Discharger and free piston Stirling device

Abstract

The invention provides an ejector and a free piston Stirling device. The ejector comprises an ejector piston; the Dome cylinder is connected with the discharger piston, a supporting sleeve is arranged in the Dome cylinder in the axial direction, one end of the supporting sleeve is connected with the end face of the Dome cylinder, the other end of the supporting sleeve is connected with the discharger piston, multiple stages of first anti-radiation screens are arranged in the supporting sleeve in the axial direction at intervals, and multiple stages of second anti-radiation screens are arranged between the Dome cylinder and the supporting sleeve in the axial direction at intervals; according to the Dome cylinder, the supporting sleeve is arranged in the Dome cylinder in the axial direction, the effects of supporting the end face of the Dome cylinder and preventing the end of the Dome cylinder from being pressed to deform or collapse can be achieved, the cavity in the Dome cylinder can be divided, and the natural convection phenomenon of hot gas in the cavity of the Dome cylinder is reduced; due to the design of the double radiation-proof screens, the inner cavity of the Dome cylinder is divided into a plurality of small cavities, the effect of restraining natural convection is achieved, meanwhile, heat radiation is blocked, the working environment temperature of the motor side of the compressor is effectively reduced, and efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat engines, and particularly to an ejector and a free piston Stirling device. Background Art

[0002] A free piston Stirling heat engine includes a Stirling generator, a refrigerator, and a heat pump. It is a regenerative heat engine (including a generator and a refrigerator), which has the advantages of wide applicable heat sources, high efficiency, low vibration and noise, etc., and is widely used in fields such as solar power generation, superconducting cooling, and heating. In a free piston Stirling heat engine, the acoustic work in the expansion chamber is transmitted to the compression chamber through the ejector. For the acoustic work transmitted to the compression chamber, a part of it pushes the power piston to reciprocate in the linear motor, realizing the conversion of acoustic work to electric work; the other part flows into the room temperature heat exchanger to form a thermodynamic cycle. Therefore, the ejector is an important component for transmitting acoustic work to the compression chamber and adjusting the phase of the sound field, which has a crucial impact on the performance of the whole machine.

[0003] As Figure 1 shown, the current ejector mainly consists of a rod body, an ejector piston, a radiation shield, and a Dome cylinder; among them, one end of the Dome cylinder close to the expansion chamber is in a high temperature or low temperature state, and the end close to the compression chamber is in a normal temperature state. The Dome cylinder adopts a thin-walled structure to reduce the moving mass of the ejector and correspondingly reduce the spring stiffness required for the resonant motion of the ejector; the end face of the Dome cylinder close to the expansion chamber is close to a plane. If the diameter of the Dome cylinder is small, when adopting a thin-walled structure, the strength of the front end of the Dome cylinder is still sufficient, and the end face will not produce large deformation or collapse failure due to pressure.

[0004] However, with the increase of the diameter of the Dome cylinder, if the thin-walled structure is still adopted, the front end of the Dome cylinder is prone to deformation and even collapse; if the front end face of the Dome cylinder is thickened to improve the strength, it will inevitably greatly increase the mass of the Dome cylinder, which not only increases the spring stiffness required for the resonance of the ejector, but also makes the center of gravity of the ejector shift to the side of the Dome cylinder. Under the action of gravity, the ejector will tilt, resulting in uneven air floating and even failure.

[0005] In addition, with the increase of the diameter of the ejector, the volume of the internal cavity of the Dome cylinder will also increase correspondingly. Under the action of gravity, the natural convection in the Dome cylinder will also increase accordingly, ultimately leading to a decrease in exergy efficiency. Summary of the Invention

[0006] The present invention provides an ejector and a free piston Stirling device to solve the problems that the front end of the Dome cylinder is prone to deformation and collapse, and the natural convection inside the Dome cylinder increases and the exergy efficiency decreases when using an ejector with a large diameter in the prior art.

