A hydraulic method and device for dismounting an aeroengine fan shaft nut

Abstract

The application discloses a kind of hydraulic dismounting method and device of aero-engine fan shaft nut.The dismounting method includes: S1, according to the mechanical properties of fan shaft, determine the maximum hydraulic pressure;S2, establish the force transmission path from hydraulic power source to fan shaft, ensure the thread engagement requirement;S3, apply controllable axial tension to fan shaft, make it produce elastic elongation to unload nut preload;S4, rotate nut in the state of maintaining tension;S5, repeat the above steps to complete dismounting after releasing tension.The corresponding dismounting device includes a support positioning assembly with an operating window, a hollow hydraulic cylinder, a pull rod that penetrates the hydraulic cylinder and is threadedly connected with the fan shaft, and an operating assembly that engages with the fan shaft nut through the window.The application converts the circumferential rotation friction that is difficult to overcome into controllable axial hydraulic tension, and realizes safe, efficient and non-destructive dismounting of high preload fan shaft nut.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology, and in particular to a hydraulic disassembly method and apparatus for aero-engine fan shaft nut. Background Technology

[0002] During aero-engine overhauls, disassembling core rotating components is a necessary step, such as the disassembly of the fan rotor assembly. This disassembly process requires overcoming the preload of the fan shaft nut. Related technologies primarily rely on specialized hydraulic tools such as shaft tension clamps. Operation involves applying hydraulic pressure directly to the nut or its connection interface using tools based on fixed pressure values ​​given in the manual, overcoming rotational friction and thus initiating disassembly. However, this method of applying force cannot completely separate the direct force on precision threaded pairs (especially the external threads of the fan shaft) from a mechanical perspective, posing an inherent risk of damaging precision components. Furthermore, the adjustment of operating pressure and steps lacks a theoretical basis for calculations specific to the fan shaft material and thread strength, relying on experience and manuals in a trial-and-error process, resulting in insufficient safety, controllability, and operational accuracy. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] To address this, embodiments of the present invention propose a hydraulic disassembly method and apparatus for aero-engine fan shaft nuts, which, based on the principle of unloading preload from the axially stretched shaft, solves the risk of damage to the precision external threads of the aero-engine fan shaft during disassembly.

[0005] The hydraulic disassembly method for the aero-engine fan shaft nut according to an embodiment of the present invention includes: S1. Based on the mechanical properties of the fan shaft, determine the maximum hydraulic pressure to be applied when axially stretching the fan shaft; S2. Establish a force transmission path from the hydraulic power source to the fan shaft, and ensure that the threaded connections on the force transmission path meet the predetermined meshing requirements. S3. Apply a controllable axial tensile force to the fan shaft to produce a controllable axial elastic elongation of the fan shaft, thereby unloading the preload between the fan shaft nut and the external thread of the fan shaft. During the application of the axial tensile force, the corresponding hydraulic pressure gradually increases from the initial value, and the final value does not exceed the maximum hydraulic pressure. S4. While maintaining axial tension, rotate the fan shaft nut; S5. After releasing the axial tension, allow the fan shaft to elastically recover. Repeat steps S3 and S4 until the fan shaft nut is removed.

[0006] In some embodiments, the logic for determining the maximum hydraulic pressure in step S1 includes: The maximum allowable tensile force F_axis of the fan shaft body is calculated based on the material yield strength. The allowable tensile force F_thread of the internal thread is calculated based on the shear strength of the internal thread at the end of the fan shaft. The smaller value between F_axis and F_thread is taken as the maximum permissible axial tensile force F_max; The maximum hydraulic pressure P_max is calculated using the formula P_max=F_max / A, where A is the effective working area of ​​the hydraulic actuator.

[0007] In some embodiments, in step S2, the threaded connection includes a threaded connection portion for transmitting axial tensile force to the fan shaft, and the effective number of engagement turns during installation is greater than or equal to a safety threshold.

[0008] In some embodiments, step S2 further includes cleaning and lubricating the threaded connection on the force transmission path.

[0009] In some embodiments, in step S3, if the fan shaft nut does not rotate when the axial tension is applied at the current hydraulic pressure, after releasing the pressure, the hydraulic pressure is increased by a preset pressure increment without exceeding the maximum hydraulic pressure, and steps S3 and S4 are re-executed.

[0010] In some embodiments, step S3 further includes centering the force transmission path before applying the axial tensile force, so that the axial tensile force is applied along the axial direction of the fan shaft.

[0011] The hydraulic disassembly device for the aircraft engine fan shaft nut of this invention is used to implement the disassembly method described in the above embodiments. The disassembly device includes: A support positioning component is provided, which is connected to the fan shaft to provide reaction force support, and the support positioning component is provided with an operation window; A hydraulic cylinder is disposed on the support and positioning assembly, and the hydraulic cylinder has a hollow structure. A pull rod passes sequentially through the hydraulic cylinder and the support and positioning assembly. One end of the pull rod is provided with an external thread for engaging with the central threaded hole at the end of the fan shaft, and the other end of the pull rod is provided with a force-applying part that abuts against the lifting piston of the hydraulic cylinder. A nut operating assembly extends through the operating window and engages with the fan shaft nut to allow the nut operating assembly to tighten the fan shaft nut within the operating window.

[0012] In some embodiments, the support positioning assembly includes a first bracket and a second bracket whose support body is cylindrical. A first end of the first bracket is connected to a fan disc on the fan shaft. An operation window is located on the side wall of the first bracket. A first end of the second bracket is detachably connected to a second end of the first bracket. A hydraulic cylinder is mounted on the second end of the second bracket.

