthermore, the present invention is characterized in that, in the above invention, the magnetic material is a magnetic refrigeration material.

[0029] Furthermore, the present invention is characterized in that, in the above invention, the magnetic refrigeration material is arranged in a plurality of different magnetic refrigeration materials from the low-temperature end side of the displacer.

[0030] Furthermore, the present invention is characterized by comprising a drive device for controlling the position of the displacer, and adjusting the position of the displacer.

[0031] Furthermore, the present invention is characterized in that, in the above invention, the magnetic circuit and the other magnetic circuit each generate a magnetic field that is directional with respect to the magnetization region of the magnetic refrigerant and the magnetic material, respectively.

[0032] Furthermore, the present invention is characterized in that, in the above invention, the magnetic refrigeration material is positioned with the low-temperature end face of the magnetic circuit as the neutral position, and is demagnetized when the magnetic refrigeration material moves from the neutral position to the low-temperature end, and is magnetized when it moves from the neutral position to the high-temperature end. [Effects of the Invention]

[0033] According to the present invention, when adding a magnetic refrigeration function to achieve highly efficient refrigeration performance, a constant amplitude reciprocating motion by the displacer can be ensured, thereby enabling the refrigeration to exhibit the highly efficient refrigeration capacity as designed. [Brief explanation of the drawing]

[0034] [Figure 1] Figure 1 is a schematic diagram showing the overall configuration of a refrigerator that forms the basis of an embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view taken along line AA in Figure 1. [Figure 3] Figure 3 shows the time-series data of the compression piston position, the displacer position, and the low-temperature end flow rate. [Figure 4]Figure 4 shows the positional relationship between a magnetic circuit with permanent magnet pieces arranged in a Halbach array and a displacer. [Figure 5] Figure 5 shows an example of the magnitude of the magnetic field applied from the magnetic circuit in relation to the position of the displacer. [Figure 6] Figure 6 shows the material properties of the magnetic refrigeration material described in Non-Patent Document 1. [Figure 7] Figure 7 shows an example of a magnetic circuit. [Figure 8] Figure 8 shows the configuration of a magnetic circuit using a pair of permanent magnets. [Figure 9] Figure 9 is a schematic diagram showing the configuration of the refrigerator according to this embodiment. [Figure 10] Figure 10 shows the relationship between the electromagnetic force acting on the magnetic refrigeration material, the electromagnetic force acting on the magnetic material, and the electromagnetic force acting on the displacer as the displacer moves as shown in Figure 9. [Figure 11] Figure 11 is a schematic diagram showing the configuration of the displacer device 10c in a refrigerator, which forms the basis of Modification 1 of this embodiment. [Figure 12] Figure 12 shows a configuration in which multiple magnetic materials and multiple magnetic circuits are arranged in accordance with the embodiment, relative to the basic configuration of Modification 1. [Figure 13] Figure 13 shows a configuration in which one magnetic material 115d and one magnetic circuit 140d are arranged in accordance with the embodiment, relative to the basic configuration of Modification 1. [Figure 14] Figure 14 shows the configuration of a displacer device in a refrigerator, which is a modified example 2 of this embodiment. [Figure 15] Figure 15 is a schematic diagram showing the configuration of a displacer device, which is a modified example 3 of this embodiment. [Modes for carrying out the invention]

[0035] Hereinafter, embodiments for carrying out this invention will be described with reference to the attached drawings.

[0036] <Overall configuration of the basic refrigeration unit> Figure 1 is a schematic diagram showing the overall configuration of a refrigerator 100, which is the basis of an embodiment of the present invention. The refrigerator 100 is a Stirling refrigerator that has a displacer device 10, which is an expansion device, a compressor 20, and piping 30 connecting them, and has a working fluid G inside that is filled at a constant pressure, and incorporates a magnetic refrigeration material, making it a combined refrigerator that has both a Stirling refrigeration function (gas refrigeration function) and a magnetic refrigeration function with high refrigeration performance. Furthermore, the refrigerator 100 is a refrigerator for producing liquefied hydrogen (20K). In Figure 1, the displacer device 10 and the compressor 20 are connected by piping 30, but an integrated configuration in which the displacer device 10 is directly attached to the connection part of piping 30 on the compressor 20 side is also possible.

[0037] The compressor 20 generates a pressure amplitude in the working fluid G through the reciprocating motion of compression pistons 23 and 24. Helium gas is typically used as the working fluid G. The compression pistons 23 and 24 are initially positioned in a neutral position, with one piston moving in the + direction and the other in the - direction, moving in the same phase in the X direction. In Figure 1, this movement is performed by movable magnet type linear motors 21 and 22. The compression pistons 23 and 24 are positioned opposite each other to absorb primary vibrations and reduce vibration. The compression pistons 23 and 24 operate at a high operating frequency, for example, several tens to several hundred Hz. This reciprocating motion of the compression pistons 23 and 24 repeatedly compresses and expands the working fluid G, and the pressure amplitude is transmitted to the displacer device 10 via the piping 30. Of course, the compressor 20 may also generate the pressure amplitude using a single piston.

[0038] The displacer device 10 has a storage container 50 that forms a working fluid space filled with working fluid G having a pressure amplitude generated by the compressor 20. The storage container 50 is configured by sequentially connecting a room temperature container 51, a first-stage container 16, and a second-stage container 17. The displacer device 10 has a displacer 11 placed inside the storage container 50. The displacer 11 has a first-stage regenerator 13 and a second-stage regenerator 14, both containing a regenerative material that exchanges heat with the working fluid G. The regenerative material for the first-stage regenerator 13 is usually a fine mesh such as stainless steel, and the regenerative material for the second-stage regenerator 14 is usually a lead ball or the like with a high specific heat at low temperatures. In addition, the displacer 11 has a magnetic refrigeration material 15 placed at the tip of the cold head (the low-temperature end of the second-stage regenerator 14) as part of the magnetic refrigerator described above.

[0039] The magnetic refrigeration material 15 is, for example, La(Fe X Si 1-X ) 13 Conventional materials exhibiting the magnetocaloric effect, such as HoB2, which undergo a ferromagnetic transition from paramagnetic to ferromagnetic upon application of a magnetic field, can be used. Furthermore, the magnetic refrigeration material 15 can also be a broad-sense antiferromagnetic material. Here, a broad-sense antiferromagnetic material is a material in which the spins within the material are not all aligned in a specific direction, but are in a magnetically ordered state. This includes not only narrow-sense antiferromagnetic materials where the absolute values ​​of adjacent spins are the same and the angle between them is 180°, but also ferrimagnetic materials where the absolute values ​​of adjacent spins are not the same, and antiferromagnetic materials with helical magnetism or parasitic ferromagnetism where the angles between them are other than 180°. For example, Ho is a typical helical magnet.