[0007] In a first aspect, the present invention provides an ejector, comprising: An ejector piston; A Dome cylinder, the Dome cylinder is connected to the ejector piston, a support sleeve is axially arranged inside the Dome cylinder, one end of the support sleeve is connected to the end face of the Dome cylinder, the other end is connected to the ejector piston, and a plurality of stages of first radiation shields are axially spaced inside the support sleeve, and a plurality of stages of second radiation shields are axially spaced between the Dome cylinder and the support sleeve.

[0008] According to the ejector provided by the present invention, first air holes are provided on the support sleeve, the first radiation shield and the second radiation shield.

[0009] According to the ejector provided by the present invention, a plurality of support sleeves are provided.

[0010] According to the ejector provided by the present invention, a plurality of radially arranged reinforcing ribs are provided on the end face of the Dome cylinder.

[0011] According to the ejector provided by the present invention, a partition is radially arranged between the Dome cylinder and the support sleeve, and a plurality of the partitions are equally angularly distributed in the circumferential direction.

[0012] According to the ejector provided by the present invention, it further comprises: A rod body, the first end of the rod body is connected to the center of the end face of the ejector piston, and the second end of the rod body passes through the power piston and is connected to an elastic member in the back pressure chamber.

[0013] According to the ejector provided by the present invention, the rod body is provided with a cavity, and a plurality of second air holes are provided on the outer side of the end of the rod body facing away from the ejector piston.

[0014] In a second aspect, the present invention further provides a free piston Stirling device, comprising a housing and a power piston and the ejector described in the first aspect provided inside the housing.

[0015] According to the free piston Stirling device provided by the present invention, the space between the power piston and the ejector piston forms a compression chamber, the side of the Dome cylinder facing away from the compression chamber is an expansion chamber, the side of the power piston facing away from the compression chamber is a back pressure chamber, and the housing corresponding to the back pressure chamber is provided with the elastic member of the ejector.

[0016] According to the free piston Stirling device provided by the present invention, a plurality of air floating holes are evenly distributed on the inner wall surface of the power piston, and the air floating holes correspond to the surface of the rod body of the ejector.

[0017] An ejector provided by the present invention includes an ejector piston and a Dome cylinder. The Dome cylinder is connected to the ejector piston. In the present invention, a support sleeve is axially arranged inside the Dome cylinder. The support sleeve is connected to the end face of the Dome cylinder and extends to the ejector piston, forming a stable support structure, increasing the stress intensity of the end face of the Dome cylinder. This design can not only support the end face of the Dome cylinder to prevent the end of the Dome cylinder from being deformed or collapsed under pressure, but also divide the cavity inside the Dome cylinder, reducing the natural convection phenomenon of hot gas in the cavity of the Dome cylinder. By axially arranging multiple first radiation shields at intervals inside the support sleeve and axially arranging multiple second radiation shields at intervals between the Dome cylinder and the support sleeve, through the design of double radiation shields, dividing the cavity inside the Dome cylinder into multiple small cavities also plays a role in suppressing natural convection, and at the same time blocks thermal radiation, effectively reducing the working environment temperature on the compressor motor side, improving the exergy efficiency. This design helps to reduce the heat loss from the high-temperature area to the low-temperature area, thereby maintaining the temperature difference and improving the working efficiency of the Stirling device. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 is a schematic structural diagram of an ejector provided in the prior art.

[0020] Figure 2 is a schematic structural diagram of the ejector provided in the embodiment of the present invention.

[0021] Figure 3 is a schematic structural diagram of the ejector provided in another embodiment of the present invention.

[0022] Figure 4 is a cross-sectional view of the Dome cylinder provided in the embodiment of the present invention.

[0023] Reference Signs: 1, ejector piston; 2, Dome cylinder; 3, support sleeve; 4, first radiation shield; 5, second radiation shield; 6, first air hole; 7, partition; 8, rod body; 9, power piston; 10, elastic member; 11, second air hole; 12, air floating hole; 13, compression chamber; 14, expansion chamber; 15, back pressure chamber. Detailed Embodiments

[0024] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions in the present invention in conjunction with the accompanying drawings in the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts fall within the scope of protection of the present invention.