[0013] In some embodiments, the first end of the first bracket is provided with a contoured inner cone surface for fitting and positioning against the outer cone surface of the fan disc.

[0014] In some embodiments, the disassembly device further includes a force transmission component disposed between the lifting piston of the hydraulic cylinder and the force-applying part of the pull rod, so as to transmit the lifting force of the lifting piston of the hydraulic cylinder to the force-applying part of the pull rod through the force transmission component. The force transmission component includes a flange and at least one pad, the flange being disposed at the end of the lifting piston of the hydraulic cylinder, and the at least one pad being disposed between the flange and the force-applying part of the pull rod.

[0015] In summary, in the embodiments of this invention, the disassembly method, by scientifically calculating the safety pressure and stretching the shaft to unload the preload, fundamentally eliminates the risk of damaging the precision external threads of the fan shaft. The specialized device implementing this method solves the installation and operation problems in confined spaces through a split bracket and operating window, ensures the pulling force acts on the shaft through a through-type hollow hydraulic cylinder and pull rod, and allows the tool to quickly adapt to various working conditions through modular flanges and pads. Ultimately, this achieves efficient, standardized, and non-destructive disassembly of core components of aero-engines while ensuring safety. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a hydraulic disassembly method for the fan shaft nut of an aircraft engine according to an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the hydraulic disassembly device for the fan shaft nut of an aircraft engine according to an embodiment of the present invention.

[0018] Figure 3 This is a cross-sectional schematic diagram of the hydraulic disassembly device for the fan shaft nut of an aircraft engine according to an embodiment of the present invention.

[0019] Figure label: 11-Fan shaft; 12-Fan shaft nut; 13-Fan disc; 21-Support positioning component; 211-First bracket; 2111-Operation window; 212-Second bracket; 22-Hydraulic cylinder; 221-Lifting piston; 23-Pull rod; 231-Force application part; 24-Nut operating assembly; 25-Force transmission component; 251-Flange; 252-Panace block. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] The following is for reference. Figures 1 to 3 This invention describes a method and apparatus for hydraulically disassembling the fan shaft nut of an aircraft engine, according to embodiments of the present invention.

[0022] like Figure 1 As shown, the hydraulic disassembly method for the aero-engine fan shaft nut of this invention includes: S1. Based on the mechanical properties of the fan shaft 11, determine the maximum hydraulic pressure to be applied when axially stretching the fan shaft 11.

[0023] Step S1 determines the upper limit of the safe load for the entire disassembly operation. Traditional methods directly use fixed pressure values ​​given in the manual, ignoring individual differences in material batches, usage history, and manufacturing tolerances of specific parts. Therefore, their safety boundaries are vague and generic. The disassembly method of this invention establishes the safety of the disassembly operation on the precise mechanical load-bearing capacity of the current operating object (specific fan shaft 11), thereby reducing the risk of plastic deformation of the shaft or thread shear failure due to overload.

[0024] S2. Establish a force transmission path from the hydraulic power source to the fan shaft 11, and ensure that the threaded connections on the force transmission path meet the predetermined meshing requirements.

[0025] Step S2 constructs a reliable and efficient force transmission system, creating conditions for subsequent operations. The structure of traditional tools may disperse the reaction force or apply it to unsuitable parts. The disassembly method of this embodiment requires clearly establishing a direct path from the hydraulic power source to the fan shaft 11, ensuring that the final force point is the body of the fan shaft 11, and that the path itself has sufficient structural rigidity and connection reliability to withstand huge tensile forces without instability, slippage, or connection failure.

[0026] For example, this force transmission path can be established as follows: First, a front-end contour-following positioning bracket is needed, whose inner contour precisely matches a specific load-bearing structure on the fan shaft 11 (such as the conical surface of the fan disc 13) to achieve rapid centering and stable support. Second, a high-strength alloy steel tie rod 23 is used, one end of which is machined with an external thread that matches the central internal thread at the end of the fan shaft 11, while the other end is used to receive hydraulic thrust. Finally, a rear-end support structure is used to fix the hydraulic cylinder 22.

[0027] During installation, ensure that the depth to which the pull rod 23 is screwed into the internal thread of the fan shaft 11 (i.e., the effective number of engagement turns) reaches the safety design threshold (e.g., not less than 10.5 turns) to guarantee the strength of the threaded connection under extreme tensile force. In addition, cleaning and properly lubricating all critical threaded pairs before assembly are also auxiliary measures to ensure smooth force transmission and prevent seizing.

[0028] S3. Apply a controllable axial tension to the fan shaft 11 to cause the fan shaft 11 to produce a controllable axial elastic elongation, so as to unload the preload between the fan shaft nut 12 and the external thread of the fan shaft 11. During the application of the axial tension, the corresponding hydraulic pressure gradually increases from the initial value, and the final value does not exceed the maximum hydraulic pressure.

[0029] Step S3 creates a temporary controllable mechanical state, causing the fan shaft 11 to undergo a small amount of axial elastic stretching, thereby offsetting or eliminating the clamping force (i.e. preload) between the fan shaft nut 12 and the external thread of the fan shaft 11, thus transforming the disassembly problem from overcoming huge static friction to rotating under low friction conditions.

[0030] After completing the installation in step S2, start the hydraulic pump station. Hydraulic oil is pumped into the hydraulic cylinder 22, pushing its piston rod to extend. Since the piston rod abuts against the top of the pull rod 23 through a structure such as the pad 252, and the other end of the pull rod 23 is fixed to the fan shaft 11, and the front bracket provides reaction support, the thrust of the piston rod is converted into an axial pulling force on the pull rod 23, and then transmitted to the fan shaft 11.

