Self-adaptive reversing inter-shaft gas film sealing structure suitable for small pressure difference and working method

Abstract

The invention discloses a self-adaptive reversing inter-shaft gas film sealing structure suitable for small pressure difference and a working method. The self-adaptive reversing inter-shaft gas film sealing structure comprises an outer rotating shaft, a high-pressure sealing seat, an inner rotating shaft, a low-pressure sealing seat, a sealing ring and a sectioning ring. The high-pressure sealing seat and the low-pressure sealing seat are installed between the outer rotating shaft and the inner rotating shaft and fixedly connected with the inner rotating shaft, fluid dynamic pressure grooves are formed in the end face of the high-pressure sealing seat and the end face of the low-pressure sealing seat in the circumferential direction, and the sealing ring is arranged between the high-pressure sealing seat and the low-pressure sealing seat. A concave cavity is formed in the sealing ring, the sectioning ring is embedded into the concave cavity, and the sectioning ring is in interference fit with the outer rotating shaft. Stable sealing performance can be kept under small pressure difference, the problem of sealing failure caused by pressure difference change is avoided, and the sealing effect is improved. And meanwhile, the contact force is reduced, the abrasion of a sealing part is obviously reduced, and the service life is prolonged.

Description

Technical Field

[0001] The invention belongs to the field of aviation engines, and in particular is an adaptive reverse shaft air film sealing structure and a working method suitable for small pressure difference. Background Art

[0002] Modern aircraft engines usually adopt a high-low pressure dual shaft structure to shorten the shaft support distance, reduce the structural mass and reduce energy consumption. The high-pressure shaft of some advanced engines rotates in the opposite direction to the low-pressure shaft to offset the gyroscopic torque. The shafts are supported by intermediate bearings, and a reverse shaft seal is set between the shafts. This seal works in a high-speed and high-temperature environment and faces the challenges of large relative radial deflection and axial movement. At present, the commonly used sealing form is the comb tooth seal. However, the comb tooth seal has a large leakage, which can easily cause the bearing temperature to rise too high, thereby affecting the engine efficiency and making it difficult to meet the requirements of modern engines for sealing performance. For this reason, some scholars have proposed an air film sealing scheme for reverse shaft sealing. Currently, the main research forms are end face air film seals and cylindrical air film seals.

[0003] In the form of reverse shaft end face air film seal proposed by some researchers, the sealing ring is generally of two types: open ring or full ring, and graphite material is mostly used. When the sealing ring structure is an open ring, the outer diameter of the sealing ring is slightly larger than the inner diameter of the outer rotor before assembly, and the sealing ring and the outer rotor rotate synchronously by interference fit; when the sealing ring structure is a full ring, the fit between the sealing ring and the outer rotor is a transition fit. Both of these sealing structures form an end face sealed air film gap with the sealing seat fixedly installed on the inner rotor. In order to improve the bearing capacity of the air film, a dynamic pressure groove is usually processed on the sealing interface of the sealing seat. Foreign patent US8967627B2 discloses an inter-axial sealing structure, in which the sealing ring is composed of two half rings, and a spring is installed between the two half rings. The spring adjusts the force of the sealing ring in the axial direction. However, the structure is relatively complex, and the stability and reliability of the spring are difficult to guarantee in a high-speed and high-temperature environment. Patent US8888104B2 proposes an inter-axial end face air film sealing system, which optimizes the sealing effect by minimizing the torsion caused by pressure. High-speed gas enters the "herringbone" dynamic pressure groove through the throttle hole, forming fluid dynamic pressure, thereby effectively reducing gas leakage.

[0004] In the above end face air film sealing structure, the sealing ring is usually in contact with the outer rotor. Due to the high speed of the outer rotor and the high temperature inside the engine, when the sealing ring structure is an open ring and the outer rotor rotates synchronously with the sealing ring, the contact pressure generated by the centrifugal force and thermal deformation on the contact surface is relatively large; when the difference in gas pressure between the high-pressure side and the low-pressure side is relatively small, the sealing ring will be in a "stuck" state, unable to move axially for adaptive adjustment, or difficult to form a stable small air film gap, resulting in large leakage, and even causing the sealing ring to contact and collide with the end face of the high-pressure sealing seat, causing serious wear. When the structure of the sealing ring is a full ring, because the thermal expansion and centrifugal expansion deformation of the metal in a high temperature environment is much greater than the centrifugal expansion and thermal expansion deformation of the sealing ring, the contact surface of the sealing ring and the outer rotor will be separated and a gap will be generated, resulting in the sealing ring being unable to rotate synchronously with the outer rotor, which will increase leakage on the one hand, and on the other hand, the sealing ring will be in an "out of control" state, increasing the risk of collision and wear.

