Ejector structure for free-piston stirling refrigerator

Abstract

Provided is an ejector structure for a free-piston Stirling refrigerator. The ejector structure comprises: a first piston (1), a plate spring (3) and a second piston (2) which are sequentially arranged in an axial direction, wherein one side of the plate spring (3) is connected to the first piston (1), and the other side of the plate spring (3) is connected to the second piston (2), such that when the first piston (1) and the second piston (2) reciprocate under the action of an air pressure difference, the plate spring (3) radially supports the first piston (1) and the second piston (2) and provides axial rigidity for the first piston (1) and the second piston (2). During refrigeration, a high-pressure gas flows back and forth in an expansion cavity at one end of the second piston (2) away from the plate spring (3) and in a compression cavity at one end of the first piston (1) away from the plate spring (3), and the gas in the expansion cavity does positive work to the ejector structure, thereby conducting refrigeration. A link mechanism in a conventional ejector structure is removed, so that the motion damping of the ejector is reduced and the stability is improved.

Description

A displacer structure for a free piston Stirling refrigerator Technical Field

[0001] The present application relates to the field of refrigeration and cryogenic technology, and in particular to an ejector structure for a free piston Stirling refrigerator. Background Art

[0002] The Stirling refrigeration principle is based on the reverse Stirling cycle, which uses the expansion of alternating flow of compressible gas for refrigeration. The theoretical efficiency is the Carnot efficiency. The working fluid inside the system is pollution-free inert gas helium. There is no phase change during operation. The sealing method adopts gap sealing. The refrigerator can flexibly adjust the cooling temperature and cooling capacity by changing the stroke and frequency of the driving piston. It has the advantages of low vibration, compact structure, small size, energy saving and environmental protection, strong reliability, long service life and wide cooling temperature range.

[0003] A Stirling refrigerator has two piston components: the power piston and the displacer piston. The displacer piston extends through both the cold and hot ends. There is a phase difference between the power piston and the displacer piston, with the displacer piston generally leading the power piston in phase. The phase difference between the power piston and the displacer piston has a great influence on the cooling efficiency. Early Stirling refrigerators controlled the phase difference between the power piston and the displacer piston more by mechanical structure or by separately controlling the two components. The displacer of the later developed free piston Stirling refrigerator was not separately controlled or connected to the power piston by mechanical structure. Instead, the displacer was fixed separately to the leaf spring. The two ends of the displacer were the compression chamber and the expansion chamber respectively. Since there were low-porosity structures such as radiators and regenerators between the compression chamber and the expansion chamber in the gas channel, there was a certain phase difference between the pressure waves of the expansion chamber and the compression chamber. The displacer was subjected to the gas force from the gas pressure difference on both sides of the compression chamber and the expansion chamber. Under the action of its own inertia force, the spring force of the leaf spring, the damping force during the movement and the above-mentioned gas force, the displacer would produce a periodic reciprocating motion process and form a certain phase difference with the power piston. The Stirling refrigerator with this structure has a simpler mechanical structure and higher stability. Damping has a greater negative impact on the cooling effect of the free piston refrigerator.

[0004] Since the free-piston Stirling refrigerator was first proposed, the structural design of the displacer has been crucial in determining the cooling effect and overall structure. The existing displacer structure primarily consists of a thin rod connected to the power piston near the compression chamber. The rod passes through the power piston and the linear motor, and the end of the rod is connected and fixed to a leaf spring fixed in the back-pressure chamber, forming a free piston. The disadvantage of this piston-through-rod structure is that the power piston and displacer are prone to mutual motion interference, increasing the damping of the displacer and resulting in a decrease in cooling effect. It also increases the design difficulty of the power piston, resulting in low stability and difficult installation.

[0005] Therefore, the present application urgently needs to develop an ejector structure for a free piston Stirling refrigerator, which eliminates the connecting rod mechanism in the conventional ejector structure, greatly reduces the ejector motion damping, and has a high stability.

[0006] Summary of the Invention

[0007] The purpose of the present application is to provide a displacer structure for a free piston Stirling refrigerator, which eliminates the connecting rod mechanism in a conventional displacer structure, significantly reduces piston motion damping, and provides a highly stable displacer structure for a free piston Stirling refrigerator.

[0008] The present application provides an ejector structure for a free piston Stirling refrigerator, comprising:

[0009] The first piston, the leaf spring, and the second piston are arranged axially in sequence.

[0010] The leaf spring is connected to the first piston and the second piston by a first fastener, so that when the first piston and the second piston reciprocate under the action of the gas pressure difference, the leaf spring radially supports the first piston and the second piston and provides axial rigidity for the first piston and the second piston;

[0011] During the refrigeration process, high-pressure gas flows back and forth in the expansion chamber of the second piston at one end away from the leaf spring and the compression chamber of the first piston at one end away from the leaf spring. The gas in the expansion chamber does positive work on the displacer structure, thereby providing refrigeration.

[0012] In another preferred example, the leaf spring is located between the first piston and the second piston.

[0013] In another preferred embodiment, the leaf spring is composed of a double leaf spring.

[0014] In another preferred example, the central axes of the first piston and the second piston are on the same straight line.

[0015] In another preferred example, the central axes of the first piston and the second piston pass through the center point of the leaf spring.