[0031] The system pressure is increased slowly and smoothly (i.e., gradually increased from the initial value), monitored in real time by a pressure gauge. As the tension increases, the fan shaft 11 is elongated within its elastic range. This process continues until the pressure reaches a preset working pressure sufficient to fully unload the nut preload, but this pressure is strictly lower than or equal to the maximum hydraulic pressure determined in step S1. Through precise pressure control, the elongation of the shaft can be precisely controlled to be sufficient to unload the preload while remaining well below the limit that would cause permanent deformation.

[0032] S4. While maintaining axial tension, rotate the fan shaft nut 12.

[0033] Step S4 utilizes the favorable mechanical state created in step S3 to perform low-resistance rotation of the fan shaft nut 12.

[0034] S5. After releasing the axial tension, allow the fan shaft 11 to elastically recover. Repeat steps S3 and S4 until the fan shaft nut 12 is removed.

[0035] Step S5 uses a cyclic operation mode to break down the entire disassembly process into safe and controllable short steps, thereby completing the disassembly of the entire fan shaft nut 12.

[0036] When the system pressure is maintained at the working pressure reached in step S3, use a special wrench to engage with the fan shaft nut 12 through the pre-reserved operating window 2111 on the front bracket. At this time, since the preload has been unloaded, the nut can be easily turned with only a small torque.

[0037] After rotating a certain angle (e.g., half a turn or until blocked by the structure), step S4 is completed. Then, step S5 is executed to operate the hydraulic system unloading valve and safely release the hydraulic pressure. After the pressure is released, the fan shaft 11 returns to its original length under its own elastic force.

[0038] Remove the special wrench from the nut and return it to the next engaging position. Then, repeat steps S3 and S4, i.e., apply pressure again to the working pressure and rotate the nut a small angle again. Repeat this cycle of applying pressure, rotating, depressurizing, and returning, each cycle completing only a small part of the total disassembly work, until the nut is completely loosened and can be easily removed by hand.

[0039] The hydraulic disassembly method for the fan shaft nut of the aircraft engine in this embodiment of the invention guides the force to the fan shaft 11 and uses its elastic deformation to unload the preload, avoiding direct shearing or squeezing between the tool and the high-precision external thread of the fan shaft 11, thus solving the inherent risk of damaging the precision mating surface from a mechanical principle perspective.

[0040] By establishing the operational safety boundary on the theoretical calculation of the mechanical properties of specific components, the blindness of empirical values ​​is replaced. Through the gradual increase of pressure and the limitation of not exceeding the maximum value, the process is managed in a refined manner, which together constitutes a dual safety control mechanism and improves the controllability and safety of the operation.

[0041] Therefore, the hydraulic disassembly method for the aero-engine fan shaft nut of this invention transforms the traditional high-risk, high-intensity trial-and-error, impact-based operation into a low-intensity, predictable, and repeatable standardized procedure, reducing reliance on the physical strength and experience of operators, increasing the success rate of the operation, and improving the overall efficiency and reliability of the disassembly operation.

[0042] In some embodiments, the logic for determining the maximum hydraulic pressure in step S1 includes: The maximum allowable tensile force F_axis of the fan shaft 11 is calculated based on the material yield strength. The allowable tensile force F_thread of the internal thread is calculated based on the shear strength of the internal thread at the end of the fan shaft 11. The smaller value between F_axis and F_thread is taken as the maximum permissible axial tensile force F_max; The maximum hydraulic pressure P_max is calculated using the formula P_max=F_max / A, where A is the effective working area of ​​the hydraulic actuator.

[0043] It is understandable that excessive tension causes the stress on the fan shaft 11 body (cylindrical section) to exceed the yield strength of its material, resulting in plastic elongation or even fracture; and causes shearing damage or disengagement of the internal thread at the end of the fan shaft 11 used to connect the tie rod 23.

[0044] Based on the tensile strength theory in mechanics of materials, the maximum allowable tensile force F_axis of the fan shaft 11 is determined by the product of its minimum cross-sectional area (usually the cross-sectional area at the root diameter of the thread or the cross-sectional area at the minimum diameter of the shaft body) and the allowable tensile stress of the material under the safety factor (usually obtained by dividing the yield strength by the safety factor).

[0045] Based on the strength theory of threaded connections, the allowable tensile force F_thread of an internal thread is determined by the product of the effective shear area of ​​the thread (related to the thread engagement length, pitch, and thread profile) and the allowable shear strength of the thread material, ensuring that the thread teeth do not undergo shear failure under tensile force.

[0046] Once the maximum permissible axial tensile force F_max is obtained, it is converted according to the hydraulic transmission formula P_max=F_max / A (pressure = force / area). Here, A is the effective pressure-bearing area of ​​the lifting piston 221 of the hydraulic actuator (i.e., hydraulic cylinder 22). Through this conversion, the force limit F_max is transformed into the observable and controllable pressure limit P_max on the hydraulic system, allowing safety control to be intuitively realized on the operating interface (pressure gauge).

[0047] Therefore, unlike related technologies that use uniform empirical stress values ​​that may be too conservative or overly aggressive, the method of this invention requires targeted strength calculations for the fan shaft 11 of each engine to be repaired (or at least for representative shafts of the same model and batch).

[0048] By simultaneously verifying the strength of the shaft and the threaded connection, and taking the weakest link as the control benchmark, the disassembly operation is ensured to be safe in all possible failure paths, thereby eliminating accidental damage caused by inadequate consideration (e.g., only considering the strength of the shaft while ignoring the strength of the thread).

[0049] The calculated P_max becomes the red line for the entire hydraulic loading process (step S3). As the pressure is gradually increased, the operator knows precisely that the upper limit is based on scientific calculation rather than empirical estimation, thus improving the certainty of the operation.

