A free piston stirling engine and its gas bearing

Abstract

The present application relates to the technical field of gas bearing, and provides a free piston Stirling engine and a gas bearing thereof, the gas bearing comprising a cylinder and a piston, the piston being coaxially arranged in the cylinder, a gas gap being reserved between the piston and the cylinder, and the piston being capable of reciprocating in the cylinder; the gas bearing further comprises a first gas channel and a second gas channel arranged in the side wall of the cylinder; one end of the first gas channel and the second gas channel respectively communicates with the cavity of the cylinder, the other end of the first gas channel and the second gas channel respectively extends out of the cavity of the cylinder, and the other end of the first gas channel and the second gas channel is respectively connected with the gas outlet and the gas return port of the gas pump; the gas pump for external gas supply provides a stable gas supply and exhaust environment for the gas bearing, ensures the stability of the gas bearing in the working state, and the gas bearing can still work normally in the starting state of the Stirling engine, effectively prevents the phenomenon of "dry grinding" between the piston and the cylinder, and ensures the service life of the Stirling engine.

Description

Technical Field

[0001] The present invention relates to the technical field of gas bearings, and in particular to a free-piston Stirling engine and a gas bearing thereof. Background Art

[0002] The free-piston Stirling engine is a new type of engine with high efficiency and long service life. Currently, thermodynamic research on the free-piston Stirling engine is largely mature, and its prototype efficiency is comparable to, or even higher than, that of an internal combustion engine. However, the mechanical design and manufacturing process of the free-piston Stirling engine are still not very mature. The main factor limiting its development is the support method of the two moving parts within the free-piston Stirling engine: the displacer and the power piston. These two moving parts are supported to prevent contact between the moving part (the power piston) and the cylinder. A gap of the order of 10 microns is used to achieve pressure differential sealing between the cavities on both sides of the moving parts, as well as oil-free relative movement.

[0003] Currently, there are two methods for supporting the moving parts of free-piston Stirling engines. One method involves using leaf springs to support the displacer or power piston. Due to the limited support stiffness of leaf springs, this type of support is only suitable for free-piston Stirling engines with power levels of kilowatts or less. Furthermore, the lifespan of free-piston Stirling engines using this support method is severely limited by the lifespan of the leaf springs, placing very high demands on their processing and design. Furthermore, during assembly of the free-piston Stirling engine, the multiple leaf springs must maintain strict coaxiality with the displacer or power piston, which increases the difficulty of assembly.

[0004] Another method of supporting the moving parts of a free-piston Stirling engine is to use a gas bearing to support the displacer or power piston. The principle of a gas bearing between the piston and cylinder utilizes the viscosity of the gas. When the axial walls approach each other, the viscosity of the gas prevents the gas from being discharged in time. As the gap decreases, the pressure increases, which in turn resists further reduction in the gap between the shaft and the wall, thereby supporting the shaft and maintaining contact between the shaft and the cylinder. Based on the principle of pressure generation, gas bearings can be divided into dynamic pressure, static pressure, and film-type. In free-piston Stirling engines, static pressure and dynamic pressure gas bearings are mostly used. The dynamic pressure type requires a small motor to rotate the piston to a certain speed, thereby achieving dynamic pressure bearing support. Although dynamic pressure gas bearings have lower losses than static pressure gas bearings and do not require a pressure source, existing analysis and experimental accumulation indicate that the stability of dynamic pressure gas bearings is still immature for practical application. In addition, the rotational excitation device in the dynamic pressure gas bearing increases the complexity of the system, and the compact internal structure of the free piston makes it difficult to integrate an additional rotating motor. Therefore, the prior art generally adopts a hydrostatic gas bearing to support the displacer or the power piston.

[0005] At present, the main air supply method for static pressure gas bearings is internal air supply, which can be divided into two methods. The first internal air supply method of static pressure gas bearings is as follows: Figure 1 As shown, the air supply principle of the gas bearing is to utilize the fluctuating pressure on both sides of the piston. When it is in the appropriate position, the gas on the high-pressure side is discharged into the high-pressure air storage chamber 3 through the first air supply pipe 1 on the cylinder 13 and the first air hole 2 on the high-pressure air storage chamber 3. Then the gas in the high-pressure air storage chamber 3 flows into the air gap between the piston 14 and the side wall of the cylinder 13 through its second air hole 4, and then enters the low-pressure air storage chamber 7 through the third air hole 5 on the low-pressure air storage chamber 7. After the piston 14 moves to the appropriate position, the gas in the low-pressure air storage chamber 7 is discharged into the lower pressure side of both ends of the piston through the fourth air hole 6 on the low-pressure air storage chamber 7 and the second air supply pipe 8 on the cylinder 13.