[0005] In addition, since the rotating shaft of the aircraft engine will have a relatively large axial movement (the amount of axial movement is much larger than the gap left by the sealing interface), the sealing ring will come into contact with the high-pressure sealing seat or the low-pressure sealing seat in the opposite direction, resulting in "counter-grinding" phenomenon, causing the sealing ring to heat up, wear and even damage. Patent 202111435416.2 proposes an air film sealing structure for the main bearing cavity of an aircraft engine, but because the structural components are relatively simple, it is difficult to achieve an ideal sealing effect under conditions of small pressure differences. Patent 201610621389.0 proposes a contact-type floating air film shaft sealing structure, which adopts a two-level sealing form to improve the sealing effect, but the structure is relatively complex and it is difficult to ensure that the engine does not fail under harsh working conditions. Patent 202410786791.9 proposes an improved inter-axial sealing structure of the main sealing ring, which combines the two sealing structures of comb seal and air film seal. Although it can reduce leakage to a certain extent, it still fails to effectively solve the problem of inner and outer rotor movement due to its complex structure. In addition, the integral main sealing ring has an asymmetric structure and uneven mass distribution, which is prone to eccentricity and causes failure of the sealing ring. Summary of the invention

[0006] The purpose of the present invention is to provide an adaptive reverse shaft air film sealing structure and a working method suitable for small pressure differences, so as to solve the problem that the adaptive adjustment effect of the existing air film under small pressure differences is poor.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: An adaptive reverse shaft air film seal structure suitable for small pressure difference comprises an outer shaft, a high pressure seal seat, an inner shaft, a low pressure seal seat, a seal ring and a petal ring; The high-pressure sealing seat and the low-pressure sealing seat are installed between the outer rotating shaft and the inner rotating shaft, and the high-pressure sealing seat and the low-pressure sealing seat are fixedly connected to the inner rotating shaft. The high-pressure sealing seat and the low-pressure sealing seat are both provided with fluid dynamic pressure grooves along the circumferential direction. The sealing ring is arranged between the high-pressure sealing seat and the low-pressure sealing seat, and a concave cavity is provided on the sealing ring. The petal ring is embedded in the concave cavity, and the petal ring and the outer rotating shaft are interference fit.

[0008] Furthermore, the sealing ring is a full-ring structure, the sealing ring and the outer shaft are clearance-fitted, and the material of the sealing ring is graphite or a carbon / carbon composite material.

[0009] Furthermore, the fluid dynamic pressure groove is a spiral deep and shallow groove.

[0010] Furthermore, the petal ring is installed in a concave cavity on the outer diameter side of the sealing ring, and there is an interference fit between the petal ring and the sealing ring.

[0011] Furthermore, the petal ring is a petal-type structure, and the petal ring includes a plurality of petal pieces, and the plurality of petal pieces are spliced ​​in a circumferential direction.

[0012] Furthermore, a separation ring is provided between the high-pressure sealing seat and the low-pressure sealing seat, and the axial width of the separation ring is greater than the axial width of the sealing ring.

[0013] Furthermore, the high-pressure sealing seat, the low-pressure sealing seat and the separation ring are all connected to the inner rotating shaft via a fixing ring.

[0014] Furthermore, the fluid dynamic pressure groove includes a first fluid dynamic pressure groove and a second fluid dynamic pressure groove, the first fluid dynamic pressure groove is opened at the top of the end surface of the high-pressure sealing seat, and the inner diameter side of the second fluid dynamic pressure groove is aligned with the outer circumferential surface of the separation ring.

[0015] Furthermore, the structure of the fluid dynamic pressure groove is designed according to the rotation direction of the inner rotating shaft and the outer rotating shaft.

