A frame and a free-piston split Stirling refrigerator

Abstract

The frame and the free-piston split Stirling refrigerator according to the present invention, the frame includes a flange and two piston tubes, the two piston tubes are respectively arranged on the flange and symmetrically distributed on both sides of the flange. The flange is in a disc shape, and a first disc, a circular groove, a second disc, and a protruding circular band are respectively arranged on both sides. The first disc, the circular groove, the second disc, and the protruding circular band are adjacent to each other in ascending order. On the circumference of the flange, there are respectively a first boss for connecting with a connecting pipe, a second boss for an inflation port, and a third boss for a connector port. The first boss, the second boss, and the third boss are adjacent to each other. The piston tube has a cylindrical inner cavity, and the axis of the compression piston tube is collinear with the axis of the flange. On the outer wall of the piston tube, there are symmetrically arranged concave intake grooves, and the intake grooves are axially arranged from the free end towards the flange direction. Through holes communicating the intake grooves with the inner cavity of the piston tube are arranged in the intake grooves.

Description

Technical Field

[0001] The present invention belongs to the field of refrigeration, and particularly relates to a frame and a free-piston split Stirling refrigerator. Background Art

[0002] The last three decades have been a period of rapid development of aerospace technology, infrared technology, atomic energy technology, superconducting technology, as well as cryoelectronics, cryophysics, cryomedicine, and cryobiology. As an important branch of cryogenic technology - cryocoolers have developed rapidly with the development of the above-mentioned science and technology.

[0003] The theoretical refrigeration efficiency of a Stirling refrigerator is equal to the Carnot efficiency, and its actual operating efficiency is also the highest among all current cryocoolers. The mechanism of the free-piston Stirling refrigerator was proposed by William Beale in the 1960s. Its main features are the use of technologies such as a linear compressor drive, flexible spring support, clearance seal combined with gas bearings, and it has the advantages of a compact structure, low noise, long life, and high reliability.

[0004] Currently, the mainstream space cryocoolers are Stirling refrigerators and pulse tube refrigerators. From a thermodynamic perspective, the Stirling refrigerator has a higher efficiency under the same temperature limit. Due to the strict requirements of space refrigeration for energy consumption, life, and vibration, how to improve the efficiency, life, and reduce vibration of cryocoolers has always been the main problem of space cryocoolers. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a motor bracket for a linear compressor and a free-piston split Stirling refrigerator.

[0006] The present invention provides a frame, having the following features, including a flange; and two piston tubes, respectively arranged on the flange, symmetrically distributed on both sides of the flange. Among them, the flange is in a disc shape, with a first disc, a circular groove, a second disc, and a protruding circular band respectively arranged on both sides. The first disc, the circular groove, the second disc, and the protruding circular band are adjacent to each other in ascending order. On the circumference of the flange, there are respectively a first boss for connecting with a connecting pipe, a second boss for an inflation port, and a third boss for a connector port. The first boss, the second boss, and the third boss are adjacent to each other. The piston tube has a cylindrical inner cavity, and the axis of the compression piston tube is collinear with the axis of the flange. On the outer wall of the piston tube, there are symmetrically arranged concave intake grooves, which are axially arranged from the free end towards the flange direction. Through holes for connecting the intake grooves with the inner cavity of the piston tube are arranged in the intake grooves.

[0007] In the frame provided by the present invention, it may further have the following features: among them, the first disc is used to place the inner yoke, there is an assembly gap between the circular groove and the second disc, and the protruding circular band is used to position the outer yoke.

[0008] In addition, in the frame provided by the present invention, it may further have the following feature: among them, the first boss is radially provided with a first through hole communicating the outside with the inner cavity of the piston tube.

[0009] In addition, in the frame provided by the present invention, it may further have the following feature: among them, the second boss is radially provided with an inflation through hole communicating the outside with the assembly gap, and the third boss is radially provided with a wire threading through hole communicating the outside with the assembly gap.