[0006] The second internal air supply of hydrostatic gas bearings is as follows Figure 2 As shown, the piston cavity 24 of the piston 14 serves as a high-pressure gas storage chamber, and a one-way valve 9 and a fifth air hole 10 are provided on the piston 14. The one-way valve 9 is pressure-controlled. When the pressure exceeds the threshold set by the one-way valve 9, the one-way valve 9 opens, allowing the high-pressure gas outside the piston to enter the piston cavity 24. The high-pressure gas then enters the air gap between the piston 14 and the side wall of the cylinder 13 through the fifth air hole 10, and is finally discharged into the compression chamber 11 and the piston back cavity 12.

[0007] Although the above-mentioned two internal air supply structures of the hydrostatic gas bearing are relatively compact, this type of gas bearing operates in a fluctuating pressure environment, which will lead to a decrease in the stability of the gas bearing and even jamming after a pressure imbalance. The greater the pressure fluctuation on both sides of the piston, the more serious this problem is. At the same time, since this type of gas bearing is driven by fluctuating pressure, during the startup phase of the free-piston Stirling engine, no appropriate pressure fluctuation is formed in the system. At this time, the gas bearing is ineffective and the piston will experience "dry grinding" for a period of time, which will reduce the life of the free-piston Stirling engine to a certain extent. Summary of the Invention

[0008] (1) Technical issues to be solved

[0009] One of the purposes of the present invention is to provide a gas bearing to solve the problem of poor stability of the current static pressure type gas bearing driven by fluctuating pressure.

[0010] Another object of the present invention is to provide a free-piston Stirling engine using the above-mentioned gas bearing, so as to solve the problem that the current static pressure gas bearing driven by fluctuating pressure fails when pressure fluctuations are not formed, causing "dry grinding" of the piston of the Stirling engine, thereby affecting the service life of the Stirling engine.

[0011] (II) Technical Solution

[0012] To solve the above technical problems, the present application provides a kind of gas bearing, including cylinder and piston, the piston is coaxially placed in the cylinder, the air gap is reserved between the piston and the cylinder, and the piston can reciprocate in the cylinder;

[0013] It also includes the first air duct and the second air duct arranged in the side wall of the cylinder;

[0014] Wherein, one end of the first air duct and the second air duct respectively communicates with the cavity inside the cylinder, and the other end of the first air duct and the second air duct respectively extends to the outside of the cavity of the cylinder and is correspondingly connected with the air outlet and the air return port of the air pump.

[0015] Preferably, the present application further includes a plurality of groups of inlet holes and a plurality of groups of exhaust holes arranged respectively along the radial direction on the inner wall of the cylinder;

[0016] Each group of inlet holes is uniformly arranged along the circumference and arranged in the same plane relative to the central axis of the cylinder, and is connected with the first air duct;

[0017] Each group of exhaust holes is uniformly arranged along the circumference and arranged in the same plane relative to the central axis of the cylinder, and is connected with the second air duct.

[0018] Preferably, the axial distance between the exhaust hole and the end of the piston in the present application is greater than 100 mm;Or, a convex stepped surface is arranged on the side wall of each end of the piston.

[0019] Preferably, in the present application, two groups of inlet holes and one or two groups of exhaust holes are provided, and the exhaust holes are arranged between the two groups of inlet holes or on the outside of the two groups of inlet holes;The axial length of the inlet holes and the exhaust holes arranged on the inner wall of the cylinder is less than the length of the piston;The stroke of the reciprocating motion of the piston is less than the axial arrangement distance of the inlet holes and the exhaust holes.