[0016] A working method of the adaptive inverted inter-axial air film structure suitable for small pressure difference comprises: The petal ring rotates synchronously with the outer shaft, and the contact pressure generated on the contact surface is converted into friction. When the gas flows into the sealing gap through the gap between the high-pressure sealing seat and the outer shaft, one end face of the sealing ring is subjected to the thrust of the intake air, and one end face of the petal ring is also subjected to the force from the high-pressure side gas on the end face of the sealing ring. This force always causes friction between the two side faces of the sealing ring and the two side faces of the petal ring, thereby preventing the petal ring from fitting closely to the inner diameter side of the outer shaft, reducing the contact force on the contact surface between the petal ring and the outer shaft, and thus reducing the friction. Under the action of the intake thrust on the high-pressure side, the petal ring is displaced along the axial direction, forming an air film with a certain thickness to achieve an axial equilibrium state.

[0017] When the outer shaft undergoes a large axial displacement, when the end faces on both sides of the sealing ring contact one of the end faces of the high-pressure sealing seat or the low-pressure sealing seat, the gas can enter the fluid dynamic pressure groove, generating a sufficiently large air film force to "push open" the sealing ring, thereby avoiding direct contact between the sealing ring and the end face, and finally achieving an axial balance state under this working condition.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides an adaptive reverse shaft air film sealing structure suitable for small pressure difference, by installing a high-pressure sealing seat and a low-pressure sealing seat between an outer rotating shaft and an inner rotating shaft, and the high-pressure sealing seat and the low-pressure sealing seat are both fixedly connected to the inner rotating shaft. A sealing ring is arranged between the high-pressure sealing seat and the low-pressure sealing seat, and a petal ring is embedded in a concave cavity provided on the sealing ring, and is connected to the outer rotating shaft through an interference fit. The sealing structure is formed by combining the sealing ring and the petal ring, which effectively reduces the contact force between the sealing ring and the outer rotating shaft, and at the same time ensures that under a small pressure difference, the force difference between the left and right end faces of the sealing ring is large enough, and the difference is less than the friction force on the contact surface of the petal ring, thereby realizing adaptive adjustment of the air film and reducing leakage. At the same time, fluid dynamic pressure grooves are provided on the end faces of the high-pressure sealing seat and the low-pressure sealing seat to balance the axial excitation, ensure that the two end faces of the sealing ring do not contact the two end faces of the high-pressure sealing seat and the low-pressure sealing seat, thereby reducing wear. The present invention is suitable for an adaptive reverse shaft air film seal structure with a small pressure difference, which can maintain stable sealing performance under a small pressure difference, effectively avoid the problem of sealing failure caused by pressure difference changes, and improve the sealing effect. In addition, it also reduces the contact force, significantly reduces the wear of the sealing parts, and prolongs the service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 It is a schematic diagram of the structure of the adaptive inverted inter-axial air film seal suitable for small pressure difference of the present invention.

[0021] FIG2 is a schematic diagram of the end surface structure of the high-pressure sealing seat and the low-pressure sealing seat of the present invention, wherein (a) is a schematic diagram of the end surface structure of the high-pressure sealing seat, and (b) is a schematic diagram of the end surface structure of the low-pressure sealing seat.

[0022] Figure 3 It is a three-dimensional schematic diagram of the petal ring structure of the present invention.

[0023] Figure 4It is a schematic diagram of the sealing ring structure of the present invention.

[0024] Figure 5 It is a schematic diagram of the end face seal adaptive adjustment process of the present invention.

[0025] Figure 6 It is a schematic diagram of the axial force on the petal ring and the sealing ring in the working state of the present invention.

[0026] Among them: 1-outer rotating shaft, 2-high pressure sealing seat, 3-inner rotating shaft, 4-separating ring, 5-fixing ring, 6-low pressure sealing seat, 7-sealing ring, 8-petal ring, 9-first fluid dynamic pressure groove, 10-second fluid dynamic pressure groove. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0030] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0031] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0032] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings: See also Figure 1 The present invention provides an adaptive inverted inter-shaft air film sealing structure suitable for small pressure differences, including an outer rotating shaft 1, a high-pressure sealing seat 2, an inner rotating shaft 3, a separating ring 4, a fixing ring 5, a low-pressure sealing seat 6, a combined sealing ring, a first fluid dynamic pressure groove 9 and a second fluid dynamic pressure groove 10. The high-pressure sealing seat 2 and the low-pressure sealing seat 6 are installed between the outer rotating shaft 1 and the inner rotating shaft 3, and the high-pressure sealing seat 2 and the low-pressure sealing seat 6 are fixedly connected to the inner rotating shaft 3. The combined sealing ring includes a sealing ring 7 and a petal ring 8, and the sealing ring 7 is arranged between the high-pressure sealing seat 2 and the low-pressure sealing seat 6. Figure 4 As shown, a concave cavity is provided in the middle of the outer diameter side of the sealing ring 7, and the petal ring 8 is embedded in the concave cavity. The sealing ring 7 and the petal ring 8 are interference fit, which ensures that the sealing ring 7 and the petal ring 8 will not "detach" during operation, and there is contact pressure between the two, and the sealing ring 7 rotates synchronously with the petal ring 8. The sealing ring 7 and the outer rotating shaft 1 are clearance-matched, ensuring that the intake thrust exerted by the gas on the high-pressure side on the end face of the sealing ring 7 can be in close contact with the side of the petal ring 8, and rotate synchronously with the petal ring 8.