[0040] The magnetic refrigeration material 15 can be constructed as an aggregate of polycrystalline spherical grains. In this configuration, if a broad-sense diamagnetic material is used for the magnetic refrigeration material 15, the broad-sense diamagnetic material should be selected to have the smallest possible (virtually no) anisotropy in the metamagnetic transition field.

[0041] The displacer 11 reciprocates in the X direction according to the pressure amplitude of the working fluid G. The driving force of the displacer 11 is the pressure difference between the ambient temperature space E1 and the 77K space E21 and 20K space E22. Since the phase of this pressure difference is in phase with the flow rate, the displacer 11 operates with a phase difference that leads the movement of the compression pistons 23 and 24. In this case, the displacer 11 does not move by its own power but moves passively, and is therefore also called a free piston. The displacer 11 moves due to the pressure difference caused by the viscous resistance of the working fluid G, and the optimal value for the phase difference with respect to the compression pistons 23 and 24 is π / 4.

[0042] The ambient temperature container 51 is an ambient temperature container that connects the working fluid G to the compressor 20 via the piping 30, and also has a flexure bearing structure that supports the shaft 12 of the displacer 11. The flexure bearing 53 is a leaf spring that operates only in one axial direction and does not basically operate in the radial direction (YZ plane) perpendicular to the shaft 12, and also serves as a support member that reciprocates between the piston (displacer 11) and the cylinder (first stage container 16 and second stage container 17) with a constant gap.

[0043] The ambient temperature container 51 has an aftercooler 52 positioned between it and the first stage container 16, which dissipates heat to a water-cooling jacket or the like installed outside the ambient temperature container 51. In addition, a fixing part for attaching a flexure bearing 53 is located inside the ambient temperature container 51.

[0044] The interior of the displacer 11 consists of a first-stage regenerator 13 and a second-stage regenerator 14. The cylinder housing the displacer 11 also consists of a first-stage container 16 and a second-stage container 17. The low-temperature section of the first-stage container 16 has a first-stage cold head 18, and this stage is cooled to approximately 77K. The low-temperature section of the second-stage container 17 has a second-stage cold head 19, and is cooled to below 20K. As mentioned earlier, stainless steel mesh is used for the first-stage regenerator 13, and lead spheres are used for the second-stage regenerator 14. This is because the volumetric specific heat of helium gas increases at low temperatures, so a regenerator material with a high volumetric specific heat even at low temperatures is required. For this reason, methods such as using stainless steel mesh with a thinner wire diameter and higher mesh count for the second-stage regenerator 14, or using lead spheres, which have a high volumetric specific heat even at low temperatures, or passive magnetic materials such as Er3Ni or its composites are also used.

[0045] A small gap exists between the cylinder (first-stage container 16 and second-stage container 17) and the displacer 11, which forms a sealing function (a so-called clearance seal). This is achieved by the flexure bearing 53, which moves only in one axial direction as described earlier. This allows the refrigeration unit to maintain its performance for a long time and provides a highly reliable refrigeration unit. Of course, a sliding material to prevent wear may be applied between the cylinder and the displacer 11 to allow them to slide. As the sliding material, a Teflon®-based low-friction resistance material is commonly used, but there is also a method of depositing a DLC (Diamond-Like Carbon) film on both sealing surfaces. In this case, the amount of wear on the sealing surface can be reduced, contributing to a longer lifespan. In this case, the structure can be simplified by using a general coil spring instead of a flexure bearing.

[0046] A magnetic refrigerant 15 is placed on the low-temperature side of the second-stage regenerator 14. Figure 1 shows the state when the displacer 11 is in the neutral position. At this time, the magnetic circuit 40 is positioned outside the second-stage container 17 as shown in Figure 1. When the displacer 11 is in the neutral position, the magnetic circuit 40 applies a magnetic field of intermediate magnitude to the magnetic refrigerant 15. When the displacer 11 moves to the low-temperature end (left side of Figure 1), the magnetic field applied to the magnetic refrigerant 15 decreases, resulting in a demagnetized state and cooling. Conversely, when the displacer 11 moves to the high-temperature end (right side of Figure 1), the magnetic field increases, resulting in an increased magnetization state and heating. The explanation of how this heating and cooling due to the magnetocaloric effect matches the timing of heating and cooling by a gas-type refrigerator will be explained later.

[0047] Figure 2 is a cross-sectional view taken along line AA in Figure 1. As shown in Figures 2 and 1, it is preferable that the magnetic circuit 40 be configured to efficiently control the magnetic state of the magnetic refrigerant 15. In other words, the displacer 11 is configured such that the magnetic circuit 40 is magnetized and heated when the magnetic field it creates in the direction perpendicular to the operating direction X of the displacer 11 (YZ plane) is relatively large, and demagnetized and cooled when the magnetic field it creates is relatively small. As a result, the magnetization (heating) and demagnetization (cooling) of the magnetic refrigerant 15 are repeated in synchronization with the reciprocating motion of the displacer 11. For this reason, it is preferable that the axial width (X direction) of the magnetic refrigerant 15 be the same as, or approximately the same as, the stroke width of the displacer 11. This is because the magnetic refrigerant 15 can be effectively used over its entire range. Although the displacer 11 moves back and forth at high speed, the heating and cooling due to the magnetization and demagnetization of the magnetic refrigerant 15 are equivalent to the rate at which magnetic phase transitions occur within the magnetic refrigerant 15, so there is no time delay. However, there is a time delay in heat transfer from the magnetic refrigerant 15 to the gas. This will be explained later.

[0048] The magnetic circuit 40 is designed to form a highly directional spatial magnetic field so that the magnetic state of the magnetic refrigeration material 15 can be effectively controlled. Here, effective control of the magnetic state means providing a magnetic field change that allows for a sufficient magnetocaloric effect through a ferromagnetic transition from a paramagnetic material to a ferromagnetic material, or providing a magnetic field change that allows for a sufficient magnetocaloric effect through a metamagnetic transition from a broadly defined antiferromagnetic material to a ferromagnetic material. Generally, metamagnetic transitions are often sharper phase transitions than ferromagnetic transitions, and a large magnetocaloric effect can be obtained with a small change in the magnetic field.