[0050] For ease of understanding, let's assume a simplified operating condition: The fan shaft 11 is made of high-strength alloy steel with a yield strength of 900 MPa. With a safety factor of 1.5, the allowable tensile stress is the ratio of the yield strength to the safety factor, which is 600 MPa.

[0051] The minimum diameter at the root of the thread on fan shaft 11 is 36mm. Calculate the F-axis: A_axis=π (0.036m)² / 4≈1.017×10 - ³m².

[0052] F_axis = 1.017 × 10 - ³m² 600×10 6 Pa≈610,200N (approximately 62.2 tons of force).

[0053] The internal thread parameters are M40×1.5, the engagement length is 60mm, and the allowable shear strength of the material is 450MPa.

[0054] Calculate F_thread (simplified calculation, estimated based on thread shear area): Thread shear area A_thread ≈π Thread pitch diameter Length of engagement Coefficient (related to tooth type, assumed to be 0.8).

[0055] Taking the mean diameter as approximately 38.5mm, then A_thread ≈ π 0.0385m 0.06m 0.8 ≈ 5.8 × 10 - ³m².

[0056] F_thread = 5.8 × 10 - ³m² 450×10 6 Pa≈2,610,000N (approximately 266 tons of force).

[0057] Determine F_max: Compare F_axis (610kN) and F_thread (2610kN), and take the smaller value. Therefore, F_max = 610kN.

[0058] Hydraulic cylinder 22 parameters: Select single-acting hydraulic cylinder 22 with a piston diameter of 100mm.

[0059] Calculate P_max: Piston effective area A=π (0.1m)² / 4≈7.854×10 - ³m².

[0060] P_max=F_max / A=610,000N / 7.854×10 - ³m²≈77.7×10 6 Pa = 77.7 MPa.

[0061] Therefore, under this operating condition, the maximum permissible working pressure of the hydraulic system should be set to no more than 77.7 MPa. Any manual recommendation higher than this value should be based on this calculated value; if lower, the manual value should be used. This pressure value becomes the absolute upper limit for all subsequent loading operations.

[0062] In some embodiments, in step S2, the threaded connection includes a threaded connection portion for transmitting axial tensile force to the fan shaft 11, and the effective number of engagement turns during installation is greater than or equal to a safety threshold.

[0063] Understandably, when a threaded connection is subjected to axial tensile force, the load is not evenly distributed across all the engaging thread teeth. Typically, the first thread bears the highest proportion of the load, with the load decreasing sequentially across subsequent threads. If the number of engaged turns is too small, a limited number of thread teeth will bear almost all the tensile force, making them highly susceptible to localized plastic deformation and leading to thread skipping and failure.

[0064] The safety threshold number of turns refers to providing sufficient engagement length so that more thread teeth participate in load sharing, thereby significantly reducing the stress level of individual thread teeth. When the number of engagement turns reaches or exceeds the safety threshold, the load distribution of the entire threaded connection tends to be reasonable, and its pull-out resistance can reach or approach the theoretical calculation value.

[0065] In the force transmission path established in step S2, the connection between the tie rod 23 and the internal thread at the end of the fan shaft 11 is the starting point and key force-bearing node of the entire force transmission chain. All subsequent hydraulic tension is introduced into the fan shaft 11 body without loss through the threaded pair here.

[0066] The effective number of engagement turns is greater than or equal to the safety threshold, ensuring that the mechanical connection formed here is strong enough to serve as a reliable foundation for subsequent operations, preventing the force from being interrupted at the starting point of transmission due to connection failure, which could lead to operation failure or safety accidents.

[0067] Effective engagement refers to the number of turns in which the threaded pair fully forms mechanical contact, excluding the number of ineffective turns caused by thread termination, chamfering, or incomplete engagement. It requires the actual load-bearing contact length.

[0068] Therefore, when installing tie rod 23, it is screwed in to a sufficient depth to prevent shallow engagement installation caused by shortcuts or misjudgment, thereby reducing the safety hazard of pull-out or shearing damage due to insufficient thread connection strength during operation.

[0069] When calculating F_thread (allowable tensile force of internal thread), the theoretical model is based on the assumption that the thread has sufficient engagement length. By satisfying the safety threshold number of turns, it is ensured that the actual threaded connection state in the field matches the premise of the theoretical calculation model, thus making the calculated safety pressure P_max effective in reality.

[0070] By incorporating the safety threshold as a clear process parameter (e.g., by writing it into the work instructions), a uniform standard of connection reliability can be achieved when different operators perform the same task at different times, reducing performance fluctuations and quality risks caused by human factors.

[0071] For example, the disassembly of the engine fan shaft 11.

[0072] Thread specifications: The connection thread between the tie rod 23 and the end of the fan shaft 11 is M36×2 (nominal diameter 36mm, pitch 2mm).

[0073] Material strength: The threads of the fan shaft 11 and the tie rod 23 are both made of high-strength alloy steel, and the allowable shear stress of their thread pair is relatively high.

[0074] Determination of the safety threshold: This safety threshold is typically determined by the tool designer or engine manufacturer through mechanical analysis, experimental verification, or industry standards. For example, based on mechanical calculations and past experience for this thread specification, it may be stipulated that the effective number of engagement turns must not be less than 10 turns.

[0075] Brief analysis of the calculation basis: The thread engagement length (L) is equal to the effective number of engagement turns (N) multiplied by the pitch (P). If N≥10 and P=2mm are required, then the minimum engagement length L≥20mm is required. This length ensures that the thread shear area is large enough and the load can be relatively evenly distributed on a large number of thread teeth.