[0034] The separator ring 4 is arranged between the high-pressure sealing seat 2 and the low-pressure sealing seat 6 to separate the high-pressure sealing seat 2 and the low-pressure sealing seat 6 for axial positioning therebetween, and the axial width of the separator ring 4 is slightly larger than the axial width of the sealing ring 7. The high-pressure sealing seat 2, the low-pressure sealing seat 6 and the separator ring 4 are all fixed on the inner rotating shaft 3 by the fixing ring 5, and rotate synchronously with the inner rotating shaft 3. The fixing ring 5 plays a role in positioning and fastening, and the fastening method can be a nut or a pin. The high-pressure sealing seat 2, the low-pressure sealing seat 6, the sealing ring 7 and the petal ring 8 are all high-flatness end face seals. Fluid dynamic pressure grooves are opened on both end faces of the high-pressure sealing seat 2 and the low-pressure sealing seat 6 in the circumferential direction to balance the axial load of the sealing device, keep the sealing end faces non-contact and keep the leakage low.

[0035] A first fluid dynamic pressure groove 9 is provided on the end face of the high-pressure sealing seat 2. The structural form of the first fluid dynamic pressure groove 9 needs to be designed according to the rotation direction of the inner rotating shaft 3 and the outer rotating shaft 1. As shown in Figure 2 (a), the first fluid dynamic pressure groove 9 is a spiral deep and shallow groove. The depth of the deep groove is greater than the shallow groove. The spiral deep and shallow groove has a secondary step effect, which can enhance the dynamic and static pressure effect, greatly reduce leakage, and improve the sealing performance. When the outer rotating shaft 1 moves to the left or the inner rotating shaft 3 moves to the right, the sealing ring 7 will come into contact with the right end face of the high-pressure sealing seat 2. Due to the different directions of the inner rotating shaft 3 and the outer rotating shaft 1, "counter-wear" will occur. At this time, the first fluid dynamic pressure groove 9 provided on the end face of the high-pressure sealing seat 2 will generate a sufficiently large fluid dynamic and static pressure to make the sealing ring 7 drive the petal ring 8 to move to the right along the axial direction to reach a new equilibrium state.

[0036] A second fluid dynamic pressure groove 10 is provided on the end face of the low-pressure sealing seat 6. The inner diameter side of the second fluid dynamic pressure groove 10 is aligned with the outer circumferential surface of the separation ring 4. The structural form of the second fluid dynamic pressure groove 10 is designed according to the rotation direction of the inner shaft 3 and the outer shaft 1. As shown in Figure 2 (b), the second fluid dynamic pressure groove 10 is a spiral deep and shallow groove. The spiral deep and shallow groove has a secondary step effect, which can enhance the dynamic and static pressure effect, greatly reduce leakage, and improve the sealing performance. When the outer shaft 1 moves to the right and the inner shaft 3 moves to the left, the low-pressure sealing seat 6 will contact the right end face of the sealing ring 7, and the two end faces will "grind". The gas entering the second fluid dynamic pressure groove 10 will generate fluid dynamic and static pressure, separating the sealing ring 7 from the low-pressure sealing seat 6 to achieve a new balance. When no axial movement occurs, the second fluid dynamic pressure groove 10 will generate a sufficiently large air film force to achieve a dynamic balance with the intake thrust generated by the gas on the high-pressure side and the friction force generated by the contact surface between the petal ring 8 and the outer rotating shaft 1, maintaining a non-contact state to reduce leakage.