[0016] In another preferred example, the leaf spring is fixedly connected to the first piston and the second piston via a first fastener.

[0017] In another preferred example, the first piston, the second piston and the leaf spring are coaxially installed.

[0018] In another preferred example, the first piston includes a cylindrical structure with a protruding bottom surface, the second piston includes a cylindrical structure with a protruding bottom surface, the first piston includes a first protruding bottom surface protruding toward the leaf spring, and the second piston includes a second protruding bottom surface protruding toward the leaf spring.

[0019] In another preferred example, the ejector structure further includes a first fastener, the first protruding bottom surface is provided with a first protruding portion, the second protruding bottom surface is provided with a second protruding portion, the first fastener passes through the leaf spring and is connected to the first protruding portion and the second protruding portion, thereby fixing the leaf spring to the first piston and the second piston.

[0020] In another preferred embodiment, the first protrusion is located at the center of the first protruding bottom surface, and the first protrusion is a cylindrical structure extending toward the leaf spring.

[0021] In another preferred embodiment, the second protrusion is located at the center of the second protrusion bottom surface, and the second protrusion is a cylindrical structure extending toward the leaf spring.

[0022] In another preferred embodiment, the first fastener is a stud.

[0023] In another preferred example, the first protrusion is a cylindrical structure with an internal thread, and the second protrusion is a cylindrical structure with an internal thread. The internal thread cooperates with the external thread of the stud to complete the connection. Preferably, an appropriate amount of thread glue is applied when the first protrusion and the second protrusion are threadedly connected to the stud.

[0024] In another preferred example, when the leaf spring is connected to the first protrusion and the second protrusion by the first fastener, the end face of the first protrusion is in contact with one surface of the leaf spring, and the end face of the second protrusion is in contact with the other surface of the leaf spring.

[0025] In another preferred example, the maximum axial distance between the first protruding bottom surface of the first piston and the leaf spring should be greater than the maximum amplitude of the ejector structure, and the maximum axial distance between the second protruding bottom surface of the second piston and the leaf spring should also be greater than the maximum amplitude of the ejector structure.

[0026] In another preferred embodiment, it further includes a first cylinder and a second cylinder, and both ends of the leaf spring are fixedly connected to the first cylinder or the second cylinder, so that the first piston can reciprocate in the first cylinder and the second piston can reciprocate in the second cylinder.

[0027] In another preferred embodiment, the ends of the leaf spring away from the center are fixedly connected to the end surface of the first cylinder via a second fastener.

[0028] In another preferred embodiment, the second fastener is a hexagon socket screw.

[0029] In another preferred example, the second cylinder includes a connecting section and a accommodating section. The connecting section is located outside the first cylinder in the radial direction of the cylinder, and a gap between the connecting section and the first cylinder is sealed.

[0030] In another preferred example, the first cylinder and the second cylinder are gap-sealed by a cylinder seal.

[0031] In another preferred embodiment, the interface between the connecting section of the second cylinder and the first cylinder is coated with glue, thereby fixing the second cylinder and the first cylinder.

[0032] In another preferred example, the first cylinder is inserted into the connecting section of the second cylinder.

[0033] In another preferred example, the inner diameter of the first cylinder is the same as the inner diameter of the accommodating section of the second cylinder, and the inner diameter of the connecting section of the second cylinder is larger than the inner diameter of the accommodating section of the second cylinder.

[0034] In another preferred embodiment, a plurality of grooves are provided on the inner wall of the accommodating section to reduce the amount of air cross-talk between the compression chamber and the expansion chamber through the gap, which has a positive effect on the sealing effect.

[0035] In another preferred embodiment, the positional relationship between the first piston, the second piston and the leaf spring must satisfy the following formula:

[0036] Wherein, m1 is the mass of the first piston, m2 is the mass of the second piston, L1 is the axial distance between the center point of the first piston and the center point of the leaf spring along the axial direction of the first piston, L2 is the axial distance between the center point of the second piston and the center point of the leaf spring along the axial direction of the second piston, g is the acceleration due to gravity, k is the radial stiffness of the leaf spring, and δ is the air gap height between the outer wall surface of the first piston and the inner wall surface of the first cylinder.

[0037] In another preferred example, the first piston is a hollow structure, and the first piston includes a first piston outer shell and a first piston top cover, and the first piston outer shell and the first piston top cover are sealed by a first piston seal.

[0038] In another preferred example, the first piston outer shell and the first piston top cover are fixed by a first piston fastener.

[0039] In another preferred embodiment, the first piston outer shell is a cylindrical structure with a bottom surface.

[0040] In another preferred example, the second piston outer shell is a cylindrical structure with a bottom surface.

[0041] In another preferred example, the second piston includes a second piston outer shell and a second piston top cover, and the second piston outer shell and the second piston top cover are fixedly connected and sealed by threads.

[0042] In another preferred example, the first piston outer shell and the second piston outer shell are close to the leaf spring and arranged opposite to each other.

[0043] In another preferred embodiment, the first piston is made of aluminum alloy, and the second piston is made of engineering plastic.

[0044] In another preferred embodiment, the outer surface of the first piston is sprayed with a wear-resistant lubricating coating, preferably, sprayed with a Teflon coating.

[0045] In another preferred embodiment, the first cylinder is made of aluminum alloy, and the second piston is made of engineering plastic.