[0076] During on-site operation: The operator screws the threaded end of the pull rod 23 into the internal threaded hole of the fan shaft 11.

[0077] During the screwing process, it is necessary to visually mark, feel, or use measuring tools to ensure that the length of the unscrewed portion of the thread (or the number of exposed turns) of the pull rod 23 meets the requirements after screwing it in, so as to infer that the effective engagement turns have met the safety threshold of not less than 10 turns.

[0078] Only after this quantitative requirement is met can it be considered that the part of step S2 in which the threaded connection reaches the predetermined engagement requirement has been completed, and the subsequent loading step can proceed.

[0079] Therefore, in this example, an effective engagement count of ≥10 turns is the safety threshold under this operating condition.

[0080] In some embodiments, step S2 further includes cleaning and lubricating the threaded connection on the force transmission path.

[0081] The areas to be cleaned refer to the critical threaded joints used to transmit axial tensile force. Specifically, this includes the external thread portion of the tie rod 23 and the internal threaded hole at the center of the end of the fan shaft 11. In addition, other threaded connections in the tool system that bear major loads (such as the connecting threads of the conversion flange) should also be cleaned. Cleaning operations must remove contaminants from the thread surfaces, primarily including: old lubricant and oil, metal shavings and dust, rust, or oxide layers.

[0082] After cleaning, apply the selected lubricant evenly and in a thin layer to the cleaned threaded surfaces (threads of tie rod 23 and shaft end hole threads). The goal is to fill in microscopic unevenness and form a continuous lubricating film, rather than piling up excessive amounts. Ensure that the thread crest, flank, and root are all covered with lubricant, especially the stress-bearing thread sides. During the process, prevent lubricant from contaminating non-threaded areas, especially the high-precision external threads of fan shaft 11 that will mate with the nut.

[0083] Proper cleaning and lubrication reduce wear on tools (pull rod 23) and engine components (shaft end threads) during each operation, ensuring a high success rate for each job, extending the service life of high-value specialized tools and critical engine components, and improving the economics of aviation maintenance.

[0084] In some embodiments, in step S3, if the fan shaft nut 12 does not rotate when the axial tension is applied at the current hydraulic pressure, after releasing the pressure, the hydraulic pressure is increased by a preset pressure increment without exceeding the maximum hydraulic pressure, and steps S3 and S4 are executed again.

[0085] Understandably, in complex operating conditions (such as when the preload is higher than expected due to corrosion, long-term creep, etc.), the initial working pressure may be insufficient. If the nut does not move under the current pressure, the system pressure should be safely released to zero before proceeding to the next attempt. The pressure value for the next attempt is defined as the previous pressure plus a preset pressure increment. This preset pressure increment can be set based on engineering experience, the potential fluctuation range of the preload, or as a conservative process parameter, ensuring that the pressure increase is discrete and controllable, rather than continuous and arbitrary.

[0086] The pressure increment process involves an ordered search within the safety region (0 to P_max). Starting with a lower initial pressure, it gradually approaches the minimum effective pressure required to induce sufficient elastic deformation in the shaft to unload the preload. Once the pressure reaches P_max, the iteration stops regardless of whether the nut is loose, as this indicates that the component's safety limit has been reached, and other causes need to be investigated.

[0087] In this embodiment, by introducing a feedback-based stepping strategy with a safety upper limit, the disassembly method can safely and efficiently cope with the unavoidable fluctuations in operating conditions in actual operations, reducing the unpredictability of high-risk operations.

[0088] In some embodiments, step S3 further includes centering the force transmission path before applying the axial tensile force, so that the axial tensile force is applied along the axial direction of the fan shaft 11.

[0089] Specifically, this refers to the geometric coaxiality of the entire force transmission chain, consisting of the hydraulic cylinder 22, the support structure, the tie rod 23, and their connection points with the fan shaft 11. This ensures that when the piston of the hydraulic cylinder 22 extends, the line of action of its thrust, the axis of the tie rod 23, and the axis of the fan shaft 11 coincide in space, so that the tension vector is parallel to the axis of the fan shaft 11, thereby generating only uniform tensile stress on the shaft cross-section.

[0090] The tensile force is applied strictly along the axis to ensure that the elongation of the fan shaft 11 is a uniform, pure, and predictable axial tensile deformation. Any eccentricity will cause the shaft to bend during the stretching process, which will not only render the calculation model invalid (the actual stress far exceeds the calculated value), but may also generate huge compressive and shear stresses in the local area of ​​the external thread of the fan shaft 11, violating the original intention of the invention to provide non-destructive protection, and may damage adjacent components such as the fan disc 13.

[0091] like Figure 2 and Figure 3 As shown, the hydraulic disassembly device for the aero-engine fan shaft nut of this embodiment of the invention is used to implement the disassembly method in the above embodiment. The disassembly device includes a support and positioning component 21, a hydraulic cylinder 22, a pull rod 23, and a nut operating component 24.

[0092] The support positioning assembly 21 is used to connect with the fan shaft 11 to provide reaction force support. The inner contour of the assembly (such as a tapered bore) is precisely fitted with a specific structure on the fan shaft 11 (such as the tapered surface of the fan disc 13) to achieve axial positioning. Through rigid contact, the reaction force generated during disassembly is transmitted from the hydraulic cylinder 22 and distributed to the robust structure of the engine body (rather than the fragile casing).

[0093] The support positioning component 21 is provided with an operation window 2111, which is a radial notch or through groove on the side wall of the component. Its design allows the nut operating component 24 to move in and out and swing without obstruction, thereby solving the problem of spatial interference while maintaining the overall support rigidity.