[0049] However, the metamagnetic transition field of antiferromagnetic materials in the broad sense can exhibit anisotropy, and in some cases, applying a magnetic field to an unoriented magnetic refrigeration material 15 may result in an unclear metamagnetic transition. To prevent this, oriented single crystals are sometimes used, but from the standpoint of mass production, it is preferable to select a material with less anisotropy in the metamagnetic transition field.

[0050] Furthermore, when a material that causes a metamagnetic transition is used for the magnetic refrigeration material 15, it is sufficient for the magnetic field that the magnetic refrigeration material 15 receives due to the reciprocating motion of the displacer 11 to move back and forth between the static magnetic field created by the external magnetic circuit 40, and it is not necessarily required to create a state in which the magnetic refrigeration material 15 receives almost no magnetic field during the reciprocating motion of the displacer 11.

[0051] Furthermore, when the magnetic refrigeration material 15 is a material that causes a metamagnetic transition in the magnetic circuit 40, the magnetic field received by the displacer 11 when it is located at the point furthest from the magnetic circuit 40 during its reciprocating motion is less than the magnetic field that causes the metamagnetic transition, and the magnetic field received by the displacer 11 when it is located at the point closest to the magnetic circuit 40 during its reciprocating motion is greater than or equal to the magnetic field that causes the metamagnetic transition.

[0052] The first-stage container 16 and the second-stage container 17 are housed within a vacuum container 41. The magnetic circuit 40 is supported by a separate structure, for example, from the high-temperature side of the first-stage cold head 18 or the second-stage container 17. The magnetic circuit 40 may basically be at room temperature, but in this embodiment, since the part of the magnetic circuit 40 that faces the second-stage container 17 is at a low temperature of about 20K, it is desirable to cool the magnetic circuit 40 to a temperature similar to that of the first-stage container 16 by anchoring in order to reduce radiant heat transfer to the second-stage container 17. In addition, the first-stage container 16, the first-stage cold head 18, the second-stage container 17, and the second-stage cold head 19 are all covered with multi-layer insulation to block heat from radiation.

[0053] When generating liquefied hydrogen (20K) with this refrigerator 100, heat exchangers (first-stage heat exchanger and second-stage heat exchanger) through which hydrogen gas can pass are installed around the outer circumference of the first-stage cold head 18 and the second-stage cold head 19, and the two heat exchangers are connected by low-temperature piping. First, hydrogen gas from room temperature is passed through the first-stage heat exchanger, where its sensible heat is removed and it is cooled to around 77K. This gas is then guided to the second-stage heat exchanger, where its sensible heat, latent heat, and the heat of conversion specific to hydrogen are removed, causing it to liquefy. The liquefied hydrogen is extracted separately, but the details are omitted here. Note that the temperature of the second-stage cold head 19 must be maintained at or below the temperature of liquefied hydrogen.

[0054] Furthermore, when used as a zero-boil-off (ZBO) system, which involves attaching the unit to the top of an insulated container filled with liquefied hydrogen (20K) to recondense evaporated hydrogen gas, the second-stage cold head 19 is simply attached to the top of the insulated container. Additionally, attaching a heat exchanger with a larger heat transfer surface area to the cold head section will increase efficiency.

[0055] <Refrigeration function of a Stirling refrigerator> Figure 3 shows time-series data of the compression piston position, displacer position, and low-temperature end flow rate, with the neutral position of the compression piston being the reference point (0 point). For clarity, the horizontal axis is shown as the angle (ωt) obtained by multiplying time t by the angular frequency ω. The unit is rad. Waveforms L1, L2, and L3 show the positions of compression pistons 23 and 24, displacer 11, and gas flow rate at the low-temperature end, respectively. First, the operating principle of the Stirling refrigerator will be explained using thermoacoustic theory. A Stirling refrigerator is basically a traveling-wave refrigerator, and there is a phase difference between the pressure and the gas position. There is also a phase difference between the compression piston and the displacer. In the case of a free-piston type displacer, the cooling output is theoretically maximum when the displacer position is π / 4 phase ahead of the compression piston position, and this is shown in Figure 3. The pressure in the system is almost entirely determined by the compression piston position. First, when the compression pistons 23 and 24 are at top dead center (the point where both pistons are closest) (between time points A and B in Figure 3), heating occurs due to compression. This means that acoustic power (compression work) has been converted into heat. The gas, whose temperature has risen, is moved towards the high-temperature end because the direction of flow is toward the high-temperature end, and transfers heat to the nearby wall (regenerator). Here, if ωτ (the product of angular frequency and thermal relaxation time, which is the factor governing heat transfer between the wall and the gas in an oscillating flow) is sufficiently less than 1, heat exchange occurs without time delay. Typically, the ωτ in a regenerator is configured to be sufficiently less than 1.

[0056] Then, in the next step, the compression piston moves towards the bottom dead center (the point where the two pistons are furthest apart) (between time points C and D in Figure 3), causing cooling due to gas expansion. This cooled gas is then carried to the low-temperature end. At the low-temperature end, heat is absorbed from outside the system and maintained at a constant temperature. This is the generation of cold. The gas then returns to its original position, and this vibration is repeated. By repeating this process, the first-stage regenerator 13 and the second-stage regenerator 14 sequentially exchange heat between the gas that has moved to the high-temperature end and the wall, and between the wall and the gas, and the heat of the gas whose temperature has risen is sequentially transferred to the high-temperature end. In terms of entropy, the gas is moving unilaterally from the low-temperature end to the high-temperature end within the first-stage regenerator 13 and the second-stage regenerator 14, and the entropy is increasing. That is, the second law of thermodynamics is satisfied. The acoustic power (work) entering from the high-temperature end is gradually converted into heat within the regenerator, and all of it is converted into heat in the second-stage cold head 19. Some parts are not converted, and these remain as enthalpy. This means that the first law of thermodynamics is satisfied at every cross-section within the displacer device 10. This is the cooling principle of the Stirling refrigerator from a thermoacoustic perspective.

[0057] The refrigeration capacity Qsc of a Stirling refrigerator can be calculated by solving the basic equation from the thermoacoustic perspective described above. For example, it can be calculated using software such as DeltaEC provided by Los Alamos National Laboratory in the United States. Alternatively, a simpler method can be used, which involves subtracting the heat loss Qsls from the refrigeration output Qpv at the low-temperature end. This method has been commonly used because it makes it easier to understand the physical meaning of the refrigeration capacity. In other words, the refrigeration capacity Qsc is expressed by the following equation (1). Qsc = Qpv - Qsls …(1)

[0058] Here, the refrigeration output Qpv can be calculated from the pressure change and volume change at the low-temperature end. That is, it can be obtained by solving the equations of motion for the compression piston and displacer, and is expressed as shown in equation (2) below. Qpv=πf·ΔPc·ΔV·sinφ …(2) Here, f is the operating frequency, ΔPc is the pressure amplitude at the low-temperature end, ΔV is the volume change at the low-temperature end (the displacer amplitude multiplied by the cross-sectional area), and φ is the phase difference between the pressure and the displacer position. Equation (2) can be obtained by solving the equations of motion for the compressor and the displacer.

