A method and system for determining the working pre-tightening force of an aero-engine shaft end nut

Abstract

The application discloses an aero-engine shaft end nut working pre-tightening force determination method and system, and belongs to the technical field of aero-engines. The method comprises the following steps: establishing a rotor system finite element model comprising a shaft, a bearing, a shaft end nut and adjacent components; simulating a transient process of rapidly pushing the engine from an idle state to a maximum state and rapidly pulling the engine from the maximum state to a parking state, applying a transient temperature field and a rotating speed field, performing a thermal-structure coupling transient analysis, obtaining pre-tightening force change curves of the rapid pushing and rapid pulling processes respectively, extracting a minimum working pre-tightening force and a maximum working pre-tightening force, and checking a bearing contact surface compression state and a shaft end nut strength; determining a safe working pre-tightening force range according to comprehensive checking results, and inversely deducing an initial installation tightening torque according to the safe working pre-tightening force range. The application can scientifically determine a safe pre-tightening force range by capturing transient pre-tightening force extreme values under rapid variable working conditions, and effectively avoids looseness vibration and overload damage.

Description

Technical Field

[0001] This invention relates to the field of aero-engine technology, specifically to a method and system for determining the working preload of an aero-engine shaft end nut. Background Technology

[0002] The shaft end nut is a critical connecting component in the aero-engine rotor system. The accuracy of its preload directly affects the axial positioning of the bearing, the rigidity of the entire rotor system, and the stability of the force transmission path. Insufficient preload can lead to drastic changes in thermally induced preload during engine operation, especially during rapid changes in operating conditions (such as acceleration and deceleration). The different materials and thermal expansion coefficients of the shaft, bearing housing, and nut can cause "thermal relaxation" or "thermal overtightening," potentially resulting in axial clearance in the bearing, compromising the rotor system's support rigidity, and ultimately inducing severe vibrations that threaten flight safety. Conversely, excessive preload can cause thread stripping, plastic deformation of the nut or journal, or even breakage.

[0003] Currently, some technical solutions have attempted to optimize the preload of shaft-end nuts. For example, some solutions use theoretical calculations, finite element simulations, and reliability analysis to consider the impact of thermal deformation on the preload, adjusting the upper and lower limits of the preload index to meet operational requirements. However, these solutions mainly focus on steady-state or quasi-static thermal deformation analysis, failing to fully consider the problem of instantaneous extreme values ​​in the preload caused by asynchronous temperature rise / fall of components due to thermal inertia under rapid transient operating conditions of aero-engines. Another solution uses experimental measurement of shaft tensile deformation and torque, employing dual-parameter (torque and deformation) control to determine the tightening torque of the shaft-end nut. However, this solution is based on static or quasi-static experimental loading and is mainly applied in the turbocharger field, making it difficult to realistically simulate the complex and rapid transient thermo-mechanical coupling service environment of aero-engines. Existing technologies have failed to accurately and reliably determine the safe operating preload range of aero-engine shaft-end nuts under all operating conditions (especially rapid transient processes), making it difficult to fundamentally prevent vibration failures or structural damage caused by these conditions.