[0020] Preferably, in the present application, a first return hole and a third air duct are arranged on the piston;The first return hole is located on the outer side wall of the piston between the two stepped surfaces, and the first return hole corresponds to the exhaust hole;The third air duct is located in the piston, one end of the third air duct communicates with the first return hole, and the other end of the third air duct extends to the end of the piston.

[0021] Preferably, the side wall of the cylinder in the application is provided with a second back hole, and a fourth gas passage is arranged in the side wall of the cylinder, one end of the fourth gas passage is communicated with the cavity inside the cylinder through the second back hole, and the other end extends to the outside of the cavity of the cylinder; the first back hole corresponds to the second back hole.

[0022] Preferably, the piston in the application has a piston cavity, and a transfer gas hole is arranged on the side wall of the piston, which is used to communicate the piston cavity with the outside of the piston.

[0023] Preferably, the side wall of the cylinder in the application is further provided with a transfer gas cavity, which communicates the exhaust hole with the second gas passage.

[0024] Preferably, the application further provides a free piston Stirling engine, which comprises the above-mentioned gas bearing, and the cylinder and the piston in the Stirling engine correspondingly adopt the cylinder and the piston in the gas bearing.

[0025] (III) Technical effects

[0026] The gas bearing provided by the application communicates the gas gap between the cylinder and the piston with the outside through the first gas passage and the second gas passage arranged on the side wall of the cylinder. In actual use, the gas outlet and the gas return port of the air pump are correspondingly communicated with the first gas passage and the second gas passage. The gas pressurized by the air pump enters the gas gap through the first gas passage and forms a gap seal at the gas gap at both ends of the piston to provide stable support for the piston, and the gas in the gas gap can return to the air pump through the second gas passage. Therefore, under the joint action of the air pump for external gas supply and the gap seal at both ends of the piston, the gas supply structure can provide a stable gas supply and exhaust environment for the gas bearing, ensuring the stability of the working state of the gas bearing.

[0027] At the same time, the free piston Stirling engine provided by the application can keep normal working under the starting state of the Stirling engine, effectively prevents the phenomenon of "dry grinding" between the piston and the cylinder of the Stirling engine, and ensures the service life of the Stirling engine. In addition, the carrying capacity of the piston can be controlled by adjusting the air pump according to the change of the running environment, thereby improving the adaptability of the Stirling engine under different running conditions. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order 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. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 Schematic diagram of a partial cross-sectional structure of a static pressure gas bearing using the first internal air supply in the prior art;

[0030] Figure 2 Schematic diagram of a partial cross-sectional structure of a static pressure gas bearing using the second internal gas supply in the prior art;

[0031] Figure 3 A schematic diagram of a partial cross-sectional structure of a gas bearing of the first structure shown in an embodiment of the present invention;

[0032] Figure 4 A schematic diagram of a partial cross-sectional structure of a gas bearing of a second structure shown in an embodiment of the present invention;

[0033] Figure 5 A schematic diagram of a partial cross-sectional structure of a gas bearing of a third structure shown in an embodiment of the present invention;

[0034] Figure 6 Schematic diagram of a partial cross-section of a gas bearing of a fourth structure shown in an embodiment of the present invention;

[0035] Figure 7 Schematic diagram of the cross-sectional structure of a free-piston Stirling engine shown in an embodiment of the present invention.

[0036] In the figure: 1-first air supply pipe, 2-first air hole, 3-high-pressure air storage chamber, 4-second air hole, 5-third air hole, 6-fourth air hole, 7-low-pressure air storage chamber, 8-second air supply pipe, 9-one-way valve, 10-fifth air hole, 11-compression chamber, 12-piston back cavity, 13-cylinder, 14-piston, 15-first air channel, 16-second air channel, 17-air inlet, 18-exhaust hole, 19-step surface, 20-first return hole, 21-third air channel, 22-second return hole, 23-fourth air channel, 24-piston inner cavity, 25-transfer air hole, 26-transfer air chamber, 27-cylinder, 28-high-temperature end heat exchanger, 29-regenerator, 30-low-temperature end heat exchanger, 31-first flange, 32-discharger, 33-hot end gas spring, 34-cold end gas spring, 35-second flange. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0039] See also Figure 3 This embodiment provides a gas bearing, comprising a cylinder 13 and a piston 14. The piston 14 is coaxially disposed in the cylinder 13, with an air gap reserved between the piston 14 and the cylinder 13, and can reciprocate in the cylinder 13.