[0037] The sealing ring 7 adopts a full-ring structure, and the material used is graphite or carbon / carbon composite material with high wear resistance. When the gas flows into the gap between the high-pressure sealing seat 2 and the left side of the sealing ring 7, a relatively large intake thrust will be generated to make the sealing ring 7 and the left side of the petal ring 8 in close contact, and move to the right along the axial direction to form a stable air film. When the working conditions change, if the air film gap tends to increase, the sealing ring 7 will cause the petal ring 8 to move to the left along the axial direction. At this time, the petal ring 8 is still in close contact with the two side surfaces of the sealing ring 7. When the air film gap tends to decrease, the gas on the high-pressure side will continue to move the sealing ring 7 and the petal ring 8 to the right along the axial direction to reach a new balance.

[0038] The material of the petal ring 8 is graphite or carbon / carbon composite material with high wear resistance, such as Figure 3As shown, it is a petal-type structure, including a plurality of petal pieces, and the plurality of petal pieces are spliced ​​in the circumferential direction. The petal ring 8 and the outer shaft 1 are interference fit to ensure that the petal ring 8 rotates synchronously with the outer shaft 1. When the engine is working, due to the small overall volume of the structure, the axial friction force generated on the contact surface will be smaller than that of the open sealing ring. Therefore, under the condition of small pressure difference, the high-pressure gas on the inlet side can push the sealing ring 7 to move along the axial direction. At this time, the sealing ring 7 will contact the side of the petal ring 8 to generate axial displacement, so that an air film is formed between the right end face of the sealing ring 7 and the left end face of the low-pressure sealing seat 6, and the sealing ring 7 rotates synchronously with it.

[0039] The working method of the adaptive reverse shaft air film seal structure suitable for small pressure difference of the present invention is as follows: Figure 5 As shown, including: Under normal working conditions, the petal ring 8 contacts the outer shaft 1, and under the action of the friction torque, the petal ring 8 rotates synchronously with the outer shaft 1. At this time, a certain amount of contact pressure will be generated on the contact surface of the outer shaft 1 and the petal ring 8, and the contact pressure can be converted into a certain amount of friction. There is a clearance fit between the sealing ring 7 and the outer shaft 1. When the gas flows into the sealing gap through the gap between the high-pressure sealing seat 2 and the outer shaft 1, an intake thrust will be generated on the left end face of the sealing ring 7. The left side of the petal ring 8 will be subjected to the force from the high-pressure side gas on the left end face of the sealing ring 7. Figure 6 As shown. The sealing ring 7 and the petal ring 8 are in interference fit, and the contact between the two is friction contact, which will always cause friction between the two side surfaces of the sealing ring 7 and the two side surfaces of the petal ring 8, hindering the tendency of the petal ring 8 to fit closely to the inner diameter side of the outer shaft 1 outward, which to a certain extent reduces the contact pressure on the contact surface between the petal ring 8 and the outer shaft 1, thereby reducing the friction. Under the action of the high-pressure side intake thrust, the petal ring 8 will displace along the axial direction to form an air film with a certain thickness to achieve axial balance. The interference fit between the sealing ring 7 and the petal ring 8 reduces the "uncentering" state of the sealing ring 7 to a certain extent, and the mass of the sealing ring 7 is evenly distributed, which will avoid damage to the sealing ring 7. A fluid dynamic pressure groove is opened on the end face of the low-pressure sealing seat 6. When the gas passes through the outer diameter of the separation ring 4 and the inner diameter of the sealing ring 7, it directly flows into the fluid dynamic pressure groove. The fluid dynamic pressure groove is a spiral deep and shallow groove. The depth of the deep groove is greater than that of the shallow groove. The spiral deep and shallow groove has a secondary step effect, which can enhance the dynamic and static pressure effects, can greatly reduce leakage, and improve sealing performance.

[0040] When the outer shaft 1 undergoes a large axial displacement, no matter the left or right end faces of the sealing ring 7 are in contact with one of the end faces of the high-pressure sealing seat 2 or the low-pressure sealing seat 6, the gas can enter the fluid dynamic pressure groove to generate a sufficiently large air film force to "push open" the sealing ring 7, so that the sealing ring 7 does not directly contact the two end faces, and finally reaches an axial equilibrium state under this working condition.