[0004] Therefore, there is an urgent need in this field for a method that can accurately simulate transient thermal processes and scientifically determine the safe working preload range of the shaft end nut, so as to fundamentally prevent vibration failures or structural damage caused by them. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and system for determining the working preload of the shaft end nut of an aero-engine. By considering transient thermal effects, the preload is ensured to remain within a safe range under all operating conditions, thereby improving the reliability of engine operation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for determining the working preload of an aero-engine shaft end nut includes the following steps: S1. Establish a finite element model of the engine rotor system, including the shaft, bearing, shaft end nut, and components adjacent to the bearing. S2, Determining the minimum working preload condition: Applying an initial preload in the model. Then, the transient process of the engine rapidly accelerating from idle to maximum speed is simulated, and the transient temperature field and speed field under this transient process are applied to perform thermal-structural coupled transient analysis to obtain the instantaneous preload change curve F_min(t) of the shaft end nut during this process. S3. Extract the minimum value from the curve F_min(t) as the minimum working preload. And verify in Under the action, whether the contact surfaces of the relevant parts that come into contact with the bearing remain in a pressed state; S4. Determining the working condition of maximum working preload: Apply the initial preload F0 to the model to simulate the transient process of the engine rapidly pulling down from its maximum state to a stop state, and apply the transient temperature field and speed unloading load under this transient process to perform thermal-structural coupled transient analysis to obtain the instantaneous preload change curve F_max(t) of the shaft end nut during this process. S5. Extract the maximum value from the curve F_max(t) as the maximum working preload. And verify in Under the action of the load, do the shear stress and bending stress of the thread teeth of the nut at the shaft end meet the allowable strength requirements of the material? S6. Based on the verification results of steps S3 and S5, determine the safe working preload range of the shaft end nut as [ , Based on this, the initial installation tightening torque can be calculated. .

[0008] Furthermore, the verification in step S3 is performed in... Whether the contact surfaces of the relevant parts that come into contact with the bearing remain in a pressed state under the action is specifically determined by whether the contact pressure of the contact surfaces is greater than zero.

[0009] Furthermore, the verification in step S5 is performed in... The shear stress and bending stress of the thread teeth of the nut at the shaft end under action are specifically determined by the formula. Calculate shear stress And according to the formula Calculate bending stress And determine whether it satisfies and ,in and These represent the allowable shear stress and allowable bending stress of the material, respectively; b is the root width of the thread teeth of the shaft end nut; d is the major diameter of the thread of the shaft end nut; z is the effective number of working thread turns of the shaft end nut; and h is the stress height of the thread teeth.

[0010] Furthermore, the calculation of the initial installation tightening torque in step S6... According to the formula: ;in, This refers to the frictional resistance torque between the threaded pairs. This is the frictional resistance torque between the end face of the nut on the shaft and the contact surface of the bearing.

[0011] Furthermore, the contact area between the shaft end nut and the bearing is reduced to lower the [missing information]. Specifically, the contact surface between the shaft end nut and the bearing is designed as an annular boss.

[0012] Furthermore, by lubricating the threaded pair to reduce the thread friction coefficient, the aforementioned... .

[0013] The present invention also provides a system for determining the working preload of an aero-engine shaft end nut, for implementing the above method, the system comprising: Modeling module: Used to create a finite element parametric model of the engine rotor system, including the shaft, bearings, shaft end nuts, and components adjacent to the bearings; Load application module: used to apply initial preload. The transient load spectrum is used to apply the engine from idle state to maximum state rapidly and from maximum state to stop state rapidly, the transient load spectrum including transient temperature field and / or speed field; Solver module: used to perform transient thermo-structural coupling analysis of the rapid push-up and rapid pull-down processes to calculate the preload variation curves F_min(t) and F_max(t) respectively; Post-processing and verification module: used to extract the minimum working preload from the curves F_min(t) and F_max(t), respectively. and maximum working preload And automatically verify in Whether the contact surfaces of the parts that come into contact with the bearing are kept in a pressed state, and in Whether the shear stress and bending stress of the thread teeth of the nut at the lower shaft end meet the allowable strength requirements of the material; Preload output module: Used to output the safe working preload range based on the verification results of the post-processing and verification module. , and initial tightening torque .

[0014] Furthermore, the post-processing and verification module verifies in... Whether the contact surfaces of the parts that come into contact with the bearing are kept in a pressed state is determined by whether the contact pressure of the contact surfaces is greater than zero.

[0015] Furthermore, the post-processing and verification module verifies in... The shear stress and bending stress of the thread teeth of the nut at the lower shaft end are specifically determined according to the formula. Calculate shear stress And according to the formula Calculate bending stress And determine whether it satisfies and ,in and These represent the allowable shear stress and allowable bending stress of the material, respectively; b is the root width of the thread teeth of the shaft end nut; d is the major diameter of the thread of the shaft end nut; z is the effective number of working thread turns of the shaft end nut; and h is the stress height of the thread teeth.