[0059] On the other hand, the main components of heat loss Qsls are heat conducted from the displacer tube and cylinder tube, heat brought in from the high-temperature side because the regenerator and gas cannot completely exchange heat (entropy loss), and heat transferred to the cylinder as the displacer moves back and forth (shuttle loss).

[0060] The typical operating frequency of a Stirling refrigerator is high, around 10-100 Hz. Equation (2) shows that the refrigeration output Qpv is proportional to the operating frequency f. Therefore, in the design of the refrigerator, it is possible to increase the operating frequency f and decrease other parameters such as ΔPc and ΔV to reduce the size of the refrigerator. Other refrigerators, such as GM refrigerators, typically operate at around 1-2 Hz, so it is necessary to increase ΔPc and ΔV. One of the features of the Stirling refrigerator is that it can be made smaller in size compared to other refrigerators.

[0061] <Refrigeration function of magnetic refrigerators> Next, we will explain how the part incorporating the magnetic refrigeration material 15 operates as a magnetic refrigerator. As already mentioned, in magnetic refrigeration, heating occurs when the magnetization is increased, and heat is absorbed (cooled) when the magnetization is decreased. The problem lies in the time delay when this generated heat is transferred to the gas. If the change in magnetic entropy is ΔS, the amount of heat is Q, and the temperature is T, then the following equation (3) holds. T·ΔS=ΔQ …(3) Furthermore, under adiabatic conditions where the specific heat C is constant, the following equation (4) holds true. ΔQ = C·ΔT …(4) Then, by differentiating equation (4) with respect to time and rearranging the equation to take into account that it is an oscillatory flow (sine wave), we obtain the following equation (5). T = ΔS / C·T C· sin(ωt-π / 2) …(5) Here, TC ω is the low-temperature end temperature, ω is the angular frequency, and t is time. Equation (3) shows that the temperature change lags the phase of the magnetic entropy change by π / 2. This calculation assumes that the specific heat is constant regardless of temperature, but in reality it is temperature-dependent. Also, the inside of an actual refrigerator is not under adiabatic conditions, and during magnetization, the gas flows from the low-temperature end to the high-temperature end. For this reason, the phase of the temperature change and the magnetic entropy change may also change from π / 2. Since this is forced convection heat transfer due to the gas flow, the phase lag tends to decrease.

[0062] As shown in Figure 3, in the case of a Stirling refrigerator, as mentioned above, when the compression pistons 23 and 24 are at the top dead center, that is, between times A and B, the entire gas is compressed and heated. Conversely, when they are at the bottom dead center, that is, between times C and D, the entire gas is expanded and cooled. Note that the positions of the compression pistons 23 and 24 shown in Figure 1 are neutral at time t 0, and then move towards the top dead center. The position of the displacer 11 is π / 4 in phase with the compression pistons at time t 0. The displacer 11 then moves towards the cold end (+) to approach the coldest end, and then returns to the neutral position.

[0063] As shown in Figure 3, both Stirling refrigeration and magnetic refrigeration have heating and endothermic processes within a single cycle. In order to utilize the cooling functions of both Stirling and magnetic refrigeration, the heating and endothermic processes of one must be timed so that they do not overlap. If they overlap, the cooling functions will cancel each other out, and the high cooling performance that can be expected from the synergistic effect of Stirling and magnetic refrigeration will not be realized. First, in Stirling refrigeration, heating occurs through gas compression. In Figure 3, heating occurs between time points A and B. This heat is transferred to the regenerative material, and since the configuration is such that ωτ (the product of angular frequency and relaxation time, which, from a thermoacoustic perspective, determines the heat transfer between gas and material under oscillating flow) is sufficiently smaller than 1, heat transfer from the gas to the regenerative material occurs without time delay. Similarly, heat transfer from the regenerative material to the gas also occurs without time delay. It may seem surprising, but heat is transferred without delay even at high frequencies of several tens to several hundred Hz. Simply put, typical thermal storage materials use metal wires with a diameter of several tens of microns, and the amount of helium gas (heat capacity of the gas) surrounding them is small and exists within the thermal boundary layer, so heat is transferred between the two without time delay. The heating generated by the Stirling refrigeration function is carried to the high-temperature end side via the thermal storage material. This is done by the gas flow that flows towards the high-temperature end side between time points B and C. On the other hand, between time points C and D, the gas expands, resulting in endothermic (cooling). From time point D to near time point D', the gas flow flows towards the low-temperature end side, so the low-temperature gas moves to the low-temperature end and cooling proceeds.

[0064] Next, we will explain how the magnetic refrigeration function can generate cold without impairing the Stirling refrigeration function. In order for the magnetic refrigeration function to exert its refrigeration capacity, as mentioned earlier, magnetization is increased or decreased by considering the phase of temperature change and magnetic entropy change according to equation (5). In Figure 3, magnetization increases from time tz to time A', and as shown in equation (5), heating occurs from time A' to time B' with a phase delay of π / 2. However, between time C and time B', the endothermic effect of the Stirling refrigeration function and a portion of the heating effect of the magnetic refrigeration function overlap, and the endothermic effect of the Stirling refrigeration function during this period cancels out. Also, the magnetic refrigeration material is demagnetized from time B' to time C', and similarly, according to equation (5), the phase delay is π / 2, and heat is absorbed between time C' and time D'. However, between time E and time D', the heating effect of the Stirling function and a portion of the endothermic effect of the magnetic refrigeration function overlap, and the endothermic effect of the magnetic refrigeration function during this period cancels out. This prevents the magnetic refrigeration function and the Stirling refrigeration function from working synergistically, resulting in insufficient refrigeration performance.

[0065] Theoretically, this is as described above, but to verify this, a principle verification machine was constructed and experimental confirmation was carried out. The principle verification machine is equivalent to the one shown in Figure 4. The performance of a Stirling refrigerator with a magnetic circuit attached, i.e., a Stirling refrigerator + magnetic refrigerator (referred to as a "magnetic Stirling refrigerator"), and a pure Stirling refrigerator without a magnetic circuit were compared. As a result of this experimental verification, the magnetic Stirling refrigerator showed clearly higher cooling performance compared to the pure Stirling refrigerator. This suggests that the phase lag of heating after magnetization does not lag to π / 2, and as mentioned above, the phase lag is smaller. In other words, it is thought that the interval in which heat cancels out between time point C and time point B' is smaller or disappears. To put it another way, it is thought that time points A' and B' move forward (to the left in Figure 3). The same applies to the phase lag of endothermic heat after demagnetization. It is thought that the interval in which heat cancels out between time point E and time point D' is smaller or disappears.

