Displacer device and cooler

Abstract

The purpose of the present invention is to provide a displacer device and a cooler with which it is possible, when highly efficient cooler performance is realized through addition of a magnetic cooling function, to ensure a constant-amplitude reciprocating motion performed by the displacer and achieve highly efficient cooling capacity as per a design. For this purpose, a magnetic cooling material 15 is disposed on the low-temperature-end side of a displacer 11, a magnetic circuit 40 for changing the magnetic state of the magnetic cooling material 15 is provided outside a storage container 50 corresponding to the magnetic cooling material 15, the magnetic circuit 40 magnetizes and demagnetizes the magnetic cooling material 15 according to the position of the displacer 11, a magnetic material 115 having a shape through which a working fluid can pass is disposed on the high-temperature-end side of the displacer 11, another magnetic circuit 140 for changing the magnetic state of the magnetic material 115 is provided outside the storage container 50 corresponding to the magnetic material 115, and the direction of electromagnetic force F1 acting on the magnetic cooling material 15 is different from the direction of electromagnetic force F2 acting on the magnetic material 115.

Description

Displacer devices and refrigerators

[0001] The present invention relates to a displacer device and a refrigerator that, when adding a magnetic refrigeration function to achieve high-efficiency refrigerator performance, ensure a constant amplitude reciprocating motion by the displacer, thereby exhibiting the high-efficiency refrigeration capacity as designed.

[0002] Generally, well-known refrigerators include Stirling refrigerators, which consist of an expander that generates extremely low temperatures through the reciprocating motion of a displacer, and a compressor that generates an oscillating flow. In this Stirling refrigerator, the displacer operating within the expander's cylinder and the piston operating within the compressor's cylinder reciprocate within their respective cylinders.

[0003] On the other hand, Patent Document 1 describes a cooling device (3) which is a magnetic refrigeration device. Specifically, 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) which is placed outside the cooling device (3) and generates a magnetic field inside the cooling device (3), and a magnetic material (20) which is placed inside the cooling device (3). This magnetic material preferably has the shape of a piston, and this piston is axially supported inside the cooling device (3) so as to be slidable parallel to the longitudinal direction of the cooling device.

[0004] Japanese Unexamined Patent Publication No. 182557 / 1983

[0005] Akiko Saito et al., Magnetic Refrigeration Materials for Hydrogen Liquefaction by Active Regenerative Magnetic Refrigeration (AMRR), Cryogenic Engineering 58 (2023), pp. 51-57.

[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, which requires 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 device described in Patent Document 1 cannot be expected to have high 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.

[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, the present invention is characterized in that, in the above invention, 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.

[0016] Furthermore, the present invention is characterized in that, in the above invention, the magnetic refrigeration material is arranged in multiples with a cold storage material in between, starting from the low-temperature end side of the displacer.

[0017] Furthermore, the present invention is characterized in that, in the above invention, the magnetic material is arranged in multiples with a cooling material in between on the high-temperature end side of the displacer.

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

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] Furthermore, the refrigerator according to the present invention comprises a compressor that generates a pressure amplitude in a working fluid by the reciprocating motion of a compression piston, and a displacer device which has a mechanism to support the displacer in the storage container that is connected to the compressor and is filled with a working fluid space having a pressure amplitude generated by the compressor, and in the storage container a displacer that reciprocates with a phase difference with respect to the reciprocating motion of the compression piston and has a cold storage material inside, and 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 through which the working fluid can pass is placed 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.

[0024] 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.

[0025] Furthermore, the present invention is characterized in that, in the above invention, 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.

[0026] Furthermore, the present invention is characterized in that, in the above invention, the magnetic refrigeration material is arranged in multiples with a cold storage material in between, starting from the low-temperature end side of the displacer.

[0027] Furthermore, the present invention is characterized in that, in the above invention, the magnetic material is arranged in multiples with a cooling material in between 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.

[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 cooling capacity as designed.