[0025] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0026] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "mode", "specific mode", or "some modes" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or mode are included in at least one embodiment or mode of the embodiments of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or mode. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or modes. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or modes described in this specification and the features of different embodiments or modes.

[0027] Such as Figure 1As shown in the figure, the existing ejector mainly consists of a rod body 8, an ejector piston 1, a radiation shield, and a Dome cylinder 2. Among them, the Dome cylinder 2 refers to a cylindrical object with a dome shape or characteristics. Define the end of the Dome cylinder 2 close to the expansion chamber 14 as the front end, and the front end is in a high-temperature or low-temperature state, while the end close to the compression chamber 13 is in a normal-temperature state. The Dome cylinder 2 adopts a thin-wall structure to reduce the moving mass of the ejector and correspondingly reduce the spring stiffness required for the resonant motion of the ejector. The end face of the end of the Dome cylinder 2 close to the expansion chamber 14 is close to a plane. If the diameter of the Dome cylinder 2 is small, when adopting a thin-wall structure, the strength of the front end of the Dome cylinder 2 is still sufficient, and the end face will not produce large deformation or collapse failure due to pressure. However, as the diameter of the Dome cylinder 2 increases, if the thin-wall structure is still adopted, the front end of the Dome cylinder 2 is prone to deformation and even collapse. If the front end face of the Dome cylinder 2 is thickened to improve the strength, it will inevitably greatly increase the mass of the Dome cylinder 2, not only increasing the spring stiffness required for the resonance of the ejector, but also causing the center of gravity of the ejector to move towards the side of the Dome cylinder 2. Under the action of gravity, the ejector will tilt, resulting in uneven air flotation and even failure. Moreover, the volume of the internal cavity of the Dome cylinder 2 will also increase correspondingly, and under the action of gravity, the natural convection inside the Dome cylinder 2 will also increase accordingly, ultimately leading to a decrease in exergy efficiency.

[0028] The following combines Figures 2 - 4 to describe an ejector and a free piston Stirling device of the present invention.

[0029] An embodiment of the present invention provides an ejector, as Figures 2 - 3 shown, including: an ejector piston 1 and a Dome cylinder 2.

[0030] Among them, the Dome cylinder 2 is connected to the ejector piston 1, preferably in a sealed connection. For example, sealing treatment is carried out at the connection by using a sealing ring or a rubber sleeve to prevent gas leakage at the connection of the Dome cylinder 2.

[0031] A support sleeve 3 is arranged axially inside the Dome cylinder 2. One end of the support sleeve 3 is connected to the end face of the Dome cylinder 2, and the other end is connected to the ejector piston 1. A plurality of first radiation shields 4 are arranged axially at intervals inside the support sleeve 3, and a plurality of second radiation shields 5 are arranged axially at intervals between the Dome cylinder 2 and the support sleeve 3.

[0032] With such a setting, in the present invention, a support sleeve 3 is axially arranged inside the Dome cylinder 2. The support sleeve 3 is connected to the end face of the Dome cylinder 2 and extends to the displacer piston 1, forming a stable support structure, increasing the stress intensity of the end face of the Dome cylinder 2. This design can not only support the end face of the Dome cylinder 2 to prevent the end of the Dome cylinder 2 from being deformed or collapsed under pressure, but also divide the cavity inside the Dome cylinder 2, reducing the natural convection phenomenon of the hot gas in the cavity of the Dome cylinder 2; by axially arranging multiple levels of first radiation shields 4 at intervals inside the support sleeve 3 and axially arranging multiple levels of second radiation shields 5 at intervals between the Dome cylinder 2 and the support sleeve 3, through the design of the double radiation shields, dividing the inner cavity of the Dome cylinder into multiple small cavities also plays a role in suppressing natural convection, further enhancing the thermal insulation effect. These radiation shields not only block thermal radiation but also act as a heat insulation barrier, reducing the possibility of heat conduction, capable of gradually reducing heat conduction and thermal radiation, effectively reducing the working environment temperature on the compressor motor side, improving the exergy efficiency. This design helps to reduce the heat loss from the high-temperature area to the low-temperature area, thereby maintaining the temperature difference and enhancing the working efficiency of the Stirling device.