[0040] It also includes a first air passage 15 and a second air passage 16 provided in the side wall of the cylinder 13;

[0041] Among them, one end of the first air channel 15 and the second air channel 16 are respectively connected to the cavity inside the cylinder 13, and the other ends of the first air channel 15 and the second air channel 16 extend outside the cavity of the cylinder 13 and are correspondingly connected to the air outlet and the air return port of the air pump.

[0042] The gas bearing described in this embodiment is provided with a first air channel 15 and a second air channel 16 on the side wall of the cylinder 13, and the two air channels respectively connect the air gap between the cylinder 13 and the piston 14 to the outside world. In actual use, the air outlet and the air return port of the air pump can be connected to the first air channel 15 and the second air channel 16 respectively, and the gas pressurized by the air pump enters the air gap through the first air channel 15, and a gap seal is naturally formed at both ends of the air gap due to the viscosity of the gas to provide stable support for the piston, and the gas in the air gap can return to the air pump from the second air channel 16, so that the air pump with external air supply provides a stable supply and exhaust environment for the gas bearing, ensuring the stability of the gas bearing in working state; at the same time, since the working state of the gas bearing is independently controlled by the air pump, when the operating environment changes, the bearing capacity of the piston is controlled accordingly by adjusting the air supply pressure of the air pump, thereby improving the adaptability of the gas bearing in different operating conditions.

[0043] Furthermore, in order to improve the efficiency of air supply and exhaust and ensure the balance of force on the piston 14 in the cylinder 13, this embodiment also includes multiple groups of air intake holes 17 and multiple groups of exhaust holes 18 respectively arranged radially on the inner wall of the cylinder 13; each group of air intake holes 17 is evenly arranged and coplanarly arranged along the circumference relative to the central axis of the cylinder 13, and is connected to the first air duct 15; each group of exhaust holes 18 is evenly arranged and coplanarly arranged along the circumference relative to the central axis of the cylinder 13, and is connected to the second air duct 16.

[0044] Furthermore, in order to ensure the stability of the piston 14 operating in the cylinder 13, the axial distance between the exhaust hole 18 and the end of the piston 14 in this embodiment is greater than 100 mm, wherein the diameter and length of the piston 14 are both 255 mm, the length of the cylinder 13 is the sum of twice the stroke of the piston 14 and the length of the piston, and the inner diameter of the cylinder 13 is 30 μm larger than the outer diameter of the piston 14; by ensuring the length between the exhaust hole 18 and the end of the piston 14, a good gap seal is formed between the two ends of the piston 14 and the side wall of the cylinder 13, thereby ensuring the stability of the air pressure in the air gap area and effectively isolating the fluctuating air pressure in the cylinder 13.

[0045] Alternatively, a raised step surface 19 is provided on the side walls at both ends of the piston 14, so that the air gap spacing at both ends of the piston 14 is smaller than the air gap spacing in the middle of the piston 14. The viscosity of the gas can be used to form a better gap seal at the air gap corresponding to the two step surfaces 19, thereby ensuring the stability of the air pressure in the air gap area and effectively isolating the fluctuating air pressure in the cylinder 13.

[0046] Furthermore, in order to ensure better gas support for the piston 14 reciprocating in the cylinder 13 and to ensure the normal operation of the gas bearing, in this embodiment, the axial length of the air inlet hole 17 and the exhaust hole 18 arranged on the inner wall of the cylinder 13 is smaller than the length of the piston 14; the reciprocating stroke of the piston 14 is smaller than the axial distance between the air inlet hole 17 and the exhaust hole 18.

[0047] Furthermore, in order to ensure that the piston 14 reciprocates relative to its operating center in the cylinder 13 and prevent the operating center of the piston 14 from drifting, on the one hand, this embodiment provides a first return center hole 20 and a third air channel 21 on the piston 14; the first return center hole 20 is located on the outer wall of the piston 14 between the two step surfaces 19; the third air channel 21 is located in the piston 14, one end of the third air channel 21 is connected to the first return center hole 20, and the other end extends to the end of the piston 14.