[0034] 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 is a cross-sectional view taken along line A-A in Figure 1. Figure 3 is a diagram showing time-series data of the position of the compression piston, the position of the displacer, and the low-temperature end flow rate. Figure 4 is a diagram showing the positional relationship between a magnetic circuit, in which permanent magnet pieces are arranged in a Halbach array, and the displacer. Figure 5 is a diagram showing an example of the magnitude of the magnetic field applied from the magnetic circuit corresponding to the position of the displacer. Figure 6 is a diagram showing the material properties of the magnetic refrigeration material described in Non-Patent Literature 1. Figure 7 is a diagram showing an example of a magnetic circuit. Figure 8 is a diagram showing the configuration of a magnetic circuit using a pair of permanent magnets. Figure 9 is a schematic diagram showing the configuration of a refrigerator according to this embodiment. Figure 10 is a diagram showing 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 is a schematic diagram showing the configuration of a displacer device 10c in a refrigerator that forms the basis of Modification 1 of this embodiment. Figure 12 is a diagram showing a configuration in which a plurality of magnetic materials and a plurality of magnetic circuits are arranged in accordance with the embodiment, relative to the basic configuration of Modification 1. 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 shows the configuration of a displacer device in a refrigerator, which is Modification 2 of this embodiment. Figure 15 is a schematic diagram showing the configuration of a displacer device, which is Modification 3 of this embodiment.

[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 the 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 composite refrigerator that has both a Stirling refrigeration function (gas type 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 the 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, facing each other and operating in the same phase in the X direction. In Figure 1, this operation 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 a working fluid G having a pressure amplitude generated by the compressor 20. The storage container 50 is configured such that a normal temperature container 51, a first-stage container 16, and a second-stage container 17 are connected in sequence. The displacer device 10 has a displacer 11 disposed in the storage container 50. The displacer 11 has a first-stage regenerator 13 and a second-stage regenerator 14 containing a regenerator material that performs heat exchange with the working fluid G. The regenerator material of the first-stage regenerator 13 uses a fine mesh such as a normal stainless material, and the regenerator material of the second-stage regenerator 14 uses lead balls having a high specific heat at low temperatures. Note that, as a part of the magnetic refrigerator described above, a magnetic refrigerant 15 is disposed on the tip side of the cold head (the low-temperature end of the second-stage regenerator 14) in the displacer 11.

[0039] The magnetic refrigerant 15 can use, for example, a material having a conventional magnetocaloric effect that undergoes a ferromagnetic transition from a paramagnetic substance to a ferromagnetic substance by the application of a magnetic field, such as La(Fe Ｘ Si １－Ｘ ). １３ Or HoB ２ And the like. Also, the magnetic refrigerant 15 can use a generalized antiferromagnet. Here, the generalized antiferromagnet is a substance that is not in a state where all the spins in the substance are aligned in a specific direction but is in a magnetic order state. In addition to a narrow sense antiferromagnet in which the absolute values of adjacent spins are the same and the angle between them is 180°, it may be a ferrimagnet in which the absolute values of adjacent spins are not the same, a helical magnet, or an antiferromagnet having parasitic ferromagnetism in which the angle between them is other than 180°. For example, Ho is a typical substance of a helical magnet.

[0040] The magnetic refrigerant 15 can be configured as an aggregate of polycrystalline spherical grains. When a generalized diamagnet is used for the magnetic refrigerant 15 in this configuration, a material with the smallest possible (substantially no) anisotropy in the metamagnetic transition magnetic field is selected as the generalized diamagnet.

[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 normal temperature space E1, the 77K space E21, and the 20K space E22. Since the phase of this pressure difference is the same as the phase of the flow rate, the displacer 11 operates with a phase difference advanced with respect to the operations of the compression pistons 23 and 24. In this case, since the displacer 11 does not move by its own power but moves passively, it is 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 optimum value with respect to the compression pistons 23 and 24 is a phase difference of π / 4.

[0042] The normal temperature container 51 is a normal temperature container that connects the working fluid G with the compressor 20 via the pipe 30, and 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 basically does not operate in the radial direction (Y-Z plane) perpendicular to the shaft 12, and also serves as a support member that reciprocates with a certain gap between the piston (displacer 11) and the cylinder (the first-stage container 16 and the second-stage container 17).

[0043] An aftercooler 52 is arranged between the normal temperature container 51 and the first-stage container 16, and heat is dissipated to a water-cooled jacket provided outside the normal temperature container 51. Also, a fixing portion for attaching the flexure bearing 53 is arranged inside the normal temperature container 51.