[0046] In another preferred embodiment, the inner cylinder wall surface of the first cylinder is polished and hard-oxidized.

[0047] The present application also provides a free piston Stirling refrigerator, comprising the above-mentioned displacer structure.

[0048] It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features described in detail below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be listed here one by one. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. It should be understood that the drawings described below are merely some implementation examples of the present invention, and those skilled in the art can also derive other implementation examples based on these drawings without inventive effort.

[0050] FIG1 is a schematic structural diagram of a displacer of a free piston Stirling refrigerator according to an embodiment of the present application;

[0051] FIG2 is a schematic cross-sectional view of the displacer structure of a free-piston Stirling refrigerator according to an embodiment of the present application;

[0052] FIG3 is a schematic structural diagram of a leaf spring of an ejector structure according to an embodiment of the present application;

[0053] FIG4 is a schematic structural diagram of a second cylinder (in which a second piston is disposed) according to an embodiment of the present application.

[0054] In the drawings, the symbols are as follows: 1 - first piston 10 - first protruding bottom surface 101 - first protruding portion 11 - first piston outer housing 12 - first piston top cover 13 - first piston seal 14 - first piston fastener 2 - second piston 20 - second protruding bottom surface 201 - second protruding portion 21 - second piston outer housing 22 - second piston top cover 3 - leaf spring 31 - first fastener 32 - second fastener 4 - first cylinder 5 - second cylinder 51 - connecting section 52 - accommodating section 522 - groove 6 - cylinder seal L1 - axial distance between the center point of the first piston and the center point of the leaf spring in the axial direction of the first piston L2 - axial distance between the center point of the second piston and the center point of the leaf spring in the axial direction of the second piston δ - air gap height between the outer wall surface of the first piston and the inner wall surface of the first cylinder DETAILED DESCRIPTION

[0055] Through extensive and in-depth research, the inventors have developed a novel displacer structure for a free-piston Stirling refrigerator. This structure, which eliminates the slender connecting rod structure of a leaf spring known in the prior art, utilizes a dual-cylinder, dual-piston, and leaf spring configuration to reduce heat leakage from the hot end of the displacer to the cold end, eliminate direct interference and wear between the displacer and other refrigerator components, and significantly reduce frictional damping. This design also achieves airtightness, low axial heat conduction, and low mass, resulting in improved cooling performance. The leaf spring is positioned between the dual pistons, significantly reducing the distance between the leaf spring and the center of the displacer. This results in more stable displacer motion and a longer refrigerator life.

[0056] the term

[0057] As used herein, "ejector" and "ejector structure" are used interchangeably.

[0058] As used herein, "housing," "casing," and "housing body" are used interchangeably.

[0059] As used herein, “axial distance” refers to a distance along the axial direction of the first piston or the second piston.

[0060] As used herein, "hot end piston," "hot end discharge piston," and "first piston" refer to the same component;

[0061] As used herein, "cold end piston," "cold end discharge piston," and "second piston" refer to the same component;

[0062] As used herein, "first cylinder" and "hot end cylinder" refer to the same component;

[0063] As used herein, "second cylinder" and "cold-end cylinder" refer to the same component;

[0064] It should be noted that in this patent application, relational terms such as first and second are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. Without further limitation, an element specified by the phrase "comprising a" does not preclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element. In this patent application, reference to performing an action in accordance with an element means performing the action in accordance with at least that element, including two situations: performing the action in accordance with that element alone, and performing the action in accordance with that element and other elements. Expressions such as "plurality," "multiple times," and "many" include "two," "twice," "two kinds," and "more than two," "more than two times," and "more than two kinds."

[0065] In the present invention, all directional indications (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0066] Main advantages of the present invention

[0067] (a) The ejector structure of the present application eliminates the leaf spring slender connecting rod structure known in the prior art. By removing redundant parts other than the cylinder that can directly wear against the ejector, the friction damping of the ejector structure is greatly reduced during movement.

[0068] (b) The displacer structure of the present application eliminates direct interference and wear between the displacer piston and other components of the refrigerator, thereby improving the refrigeration efficiency and stability of the refrigerator;

[0069] (c) The ejector structure of the present application solves the problem of excessive distance between the leaf spring and the ejection piston in the prior art by arranging the leaf spring between the first piston and the second piston, thereby making the coaxiality of the entire ejector easier to control, reducing the difficulty of installation, and improving stability;

[0070] (d) The ejector structure of the present application is smaller in size, which reduces the weight of the refrigerator and reduces the difficulty of installation.

[0071] In the following description, many technical details are provided to help readers better understand this application. However, those skilled in the art will understand that even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in this application can be implemented.

[0072] The displacer is a key component of a free-piston Stirling refrigerator, regulating the phase of the working fluid flow within the refrigerator. A Stirling refrigerator consists of alternating oscillations between the compression piston and the displacer. High-pressure gas (helium) flows back and forth between the compression chamber, the hot-end radiator, the regenerator, the cold-end heat exchanger, and the expansion chamber. During a single refrigerator cycle, the gas in the expansion chamber performs positive work on the displacer, generating cooling capacity in the expansion chamber. Simultaneously, the displacer transfers the work done by the gas in the expansion chamber to the compression chamber, recovering acoustic work and improving the refrigerator's efficiency.