[0033] It should be noted that compared with the prior art, the quality of the Dome cylinder 2 provided by the present invention still remains at a relatively low level. The Dome cylinder 2 still adopts a thin-wall structure, so that the displacer will not tilt towards the side of the Dome cylinder 2 under the action of gravity. While keeping the moving mass of the displacer at a relatively low level, this structure improves the strength of the front end face of the Dome cylinder 2, suppresses the natural convection inside the Dome cylinder 2, improves the exergy efficiency, and can be applied to a free-piston Stirling device with a higher power level.

[0034] In this embodiment, first air holes 6 are provided on the support sleeve 3, the first radiation shield 4 and the second radiation shield 5. With such a setting, the existence of the first air holes 6 allows gas to flow between different regions, which helps to maintain the pressure balance inside the Dome cylinder 2. Since the working principle of the Stirling device relies on the circulation of the working medium, usually gas, between the hot end and the cold end, the air holes can ensure the reasonable flow of gas between the support sleeve 3, the first radiation shield 4 and the second radiation shield 5, allowing part of the heat to be transferred to the required place by means of gas convection, avoiding the problem of local overheating or overcooling, and thus supporting an efficient heat exchange process.

[0035] Furthermore, multiple support sleeves 3 are provided. By using the support sleeves 3 to divide the inner space of the Dome cylinder 2 into multiple regions, the natural convection phenomenon of the hot gas in the cavity is reduced. Natural convection is one of the important ways of heat transfer. Suppressing natural convection can reduce unnecessary heat loss and improve the thermal energy utilization efficiency.

[0036] Preferably, a plurality of support sleeves 3 are arranged inside the Dome cylinder 2 in the circumferential direction. That is to say, in the cross-section of the Dome cylinder 2, the circular cross-sections of the plurality of support sleeves 3 are equally angularly distributed in the circumferential direction. In this way, the pressure on the end face of the Dome cylinder 2 can be shared more evenly, significantly improving the overall structural strength of the Dome cylinder 2 and preventing deformation or collapse caused by excessive local stress. Each support sleeve 3 further divides the internal space of the Dome cylinder 2 into a plurality of independent small regions, effectively suppressing the natural convection phenomenon and reducing unnecessary heat loss.

[0037] Furthermore, a plurality of radially arranged reinforcing ribs are provided on the end face of the Dome cylinder 2. With this arrangement, by providing radially arranged reinforcing ribs on the end face, on the one hand, the stress can be effectively dispersed, enhancing the overall structural strength of the Dome cylinder 2. Since the Dome cylinder 2 is prone to end collapse in high-pressure or high-temperature environments, especially in a Stirling device, the pressure change of the working medium will have a greater impact on its structure. The radially arranged reinforcing ribs can evenly distribute the stress on the end face to the entire Dome cylinder 2, thus significantly reducing the risk of collapse. On the other hand, the reinforcing ribs not only play a mechanical support role but also can be part of the heat conduction path, guiding heat to be transferred along a specific path, making the temperature distribution on the end face of the Dome cylinder 2 more uniform and avoiding problems such as local overheating or uneven cooling, which is crucial for the efficient operation of the Stirling device.

[0038] Referring to Figure 3 , in some embodiments, a partition 7 is provided between the Dome cylinder 2 and the support sleeve 3 in the radial direction, and a plurality of partitions 7 are equally angularly distributed in the circumferential direction.

[0039] With this arrangement, the partition 7 divides the cavity between the Dome cylinder 2 and the support sleeve 3 into a plurality of independent small regions, increasing the path length of heat conduction, thereby reducing the direct transfer speed of heat energy from the hot end to the cold end. Due to the presence of the partition 7, heat needs to be transferred through multiple small regions step by step to reach the cold end. This step-by-step transfer method helps to reduce the temperature difference in each region, improve the heat exchange efficiency and reduce heat loss. Thus, by the synergistic effect of the partition 7 and the multi-stage second radiation shield 5, the heat isolation effect is further enhanced, forming a more perfect heat barrier system.