[0044] The interior of the displacer 11 is composed of a first-stage regenerator 13 and a second-stage regenerator 14. The cylinder housing the displacer 11 is also composed 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 about 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 a higher mesh count for the second-stage regenerator 14, or using lead spheres or Er, which have a high volumetric specific heat even at low temperatures, are used. ３ In some cases, passive magnetic materials such as Ni or its composites are 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 generally used, but there is also a method of depositing DLC ​​(Diamond-Like Carbon) on both sealing surfaces, in which case the amount of wear on the sealing surface can be suppressed and the lifespan can be extended. 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 A-A 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 so that the magnetic refrigerant 15 can be used effectively 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 viewpoint 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 when the displacer 11 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 when the displacer 11 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 from, for example, 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 portion of the magnetic circuit 40 facing 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 material to block heat from radiation.

[0053] When generating liquefied hydrogen (20K) using this refrigerator 100, heat exchangers (first-stage heat exchanger and second-stage heat exchanger) through which hydrogen gas can pass are installed on 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 Stirling Refrigeration Machine> Figure 3 shows time-series data of 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, the position of displacer 11, and the 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 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 heat is transferred 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 cold 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 value at the cold end, ΔV is the volume change width at the cold end (value obtained by multiplying the displacer amplitude by the cross-sectional area), and φ is the phase difference between the pressure and the displacer position.

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

[0060] The typical operating frequency of a Stirling refrigerator is high, around 10 to 100 Hz. From equation (2), it can be seen 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 to 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 Refrigeration Machine> 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 is 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) Also, under adiabatic conditions where the specific heat C is constant, the following equation (4) holds: ΔQ=C・ΔT …(4) Then, differentiating equation (4) with respect to time and rearranging the equation considering that it is an oscillating flow (sine wave), we obtain the following equation (5): T=ΔS / C・TＣ・ sin(ωt - π / 2) ... (5) Here, T Ｃ ω is the low-temperature end temperature, ω is the angular frequency, and t is time. Equation (5) 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 described 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 in the neutral position at time t 0, and then move towards the top dead center. At time t 0, the position of the displacer 11 is π / 4 ahead in phase with the compression pistons. 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 it 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, the results are 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 segment (arc type) with a different magnetization direction AR, 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 zero 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 shows 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, and the magnitude of the change is 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 magnitude of 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 widths are the same, 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 refrigeration material 15 is demagnetized, with a demagnetization width of 0.57 T. As with the magnetization, heat is absorbed (cooled) with a delay of π / 2 minutes, so the period between time C' and D' is endothermic (cooled). 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 heating timing by the Stirling refrigeration function and the heating timing by the magnetic refrigeration function occur with almost no overlap. Furthermore, the endothermic timing by the Stirling refrigerator and the endothermic timing by the magnetic refrigeration function also 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, for the refrigeration output Qmc by the magnetic refrigeration function, an equation for simple calculation by a method similar to that of a Stirling refrigerator is shown. The refrigeration output Qmc can be expressed by the following equation (6). Qmc = Qmt - Qmls................................................................(6) Here, Qmt is the magnetic refrigeration capacity.

[0072] Also, the magnetic refrigeration capacity Qmt in equation (6) can be calculated by 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 magnetic entropy change. Qmls in equation (6) is the heat loss generated in the magnetic refrigerant, and the main losses are the hysteresis loss and the eddy current loss.

[0073] <Magnetic Refrigerant>By the way, there are various candidate materials as the magnetic refrigerant 15. FIG. 6 is a diagram showing the material characteristics of the magnetic refrigerant described in Non-Patent Document 1. In FIG. 6, the horizontal axis represents temperature and the vertical axis represents the magnetic entropy change (ΔS). Here, in the region from around 20K to 80K, the materials that are candidates for application as the magnetic refrigerant 15 are listed below. RAl ２ , RNi ２ , (R is Er, Ho, Dy), etc., rare earth compounds having a Laves structure (cubic crystal) can be used as the magnetic refrigerant 15. These are basically second-order transition type magnetic materials, and the peak value of the magnetic entropy change is not very large, but it is broad with respect to temperature. Also, ErCo ２ has the same Laves structure but is a first-order transition material due to itinerant electron metamagnetic transition. ErCo<000001

[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 Refrigeration Function of 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 of the Stirling refrigerator and the refrigeration capacity Qmc of 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, and a high refrigeration capacity can be generated.