[0073] A free-piston Stirling refrigerator is a pneumatic refrigerator, meaning the movement of the displacer is driven by the pressure difference between the compression and expansion chambers, without any additional force driving its motion or phasing the internal gases. In a free-piston Stirling refrigerator, the displacer is directly connected to the leaf spring and independent of the compression system, effectively acting as a "free" piston. The mass of the displacer, the stiffness of the leaf spring, and the damping during the displacer's motion play a key role in its phasing function.

[0074] The present application provides an ejector structure for a free-piston Stirling refrigerator. The structure adopts a dual-cylinder-dual ejector, which can reduce the damping of the ejector movement process, reduce the axial heat conduction from the hot end through the cylinder and the ejector to the cold end (for example, the second piston is made of engineering plastic with a low thermal conductivity coefficient), reduce the cross-flow between the compression chamber and the expansion chamber through the ejector, ensure the stable operation of the ejector, reduce the difficulty of installation, and improve the stability and cooling efficiency of the refrigerator.

[0075] Displacer structure for free piston Stirling refrigerator

[0076] 1 , the displacer structure includes a double cylinder (a first cylinder 4 and a second cylinder 5), a double piston displacer (a first piston 3 and a second piston 4), and a leaf spring 3; the leaf spring 3 is disposed between the first piston 3 and the second piston 4;

[0077] The first piston 3 and the second piston 4 are connected and fixed to the leaf spring 3 by a first fastener 31. As a result, when the first piston 1 and the second piston 2 reciprocate under the action of the gas pressure difference, the leaf spring 3 radially supports the first piston 1 and the second piston 2 and provides axial rigidity for the first piston 1 and the second piston 2. During the refrigeration process, high-pressure gas flows back and forth in the expansion chamber of the second piston 2 at the end away from the leaf spring 3 and the compression chamber of the first piston 1 at the end away from the leaf spring 3. The gas in the expansion chamber performs positive work on the displacer structure, thereby providing refrigeration.

[0078] In one embodiment, the first fastener 31 is a stud of appropriate size. In one embodiment, the leaf spring 3 is composed of a double leaf spring. In one embodiment, the central axes of the first piston 1 and the second piston 2 are collinear. In one embodiment, the central axes of the first piston 1 and the second piston 2 pass through the center point of the leaf spring. In one embodiment, the leaf spring 3 is fixedly connected to the first piston 1 and the second piston 2 via the first fastener 31. In one embodiment, the first piston 1, the second piston 2, and the leaf spring 3 are coaxially mounted.

[0079] leaf spring

[0080] 2 and 3 , wherein FIG. 2 shows a schematic cross-sectional view of the displacer structure of a free-piston Stirling refrigerator; FIG. 3 shows a schematic structural view of a leaf spring of the displacer structure according to an embodiment of the present application;

[0081] Both ends of the leaf spring 3 are fixedly connected to the first cylinder 4 or the second cylinder 5 , so that the first piston 1 can reciprocate in the first cylinder 4 and the second piston 2 can reciprocate in the second cylinder 5 .

[0082] In one embodiment, both ends of the leaf spring 3 (ends away from the center of the leaf spring) are connected and secured to the end surface of the first cylinder 4 (end facing the second cylinder 5) via second fasteners 32. In one embodiment, the second fasteners 32 are second hexagon socket head cap screws. In one embodiment, the edges (ends) of the leaf spring 3 away from the center are connected to the first cylinder 4 via screws.

[0083] First cylinder and second cylinder

[0084] 1 to 4 , the ejector structure of the present application adopts a double-cylinder structure, which includes a first cylinder 4 and a second cylinder 5 . A first piston 1 reciprocates in the first cylinder 4 , and a second piston 2 reciprocates in the second cylinder 5 .

[0085] The second cylinder 5 includes a connecting section 51 and a accommodating section 52 (see Figure 4, in order to more clearly show the second cylinder 5, a structural schematic diagram of the second cylinder is shown). In the radial direction of the cylinder, the connecting section 51 is located on the outside of the first cylinder 4. In other words, the first cylinder 4 is inserted into the connecting section 51 of the second cylinder 5, wherein the gap between the connecting section 51 and the first cylinder 4 is sealed.

[0086] In one embodiment, a plurality of grooves 522 are provided on the inner wall of the accommodating section 52 to reduce the amount of cross-flow between the compression chamber and the expansion chamber through the gap, which has a positive effect on the sealing effect.

[0087] In one embodiment, the first cylinder 4 and the second cylinder 5 are gap-sealed by a cylinder seal 6. In one embodiment, the first cylinder 4 and the second cylinder 5 are gap-sealed by an O-ring and the interface between the first cylinder 4 and the second cylinder 5 is secured with glue. In one embodiment, the interface between the connecting section 51 of the second cylinder 5 and the first cylinder 4 is coated with glue, thereby securing the second cylinder 5 to the first cylinder 4.

[0088] For the first cylinder, the power piston (not shown) and the first piston reciprocate and vibrate inside the cylinder, playing the role of gas sealing. The air gap between the first cylinder and the first piston (hot end ejector piston) is very small to ensure good airtightness.