[0040] In addition, the natural convection phenomenon of the gas in these regions is also significantly reduced, enhancing the structural stability. The presence of the partition 7 strengthens the connection between the Dome cylinder 2 and the support sleeve 3, improving the rigidity of the overall structure and preventing deformation or collapse caused by high temperature or high pressure.

[0041] In some embodiments, a rod body 8 is also included, a first end of the rod body 8 is connected to the center of the end face of the ejector piston 1, and a second end of the rod body 8 passes through the power piston 9 and is connected to the elastic member 10 of the back pressure chamber 15. The elastic member 10 can be a spring, and the specific form of the spring can be a leaf spring, a gas spring, etc., and its function is to provide a restoring force opposite to the displacement direction to meet the resonance condition of the ejector.

[0042] In this arrangement, the rod body 8, as a mechanical connection component, is responsible for converting the reciprocating motion of the displacer piston 1 into the motion of the power piston 9, and realizing the axial reciprocating movement of the rod body 8 through the elastic member 10 of the back pressure chamber 15. This design closely links the motion of the displacer piston 1 with the motion of the power piston 9, realizing the synchronous and coordinated work of the two. Through the connection of the rod body 8, the mechanical energy generated by the displacer piston 1 can be directly transmitted to the power piston 9, reducing the energy loss in the intermediate link, thereby improving the energy transfer efficiency of the entire system. The presence of the elastic member 10 enables the rod body 8 to absorb part of the mechanical shock and vibration, and enhances the system's adaptability to complex working conditions, especially in the case of load changes or environmental fluctuations. Since the rod body 8 can efficiently transmit mechanical energy and dynamically adjust the pressure of the back pressure chamber 15, this design enables the Stirling device to operate stably under higher power conditions.

[0043] Furthermore, the rod body 8 is provided with a cavity, and a plurality of second air holes 11 are provided on the outer side of the end of the rod body 8 away from the ejector piston 1. In this way, the second air holes 11 are used to connect the Dome tube 2 with the back pressure chamber 15 to prevent the pressure difference between the inside and outside of the ejector from being too large, which may cause the Dome tube 2 to deform.

[0044] The ejector provided by the present invention improves structural stability, prevents the Dome tube 2 from collapsing, can suppress natural convection, reduces unnecessary heat loss, significantly reduces the influence of heat radiation and heat conduction, optimizes thermal management performance, and maintains the temperature difference between the hot end and the cold end to the maximum extent, thereby improving exergy efficiency and overall energy utilization.

[0045] The embodiment of the present invention further provides a free piston Stirling device, comprising a housing, a power piston 9 arranged in the housing, and the above-mentioned displacer. Due to the use of the above-mentioned displacer, the free piston Stirling device has all the advantages of the above-mentioned displacer.

[0046] In this embodiment, a plurality of air-floating holes 12 are evenly distributed on the inner wall surface of the power piston 9, and the air-floating holes 12 correspond to the surface of the rod body 8 of the ejector. With such a setting, the air-floating holes 12 form a stable gas film between the inner wall surface of the power piston 9 and the surface of the rod body 8 by spraying gas onto the surface of the rod body 8, thereby forming a gas bearing for supporting the rod body 8. This gas film can effectively reduce the friction between the two, thus achieving low-friction and high-precision movement; the design of the air-floating holes 12 significantly reduces the wear of the power piston 9 and the rod body 8 and extends the service life of both.