[0094] Hydraulic cylinder 22 is mounted on support and positioning assembly 21. Hydraulic cylinder 22 has a hollow structure, allowing pull rod 23 to pass through the center of lifting piston 221. When high-pressure oil enters the oil chamber, it pushes the piston rod out. Since the end of lifting piston 221 (or through a conversion structure) abuts against the force-applying part 231 of pull rod 23, and the cylinder body is fixed by support and positioning assembly 21, the pushing force of lifting piston 221 is converted into axial pulling force on pull rod 23.

[0095] The tie rod 23 passes through the hydraulic cylinder 22 and the support and positioning assembly 21 in sequence. One end of the tie rod 23 is provided with an external thread for engaging with the central threaded hole at the end of the fan shaft 11, and the other end of the tie rod 23 is provided with a force-applying part 231 that abuts against the lifting piston 221 of the hydraulic cylinder. The tie rod 23 passes through the entire device and plays a dual role of connecting and transmitting force.

[0096] One end of the pull rod 23 is screwed into the process hole at the end of the fan shaft 11, establishing a direct force connection between the device and the workpiece; the force-applying part 231 at the other end (usually a thickened shoulder or connecting nut) forms a pressure-bearing surface with the end of the lifting piston 221 of the hydraulic cylinder 22. When the hydraulic cylinder 22 applies pressure, the force pushes the pull rod 23 through this pressure-bearing surface, and the pull rod 23 applies this tension to the internal thread of the fan shaft 11 and finally transmits it to the shaft body, causing it to stretch.

[0097] Nut operating assembly 24 passes through operating window 2111 and engages with fan shaft nut 12, so that nut operating assembly 24 can tighten fan shaft nut 12 within the range of operating window 2111. Nut operating assembly 24 is a specially made irregular wrench whose jaw shape is consistent with the special spline or outline of fan shaft nut 12.

[0098] The nut operating assembly 24 is a torque input interface, with a narrow rod or head to accommodate the narrow operating window 2111. After the nut operating assembly 24 engages with the fan shaft nut 12, the rotational torque applied by the operator is directly transmitted to the fan shaft nut 12. Because the nut operating assembly 24 operates within the range defined by the operating window 2111, rotational operation can be safely and conveniently performed under hydraulic loading.

[0099] The hydraulic disassembly device for the fan shaft nut of an aircraft engine according to an embodiment of the present invention firstly mounts the support and positioning component 21 (such as the split first bracket 211) onto the load-bearing part (such as the fan disc 13) of the fan shaft 11 using its conformal structure. Then, the pull rod 23 is inserted from one side of the hydraulic cylinder 22 and the support and positioning component 21, and its threaded end is screwed into the central threaded hole at the end of the fan shaft 11 until the required number of engagement turns are achieved.

[0100] Position the hydraulic cylinder 22 on the other side of the support and positioning assembly 21 (such as the second bracket 212), and ensure that the force-applying part 231 of the pull rod 23 is properly engaged with the piston of the hydraulic cylinder 22. Connect the hydraulic pump pipeline. Insert the nut operating assembly 24 through the operating window 2111 on the support and positioning assembly 21 and engage it with the fan shaft nut 12.

[0101] The hydraulic pump is started, and the hydraulic cylinder 22 begins to work, applying tension to the pull rod 23, thereby stretching the fan shaft 11. When the pressure reaches the working value, the nut is rotated via the nut operating assembly 24 while maintaining the pressure. After rotating a certain angle, the pressure is released, allowing the shaft to return to its original position, and the operating assembly is reset or adjusted to the next working position. This pressurization, rotation, and pressure release cycle is repeated until the nut is completely removed. If the nut does not move upon initial loading, a fault-tolerant iteration is performed according to the rules in the disassembly method of the above embodiment.

[0102] The hydraulic disassembly device for the fan shaft nut of the aircraft engine in this embodiment of the invention constructs a dedicated force transmission path that bypasses the high-precision external thread of the fan shaft 11, thereby achieving non-destructive protection of the precision threaded pair in terms of structure. At the same time, its integrated design of split support and operation window 2111 simultaneously solves the contradiction between providing rigid reaction force and retaining the necessary rotation operation space in extremely narrow maintenance space, so that the disassembly method of controllable tension, unloading preload, and cyclic rotation can be executed, improving the standardization and safety of disassembly operations.

[0103] In some embodiments, such as Figure 2 and Figure 3 As shown, the support positioning assembly 21 includes a first bracket 211 and a second bracket 212 with a cylindrical support body. The first end of the first bracket 211 is used to connect to the fan disc 13 on the fan shaft 11. The operation window 2111 is provided on the side wall of the first bracket 211. The first end of the second bracket 212 is detachably connected to the second end of the first bracket 211. The hydraulic cylinder 22 is installed on the second end of the second bracket 212.

[0104] The main body of the first support 211 is cylindrical, giving it good compressive and bending stiffness, and enabling it to evenly bear and transmit the enormous reaction force from the hydraulic system. Optionally, the inner hole at the first end of the first support 211 is machined into a contoured conical hole that precisely matches the outer conical surface of the fan disc 13, to achieve rapid and accurate positioning and self-alignment. This connection becomes the most direct stress point between the entire device and the engine body, utilizing the engine's own robust structure as a support foundation. The operating window 2111 (usually a circumferential rectangular or fan-shaped opening) provides the only channel for inserting, engaging, rotating, and removing the wrench (nut operating assembly 24) while ensuring the strength of the main cylindrical structure.