[0066] Here, the magnetic refrigeration function will be explained by referring to a specific example of the positional relationship between the magnetic circuit 40 and the displacer 11. First, Figure 4 shows the positional relationship between the magnetic circuit 40, which has permanent magnet pieces 43 arranged in a Halbach array, and the displacer 11. In this magnetic circuit 40, permanent magnet pieces 43, each with a different magnetization direction AR (arc type), are arranged in a Halbach array as shown in Figure 4, within a cylindrical fixed frame 42. In Figure 4, there are 12 permanent magnet pieces 43, but this can be increased or decreased as long as it is an even number (a multiple of 4 is preferable). With this Halbach array of permanent magnet pieces 43, a high magnetic field can be formed in the +Z direction (from top to bottom in Figure 4) with respect to the center space in which the magnetic refrigeration material 15 is contained. Of course, the magnetization direction of the permanent magnet pieces is not limited to this.

[0067] In Figure 4(b), a magnetic circuit 40 composed of Halbach array magnets is housed and arranged within a fixed frame 42. In the displacer device 10a shown in Figure 4(b), the tip of the low-temperature end of the displacer 11 located inside the expansion cylinder 50a is filled with small spherical or linear magnetic refrigerant 15, while the rest of the displacer 11 is filled with a cold storage material 14a. For the sake of explanation, Figure 4(b) is a single-stage displacer device and only shows the displacer 11 and a portion of the expansion cylinder 50a; springs, position control devices, etc., that are normally connected to the displacer 11 are not shown. The same explanation applies to the two-stage displacer 11 shown in Figure 1.

[0068] In Figure 4(b), the displacer 11 is in its neutral position and oscillates in the ±X direction around the reference position XP of the magnetic circuit 40. The neutral position of the displacer 11 shown in Figure 4(b) is where the position of the displacer 11 in Figure 3 is the 0 point. This neutral position may be where the displacer 11 has moved from the reference position XP toward the low-temperature end (+ side) or toward the high-temperature end (- side).

[0069] Figure 5 shows an example of the magnitude of the magnetic field applied from the magnetic circuit 40 corresponding to the position of the displacer 11. Figure 5 is an example of the calculation results of the magnetic field by the magnetic circuit 40, in which neodymium magnet pieces are arranged in a Halbach array as shown in Figure 4. In Figure 5, when the displacer 11 moves from -5 mm to +5 mm with the reference position XP as the neutral position, the magnetic field changes from +1.09 T to 0.36 T, with a change of 0.73 T. In Figure 3, the horizontal axis represents time as an angle (ωt), and one period is 2π, so from time tz to time A', the displacer 11 moves 71% of its total movable range, and the magnetization is increased within this range. In this calculation example, the increase in the magnetic field is 0.57 T. As already mentioned, from equation (3), the transfer of heat to the gas is delayed by π / 2, so heating occurs between time points A' and B'. When the displacer 11 moves from time A' to time B', the magnetization and demagnetization phases are equal, and the changes in magnetic entropy cancel each other out, meaning no thermal transfer occurs. Next, when the displacer 11 moves from time B' to time C', the magnetic field to the magnetic refrigerant 15 is demagnetized, with a demagnetization phase of 0.57T. As with the magnetization phase, heat absorption (cooling) occurs with a delay of π / 2 minutes, so the period between time points C' and D' is endothermic (cooling). As mentioned earlier, experimental verification results suggest that the thermal phase delay is much smaller than π / 2.

[0070] To summarize the above explanation, as shown in Figure 3, experimental verification suggests that the timing of heating by the Stirling refrigeration function and the timing of heating by the magnetic refrigeration function occur with almost no overlap. Furthermore, the timing of heat absorption by the Stirling refrigerator and the timing of heat absorption by the magnetic refrigeration function also appear to occur with almost no overlap. Therefore, the Stirling refrigeration function and the magnetic refrigeration function do not cancel each other out, but rather work synergistically to achieve optimal refrigeration performance.

[0071] Here, we present a formula for simply calculating the refrigeration output Qmc due to the magnetic refrigeration function using a method similar to that of a Stirling refrigerator. The refrigeration output Qmc can be expressed by the following equation (6). Qmc = Qmt - Qmls …(6) Note that Qmt represents the magnetic refrigeration capacity.

[0072] Furthermore, the magnetic refrigeration capacity Qmt in equation (6) can be calculated using the following equation (7). Qmt = πf·Vm·ΔT·ΔS …(7) Here, f is the operating frequency, Vm is the volume of the magnetic refrigerant, ΔT is the value calculated by equation (5), and ΔS is the change in magnetic entropy. In equation (6), Qmls is the heat loss generated in the magnetic refrigerant, and the main losses are hyasteresis loss and eddy current loss.

[0073] <Magnetic refrigeration material> Incidentally, there are various other candidate materials for the magnetic refrigeration material 15. Figure 6 is a diagram showing the material properties of the magnetic refrigeration material described in Non-Patent Literature 1. In Figure 6, the horizontal axis represents temperature, and the vertical axis represents the change in magnetic entropy (ΔS). Here, the following are candidate materials for application as the magnetic refrigeration material 15 in the region from around 20K to 80K. Rare earth compounds having a Raves structure (cubic crystal), such as RAl2, RNi2, (where R is Er, Ho, Dy), can be used as the magnetic refrigeration material 15. These are basically second-order transition type magnetic materials, and the peak value of the change in magnetic entropy is not very large, but it is broad with respect to temperature. Also, ErCo2 has the same Raves structure, but it is a first-order transition material due to an itinerant electron metamagnetic transition. Even at low magnetic fields of about 1T, the peak value of the change in magnetic entropy of ErCo2 is high, but the peak width is small. For this reason, it is suitable for low-magnetic-field applied configurations that use permanent magnets as magnetic circuits. The magnetic refrigeration material 15 can be either a second-order transition material or a first-order transition material. In that case, the relationship between temperature and magnetic entropy change, and the characteristics of the magnetization curve should be well understood, and the appropriate arrangement and quantity should be selected for the temperature range. Furthermore, it is possible to obtain higher performance by using a hybrid of second-order and first-order transition materials.