[0010] The present invention provides a free-piston split Stirling refrigerator, having the following features, including a compressor with a frame; and an expander, the expander is communicated with the compressor through a connecting pipe, among which, the frame is any one of the above frames.

[0011] In the free-piston split Stirling refrigerator provided by the present invention, it may further have the following feature: among them, the compressor further includes two compression units, the compression unit has a compression piston, the compression piston has a cylindrical inner cavity, an inward concave annular groove and a plurality of concave cavities are provided on its outer wall, a throttling through hole communicating the cylindrical inner cavity is provided in the concave cavity, and a ventilation hole communicating with the annular groove is provided on the end face of the open end of the compression piston.

[0012] In addition, in the free-piston split Stirling refrigerator provided by the present invention, it may further have the following feature: among them, the two compression pistons are symmetrically arranged in the cylindrical inner cavity of the piston tube respectively, and the open ends of the two compression pistons are arranged opposite to each other.

[0013] In addition, in the free-piston split Stirling refrigerator provided by the present invention, it may further have the following feature: among them, the expander includes an ejector, an ejector rod, a cold head, a cold-end heat exchanger, and an expansion cylinder, one end of the ejector is spring-connected to the expansion side plate through the ejector rod, and the other end is a free end.

[0014] In addition, in the free-piston split Stirling refrigerator provided by the present invention, it may further have the following feature: among them, the cold-end heat exchanger is a slit-type heat exchanger, which is arranged inside the cold head and closely adheres to the inner wall of the cold head, and the cold-end heat exchanger is in interference fit with the cold head.

[0015] In addition, in the free-piston split Stirling refrigerator provided by the present invention, it may further have the following feature: among them, the ejector, the expansion cylinder and the cold head form an expansion cavity.

[0016] Functions and effects of the invention

[0017] According to the bracket and the free-piston split Stirling refrigerator of the present invention, a rectangular groove is provided on the piston tube of the bracket, and a through hole is provided in the groove for guiding the gas in the back pressure chamber to reach the compression chamber through the compression piston, so as to prevent the piston stroke from decreasing due to the increase in the back pressure chamber pressure caused by the gas bearing.

[0018] In addition, the free-piston split Stirling cryocooler of the present invention eliminates the leaf spring structure of the traditional free-piston split Stirling cryocooler, and provides the required radial supporting force in the form of a gas bearing.

[0019] Furthermore, the expander is provided with flow guiding devices at both the upper and lower ends of the displacer, making the passing air flow smoother and more uniform. The cold-end heat exchanger is a slit heat exchanger that is tightly attached to the cold head through interference fit, which helps to improve the heat exchange efficiency and reduce the cold loss.

[0020] Furthermore, a groove with a certain depth is provided at the base of the expander to prevent the movement impact of the leaf spring, which can make the structure of the expander more compact and improve the cycle efficiency of the free-piston split Stirling cryocooler.

[0021] Furthermore, the gas bearing structure provided by the present invention and the motor bracket that facilitates the assembly of the whole machine and is compact make the operation of the whole machine more stable, solve the problem of the increase in the back pressure chamber pressure brought by the gas bearing and improve the efficiency of the whole machine, overcome the problems of difficult assembly and positioning of the traditional bracket, large weight of the bracket, and insufficient compactness of the whole machine, improve the assembly speed and accuracy, the compactness of the whole machine and reduce the weight of the whole machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic cross-sectional view of the free-piston split Stirling cryocooler in the embodiment of the present invention;

[0023] Figure 2 is a three-dimensional schematic view of the motor bracket in the embodiment of the present invention;

[0024] Figure 3 is Figure 2 the view from direction A in

[0025] Figure 4 is Figure 3 the sectional view taken along line C-C in

[0026] Figure 5 is Figure 3 the sectional view taken along line D-D in

[0027] Figure 6 is Figure 3 the sectional view taken along line E-E in

[0028] Figure 7 is Figure 2 the view from direction B in

[0029] Figure 8 is a three-dimensional schematic view of the compression piston in the embodiment;

[0030] Figure 9 is Figure 8 the sectional view taken along line F-F in

[0031] Figure 10 It is a three-dimensional schematic diagram of the gas bearing inner bushing in the embodiment. Detailed implementation manners

[0032] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the following embodiments will specifically describe the bracket and the free piston split Stirling refrigerator of the present invention in conjunction with the accompanying drawings.