[0048] At the same time, on the other hand, this embodiment may also be provided with a second return hole 22 on the side wall of the cylinder 13, and a fourth air duct 23 is provided on the inner side wall of the cylinder 13. One end of the fourth air duct 23 is connected to the cavity inside the cylinder 13 through the second return hole 22, and the other end extends outside the cavity of the cylinder 13.

[0049] Therefore, when the piston 14 runs to its operating center position, the air pressure in the cavity on both sides of the piston 14 can be balanced through the first return center hole 20 and its corresponding third air channel 21, or through the second return center hole 22 and its corresponding fourth air channel 23, so as to achieve calibration of the operating center position of the piston.

[0050] Furthermore, based on the improvement of the above structure, this embodiment obtains the following Figure 3 The difference between the gas bearing of the first structure shown is that, in this embodiment, two groups of air inlet holes 17 and two groups of exhaust holes 18 are provided, wherein the two groups of air inlet holes 17 are located between the two groups of exhaust holes 18. Thus, by using two groups of air inlet holes 17 to simultaneously supply air to the middle of the air gap, the gas bearing can obtain a greater load-bearing capacity.

[0051] This embodiment also includes two third air channels 21, one end of the two third air channels 21 is connected to the two groups of first return center holes 20, and the other ends of the two third air channels 21 extend to the two ends of the piston 14 respectively, wherein each group of first return center holes 20 corresponds to each group of exhaust holes 18 respectively. Therefore, by coupling the first return center holes 20 with the exhaust holes 18, when the piston 14 runs to its operating center position, each group of first return center holes 20 will be aligned one by one with each group of exhaust holes 18, which is beneficial for the piston 14 to balance the air pressure on both sides thereof with the assistance of the two second air channels 16, so as to achieve calibration of the operating center position of the piston.

[0052] Furthermore, based on the improvement of the above structure, this embodiment obtains the following Figure 4 The second gas bearing structure shown differs in that it features two sets of inlet holes 17 and one set of exhaust holes 18, with one set of exhaust holes 18 located between the two sets of inlet holes 17. This allows air to enter the gas bearing from both ends of the air gap and to exit from the center. While this structure partially reduces the bearing's load-bearing capacity and somewhat impacts the sealing of the gap at both ends of the piston 14, the placement of the two sets of inlet holes 17, which provide high-pressure gas, at both ends of the bearing significantly improves its radial torque resistance, making it suitable for bearings with relatively large diameters.

[0053] Furthermore, in order to achieve calibration of the operating center position of the piston, this embodiment sets a fourth air channel 23 on the piston 14 and a third air channel 21 on the side wall of the cylinder 13, and the first return center hole 20 connected to the third air channel 21 corresponds to the second return center hole 22 and the exhaust hole 18 connected to the fourth air channel 23.

[0054] Furthermore, based on the improvement of the above structure, this embodiment obtains the following Figure 5 The third gas bearing structure shown differs in that, in this embodiment, two groups of inlet holes 17 and one group of exhaust holes 18 are provided, wherein one group of exhaust holes 18 is located outside the two groups of inlet holes 17. Furthermore, the piston 14 has a piston cavity 24, and two groups of transit holes 25 are provided on the sidewall of the piston 14. Each group of transit holes 25 is used to connect the piston cavity 24 with the exterior of the piston 14. In this embodiment, a group of second return holes 22 is provided corresponding to each group of transit holes 25. Each group of second return holes 22 connects the air gap between the cylinder 13 and the piston 14 to the outside world via a corresponding fourth air passage 23. It should be noted that, in this structure, the exhaust holes 18 and the second return holes 22 are located at the same axial position, but their axial positions do not overlap. This design prevents the second return holes 22 from being continuously connected to the exhaust holes 18, which would affect the system's return effect.

[0055] Because the gas bearing structure described above features a transfer hole 25 for exhaust located on the piston, the exhaust from the air gap is transferred through the piston cavity 24 within the piston, reducing pressure fluctuations at the transfer hole 25 and ensuring stable piston operation. Furthermore, as the piston moves, the gas film in the gas bearing changes, and the central variation of the gas bearing's load-bearing capacity aligns with the changes in the piston's motion. Therefore, compared to the gas bearing structure described above, the gas bearing of this embodiment provides a more stable load-bearing capacity during piston movement, thereby ensuring the stability of the gas bearing.