[0016] Furthermore, the preload output module is also used to adjust the preload output according to the safe working preload range. , ] Calculate the initial preload of the assembly by reverse calculation And based on the initial preload Calculate the initial installation tightening torque .

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention is the first to systematically consider the two most dangerous transient conditions of "rapid upward push" and "rapid downward pull", accurately captures the extreme value of dynamic change of preload, and specifically performs dual verification for preventing loosening and overload, fundamentally avoiding the risks of loosening, vibration and structural damage.

[0018] 2. This invention employs a transient thermal-structural coupling analysis method, which accurately reflects the asynchronous changes in the temperature field caused by the thermal inertia of the material and its impact on the preload. This allows the design of the preload to move from traditional static and empirical judgment to quantitative analysis based on physical models, resulting in more accurate and reliable results.

[0019] 3. This invention provides a complete technical chain from transient simulation analysis and verification to reverse calculation of tightening torque, and proposes easily implemented optimization measures such as reducing contact area and ensuring adequate lubrication. These measures can be directly used to guide engineering practice and improve assembly quality and efficiency. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating the method for determining the working preload of the aero-engine shaft end nut in an embodiment of the present invention. Detailed Implementation

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] Example 1 This embodiment provides a method for determining the working preload of the shaft end nut in an aero-engine, such as... Figure 1 As shown, the specific steps include: S1. Establish the finite element model of the engine rotor system.

[0025] A finite element model of the engine rotor system was established, including the high-pressure turbine rear shaft, bearings, shaft end nuts, and adjacent components (such as spacers and bearing housings). This model is parametric, with the shaft and nut material set to GH4169 high-temperature alloy and the bearing housing material set to TC4 titanium alloy. Frictional contact pairs were established at the nut-bearing end face and threaded joints to accurately simulate contact behavior.

[0026] S2. Minimum working preload determines the working condition.

[0027] An initial preload is applied to the model. (For example, the initial value is set to 40kN as an iterative design variable). Then, the transient process of the engine rapidly accelerating from idle to maximum speed is simulated. During this process, the heating rate of the high-pressure turbine rear shaft is much faster than that of the bearing inner ring, resulting in greater axial thermal expansion of the high-pressure turbine rear shaft than the bearing inner ring. This reduces the tensile force on the nut, causing a decrease in preload. Specifically, the engine is simulated to linearly accelerate from idle (8000 rpm, average turbine rear temperature 600℃) to maximum continuous speed (15000 rpm, average turbine rear temperature 1100℃) within 30 seconds. During this process, a time-varying transient temperature field and a synchronized speed field are applied. Subsequently, a thermo-structural coupled transient analysis is performed to calculate the instantaneous preload change curve of the shaft end nut during this process, denoted as F_min(t).

[0028] S3. Extract and verify the minimum working preload.

[0029] Extract the minimum value (i.e., the lowest point of the curve) from the curve F_min(t) obtained in step S2, and denote it as the minimum working preload. (For example, simulation calculations yielded) = 15kN). Then, the verification is performed on this. Under a load of 15kN, the contact surfaces of the relevant parts in contact with the bearing (such as the inner ring of the bearing and the shoulder of the shaft) are checked to ensure they remain pressed together (anti-loosening test), i.e., whether the contact pressure of the contact surfaces is greater than zero. In this embodiment, the test result is that the contact pressure is greater than 0, indicating that there is no risk of loosening and the requirements are met.

[0030] S4. Determine the working condition based on the maximum working preload.