[0033] Embodiment

[0034] As Figure 1 shown, the free piston split Stirling refrigerator includes a compressor 60 and an expander 70.

[0035] The compressor 60 is connected to the expander 70 through a connecting pipe 6.

[0036] The compressor 60 includes a linear motor 1, two compression units 4, a frame 3 and a housing 2.

[0037] As Figure 2 , 3 , 4, 5, 6, 7 shown, the frame 3 includes a flange 32 and two piston tubes 31 arranged in the flange.

[0038] The flange 32 is in a disc shape, and a disc 326, a circular groove 325, a disc 324, and a protruding circular band 327 are distributed on the corresponding two sides. The radii of the disc 326, the circular groove 325, the disc 324, and the protruding circular band 327 are arranged adjacent to each other in ascending order.

[0039] The disc 324 is used to place the inner yoke iron component.

[0040] The circular ring groove 325 is used to prevent the cylinder collision caused by the increase of the motor mover movement amplitude due to excessive input of the whole machine power.

[0041] Part of the space between the discs 325 and 326 is hollowed out, so that there is a gap between the disc 326 and the circular groove 325, which is used to reduce the weight of the whole machine, provide space for the lead wire to flow out and for inflation. And at the thicker part of the connection between the circular groove 325 and the disc 326, it is used to position the inner yoke iron mold and facilitate the motor assembly.

[0042] The disc 326 is provided with a protruding circular band 327, which is used to facilitate the positioning of the outer yoke iron and make the assembly more efficient and simple.

[0043] The flange 32 is provided with bosses 321, 322, and 323 on the circumference. The three bosses are respectively used for the connection port of the connecting pipe 6, the inflation port, and the connector port.

[0044] The piston tube 31 is a straight tube, which is arranged at the center of the flange 32 and coaxial with the flange 32. Both ends of the piston tube 31 are free ends, and the two piston tubes 31 are symmetrically distributed on both sides of the flange 32. A cylindrical through-hole is opened in the piston tube 31 as a piston chamber. Two concave intake grooves 311 are symmetrically arranged on the outer walls of the two piston tubes 31. The cross-section of the intake groove 311 is rectangular and is arranged axially from the end of the free end towards the flange 32. A through-hole 312 is arranged in the groove, and the through-hole 312 connects the intake groove 311 with the piston chamber of the piston tube 31, aiming to drain the gas in the back-pressure chamber to the compression chamber through the compression piston and prevent the piston stroke from decreasing due to the increase in the back-pressure chamber pressure caused by the gas bearing.

[0045] As Figure 4 shown, the boss 321 is located on the circumference of the flange 32. A sealing groove 3211 is opened on the boss 321 for placing a sealing gasket, and a groove 3212 is opened in the boss for placing a connecting part. A radially arranged through-hole 3213 is opened at the bottom of the groove 3212, and the through-hole 3213 connects the groove 3212 with the piston chamber in the piston tube 31.

[0046] A compression-side connecting part 5 is equipped on the boss 321 and is connected to the expander 70 through a connecting pipe 6 and an expansion-side connecting part 7 to realize the gas path between the compression side and the expansion side.

[0047] As Figure 5 shown, the boss 322 is located on the circumference of the flange 32. A radially arranged through-hole 3221 is opened on the boss 322, and the through-hole 3221 communicates with the gap between the disc 326 and the circular groove 325.