[0105] The second bracket 212 is also cylindrical in shape and is used to support and fix the hydraulic cylinder 22. The connection between the second bracket 212 and the first bracket 211 can be achieved through flanges, clamps, bolts, or precision slots to enable quick and stable assembly and disassembly. The hydraulic cylinder 22 is fixed to the end face of the second bracket 212 or in the recessed seat by bolts, ensuring that the axis of the hydraulic cylinder 22 coincides with the axis of the bracket, laying the foundation for precise force application.

[0106] The legs of the first support 211 and the second support 212 are not shown in the figure. The legs are conventional stability auxiliary components. Their principle is to adjust the length of the legs through a threaded, pin-shaped, or screw-type adjustment mechanism to adapt to maintenance tools or uneven ground conditions, ensuring that the entire device remains stable during operation and does not tip over, thereby ensuring the accuracy of the applied force direction and operational safety.

[0107] In this embodiment, the two functions of positioning and bearing, and hydraulic cylinder 22 support, are assigned to two independent components, the first bracket 211 and the second bracket 212, so that each bracket can be designed for lightweight and high strength according to its specific function. For example, the first bracket 211 focuses on contour accuracy and local compressive strength, while the second bracket 212 focuses on overall rigidity and installation interface accuracy.

[0108] In some embodiments, such as Figure 2 and Figure 3 As shown, the disassembly device also includes a force transmission component 25, which is located between the lifting piston 221 of the hydraulic cylinder 22 and the force-applying part 231 of the pull rod 23. The force transmission component 25 transmits the lifting force of the lifting piston 221 of the hydraulic cylinder 22 to the force-applying part 231 of the pull rod 23. The force transmission component 25 includes a flange 251 and at least one pad 252. The flange 251 is located at the end of the lifting piston 221 of the hydraulic cylinder 22, and at least one pad 252 is located between the flange 251 and the force-applying part 231 of the pull rod 23.

[0109] Flange 251 is a rigid disc or short sleeve with a central through hole. One side of it is designed with a connection structure (such as internal thread, specific bayonet or bolt connection hole) that matches the end of the lifting piston 221 of a specific model of hydraulic cylinder 22, while the other side is a flat load-bearing end face.

[0110] Flange 251 is used to accommodate hydraulic cylinders 22 with different working pressure specifications, thereby expanding the application range of the entire device. It is understandable that in hydraulic disassembly operations, the required maximum lifting force F needs to be calculated based on the preload requirement of the fan shaft nut 12 being disassembled. According to the basic hydraulic formula P=F / A (pressure = force / area), once the maximum output lifting force F of the system is determined, if hydraulic cylinders 22 with different working pressures P are selected, their effective working area A (corresponding to the piston diameter) will be different. Therefore, to meet the force transmission requirements under different working conditions (corresponding to different working pressures P), flange 251 needs to be able to connect hydraulic cylinders 22 with different piston diameters.

[0111] Therefore, by designing and equipping a series of flanges 251 with different bottom diameters (i.e., the diameter of the bearing surface that mates with the piston end), the same tool body (including the support and positioning assembly 21, the pull rod 23, etc.) can be connected quickly and reliably to hydraulic cylinders 22 with different piston diameters (i.e., different working pressure specifications) simply by replacing the flanges 251 of the corresponding specifications, without structural modifications. This allows the device to flexibly cope with various working pressure requirements, from low-pressure precision operation to high-pressure heavy disassembly.

[0112] In addition, the design of flange 251 also takes into account the differences in interface such as thread specifications and connection methods that may exist at the piston rod ends of different hydraulic cylinders 22, further ensuring the wide applicability and reliability of the connection.

[0113] At least one pad 252 refers to one or more high-strength steel rectangular blocks or rings of different standard thicknesses, which can be stacked and combined to form different total thicknesses. Its function is to precisely and rigidly compensate for the working stroke clearance, achieving discrete adjustment of the height.

[0114] In actual operation, after the pull rod 23 is screwed into the fan shaft 11 and the tool is installed, there is usually an initial gap between the force-applying part 231 (such as a nut) at the top of the pull rod 23 and the flange 251 mounted on the piston. Excessive gap will cause the piston's ineffective stroke to be too long, and may even exceed its working stroke.

[0115] By selecting and combining standard pads 252 of different thicknesses, this gap can be filled to an ideal range, ensuring that when the hydraulic system begins to pressurize, the piston can apply force to the tie rod 23 almost immediately, maximizing system stiffness, providing the most direct response, and maximizing energy transfer efficiency.

[0116] Different engine models, different installation configurations, or the use of tie rods 23 of varying lengths will all alter the aforementioned clearances. The modular pad set 252 provides a discrete, precisely calculable, and adjustable solution, enabling the same device to adapt to a variety of operating conditions.

[0117] The overall structural coordination principle is as follows: lifting piston 221, flange 251 (converting the dispersed concentrated thrust into planar thrust and realizing interface conversion), stacked pad 252 (compensating for height difference), and tie rod 23 force application part 231 (bearing concentrated axial thrust). This path ensures that the thrust is transmitted from hydraulic cylinder 22 to tie rod 23 in a coaxial and uniformly compressed manner.

[0118] Therefore, through the interchangeable flange 251, the device can be flexibly combined with hydraulic cylinders 22 of different specifications, so that a single tool body can cover a wider range of working pressure and tension. For example, a small-diameter hydraulic cylinder 22 is used for small tension when working on a small nut, and a large-diameter hydraulic cylinder 22 is used for large tension when working on a large nut. Only the flange 251 and the corresponding pump station need to be replaced, while the tool body and operating method remain completely unchanged, reducing the types of special tools in stock and lowering maintenance costs.