[0056] Furthermore, based on the improvement of the above structure, this embodiment obtains the following Figure 6 The fourth gas bearing structure shown differs in that a transfer air chamber 26 is further provided within the sidewall of the cylinder 13 in this embodiment. This transfer air chamber 26 connects the exhaust port 18 with the second air passage 16. The operating principle of this gas bearing is similar to that of the first structure. The addition of the transfer air chamber 26 allows for transfer of exhaust gas from the air gap, reducing pressure fluctuations at the exhaust port and ensuring stable piston operation.

[0057] Furthermore, this embodiment also provides a free piston Stirling engine with a gas bearing based on the above structure, see Figure 7The Stirling engine includes a high-temperature end heat exchanger 28, a regenerator 29, a low-temperature end heat exchanger 30 and a first flange 31, an ejector 32, a hot-end gas spring 33, a cold-end gas spring 34, a second flange 35, a cylinder 13 and a piston 14, which are sequentially installed in the cylinder 27. The first flange 31 is connected to the ejector 32, and the second flange 35 is connected to the end of the cylinder 13.

[0058] In this embodiment, the cylinder 13 and the piston 14 adopt the gas bearing structure shown above, and the first gas channel 15 and the second gas channel 16 corresponding to the above-mentioned gas bearing are provided in the second flange 35; and the ejector 32 also adopts the gas bearing structure shown above, and the first gas channel 15 and the second gas channel 16 corresponding to the above-mentioned gas bearing are also provided in the first flange 31.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A gas bearing comprising a cylinder and a piston, wherein the piston is coaxially disposed in the cylinder, an air gap is reserved between the piston and the cylinder, and the piston is capable of reciprocating motion in the cylinder, characterized in that: Also included are a first air passage and a second air passage provided in the side wall of the cylinder; One end of the first air channel and the second air channel are connected to the cavity of the cylinder respectively, and the other end of the first air channel and the second air channel extend out of the cavity of the cylinder respectively and are connected to the air outlet and the air return port of the air pump respectively; It also includes a plurality of groups of air inlet holes and a plurality of groups of air exhaust holes respectively arranged radially on the inner wall of the cylinder; Each group of the air inlet holes is evenly arranged along the circumference relative to the central axis of the cylinder and arranged in the same plane, and is connected to the first air passage; Each group of exhaust holes is evenly arranged along the circumference relative to the central axis of the cylinder and arranged in the same plane, and is connected to the second air passage; The air inlet holes are provided in two groups, and the air exhaust holes are provided in one or two groups, and the air exhaust holes are provided between the two groups of air inlet holes or outside the two groups of air inlet holes; the axial length of the air inlet holes and the air exhaust holes on the inner wall of the cylinder is shorter than the length of the piston; and the reciprocating stroke of the piston is shorter than the axial distance between the air inlet holes and the air exhaust holes; A raised step surface is respectively provided on the side walls at both ends of the piston; The piston is provided with a first return center hole and a third air channel; the first return center hole is located on the outer side wall of the piston between the two step surfaces, and the first return center hole corresponds to the exhaust hole; the third air channel is located inside the piston, one end of the third air channel is connected to the first return center hole, and the other end extends to the end of the piston.

2. The gas bearing according to claim 1, wherein A second return hole is provided on the side wall of the cylinder, and a fourth air channel is provided inside the side wall of the cylinder. One end of the fourth air channel is connected to the cavity of the cylinder through the second return hole, and the other end extends out of the cavity of the cylinder; the first return hole corresponds to the second return hole.

3. The gas bearing according to claim 1 or 2, characterized in that The piston has an inner cavity, and a transfer air hole is provided on the side wall of the piston. The transfer air hole is used to connect the inner cavity of the piston with the outside of the piston.

4. The gas bearing according to claim 1 or 2, characterized in that A transfer air cavity is further provided in the side wall of the cylinder, and the transfer air cavity is connected with the exhaust hole and the second air channel.

5. A free piston Stirling engine, characterized in that: The invention comprises a gas bearing according to any one of claims 1 to 4, wherein the cylinder and piston in the Stirling engine correspond to the cylinder and piston in the gas bearing.

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