[0048] The boss 322 is connected to the gas source through an external connecting part, and high-pressure gas is filled into the compressor through the through-hole 3221. The gas-filling hole is opened in the gap between the disc 326 and the circular groove 325, which is beneficial to simplifying the processing difficulty of the motor bracket and facilitating the rapid filling and diffusion of gas.

[0049] As Figure 6 shown, the boss 323 is located on the circumference of the flange 32. A sealing groove 3231 is opened on the boss 323 for placing a sealing gasket, and a groove 3232 is opened in the boss 323 for installing a power cord connector. A radially arranged through-hole 3233 is opened at the bottom of the groove 3232, and the through-hole 3233 communicates with the gap between the disc 326 and the circular groove 325, which can provide enough space for leading out wires and is beneficial to the assembly and connection of the whole machine.

[0050] The linear motor 1 includes an outer yoke 14, an inner yoke 16 and a mover. The outer yoke 14 and the inner yoke 16 are respectively arranged on the frame and there is a gap between the outer yoke and the inner yoke. The mover is arranged in the gap, and the mover includes a permanent magnet 15 and a permanent magnet bracket 17.

[0051] AsFigure 1 As shown in the figure, the linear motor 1 includes a coil support 11, a coil 12, an outer yoke pressing plate 13, an outer yoke 14, a permanent magnet 15, an inner yoke 16, and a permanent magnet support 17. The mover includes the permanent magnet 15 and the permanent magnet support 17, wherein the permanent magnet 15 and the permanent magnet support 17 are connected, and the piston 47 is threadedly connected to the permanent magnet support 17. The outer yoke 14 and the inner yoke 16 are made of soft magnetic materials, usually made of materials such as pure iron for electrical engineering and silicon steel sheets. The permanent magnet 15 is a permanent magnetic material, usually made of rare earth iron boron and alnico permanent magnetic materials. The outer yoke 14, the coil 12, the permanent magnet 15, and the inner yoke 16 are all annular and are arranged coaxially. The outer yoke 14 and the inner yoke 16 are respectively arranged on the support 3 and there is a gap between the outer yoke and the inner yoke. The mover is arranged in the gap.

[0052] When direct current is passed through the coil, magnetic force loops will be formed in the outer yoke 14 and the inner yoke 16, thereby generating magnetic poles on the outer yoke 14 and the inner yoke 16. When alternating current is passed through the coil, the permanent magnet 15 will be subjected to an alternating electromagnetic force and perform a reciprocating motion. When the permanent magnet 15 performs a reciprocating motion, it will drive the compression piston 47 to perform a reciprocating linear motion. Gas bearing technology is used to provide the radial supporting force of the piston.

[0053] The compression unit 4 includes a clamp 41, a clamp 46, a compression piston end cover 42, a check valve disc 43, a porous flow limiting belt 44, a gas bearing inner bushing 45, and a compression piston 47.

[0054] As Figure 8 , Figure 9 shown, the compression piston 47 has a cylindrical blind hole with an open end. A plurality of annular cavities 472 are arranged along the circumference on the outer wall of the compression piston 47. Throttle holes 474 are arranged in the annular cavities. An annular groove 473 is arranged on the outer wall of the compression piston 47. The plurality of annular cavities are respectively arranged on both sides of the annular groove 473.

[0055] A step 475 is formed inside the compression piston 47 for placing the compression piston end cover 42. A snap ring groove 476 is formed on the other side for restricting the axial movement of the compression piston end cover 42.

[0056] Two vent holes 471 are arranged on the end face of the open end of the compression piston 47. The vent holes 471 communicate with the annular groove 473. Gas enters the compression cavity from the back pressure cavity through the annular groove on the compression piston 47 via the intake hole 312 on the support 3 through the piston inner hole 471 to ensure the stability of the back pressure cavity pressure, thereby ensuring that the piston stroke remains unchanged.