[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 position x=0. 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 flexure bearing 53, that tries to return it to its original position, so it can vibrate with a constant amplitude. However, if an electromagnetic force in one direction is generated, it will hinder the original movement of the displacer 11, and it will not be able to achieve the cooling capacity as designed. 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, 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, so as to generate an electromagnetic force F2 that is symmetric to it.

[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 having 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 point, 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, thereby enabling cooling by the magnetocaloric effect even on the high-temperature side. 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 configuration where the displacer 11 is a free piston, a restoring force is required to create a constant vibration, and this role is played by a spring (flexure bearing 53). When a configuration with a magnetic material 115 and a 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 absolutely no problems 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 Configuration of Modification 1> Figure 11 is a schematic diagram showing the configuration of the displacer device 10c in the 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, a plurality of magnetic refrigeration materials 15a, 15b, 15c corresponding to the magnetic refrigeration material 15 are arranged from the low temperature side (tip side) of the second stage regenerator 14 with the cold storage material in between. Then, magnetic circuits 40a, 40b, 40c corresponding to the magnetic circuit 40 are arranged outside the second stage container 17 at positions corresponding to each magnetic refrigeration material 15a, 15b, 15c.

[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. In Figure 11, three magnetic refrigeration materials are installed, but 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] <Modification 1> Figure 12 shows a configuration in which a plurality of magnetic materials 115a, 115b, 115c and a plurality of magnetic circuits 140a, 140b, 140c are arranged in accordance with the embodiment, compared 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 cancels 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] <Modification 3> Figure 14 shows the configuration of a displacer device 10d in a refrigerator, which is 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 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 taken along line B-B in Figure 15(b). 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 made 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 TmAl ２ These are materials that exhibit large changes in magnetic entropy near 4K. Furthermore, the magnetic refrigeration material 15h is HoAl ２ These are materials that exhibit a large entropy change at 20K.

[0096] In this modified example 4, by providing multiple magnetic refrigeration materials with large magnetic entropy changes and different temperature ranges, it becomes possible to manufacture refrigerators 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.

[0100] 10, 10a, 10c, 10d, 110, 120 Displacer device 11 Displacer 12, 12a Shaft 13, 1st stage cooler 14 2nd stage cooler 14a Cooling material 15, 15a, 15b, 15c, 15g, 15h Magnetic refrigeration material 16 1st stage container 17 2nd stage container 18 1st stage cold head 19 2nd stage cold head 20 Compressor 21, 22 Linear motor 23, 24 Compression piston 30 Piping 40, 40a, 40b, 40c, 45, 46, 140, 140a-140d Magnetic circuit 41 Vacuum container 42 Fixing frame 43 Permanent magnet piece 45a Support member 45b Iron core 45c Coil 46a Yoke 46b Permanent magnet 50, 50a Storage container (expansion cylinder) 51, 51a Room temperature container 52 Aftercooler 53 Flexure bearing 60 Drive unit 61 Control unit 100 Refrigeration unit 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 comprising a displacer having a cold storage material inside, wherein the displacer reciprocates within a storage container to expand a working fluid compressed within the storage container and generate cold, wherein 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 through which the working fluid can pass is placed 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.

2. The displacer device according to claim 1, further comprising a spring that provides a restoring force against the axial reciprocating motion of the displacer, wherein 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 device 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 refrigerator comprising: a compressor that generates a pressure amplitude in a working fluid by the reciprocating motion of a compression piston; a displacer device having a displacer that reciprocates with a phase difference relative to the reciprocating motion of the compression piston and has a cold storage material inside, and a mechanism for supporting the displacer within the storage container, wherein a magnetic refrigerant is placed on the low-temperature end side of the displacer; a magnetic circuit is provided outside the storage container corresponding to the magnetic refrigerant to change the magnetic state of the magnetic refrigerant; the magnetic circuit increases and decreases the magnetization of the magnetic refrigerant depending on the position of the displacer; a magnetic material with a shape through which the working fluid can pass is placed 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 refrigerant and the electromagnetic force acting on the magnetic material are in different directions.

12. The refrigerator according to claim 11, further comprising a spring that provides a restoring force against the axial reciprocating motion of the displacer, wherein 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 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 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.

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