[0074] <Magnetic Circuit> Figure 7 shows an example of a magnetic circuit. The magnetic circuit 40 shown in Figure 4 was a Halbach arrangement of permanent magnet pieces 43, but as shown in Figure 7, the permanent magnet pieces 43 may be made of electromagnets. In the magnetic circuit 45 shown in Figure 7, twelve electromagnets, each with a coil 45c wound around an iron core 45b, are arranged in a Halbach arrangement within the support member 45a. This configuration has several advantages compared to using a fixed magnet type. One is that the timing of magnetization and demagnetization, the application time, and the magnitude of the magnetic field can be freely changed regardless of the position of the displacer 11. Furthermore, this can be done regardless of the position of the magnetic refrigeration material 15.

[0075] Alternatively, instead of using the Halbach arrangement shown in Figure 4, the magnetic circuit may be constructed using a pair of permanent magnets and a magnetic material (yoke). Figure 8 shows the configuration of a magnetic circuit 46 using a pair of permanent magnets 46b. As shown in Figure 8, the pair of permanent magnets 46b are attracted and fixed to a cylindrical yoke 46a and are arranged to sandwich the magnetic refrigeration material 15. Even using such a pair of permanent magnets 46b, a magnetic field can be applied across the displacer 11. Although Figures 7 and 8 describe a single-stage displacer 11, a two-stage displacer 11 can be similarly applied.

[0076] <Synergistic cooling function using Stirling refrigerator and magnetic refrigerator> The refrigeration capacity Qc of a Stirling refrigerator and a magnetic refrigerator can be expressed by equation (8) using equations (1) and (6). Qc = Qsc + Qmc …(8) In other words, the refrigeration capacity Qc is the sum of the refrigeration capacity Qsc from the Stirling refrigerator and the refrigeration capacity Qmc from the magnetic refrigerator. The refrigeration capacity at the low-temperature end is generated by Stirling refrigerators and magnetic refrigerators using completely different refrigeration principles. Therefore, the overall capacity of the refrigerator can be obtained by simply adding the two together, resulting in a high refrigeration capacity.

[0077] <Embodiment> Figure 9 is a schematic diagram showing the configuration of the displacer device 110 according to this embodiment. Figure 10 is a diagram showing the relationship between the electromagnetic force F1 acting on the magnetic refrigerant 15, the electromagnetic force F2 acting on the magnetic material 115, and the electromagnetic force F10 acting on the displacer 11 as the displacer 11 moves as shown in Figure 9. Since the magnetic refrigerant 15 at the low-temperature end of the displacer 11 is a magnetic material, an electromagnetic force F1 is generated by the static magnetic field generated by the magnetic circuit 40. The magnitude of this electromagnetic force F1 acting on the magnetic refrigerant 15 is determined by the positional relationship between the magnetic circuit 40 and the magnetic refrigerant 15, as shown in Figure 10.

[0078] As shown in Figure 9, if we define the neutral position of the displacer 11 as the 0 point (reference position XP), the vibration direction of the displacer 11 as the x-direction, and the low-temperature end as the positive (+) direction, then the high-temperature end of the magnetic refrigerant 15 and the left end of the magnetic circuit 40 (the negative end in the x-direction) are at the x=0 position. In this case, the electromagnetic force F1 acting on the magnetic refrigerant 15 is a negative (-) force, as shown in Figure 10. The electromagnetic force shown in Figure 10 is an example calculated under certain conditions (normalized value), but within the operating range of the displacer 11, the electromagnetic force F1 is a unidirectional force applied only in the negative (-) direction with respect to the x-direction.

[0079] Incidentally, the displacer 11 is subjected to a reciprocating force generated by the pressure difference at both ends, and there is a restoring force, i.e., a force from the flexure bearing 53, that tries to return it to its original position, allowing it to vibrate with a constant amplitude. However, if a unidirectional electromagnetic force is generated, it will hinder the original movement of the displacer 11, preventing it from achieving the designed refrigeration capacity. For this reason, in this modified example 1, in order to counteract the electromagnetic force F1 applied to the magnetic refrigeration material 15, a magnetic material 115 is placed on the high-temperature end side of the displacer 11, as shown in Figure 9, to generate a symmetrical electromagnetic force F2, and another magnetic circuit, the magnetic circuit 140, is placed on the outside of the expansion cylinder (storage container 50) corresponding to the magnetic material 115.

[0080] In other words, if the distance between magnetic circuit 40 and magnetic circuit 140 is 2L, then magnetic circuit 40 and magnetic circuit 140, and magnetic refrigeration material 15 and magnetic material 115 are arranged symmetrically with respect to the x-direction, with x = -L as the axis. Magnetic circuit 40 and magnetic refrigeration material 15 are arranged in the +x direction, and magnetic circuit 140 and magnetic material 115 are arranged in the -x direction.

[0081] Here, the magnetic material 115 can be a mesh or small spherical material made of iron or nickel. Since this magnetic material 115 is placed on the high-temperature side near the middle of the cold storage material, it is desirable that it is a material that functions as a cold storage material. Stainless steel mesh or random fiber magnetic materials such as martensitic materials are also effective. When a material with the same BH characteristics as the magnetic refrigeration material 15 is placed as the magnetic material 115, the electromagnetic force F2 acting on the magnetic material 115 becomes rotationally symmetric with the electromagnetic force F1 acting on the magnetic refrigeration material 15 around the origin, which is 0, as shown in Figure 10.

[0082] Furthermore, a magnetic refrigeration material can be used as the magnetic material 115. In this case, it is desirable to select a magnetic refrigeration material such that its phase transition temperature is the temperature of the location where the magnetic refrigeration material is placed or a nearby temperature. This allows for cooling by the magnetocaloric effect even at high temperatures. Since this acts separately from the cooling by the magnetic refrigeration material installed at the low-temperature end, the overall refrigeration performance can be greatly improved.

[0083] Therefore, as shown in Figure 10, the total electromagnetic force F10 acting on the displacer 11 is a negative force when the displacer 11 moves in the +x direction, and a positive force when it moves in the -x direction. In other words, a restoring force is applied to the displacer 11.

[0084] This acts as an oscillating force synchronized with the operating frequency of the compressor 20. The oscillating force due to this electromagnetic force F10 is determined by the BH characteristics and relative positions of the magnetic circuits 40, 140, magnetic refrigeration material 15, and magnetic material 115 in Figure 9, but the important point is that an oscillating force synchronized with the operating frequency is applied to the displacer 11.