[0089] The first piston and the second piston

[0090] Referring to Figures 1 to 3, the first piston 1 includes a cylindrical structure with a protruding bottom surface, and the second piston 2 includes a cylindrical structure with a protruding bottom surface. The first piston 1 includes a first protruding bottom surface 10 protruding toward the leaf spring 3, and the second piston 2 includes a second protruding bottom surface 20 protruding toward the leaf spring 3, wherein the first protruding bottom surface 10 and / or the second protruding bottom surface 20 are arranged to avoid the end or edge of the leaf spring 3, away from the center, from colliding with the first piston 1 and / or the second piston 2 during the movement of the piston.

[0091] In one embodiment, the ejector structure further includes a first fastener 31. The first protruding bottom surface 10 is provided with a first protrusion 101, and the second protruding bottom surface 20 is provided with a second protrusion 201. The first fastener 31 passes through the leaf spring 3 and connects with the first protrusion 101 and the second protrusion 201, thereby securely connecting the leaf spring 3 to the first and second pistons 1 and 2. In one embodiment, the first protrusion 101 is located at the center of the first protruding bottom surface 10 and is a cylindrical structure extending toward the leaf spring 3. In one embodiment, the second protrusion 201 is located at the center of the second protruding bottom surface 20 and is a cylindrical structure extending toward the leaf spring 3. In one embodiment, the first fastener 31 is a stud.

[0092] In one embodiment, the first protrusion 101 is a cylindrical structure with an internal thread, and the second protrusion 201 is a cylindrical structure with an internal thread. The internal thread cooperates with the external thread of the stud to complete the connection. Preferably, an appropriate amount of thread glue is applied when the first protrusion 101 and the second protrusion 201 are threadedly connected to the stud.

[0093] In one embodiment, when the leaf spring 3 is connected to the first protrusion 101 and the second protrusion 201 by the first fastener 31, the end face of the first protrusion 101 is in contact with one surface of the leaf spring 3, and the end face of the second protrusion 201 is in contact with the other surface of the leaf spring.

[0094] In one embodiment, the axial distance between the first protruding bottom surface 10 of the first piston 1 and the leaf spring 3 should be greater than the maximum amplitude of the displacer structure, and the axial distance between the second protruding bottom surface 20 of the second piston 2 and the leaf spring 3 should also be greater than the maximum amplitude of the displacer structure.

[0095] To achieve good airtightness, the first piston 1 should maintain a small gap with the first cylinder 3. However, under the action of gravity, the first piston may deviate from its center position and even contact the wall of the cylinder. To prevent the displacer from contacting the wall and causing a significant increase in friction, it is assumed that the axial distance between the geometric center of the first piston and the center of the leaf spring (or the axial distance between the center point of the first piston and the center point of the leaf spring along the axial direction of the first piston) L1, the axial distance between the center point of the second piston (the second piston outer shell 21 and the second piston top cover 22) and the center of the leaf spring along the axial direction of the second piston L2, the weight of the first piston 1 m1, the weight of the second piston 2 m2, the radial stiffness of the leaf spring 3, and the air gap δ between the first piston and the cylinder should maintain a certain relationship.

[0096] The positional relationship among the first piston 1, the second piston 2 and the leaf spring 3 can satisfy the following formula:

[0097] Where m1 is the mass of the hot-end discharge piston, m2 is the mass of the cold-end discharge piston, L1 is the axial distance between the center of the hot-end discharge piston and the center of the leaf spring, L2 is the axial distance between the center of the cold-end discharge piston and the center of the leaf spring, g is the acceleration due to gravity, k is the radial stiffness of leaf spring 3, and δ is the air gap height between the wall of the hot-end discharge piston and the inner wall of the hot-end cylinder. See Figure 2, where L1, L2, and δ are schematically illustrated.

[0098] (a) First piston

[0099] To reduce the mass of the displacer and make it lighter, the first piston 1 adopts a hollow structure. The first piston 1 includes a first piston outer shell 11 and a first piston top cover 12. The first piston outer shell 11 and the first piston top cover 12 are sealed by a first piston seal 13. The first piston outer shell 11 and the first piston top cover 12 are connected and fixed by a first piston fastener 14. In one embodiment, the first piston seal 13 is an O-ring. In another embodiment, the first piston fastener 14 is a hexagon socket head cap screw. Preferably, the first piston outer shell 11 is a cylindrical structure with a bottom surface.

[0100] In one embodiment, the first piston housing 11, the first piston top cover 12, the O-ring and several screws constitute the first piston assembly. The first piston housing 11 and the first piston top cover 12 are sealed by the O-ring to prevent the loss of compression work caused by the gas in the compression chamber entering and exiting the first piston assembly. The first piston housing 11 and the first piston top cover 12 are fastened by eight screws.

[0101] To prevent direct collision between the first piston and the deformed leaf spring during movement, the first piston housing has a certain slope on the side near the cold end (second piston) or leaf spring 3. The magnitude of the slope is determined by the maximum amplitude of the displacer assembly. In other words, the first piston housing includes a first protruding bottom surface 10 facing the leaf spring 3, thereby creating a slope on the bottom surface of the first piston housing. The maximum axial distance between the first protruding bottom surface 10 of the first piston 1 and the leaf spring 3 should be greater than the maximum amplitude of the displacer structure. At the same time, the first piston housing (hot end piston housing) of the displacer has a cylindrical protrusion (first protrusion 101) on the side near the expansion chamber (or near the leaf spring). The center of the protrusion is internally threaded to facilitate connection with the leaf spring 3 and the second piston 2.