[0031] The initial preload is applied again in the model. =40kN. Then, the transient process of the engine rapidly decelerating from its maximum state to a stop state was simulated. During this process, the cooling rate of the high-pressure turbine rear shaft was much faster than that of the bearing inner ring, resulting in faster shaft contraction than the bearing inner ring, increasing the compression on the nut and raising the preload. Specifically, the engine was simulated to linearly decelerate from its maximum continuous state (speed 15000 rpm, average temperature after turbine 1100℃) to a stop (speed drops to 0, temperature drops to room temperature) within 60 seconds. During this process, a transient cooling temperature field and speed unloading load that varied with time were applied. Subsequently, a thermo-structural coupled transient analysis was performed to calculate the instantaneous preload change curve of the shaft end nut during this process, denoted as F_max(t).

[0032] S5. Extract and verify the maximum working preload.

[0033] Extract the maximum value (i.e., the highest point of the curve) from the curve F_max(t) obtained in step S4, and denote it as the maximum working preload. (For example, simulation calculations yielded) = 80kN). Then, the verification is performed on this. The strength of the shaft end nut under a load of 80kN. Specifically, calculate the shear stress of the thread teeth of the shaft end nut according to the following formulas. and bending stress :

[0034]

[0035] in, This refers to the root width of the thread teeth on the shaft end nut. This is the major diameter of the thread on the shaft end nut. This refers to the effective number of working thread turns of the nut at the shaft end. This is the thread tooth stress height. The calculated... and Respectively related to the allowable shear stress of the material and allowable bending stress Compare (perform overload protection check) to determine if it meets the requirements. and .in , , Let be the yield strength of the material of the shaft end nut. In this embodiment, the calculation result satisfies... and This indicates that the strength of the nut and thread is up to standard.

[0036] S6. Determine the safe working pre-tightening force range and tightening torque.

[0037] Based on the verification results of steps S3 and S5, the safe working preload range of the shaft end nut is determined to be [ , [15kN, 80kN]. Based on this, the initial installation tightening torque can be calculated backwards. .

[0038] Specifically, to ensure the reliable connection of the high-pressure turbine rear shaft, bearing inner ring, and shaft end nut, it is possible to […]. , Select a minimum target working preload within the range. A value with an appropriate safety margin is usually chosen, which can be determined by the following formula:

[0039] in, This is an empirical coefficient, typically taken as 0.3. Therefore, in this embodiment... =34.5kN.

[0040] Minimum target working preload These are ideal values ​​during engine operation. Finite element iterative calculations are needed to find the minimum preload force that minimizes the preload during rapid thrust-up conditions. initial preload of assembly The initial preload of the assembly is calculated by reverse engineering in this embodiment. =55 kN.

[0041] Obtain initial preload Then, the initial installation tightening torque is calculated using the threaded connection tightening torque formula. :

[0042] in, This refers to the frictional resistance torque between the threaded pairs. The frictional resistance torque between the end face of the shaft nut and the contact surface of the bearing is... The thread pitch of the nut at the shaft end is... This is the coefficient of friction between the nut and bolt at the shaft end (the coefficient of friction of the threaded pair). The thread pitch diameter For the thread profile half angle of the shaft end nut, The coefficient of friction between the shaft end nut and the inner ring end face of the bearing is given. The equivalent friction diameter of the nut support surface; where , and These are the outer and inner diameters of the contact surface, respectively, obtained through geometric dimension measurements.

[0043] Furthermore, as a further optimization measure, the contact area can be reduced by designing the contact surface between the shaft end nut and the bearing as an annular boss (for example, reducing the outer diameter of the contact surface from 60mm to 55mm), thereby reducing... At the same time, the coefficient of thread friction is reduced by adequately lubricating the threaded pair (e.g., using a high-performance lubricant such as molybdenum disulfide grease). Thus reducing For example, using molybdenum disulfide-based lubricant can significantly reduce the coefficient of friction of threaded pairs from 0.30 under dry friction to 0.08. Additionally, adequate lubrication of the bearing surfaces can also reduce the coefficient of friction between the shaft end nut and the bearing inner ring end face. This further reduces For example, using molybdenum disulfide-based lubricant can reduce the coefficient of friction between the shaft end nut and the bearing inner ring end face from 0.15 in dry friction to 0.10. These measures effectively reduce the required initial installation tightening torque. The initial installation tightening torque M calculated in this embodiment is about 35% lower than that of the traditional design, which greatly reduces the assembly difficulty and preload dispersion.