[0041] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Adaptive reverse shaft air film seal structure suitable for small pressure difference, characterized by: It comprises an outer rotating shaft (1), a high-pressure sealing seat (2), an inner rotating shaft (3), a low-pressure sealing seat (6), a sealing ring (7) and a petal ring (8); The high-pressure sealing seat (2) and the low-pressure sealing seat (6) are installed between the outer rotating shaft (1) and the inner rotating shaft (3); the high-pressure sealing seat (2) and the low-pressure sealing seat (6) are fixedly connected to the inner rotating shaft (3); the end surfaces of the high-pressure sealing seat (2) and the low-pressure sealing seat (6) are both provided with fluid dynamic pressure grooves along the circumferential direction; the sealing ring (7) is arranged between the high-pressure sealing seat (2) and the low-pressure sealing seat (6); a concave cavity is provided on the sealing ring (7); the petal ring (8) is embedded in the concave cavity; the petal ring (8) and the outer rotating shaft (1) are in an interference fit.

2. The adaptive inverted inter-axial air film seal structure suitable for small pressure difference according to claim 1 is characterized in that: The sealing ring (7) is a full-ring structure, the sealing ring (7) and the outer rotating shaft (1) are clearance-fitted, and the material of the sealing ring (7) is graphite or a carbon / carbon composite material.

3. The adaptive inverted inter-axial air film seal structure suitable for small pressure difference according to claim 1 is characterized in that: The fluid dynamic pressure groove is a spiral groove with different depths.

4. The adaptive inverted inter-axial air film seal structure suitable for small pressure difference according to claim 1 is characterized in that: The petal ring (8) is installed in a concave cavity on the outer diameter side of the sealing ring (7), and there is an interference fit between the petal ring (8) and the sealing ring (7).

5. The adaptive inverted inter-axial air film seal structure suitable for small pressure difference according to claim 1 is characterized in that: The petal ring (8) is a petal-type structure, and the petal ring (8) comprises a plurality of petal pieces, wherein the plurality of petal pieces are spliced ​​in a circumferential direction.

6. The adaptive inverted inter-axial air film seal structure suitable for small pressure difference according to claim 1, characterized in that: A separation ring (4) is provided between the high-pressure sealing seat (2) and the low-pressure sealing seat (6), and the axial width of the separation ring (4) is greater than the axial width of the sealing ring (7).

7. The adaptive inverted inter-axial air film seal structure suitable for small pressure difference according to claim 6 is characterized in that: The high-pressure sealing seat (2), the low-pressure sealing seat (6) and the separation ring (4) are all connected to the inner rotating shaft (3) via a fixing ring (5).

8. The adaptive inverted inter-axial air film seal structure suitable for small pressure difference according to claim 1 is characterized in that: The fluid dynamic pressure groove comprises a first fluid dynamic pressure groove (9) and a second fluid dynamic pressure groove (10), wherein the first fluid dynamic pressure groove (9) is opened at the top of the end surface of the high-pressure sealing seat (2), and the inner diameter side of the second fluid dynamic pressure groove (10) is aligned with the outer circumferential surface of the separation ring (4).

9. The adaptive inverted inter-axial air film seal structure suitable for small pressure difference according to claim 1, characterized in that: The structural form of the fluid dynamic pressure groove is designed according to the rotation direction of the inner rotating shaft (3) and the outer rotating shaft (1).

10. A working method of the adaptive inverted interaxial air film structure suitable for small pressure difference according to any one of claims 1 to 9, characterized in that: include: The petal ring (8) rotates synchronously with the outer rotating shaft (1), and the contact pressure generated on the contact surface is converted into friction. When the gas flows into the sealing gap through the gap between the high-pressure sealing seat (2) and the outer rotating shaft (1), one end face of the sealing ring (7) is subjected to the thrust of the intake gas, and one end face of the petal ring (8) is also subjected to the force from the high-pressure side gas on the end face of the sealing ring (7). This force causes friction to always exist between the two side faces of the sealing ring (7) and the two side faces of the petal ring (8), thereby preventing the petal ring (8) from closely fitting outwardly to the inner diameter side of the outer rotating shaft (1), reducing the contact force on the contact surface between the petal ring (8) and the outer rotating shaft (1), and further reducing the friction. Under the action of the high-pressure side intake thrust, the petal ring (8) is displaced along the axial direction, forming a gas film with a certain thickness to achieve an axial equilibrium state; When the outer shaft (1) undergoes a large axial displacement, when the end faces on both sides of the sealing ring (7) contact one of the end faces of the high-pressure sealing seat (2) or the low-pressure sealing seat (6), gas can enter the fluid dynamic pressure groove, generating a sufficiently large gas film force to "push open" the sealing ring (7), thereby avoiding direct contact between the sealing ring (7) and the end face, and finally achieving an axial equilibrium state under this working condition.

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