[0102] (b) Second piston

[0103] To reduce the mass of the displacer and make it lighter, the second piston 2 adopts a hollow structure. Preferably, to reduce internal empty volume and control mass, the second piston is filled with a rollable lightweight material. The second piston 2 comprises a second piston outer shell 21 and a second piston top cover 22, which are fixedly connected and sealed via internal and external threads. Preferably, the first and second piston outer shells 11 and 21 are arranged opposite each other near the leaf spring 3. Preferably, the second piston outer shell is a cylindrical structure with a bottom surface.

[0104] Similarly, to prevent the second piston from colliding with the leaf spring during movement, the second piston outer shell has a certain slope on the side close to the leaf spring. The size of the slope is determined by the maximum amplitude of the displacer assembly. In other words, the second piston outer shell includes a second protruding bottom surface 20 facing the leaf spring 3, thereby making the bottom surface of the second piston shell have a slope, and the maximum axial distance between the second protruding bottom surface 20 of the second piston 2 and the leaf spring 3 should be greater than the maximum amplitude of the displacer structure. The second piston outer shell has a boss (second protrusion 201) close to the leaf spring, and the center of the boss has an internal threaded hole of a certain depth.

[0105] In one embodiment, a stud passes through the internal thread of the protrusion (first protrusion 101) or the boss (second protrusion 201) of the first and second piston outer shells, and connects the leaf spring to the first and second piston outer shells and fixes them with glue applied on the surface of the screw.

[0106] Materials of each component

[0107] The existing displacer structure consists of a single piston, which runs through the compression chamber at the hot end and the expansion chamber at the cold end. Displacer structures are generally made of aluminum alloy, stainless steel, or polymer (engineering plastic). Metal displacer structures have low thermal deformation, high strength, high machining accuracy, and high thermal conductivity. The gap between the cylinder and the displacer can be designed to be very small, resulting in good airtightness, low shuttle loss, and low pumping loss. However, the disadvantage is that the axial heat conduction from the compression chamber to the expansion chamber is large, and the mass of the displacer is also large. Polymer materials generally have low strength, low machining accuracy, large thermal deformation, and low thermal conductivity. Their advantages are low axial heat conduction from the compression chamber to the expansion chamber through the displacer body and low mass. Their disadvantage is that a certain gap must be maintained between the displacer and the cylinder to prevent direct friction between the displacer and the cylinder due to temperature changes, resulting in a significant increase in the displacer's damping.

[0108] The various problems caused by the use of a single material for the displacer structure (as mentioned above) are solved by minimizing the axial heat conduction loss as much as possible while ensuring the airtightness between the compression chamber and the expansion chamber (reducing shuttle loss and pumping loss) to improve the efficient cooling effect of the refrigerator.

[0109] Therefore, in order to reduce the transfer of heat from the hot end to the cold end of the refrigerator through the cylinder, and at the same time to maintain a small gap between the piston and the cylinder, in the technical solution of the present application, the cylinder structure and the ejector structure are both made of a mixture of two materials, wherein the first cylinder is made of metal material, such as aluminum alloy, stainless steel, titanium alloy, etc., and the second cylinder is made of a high molecular polymer (engineering plastic) with low thermal conductivity and high strength, and the first cylinder and the second cylinder are connected by an O-ring and glue is used to bond the two.

[0110] Preferably, the first piston 1 is made of aluminum alloy with high strength and low density, and the hot end discharge piston surface is evenly sprayed with a wear-resistant and lubricating coating such as Teflon. The second piston 2 is made of engineering plastic with low thermal conductivity, low temperature resistance, and low thermal expansion coefficient.

[0111] Preferably, the first cylinder 4 is made of an aluminum alloy material with high thermal conductivity and high strength, wherein the inner cylinder wall surface of the first cylinder 4 is polished and hard-oxidized.

[0112] The second cylinder 5 is made of engineering plastics with low thermal conductivity, high strength and low thermal expansion coefficient. The inner wall surface of the accommodating section 522 of the second cylinder 5 adopts a sealing structure with multiple grooves 522 .

[0113] Free piston Stirling refrigerator

[0114] A refrigerator including the above-mentioned ejector structure.

[0115] In order to make the purpose, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that these are only some examples that the present invention may take, but are not intended to limit the scope of the present invention.

[0116] Example

[0117] This embodiment provides an ejector structure for a free-piston Stirling refrigerator, which adopts a dual-cylinder-dual-piston structure, as shown in Figures 1 to 4. The device includes: a first piston 1, a second piston 2, a leaf spring 3, a first cylinder 4, and a second cylinder 5.

[0118] The first piston 1, the second piston 2, and the leaf spring 3 are arranged along the axial direction, with the leaf spring 3 being disposed between the first piston 1 and the second piston 2. The leaf spring 3 is connected to the first piston 1 and the second piston 2 via a first fastener 31, so that when the first piston 1 and the second piston 2 reciprocate under the action of the gas pressure difference, the leaf spring 3 radially supports the first piston 1 and the second piston 2 and provides axial stiffness for the first piston 1 and the second piston 2.