[0044] Example 2 This embodiment provides a system for determining the working preload of an aero-engine shaft end nut, used to implement the method described in Embodiment 1. The system specifically includes the following modules: Modeling Module: Used to create a finite element parametric model of the engine rotor system, including the shaft, bearings, shaft end nuts, and components adjacent to the bearings (such as spacers and bearing housings). This module allows users to input geometric parameters, material properties, contact definitions, etc.

[0045] Load application module: used to apply initial preload. More importantly, this module is used to apply two key transient load spectra: the first is the transient load spectrum for the engine rapidly accelerating from idle to maximum, which includes time-varying transient temperature and speed fields; the second is the transient load spectrum for the engine rapidly decelerating from maximum to stop, which includes time-varying transient temperature fields (cooling) and speed-unloading loads. This module can be preset to typical operating conditions such as the 30-second rapid acceleration and 60-second rapid deceleration described in Example 1.

[0046] Solver module: This module receives the model from the modeling module and the load from the load application module, and performs transient thermo-structural coupling analysis. It can calculate the preload variation curve F_min(t) during rapid upward thrust and the preload variation curve F_max(t) during rapid downward thrust.

[0047] Post-processing and verification module: Used to automatically extract the minimum value as the minimum working preload from the curves F_min(t) and F_max(t) calculated by the solver module. Extract the maximum value as the maximum working preload. This module also has built-in validation logic: it will automatically validate... Below, it checks whether the contact surfaces of the parts in contact with the bearing remain in a compressed state. Specifically, it checks whether the contact pressure of the contact surfaces is greater than zero to determine if loosening will occur. Simultaneously, it automatically verifies... Next, determine whether the shear stress and bending stress of the nut thread at the shaft end meet the allowable strength requirements of the material; specifically, according to the formula... and Automatically calculate the shear stress of the thread teeth of the shaft end nut and bending stress and the allowable shear stress of the material and allowable bending stress Compare to verify whether the nut strength meets the requirements; if it does... and If so, then the requirement is met.

[0048] Preload output module: Used to output the safe working preload range based on the verification results of the post-processing and verification module. , and recommended initial tightening torque Furthermore, this module can also adjust the preload according to the specified safe working preload range. , Select a target preload and calculate the required initial preload for assembly. And the initial installation tightening torque that should be applied during final assembly. This is to guide actual production and assembly.

[0049] Through the above system, designers can efficiently and accurately analyze and determine the working preload of the shaft end nut of an aero-engine, significantly improving the reliability and safety of the engine rotor system.

[0050] In summary, the embodiments of the present invention analyze the two key transient operating conditions of rapid upward thrust and rapid downward thrust to encompass the limit value of the working preload, ensuring that the preload remains within a safe range under all operating conditions and improving the reliability of engine operation.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations of the embodiments of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the working preload of an aero-engine shaft end nut, characterized in that, Includes the following steps: S1. Establish a finite element model of the engine rotor system, including the shaft, bearing, shaft end nut, and components adjacent to the bearing. S2, Determining the minimum working preload condition: Applying an initial preload in the model. Then, the transient process of the engine rapidly accelerating from idle to maximum speed is simulated, and the transient temperature field and speed field under this transient process are applied to perform thermal-structural coupled transient analysis to obtain the instantaneous preload change curve F_min(t) of the shaft end nut during this process. S3. Extract the minimum value from the curve F_min(t) as the minimum working preload. And verify in Under the action, whether the contact surfaces of the relevant parts that come into contact with the bearing remain in a pressed state; S4. Determining the maximum working preload condition: Applying the initial preload to the model. The transient process of the engine rapidly decreasing from its maximum state to a stop state is simulated, and the transient temperature field and speed unloading load under this transient process are applied to perform thermal-structural coupled transient analysis to obtain the instantaneous preload change curve F_max(t) of the shaft end nut during this process. S5. Extract the maximum value from the curve F_max(t) as the maximum working preload. And verify in Under the action of the load, do the shear stress and bending stress of the thread teeth of the nut at the shaft end meet the allowable strength requirements of the material? S6. Based on the verification results of steps S3 and S5, determine the safe working preload range of the shaft end nut as [ , Based on this, the initial installation tightening torque can be calculated. .