[0085] In a free-piston configuration, a restoring force is required to create constant vibration, and this role is played by a spring (flexure bearing 53). When a configuration with magnetic material 115 and magnetic circuit 140, as shown in Figure 9, is adopted, a restoring force is applied to the displacer 11 by an electromagnetic force F10 that is opposite to the thrust force generated by the pressure difference at both ends of the displacer 11. As a result, the restoring force is greater than that of a normal free-piston type, making it possible to reduce the force of the spring and leading to a simplification of the structure. There are no problems whatsoever with the performance of the refrigerator. In other words, by adopting the configuration shown in Figure 9, it is possible to create a refrigerator configuration that combines the high cooling function of the basic Stirling refrigerator with a magnetic cooling function.

[0086] Furthermore, by optimizing the magnitude of the electromagnetic force F10, it is possible to eliminate the need for the flexure bearing 53. In other words, the spring's restoring force is replaced by an electromagnetic restoring force. This results in a flexure bearing-less configuration, leading to a simplification of the structure.

[0087] <Basic structure of variation 1> Figure 11 is a schematic diagram showing the configuration of the displacer device 10c in a refrigerator that forms the basis of Modification 1 of this embodiment. As shown in Figure 11, in the refrigerator that forms the basis of Modification 1, the material of the second stage regenerator 14 is configured to alternately arrange magnetic refrigeration material and cold storage material from the low temperature side. That is, from the low temperature side (tip side) of the second stage regenerator 14, a plurality of magnetic refrigeration materials 15a, 15b, 15c corresponding to the magnetic refrigeration material 15 are arranged with the cold storage material in between. Then, at positions corresponding to each magnetic refrigeration material 15a, 15b, 15c, magnetic circuits 40a, 40b, 40c corresponding to the magnetic circuit 40 are arranged outside the second stage container 17.

[0088] The length of each magnetic refrigeration material 15a, 15b, and 15c in the X direction is arbitrary, and the length of the thermal storage material placed between each magnetic refrigeration material in the X direction is also arbitrary. In this case, the magnetic circuits 40a, 40b, and 40c are also placed in positions corresponding to the magnetic refrigeration materials 15a, 15b, and 15c. Although three magnetic refrigeration materials are installed in Figure 11, this number is also arbitrary. Typically, to achieve high refrigeration performance, the temperature profile of the displacer in the X direction is designed to be linear. Each magnetic refrigeration material is selected to have a phase transition temperature at or near the temperature at its location.

[0089] In the refrigerator that forms the basis of Modification 1, the cold generated on the magnetic refrigerator (magnetic refrigeration material) side can be further increased.

[0090] <Example 1> Figure 12 shows a configuration in which multiple magnetic materials 115a, 115b, 115c and multiple magnetic circuits 140a, 140b, 140c are arranged in accordance with the embodiment, relative to the basic configuration of Modification 1. In the displacer device 10c shown in Figure 12, the sum of the electromagnetic forces F1a to F1c acting on the magnetic refrigeration materials 15a to 15c is approximately equal to the sum of the electromagnetic forces F2a to F2c acting on the magnetic materials 115a to 115c at point 0 (see Figure 10), and they cancel each other out. As the displacer 11 moves, the difference between the sum of the electromagnetic forces F1a to F1c and the sum of the electromagnetic forces F2a to F2c acts as a restoring force.

[0091] <Modification 2> Figure 13 shows a configuration in which one magnetic material 115d and one magnetic circuit 140d are arranged in accordance with the embodiment, relative to the basic configuration of Modification 1. In the displacer device 10c shown in Figure 13, the sum of the electromagnetic forces F1a to F1c acting on the magnetic refrigeration materials 15a to 15c is approximately equal to the electromagnetic force F2d acting on the magnetic material 115d at point 0 (see Figure 10) and cancels each other out. As the displacer 11 moves, the difference between the sum of the electromagnetic forces F1a to F1c and the electromagnetic force F2d acts as a restoring force.

[0092] <Variation 3> Figure 14 shows the configuration of a displacer device 10d in a refrigerator, which is a modification 3 of this embodiment. Note that the configuration of the magnetic material 115 and the magnetic circuit 140 is omitted in Figure 14. As shown in Figure 14, in this modification 3, a drive device 60 is further provided to control the position of the shaft 12 of the displacer 11 in order to adjust the phase difference of the reciprocating motion of the displacer 11 based on the positions of the compression pistons 23 and 24.

[0093] The drive unit 60 inside the room temperature container 51a can perform axial position control with respect to the shaft 12a, which is an extension of the shaft 12 of the displacer 11, using a linear motor or the like. The control unit 61 acquires the compression piston position PD and performs feedback control via the drive unit 60 to adjust the phase difference that causes the position of the displacer 11 to advance or lag relative to the phase of the pressure.

[0094] In this modified example 3, the timing of heating and cooling of the magnetic refrigeration material 15 and the timing of heating and cooling of the Stirling refrigerator can be adjusted, thereby optimizing the refrigeration efficiency of the entire refrigerator.

[0095] <Modification 4> Figure 15 is a schematic diagram showing the configuration of a displacer device 120, which is a modification 4 of this embodiment. Note that the configuration of the magnetic material 115 and the magnetic circuit 140 is omitted in Figure 15. Figure 15(b) shows the cross-sectional structure of the displacer device 120, and Figure 15(a) is a cross-sectional view of Figure 15(b) along line BB. In this modification 4, multiple magnetic refrigeration materials are stacked in the direction of vibration of the displacer 11. As shown in Figure 15, the magnetic refrigeration material 15 is constructed by stacking two magnetic refrigeration materials 15g and 15h in the direction of vibration of the displacer 11. For example, the magnetic refrigeration material 15g is a material such as TmAl2 which has a large change in magnetic entropy near 4K. The magnetic refrigeration material 15h is a material such as HoAl2 which has a large change in entropy at 20K.

[0096] In this modified example 4, by incorporating multiple magnetic refrigeration materials with large magnetic entropy changes and different temperature ranges, it becomes possible to manufacture refrigerators operating at lower temperatures, such as 4.2K, which would be difficult with gas-type refrigeration alone.

[0097] Furthermore, the width of the magnetic refrigeration material 15 and the effective magnetic field width generated by the magnetic circuit 40 (the region in which the magnetic field created by the magnetic circuit 40 effectively causes a change in the magnetic entropy of the magnetic refrigeration material 15) are approximately the same. "Approximately the same" means that the absolute value of the difference between the width of the magnetic refrigeration material 15 and the effective magnetic field width generated by the magnetic circuit 40 is within a small ± predetermined range.