[0119] Specifically, referring to Figure 2 , the first piston 1 includes a first piston outer housing 11 and a first piston top cover 12. The first piston outer housing 11 and the first piston top cover 12 are sealed by a first O-ring (i.e., an example of the first piston seal 13) and secured together by a first hexagon socket screw (i.e., an example of the first piston fastener 14). The first piston outer housing 11 is a cylindrical structure with a protruding bottom surface. The first piston 1 includes a first protruding bottom surface 10 that protrudes toward the leaf spring 3. The first protruding bottom surface 10 is provided with a cylindrical protrusion 101 (i.e., the first protrusion 101) facing the leaf spring 3. The center of the protruding cylinder is processed with an internal thread.

[0120] The second piston 2 includes a second piston outer shell 21 and a second piston top cover 22, which are fixedly connected and sealed by internal and external threads. The second piston outer shell 21 is a cylindrical structure with a protruding bottom surface. The second piston outer shell 21 includes a second protruding bottom surface 20 that protrudes toward the leaf spring 3. The second protruding bottom surface 20 is provided with a boss (i.e., a second protrusion 201) facing the leaf spring 3. The center of the boss has an internal threaded hole of a certain depth, thereby connecting and fixing the first piston 1, the second piston 2, and the leaf spring 3 via a stud 31 of a suitable size. The stud 31 passes through the protrusion (first protrusion 101) of the first protruding bottom surface, the leaf spring 3, and the boss 201 (i.e., second protrusion 201) of the second protruding bottom surface 20. The installation coaxiality of the first piston 1, the second piston 2, and the leaf spring 3 is controlled within 0.005mm.

[0121] The leaf spring 3 is connected and fixed to the upper end surface of the first cylinder 4 by a second hexagon socket screw (ie, an example of the second fastener 32 ), and the coaxiality of the leaf spring 3 and the first cylinder 4 is controlled within 0.005 mm.

[0122] The first cylinder 4 and the second cylinder 5 are gap-sealed by a second O-ring (an example of a cylinder seal 6) and glue is applied to the interface between the first cylinder 4 and the second cylinder 5. The installation coaxiality of the first cylinder 4 and the second cylinder 5 is controlled within 0.005 mm.

[0123] In this embodiment, the first piston 1 is made of a high-strength, low-density aluminum alloy, and the hot-end discharge piston surface is uniformly sprayed with a wear-resistant, lubricating coating such as Teflon. The second piston 2 is constructed of an engineering plastic with low thermal conductivity, low-temperature resistance, and a low thermal expansion coefficient. The first cylinder 1 is constructed of a high-strength, high-thermal-conductivity aluminum alloy. The inner cylinder wall of the hot-end cylinder is polished and hard-anodized. The second cylinder 2 is constructed of an engineering plastic with low thermal conductivity, high strength, and a low thermal expansion coefficient, and the inner cylinder wall utilizes a multi-groove sealing structure.

[0124] Installation steps:

[0125] (1) Place an O-ring of appropriate size on the boss of the first piston top cover, and fix the first piston top cover to the first piston outer shell with 8 screws.

[0126] (2) Fill the second piston outer shell with lightweight material evenly, and then fix the second piston top cover to the second piston thread.

[0127] (3) Insert a stud of appropriate size and length through the circular hole in the center of the leaf spring 3, and connect the first piston assembly and the second piston through threads. The raised end surface of the second piston outer shell (i.e., the end surface of the first protrusion 101 of the first protruding bottom surface 10) and the raised end surface of the first piston outer shell (i.e., the end surface of the second protrusion 201 of the first protruding bottom surface 10) are flush with the two surfaces of the leaf spring, and an appropriate amount of thread glue is applied during the threaded connection. It should be noted that during the installation process, the coaxiality of the leaf spring, the first piston assembly (the first piston outer shell 11 and the first piston top cover 12) and the second piston assembly (the second piston outer shell 21 and the second piston top cover 22) should be maintained, and the coaxiality needs to be maintained within 0.005mm.

[0128] (4) Install the leaf spring coaxially on the end face of the first cylinder using eight screws. The coaxiality must be within 0.005 mm.

[0129] (5) Finally, the first cylinder 4 and the second cylinder 5 are sealed with an O-ring and a proper amount of anaerobic glue is filled in the gap between the two to ensure the fixation of the two. The coaxiality should be controlled within 0.005 mm during the installation process.

[0130] It is worth mentioning that all parts need to be dried in a drying oven at high temperature for a certain period of time before installation.

[0131] The applicant would like to emphasize that the displacer structure of this embodiment abandons the practice of using a displacer base placed inside the compression chamber and a leaf spring arranged inside the displacer, and removes unnecessary parts other than the cylinder that can directly wear against the displacer, thereby greatly reducing the damping while ensuring excellent air tightness between the displacer and the cylinder (small shuttle loss and pump air loss), without increasing the empty volume of the compression chamber or the expansion chamber, and having very small axial heat conduction of the displacer, which does not affect the maximum power of the refrigerator, simplifies the structure of the refrigerator, and reduces the installation difficulty while ensuring the safe and reliable operation of the refrigerator.