[0057] In the embodiment, 8 - 10 throttle holes are formed on the surface of the compression piston 47, with 4 - 5 evenly distributed at both ends, and gas is used to support the piston as a gas bearing.

[0058] As Figure 1As shown, two compression pistons 47 are symmetrically arranged in the piston chambers of the piston tube 31 respectively, and the open ends of the two compression pistons 47 are arranged opposite to each other.

[0059] One end of the compression piston 47 is connected to the permanent magnet bracket 17 by a screw, and the other end is a free end. When the permanent magnet 15 moves reciprocally, it will drive the compression piston 47 to move in a reciprocating linear motion.

[0060] The porous flow-limiting belt 44 and the gas bearing inner bushing 45 are both arranged in the cylindrical piston chamber of the compression piston 47, and the porous flow-limiting belt 44 is arranged outside the gas bearing inner bushing 45.

[0061] As Figure 10 shown, the gas bearing inner bushing 45 is provided with five square groove through holes 451 along the circumference, which can enable the gas inside the compression piston 47 to pass through the porous flow-limiting belt 11 and enter the throttle hole. A notch 452 with a width of 0.6 - 0.8 mm is axially opened on the outer wall of the gas bearing inner bushing 45, making it easier for the gas bearing inner bushing 45 to open. In addition, a clamp groove 453 is opened inside the gas bearing inner bushing 45, and the tension of the clamp 46 is used to open the gas bearing inner bushing 45, making the porous flow-limiting belt 44 fit more closely to the inner wall surface of the piston chamber.

[0062] The porous flow-limiting belt 44 is made to fit perfectly to the inner wall of the piston chamber by means of the gas bearing inner bushing 45 and the clamp 46.

[0063] A step is opened inside the compression piston 47 for placing the compression piston end cover 42, and a groove for placing the clamp 41 is opened on the other side to limit the axial movement of the compression piston end cover 42.

[0064] As Figure 1 shown, the clamp 41, the compression piston end cover 42, and the compression piston end cover 42 are respectively arranged in the piston chamber of the compression piston 47, and are arranged in sequence from the opening of the piston chamber.

[0065] The outer shell 2 is arranged outside the bracket 3, and the linear motor 1, two compression units 4, and the bracket 3 are all arranged inside the outer shell 2.

[0066] The expander 70 includes an expansion cylinder 101, a cold end heat exchanger 104, a copper cold head 105, an ejector 106, an ejector rod 107, an expander leaf spring 110, an expander middle housing 9, an expander bottom housing 10, and a shock absorption device 8.

[0067] The ejector 106 is in the shape of a cylinder with a circular cross-section and is arranged inside the expansion cylinder 101. One end is connected to the expander leaf spring 110 through the ejector rod 107, and the other end is a free end. The inside of the ejector 106 is filled with a regenerator packing. A flow guide vane 102 is provided at one end of the ejector 106, and an ejector seal head 103 is installed at the other end. A certain number of round holes are opened on the ejector seal head 103 to make the gas flowing towards the cold head more uniform. And two round holes with a larger diameter are symmetrically opened on the ejector seal head 103 to facilitate later installation. In the embodiment, the ejector 106 is a combination of a regenerator and an expansion piston. The ejector 106 serves both as a regenerator and an expansion piston.

[0068] The cold-end heat exchanger 104 is a slit-type heat exchanger, which is placed inside the copper cold head 105 and has an interference fit with the copper cold head 105 and is closely attached to the inner wall of the copper cold head 105.

[0069] The left end part of the ejector rod 107 is located inside the ejector 106, and a number of grooves are opened on the outer periphery of the ejector rod 107 to facilitate connecting the ejector rod 107 and the ejector 106 by gluing. The right end of the ejector rod 107 is connected to the expander side leaf spring 110 through a screw 111 to provide the axial restoring force and radial supporting force required for the reciprocating movement of the ejector 106. And a stainless steel sleeve 108 is provided between the right end of the ejector rod 107 and the middle housing 9 of the expander to prevent excessive wear of the housing. A leaf spring gasket 109 is provided between the expander side leaf spring 110 and the middle housing 9 of the expander to reduce the loss of the leaf spring and increase the service life of the whole machine.