[0047] A free-piston Stirling device provided by an embodiment of the present invention, by adopting the above-mentioned ejector, improves the strength of the front end of the Dome cylinder 2 in the free-piston Stirling device. Even when the diameter of the ejector is relatively large, a thin-walled Dome cylinder 2 can still be used, so that the ejector maintains a relatively light weight. This not only reduces the spring stiffness required for the ejector resonance but also enables the air-floating structure of the ejector to operate normally. In addition, by arranging several support sleeves 3 and partitions 7 in the Dome, the cavity inside the Dome cylinder 2 can be divided, weakening the natural convection inside the Dome and improving the exergy efficiency. The ejector of the present invention can be applied to free-piston Stirling systems with higher power levels.

[0048] As Figures 2 - 3 shown, the space between the power piston 9 and the ejector piston 1 is the compression chamber 13, the side of the Dome cylinder 2 facing away from the compression chamber 13 is the expansion chamber 14, the side of the power piston 9 facing away from the compression chamber 13 is the back-pressure chamber 15, and the outer shell corresponding to the back-pressure chamber 15 is provided with the elastic member 10 of the ejector.

[0049] A free-piston Stirling device provided by the present invention, the efficiency of the Stirling device is closely related to the temperature difference between its hot end and cold end. A larger temperature difference means a higher proportion of exergy efficiency of the available energy. Through the structural design of the ejector, the heat transfer from the hot end to the cold end is effectively reduced, thereby significantly improving the working environment temperature on the motor side. This not only extends the service life of the motor but also improves the stability and reliability of the entire system.

[0050] Through the above design, the device can better maintain the high temperature at the hot end and the low temperature at the cold end, thereby increasing the temperature difference and improving the exergy efficiency. At the same time, reducing heat loss also means that more energy is effectively utilized, further enhancing the overall performance of the device.

[0051] 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An ejector, characterized in that: include: Displacer piston (1); A dome cylinder (2) is connected to the ejector piston (1); a support sleeve (3) is axially arranged inside the dome cylinder (2); one end of the support sleeve (3) is connected to the end surface of the dome cylinder (2), and the other end is connected to the ejector piston (1); a plurality of first radiation protection screens (4) are axially arranged inside the support sleeve (3); and a plurality of second radiation protection screens (5) are axially arranged between the dome cylinder (2) and the support sleeve (3).

2. The ejector according to claim 1, characterized in that: The supporting sleeve (3), the first radiation protection screen (4) and the second radiation protection screen (5) are provided with first air holes (6).

3. The ejector according to claim 1, characterized in that A plurality of support sleeves (3) are provided.

4. The ejector according to claim 1 or 2, characterized in that: The end surface of the Dome tube (2) is provided with a plurality of radial reinforcing ribs.

5. The ejector according to claim 4, characterized in that A partition plate (7) is arranged radially between the Dome cylinder (2) and the supporting sleeve (3), and a plurality of partition plates (7) are distributed at equal angles along the circumferential direction.

6. The ejector according to claim 1, characterized in that Also includes: A rod body (8), wherein a first end of the rod body (8) is connected to the center of the end surface of the displacer piston (1), and a second end of the rod body (8) passes through the power piston (9) and is connected to the elastic member (10) of the back pressure chamber (15).

7. The ejector according to claim 6, characterized in that The rod body (8) is provided with a cavity, and a plurality of second air holes (11) are provided on the outer side of one end of the rod body (8) facing away from the ejector piston (1).

8. A free piston Stirling device, characterized in that: The invention comprises a housing and a power piston (9) arranged in the housing and the ejector according to any one of claims 1 to 7.

9. The free piston Stirling device according to claim 8, characterized in that The space between the power piston (9) and the ejector piston (1) forms a compression chamber (13); the side of the Dome cylinder (2) facing away from the compression chamber (13) is an expansion chamber (14); the side of the power piston (9) facing away from the compression chamber (13) is a back pressure chamber (15); and the outer shell corresponding to the back pressure chamber (15) is provided with the elastic member (10) of the ejector.

10. The free piston Stirling device according to claim 8, characterized in that The inner wall surface of the power piston (9) is evenly distributed with a plurality of air flotation holes (12), and the air flotation holes (12) correspond to the surface of the rod body (8) of the ejector.

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