[0132] The specification of this application records a large number of technical features, which are distributed in various technical solutions. If all possible combinations of technical features of this application (i.e., technical solutions) are to be listed, the specification will be too lengthy. In order to avoid this problem, the various technical features disclosed in the above-mentioned invention content of this application, the various technical features disclosed in the various embodiments and examples below, and the various technical features disclosed in the accompanying drawings can be freely combined with each other to form various new technical solutions (these technical solutions are all deemed to have been recorded in this specification), unless such a combination of technical features is technically infeasible. For example, in one example, feature A+B+C is disclosed, and in another example, feature A+B+D+E is disclosed. Features C and D are equivalent technical means that play the same role. Technically, only one of them can be used, and it is impossible to use them at the same time. Feature E can be technically combined with feature C. Then, the solution of A+B+C+D should not be considered as having been recorded because it is technically infeasible, while the solution of A+B+C+E should be considered as having been recorded.

[0133] All documents mentioned in this application are considered to be included in their entirety in the disclosure of this application so that they can be used as a basis for modification when necessary. In addition, it should be understood that after reading the above disclosure of this application, those skilled in the art may make various changes or modifications to this application, and these equivalent forms also fall within the scope of protection claimed in this application.

Claims

1. An ejector structure for a free piston Stirling refrigerator, characterized in that: include: A first piston (1), a leaf spring (3), and a second piston (2) are arranged in sequence axially. The leaf spring (3) is connected to the first piston (1) and the second piston (2) through a first fastener (31), so that when the first piston (1) and the second piston (2) reciprocate under the action of a gas pressure difference, the leaf spring (3) radially supports the first piston (1) and the second piston (2) and provides axial rigidity for the first piston (1) and the second piston (2); During the refrigeration process, high-pressure gas flows back and forth in the expansion chamber of the second piston (2) at one end away from the leaf spring (3) and the compression chamber of the first piston (1) at one end away from the leaf spring (3), and the gas in the expansion chamber performs positive work on the ejector structure, thereby providing refrigeration; The first piston (1) comprises a cylindrical structure with a protruding bottom surface, the second piston (2) comprises a cylindrical structure with a protruding bottom surface, the first piston (1) comprises a first protruding bottom surface (10) protruding toward the leaf spring (3), and the second piston (2) comprises a second protruding bottom surface (20) protruding toward the leaf spring (3); The ejector structure further comprises a first fastener (31), the first protruding bottom surface (10) is provided with a first protruding portion (101), the second protruding bottom surface (20) is provided with a second protruding portion (201), the first fastener (31) passes through the leaf spring (3) and is connected to the first protruding portion (101) and the second protruding portion (201), so that the leaf spring (3) is fixedly connected to the first piston (1) and the second piston (2); The positional relationship between the first piston (1), the second piston (2) and the leaf spring (3) must satisfy the following formula: Wherein, m1 is the mass of the first piston, m2 is the mass of the second piston, L1 is the axial distance between the center point of the first piston and the center point of the leaf spring along the axial direction of the first piston, L2 is the axial distance between the center point of the second piston and the center point of the leaf spring along the axial direction of the second piston, g is the acceleration of gravity, k is the radial stiffness of the leaf spring, and δ is the air gap height between the outer wall surface of the first piston and the inner wall surface of the first cylinder.

2. The ejector structure according to claim 1, characterized in that: The first fastener (31) is a stud, the first protrusion (101) is a cylindrical structure with an internal thread, and the second protrusion (201) is a cylindrical structure with an internal thread, and the internal thread cooperates with the external thread of the stud to complete the connection.

3. The ejector structure according to claim 1, characterized in that: When the leaf spring is connected to the first protrusion and the second protrusion by the first fastener, the end surface of the first protrusion fits with one surface of the leaf spring, and the end surface of the second protrusion fits with the other surface of the leaf spring.

4. The ejector structure according to claim 1, characterized in that: The maximum axial distance between the first protruding bottom surface (10) of the first piston (1) and the leaf spring (3) should be greater than the maximum amplitude of the ejector structure, and the maximum axial distance between the second protruding bottom surface (20) of the second piston (2) and the leaf spring (3) should also be greater than the maximum amplitude of the ejector structure.

5. The ejector structure according to claim 1, characterized in that: The first piston, the second piston and the leaf spring are coaxially installed.

6. The ejector structure according to claim 1, characterized in that: It also comprises a first cylinder (4) and a second cylinder (5), and the two ends of the leaf spring (3) are fixedly connected to the first cylinder (4) or the second cylinder (5), so that the first piston (1) can reciprocate in the first cylinder (4) and the second piston (2) can reciprocate in the second cylinder (5).

7. The ejector structure according to claim 6, characterized in that: The second cylinder (5) comprises a connecting section (51) and a receiving section (52); the connecting section (51) is located outside the first cylinder (4) in the radial direction of the cylinder; and a gap between the connecting section (51) and the first cylinder (4) is sealed.

8. The ejector structure according to claim 1, characterized in that: The first piston (1) is a hollow structure. The first piston (1) comprises a first piston outer shell (11) and a first piston top cover (12). The first piston outer shell (11) and the first piston top cover (12) are sealed by a first piston seal (13).

9. The ejector structure according to claim 8, characterized in that: The second piston (2) is a hollow structure. The second piston (2) comprises a second piston outer shell (21) and a second piston top cover (22). The second piston outer shell (21) and the second piston top cover (22) are fixedly connected and sealed by threads.

10. A free piston Stirling refrigerator, characterized in that: The ejector structure comprises the ejector structure according to any one of claims 1 to 9.

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