[0070] The bottom housing 10 of the expander is connected to the middle housing 9 of the expander by screws, and a circular groove with a certain depth is dug in the center of the bottom housing of the expander, making the structure of the whole machine more compact.

[0071] The shock absorption structure 8 includes a shock absorption block 81, a shock absorber leaf spring 82, shock absorber gaskets 83, 84, and a shock absorber fixing bolt 85. The shock absorber 8 is connected to the expander by screws.

[0072] The ejector 106 is driven by pure gas, and a refrigeration effect is generated by using the phase difference between the ejector 106 and the compression piston 47. Usually, the displacement of the ejector 106 leads the displacement of the compression piston 47 by 70° to 100°. Since the linear motor is excited by sinusoidal alternating current, the movements of the ejector 106 and the compression piston 47 also show sinusoidal curve movements. But for the purpose of explaining its working principle, it is assumed that the ejector 106 and the compression piston 47 make intermittent jumping movements according to the law.

[0073] Compression process of the compressor: The ejector 106 stays in place, and the compression piston 47 moves towards the middle. At this time, the gas is compressed into the connecting pipe 6 and the middle housing 9 of the expander. The heat generated by compression is discharged to the environment through the housing and the connecting pipe 6. Ideally, it is considered that the housing and the connecting pipe are completely heat-conducting and have an infinite heat exchange area, so the temperature of the working medium remains unchanged. However, in actual operation, isothermal compression is impossible to achieve, and the ejector 106 cannot move intermittently. When the compression piston 47 moves, the ejector 106 has already started to move.

[0074] Heat release process of the regenerator: The compression piston 47 continues to move towards the center, and the ejector also moves to the left to ensure that the volume of the gas remains unchanged until the compression piston reaches the compression vertex. When the gas passes through the wire mesh inside the ejector, the gas is cooled by the regenerator and transfers the heat to the packing. However, in the actual process, this process is not constant volume, and complete heat exchange cannot be achieved either.

[0075] Expansion refrigeration process: The compression piston 47 stops at the vertex, and the ejector 106 continues to move to the left until the left dead center. The gas expands to generate cold, and the cold is transferred to the cold head through the cold end heat exchanger. However, in actual operation, the gas does not undergo an isothermal expansion process, and the heat exchange of the cold end heat exchanger is not complete either.

[0076] Heat absorption process of the regenerator: The compression piston 47 and the ejector 106 move in opposite directions at the same time, and the gas volume remains unchanged and returns to the initial position. In this process, the gas passes through the regenerator and absorbs heat from the regenerator. However, in the actual heat exchange process, the heat exchange in the regenerator is not constant volume, and complete heat exchange in the regenerator cannot be achieved.

[0077] This embodiment is applicable to a refrigeration temperature of about 77K and can provide a considerable amount of refrigeration capacity.

[0078] Functions and effects of the embodiment

[0079] For the bracket and free piston split Stirling refrigerator according to this embodiment, a rectangular groove is provided on the piston tube of the bracket, and through holes are provided in the groove for guiding the back pressure chamber gas to reach the compression chamber through the compression piston, preventing the piston stroke from decreasing due to the increase in the back pressure chamber pressure caused by the gas bearing.

[0080] In addition, the free piston split Stirling refrigerator of this embodiment cancels the leaf spring structure of the traditional free piston split Stirling and provides the required radial supporting force in the form of a gas bearing.

[0081] Furthermore, the expander is provided with a flow guiding device at both the upper and lower ends of the ejector to make the passing air flow more gentle and uniform. The cold end heat exchanger is a slit heat exchanger that is tightly attached to the cold head through interference fit, which helps to improve the heat exchange efficiency and reduce the cold loss.