2. The method according to claim 1, characterized in that, In step S3, the verification is performed on... Whether the contact surfaces of the relevant parts that come into contact with the bearing remain in a pressed state under the action is specifically determined by whether the contact pressure of the contact surfaces is greater than zero.

3. The method according to claim 1, characterized in that, In step S5, the verification is performed. The shear stress and bending stress of the thread teeth of the nut at the shaft end under action are specifically determined by the formula. Calculate shear stress And according to the formula Calculate bending stress And determine whether it satisfies and ,in and These are the allowable shear stress and allowable bending stress of the material, respectively. This refers to the root width of the thread teeth on the shaft end nut. This is the major diameter of the thread on the shaft end nut. This refers to the effective number of working thread turns of the nut at the shaft end. This refers to the force-bearing height of the thread teeth.

4. The method according to claim 1, characterized in that, The calculation of the initial installation tightening torque in step S6 According to the formula: ;in, This refers to the frictional resistance torque between the threaded pairs. This is the frictional resistance torque between the end face of the nut on the shaft and the contact surface of the bearing.

5. The method according to claim 4, characterized in that, The reduction is achieved by decreasing the contact area between the shaft end nut and the bearing. Specifically, the contact surface between the shaft end nut and the bearing is designed as an annular boss.

6. The method according to claim 4, characterized in that, By lubricating the threaded joint to reduce the thread friction coefficient, the aforementioned... .

7. A system for determining the working preload of an aero-engine shaft end nut, characterized in that, The system for implementing the method of any one of claims 1-6 comprises: Modeling module: Used to create a finite element parametric model of the engine rotor system, including the shaft, bearings, shaft end nuts, and components adjacent to the bearings; Load application module: used to apply initial preload. The transient load spectrum is used to apply the engine from idle state to maximum state rapidly and from maximum state to stop state rapidly, the transient load spectrum including transient temperature field and / or speed field; Solver module: used to perform transient thermo-structural coupling analysis of the rapid push-up and rapid pull-down processes to calculate the preload variation curves F_min(t) and F_max(t) respectively; Post-processing and verification module: used to extract the minimum working preload from the curves F_min(t) and F_max(t), respectively. and maximum working preload And automatically verify in Whether the contact surfaces of the parts that come into contact with the bearing are kept in a pressed state, and in Whether the shear stress and bending stress of the thread teeth of the nut at the lower shaft end meet the allowable strength requirements of the material; Preload output module: Used to output the safe working preload range based on the verification results of the post-processing and verification module. , and initial tightening torque .

8. The system according to claim 7, characterized in that, The post-processing and verification module verifies that... Whether the contact surfaces of the parts that come into contact with the bearing are kept in a pressed state is determined by whether the contact pressure of the contact surfaces is greater than zero.

9. The system according to claim 7, characterized in that, The post-processing and verification module verifies that... The shear stress and bending stress of the thread teeth of the nut at the lower shaft end are specifically determined according to the formula. Calculate shear stress And according to the formula Calculate bending stress And determine whether it satisfies and ,in and These represent the allowable shear stress and allowable bending stress of the material, respectively; b is the root width of the thread teeth of the shaft end nut; d is the major diameter of the thread of the shaft end nut; z is the effective number of working thread turns of the shaft end nut; and h is the stress height of the thread teeth.

10. The system according to claim 7, characterized in that, The preload output module is also used to output the preload according to the safe working preload range. , ] Calculate the initial preload of the assembly by reverse calculation And based on the initial preload Calculate the initial installation tightening torque .

Images