[0119] By using modular pads 252 to precisely fill the gaps, the initial free stroke during loading is eliminated, making the system a rigid system with almost no elastic deformation (except for the elasticity of the fan shaft 11 itself), so that there is a precise linear relationship between the hydraulic pressure and the tension applied to the shaft, which is convenient for monitoring and control.

[0120] The pad block 252 ensures that the lifting piston 221 of the hydraulic cylinder 22 starts working at a suitable position in its stroke (usually in the middle section), avoiding force application at the stroke limit position, thereby achieving optimal mechanical performance and stability. The flat end face of the pad block 252 ensures that the thrust is evenly distributed across the entire contact surface of the force application part 231 of the tie rod 23, avoiding uneven loading.

[0121] Furthermore, the required thickness of the shim 252 can be precisely selected based on calculations or measurements for each operation, ensuring the reliability and consistency of each installation and reducing potential failure points caused by improper connections. Both the shim 252 and the flange 251 are independent standard parts, easily replaceable individually after wear or damage, reducing overall maintenance costs. At the same time, this modular design simplifies manufacturing and assembly processes, improving the reliability and lifespan of the entire system during long-term use.

[0122] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0123] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0124] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0125] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0126] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0127] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A hydraulic disassembly method for an aircraft engine fan shaft nut, characterized in that, include: S1. Based on the mechanical properties of the fan shaft, determine the maximum hydraulic pressure applied when axially stretching the fan shaft. The logic for determining the maximum hydraulic pressure includes: The maximum allowable tensile force F_axis of the fan shaft body is calculated based on the material yield strength. The allowable tensile force F_thread of the internal thread is calculated based on the shear strength of the internal thread at the end of the fan shaft. The smaller value between F_axis and F_thread is taken as the maximum permissible axial tensile force F_max; The maximum hydraulic pressure P_max is calculated using the formula P_max=F_max / A, where A is the effective working area of ​​the hydraulic actuator. S2. Establish a force transmission path from the hydraulic power source to the fan shaft, and ensure that the threaded connections on the force transmission path meet the predetermined meshing requirements. S3. Apply a controllable axial tensile force to the fan shaft to produce a controllable axial elastic elongation of the fan shaft, thereby unloading the preload between the fan shaft nut and the external thread of the fan shaft. During the application of the axial tensile force, the corresponding hydraulic pressure gradually increases from the initial value, and the final value does not exceed the maximum hydraulic pressure. S4. While maintaining axial tension, rotate the fan shaft nut half a turn or until it is blocked by the structure. S5. After releasing the axial tension, allow the fan shaft to elastically recover. Repeat steps S3 and S4 until the fan shaft nut is removed.

2. The hydraulic disassembly method for the aero-engine fan shaft nut according to claim 1, characterized in that, In step S2, the threaded connection includes a threaded connection portion for transmitting axial tensile force to the fan shaft, and the effective number of engagement turns during installation is greater than or equal to a safety threshold.

3. The hydraulic disassembly method for the aero-engine fan shaft nut according to claim 2, characterized in that, Step S2 also includes cleaning and lubricating the threaded connection parts on the force transmission path.

4. The hydraulic disassembly method for the aero-engine fan shaft nut according to claim 1, characterized in that, In step S3, if the fan shaft nut does not rotate when the axial tension is applied, after releasing the pressure, the hydraulic pressure is increased by a preset pressure increment without exceeding the maximum hydraulic pressure, and steps S3 and S4 are executed again.

5. The hydraulic disassembly method for the aero-engine fan shaft nut according to claim 1, characterized in that, In step S3, before applying the axial tensile force, the force transmission path is aligned so that the axial tensile force is applied along the axial direction of the fan shaft.

6. A hydraulic disassembly device for an aircraft engine fan shaft nut, used to implement the hydraulic disassembly method for an aircraft engine fan shaft nut according to any one of claims 1-5, characterized in that, include: A support positioning component is provided, which is connected to the fan shaft to provide reaction force support, and the support positioning component is provided with an operation window; A hydraulic cylinder is disposed on the support and positioning assembly, and the hydraulic cylinder has a hollow structure. A pull rod passes sequentially through the hydraulic cylinder and the support and positioning assembly. One end of the pull rod is provided with an external thread for engaging with the central threaded hole at the end of the fan shaft, and the other end of the pull rod is provided with a force-applying part that abuts against the lifting piston of the hydraulic cylinder. A nut operating assembly extends through the operating window and engages with the fan shaft nut to allow the nut operating assembly to tighten the fan shaft nut within the operating window.

7. The hydraulic disassembly device for the aero-engine fan shaft nut according to claim 6, characterized in that, The support and positioning assembly includes a first bracket and a second bracket with a cylindrical support body. The first end of the first bracket is used to connect to the fan disc on the fan shaft. The operation window is located on the side wall of the first bracket. The first end of the second bracket is detachably connected to the second end of the first bracket. The hydraulic cylinder is installed at the second end of the second bracket.

8. The hydraulic disassembly device for the aero-engine fan shaft nut according to claim 7, characterized in that, The first end of the first bracket is provided with a contoured inner cone surface for fitting and positioning with the outer cone surface of the fan disc.

9. The hydraulic disassembly device for the aero-engine fan shaft nut according to claim 6, characterized in that, It also includes a force transmission component, which is disposed between the lifting piston of the hydraulic cylinder and the force-applying part of the pull rod, so as to transmit the lifting force of the lifting piston of the hydraulic cylinder to the force-applying part of the pull rod through the force transmission component. The force transmission component includes a flange and at least one pad. The flange is disposed at the end of the lifting piston of the hydraulic cylinder, and the at least one pad is disposed between the flange and the force-applying part of the pull rod.

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