[0082] Furthermore, a groove with a certain depth is provided at the base of the expander to prevent the movement impact of the leaf spring, which can make the structure of the expander more compact and improve the cycle efficiency of the free-piston split Stirling refrigerator.

[0083] Furthermore, the gas bearing structure provided in this embodiment and the motor bracket that facilitates the assembly of the whole machine and is compact make the operation of the whole machine more stable, solve the problem of the increase in the back pressure chamber pressure caused by the gas bearing and improve the efficiency of the whole machine, overcome the problems of difficult assembly and positioning of the traditional bracket, large weight of the bracket, and insufficient compactness of the whole machine, improve the assembly speed and accuracy, the compactness of the whole machine and reduce the weight of the whole machine.

[0084] The above embodiments are preferred cases of the present invention and are not used to limit the protection scope of the present invention.

Claims

1. A frame for a compressor, characterized in that, Comprising: Flange; And Two piston tubes, respectively arranged on the flange and symmetrically distributed on both sides of the flange, Wherein, the flange is in a disc shape, and a first disc, a circular groove, a second disc, and a protruding circular band are respectively arranged on both sides, The first disc, the circular groove, the second disc, and the protruding circular band are successively adjacent to each other from small to large, On the circumference of the flange, a first boss for connecting with a connecting pipe, a second boss for an air inlet, and a third boss for a connector port are respectively provided, The first boss, the second boss, and the third boss are adjacent to each other, The piston tube has a cylindrical inner cavity, and the axis of the piston tube is collinear with the axis of the flange, On the outer wall of the piston tube, concave air inlet grooves are symmetrically arranged, and the air inlet grooves are axially arranged from the free end towards the flange direction, Through holes communicating the air inlet grooves with the inner cavity of the piston tube are arranged in the air inlet grooves, The first disc is used for placing an inner yoke, There is an assembly gap between the circular groove and the second disc, The protruding circular band is used for positioning an outer yoke, The first boss is radially provided with a first through hole communicating the outside with the inner cavity of the piston tube, The second boss is radially provided with an inflation through hole communicating the outside with the assembly gap, The third boss is radially provided with a wire threading through hole communicating the outside with the assembly gap.

2. A free-piston split Stirling cryocooler, characterized in that, Comprising: A compressor having a frame; And An expander, the expander is communicated with the compressor through a connecting pipe, Wherein, the frame is the frame described in claim 1.

3. The free piston split Stirling refrigerator according to claim 2, characterized in that: Among them, The compressor further includes two compression units, The compression unit has a compression piston, the compression piston has a cylindrical inner cavity, and an inner concave annular groove and a plurality of concave cavities are arranged on its outer wall. Throttle through holes communicating the cylindrical inner cavity are arranged in the concave cavities, and a ventilation hole communicating with the annular groove is arranged on the end surface of the open end of the compression piston.

4. The free piston split Stirling refrigerator according to claim 3, characterized in that: Among them, The two compression pistons are respectively symmetrically arranged in the cylindrical inner cavity of the piston tube, and the open ends of the two compression pistons are arranged opposite to each other.

5. The free piston split Stirling refrigerator according to claim 2, characterized in that: Among them, The expander includes an ejector, an ejector rod, a cold head, a cold end heat exchanger, and an expansion cylinder, One end of the ejector is spring-connected to an expansion side plate through the ejector rod, and the other end is a free end.

6. The free piston split Stirling refrigerator according to claim 5, characterized in that: Among them, The cold end heat exchanger is a slit type heat exchanger, which is arranged inside the cold head and closely adheres to the inner wall of the cold head, and the cold end heat exchanger is in interference fit with the cold head.

7. The free piston split Stirling refrigerator according to claim 5, characterized in that: Among them, The ejector, the expansion cylinder, and the cold head form an expansion cavity.

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