[0098] Furthermore, by increasing the stroke of the displacer 11 and further increasing the frequency of the compressor 20, it is possible to further miniaturize the device and improve refrigeration efficiency.

[0099] Furthermore, the configurations illustrated in the embodiments and modifications described above are functional schematics and do not necessarily have to be physically represented as shown. In other words, the forms of distribution and integration of each device and component are not limited to those shown, and all or part of them can be functionally or physically distributed and integrated in any unit according to various usage situations. [Explanation of Symbols]

[0100] 10, 10a, 10c, 10d, 110, 120 Displacer device 11 Displacer 12,12a axis 13.1st stage regenerator 14 2nd stage regenerator 14a Cold storage material 15, 15a, 15b, 15c, 15g, 15h Magnetic Refrigeration Material 16. First layer container 17. Second layer container 18. First row cold head 19. Second row cold head 20 Compressors 21,22 Linear motor 23,24 Compression piston 30 Piping 40, 40a, 40b, 40c, 45, 46, 140, 140a~140d Magnetic Circuits 41 Vacuum container 42 Fixed frame 43 permanent magnet pieces 45a Support member 45b Iron core 45c coil 46a York 46b Permanent Magnet 50,50a Storage container (expansion cylinder) 51,51a Room temperature container 52 Aftercooler 53 Flexure bearings 60 Drive unit 61 Control Unit 100 Refrigeration Units 115,115a~115d Magnetic material A,B,C,D,E,F,A',B',C',D',tz time AR magnetization direction E1 Room temperature space E21 77K space E22 20K space F1,F1a~F1c,F2,F2a~F2d,F10 Electromagnetic force G Working fluid L1,L2,L3 waveform PD Compression Piston Position XP reference position

Claims

1. A displacer device is provided, which has a displacer containing a cold storage material inside, and generates cold by expanding the compressed working fluid inside the storage container as the displacer reciprocates within the storage container, A magnetic refrigeration material is placed on the low-temperature end side of the displacer. A magnetic circuit is provided outside the storage container corresponding to the magnetic refrigeration material to change the magnetic state of the magnetic refrigeration material. The magnetic circuit increases and decreases the magnetization of the magnetic refrigeration material depending on the position of the displacer. A magnetic material with a shape that allows the working fluid to pass through is placed on the high-temperature end side of the displacer. A separate magnetic circuit is provided outside the storage container corresponding to the magnetic material to change the magnetic state of the magnetic material. A displacer device characterized in that the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material are in different directions.

2. The displacer is equipped with a spring that provides a restoring force against its axial reciprocating motion, The displacer device according to claim 1, characterized in that the restoring force is assisted by the difference between the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material.

3. The displacer device according to claim 1, characterized in that the difference between the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material becomes a restoring force against the axial reciprocating motion of the displacer.

4. The displacer device according to claim 1, characterized in that a plurality of magnetic refrigeration materials are arranged in the displacer with a cold storage material in between, starting from the low-temperature end side.

5. The displacer device according to claim 1, characterized in that a plurality of magnetic materials are arranged on the high-temperature end side of the displacer with a cooling material in between.

6. The displacer device according to claim 1, characterized in that the magnetic material is a magnetic refrigeration material.

7. The displacer apparatus according to claim 1, characterized in that a plurality of different magnetic refrigeration materials are arranged from the low-temperature end side of the displacer.

8. The displacer device according to claim 1, further comprising a drive device for controlling the position of the displacer, and characterized by adjusting the position of the displacer.

9. The displacer device according to claim 1, characterized in that the magnetic circuit and the other magnetic circuit each generate a magnetic field that is directional with respect to the magnetization region of the magnetic refrigerant and the magnetic material, respectively.

10. The displacer device according to claim 1, characterized in that the magnetic refrigeration material is positioned with the low-temperature end face of the magnetic circuit as the neutral position, and is demagnetized when the magnetic refrigeration material moves from the neutral position to the low-temperature end, and is magnetized when it moves from the neutral position to the high-temperature end.

11. A compressor that generates pressure amplitude in the working fluid through the reciprocating motion of a compression piston, A displacer device comprising a storage container connected to the compressor and filled with a working fluid space having a working fluid having the pressure amplitude generated by the compressor, a displacer having a cooling material inside that reciprocates with a phase difference relative to the reciprocating motion of the compression piston, and a mechanism for supporting the displacer within the storage container, A refrigerator equipped with, A magnetic refrigeration material is placed on the low-temperature end side of the displacer. A magnetic circuit is provided outside the storage container corresponding to the magnetic refrigeration material to change the magnetic state of the magnetic refrigeration material. The magnetic circuit increases and decreases the magnetization of the magnetic refrigeration material depending on the position of the displacer. A magnetic material with a shape that allows the working fluid to pass through is placed on the high-temperature end side of the displacer. A separate magnetic circuit is provided outside the storage container corresponding to the magnetic material to change the magnetic state of the magnetic material. A refrigerator characterized in that the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material are in different directions.

12. The displacer is equipped with a spring that provides a restoring force against its axial reciprocating motion, The refrigerator according to claim 11, characterized in that the restoring force is assisted by the difference between the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material.

13. The refrigerator according to claim 11, characterized in that the difference between the electromagnetic force acting on the magnetic refrigeration material and the electromagnetic force acting on the magnetic material becomes a restoring force against the axial reciprocating motion of the displacer.

14. The refrigerator according to claim 11, characterized in that a plurality of the magnetic refrigeration materials are arranged in the displacer with a cold storage material in between.

15. The refrigerator according to claim 11, characterized in that a plurality of magnetic materials are arranged on the high-temperature end side of the displacer with a cold storage material in between.

16. The refrigerator according to claim 11, characterized in that the magnetic material is a magnetic refrigeration material.

17. The refrigerator according to claim 11, characterized in that a plurality of different magnetic refrigeration materials are arranged from the low-temperature end side of the displacer.

18. The refrigerator according to claim 11, further comprising a drive device for controlling the position of the displacer, and characterized in that it adjusts the position of the displacer.

19. The refrigerator according to claim 11, characterized in that the magnetic circuit and the other magnetic circuit each generate a magnetic field that is directional with respect to the magnetization region of the magnetic refrigerant and the magnetic material, respectively.

20. The refrigerator according to claim 11, characterized in that the magnetic refrigeration material is positioned with the low-temperature end face of the magnetic circuit in a neutral position, and is demagnetized when the magnetic refrigeration material moves from the neutral position to the low-temperature end, and is magnetized when it moves from the neutral position to the high-temperature end.

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