Fatigue strength analysis method for input bevel gear shaft of coaxial rotor transmission system

Abstract

The invention relates to the field of aircraft component strength analysis, in particular to a fatigue strength analysis method for an input bevel gear shaft of a coaxial rotor transmission system. The method comprises the following steps: determining a dangerous profile according to the configuration of a coaxial rotor speed reducer, input bevel gear shaft load analysis and structural characteristics; static and dynamic loads of the dangerous section are determined according to the meshing loads of the upper and lower rotors and the relative motion relation of meshing load input bevel gear shafts; obtaining static and dynamic stresses according to static and dynamic loads of the dangerous section, and further obtaining equivalent dynamic stress of the section; fatigue damage of each state is obtained according to the S-N curve and the torque spectrum of the material; and according to the Miner linear cumulative damage theory, the safe fatigue life of the input bevel gear shaft is obtained.

Description

Technical Field

[0001] The invention relates to the field of aircraft component strength analysis, and in particular to a fatigue strength analysis method for an input bevel gear shaft of a coaxial rotor transmission system. Background Art

[0002] The coaxial rotor uses two sets of upper and lower coaxially reversed rotors to balance the rotor torque, and has the advantages of compact structure, high hovering efficiency, superior maneuverability, and good control performance. The transmission system configuration to achieve coaxial reverse output generally adopts cylindrical gears, bevel gears, differential gear trains or face gears as the basis to achieve coaxial reverse output. Among them, the transmission principle of the coaxial reverse output configuration based on bevel gears is to drive the upper and lower rotor shaft branches through the meshing of two pairs of bevel gears. It has the advantages of few parts, simple structure, and efficient layout of the control mechanism. Therefore, it is widely used in coaxial rotors at home and abroad.

[0003] like Figure 1-2 As shown in the figure, when performing fatigue strength analysis of the coaxial rotor reducer, it is generally believed that the torques generated by the upper and lower rotors are equal in magnitude and opposite in direction, and the torque dynamic load fluctuation is relatively small compared to the static load. Therefore, when performing load analysis on the input bevel gear shaft, it is believed that the tangential force and radial force in the meshing load of the upper and lower bevel gears cancel each other out, and only the superimposed axial force and torque are considered for low-cycle fatigue analysis. However, in special configurations, the torque dynamic load amplitude may be greater than the static load, and at the same time, the upper and lower rotors require different powers. In some states, the lower rotor is severely affected by the downwash of the upper rotor, so the torques of the upper and lower rotors are not completely offset. Summary of the invention

[0004] The purpose of the present invention is to propose a new fatigue strength analysis method for the input bevel gear shaft of a coaxial rotor transmission system to obtain the fatigue life of the input bevel gear shaft under the actual calculated torque state.

[0005] Technical solution:

[0006] A fatigue strength analysis method for an input bevel gear shaft of a coaxial rotor transmission system is provided, comprising:

[0007] Determine the dangerous section based on the coaxial rotor reducer configuration, input bevel gear shaft load analysis and structural characteristics;

[0008] According to the meshing load of the upper and lower rotors and the relative motion relationship between the meshing load input bevel gear shaft, the static and dynamic loads of the dangerous section are determined;

[0009] According to the static and dynamic loads of the dangerous section, the static and dynamic stresses are obtained, and then the equivalent dynamic stress of the section is obtained;

[0010] According to the material SN curve and torque spectrum, the fatigue damage in each state is obtained;

[0011] According to Miner's linear cumulative damage theory, the safe fatigue life of the input bevel gear shaft is obtained.

[0012] Furthermore, according to the meshing loads of the upper and lower rotors, and the relative motion relationship between the meshing loads and the input bevel gear shaft, the static and dynamic loads of the dangerous section are determined, including:

[0013] Assuming the motion state of the input bevel gear shaft is relatively static, the dynamic load includes the meshing load generated by the torque dynamic load part and the tangential force F in the meshing load generated by the torque static load part of the upper and lower rotors. t and radial force F r All are regarded as dynamic loads; determine the axial force F in the meshing load generated by the static load part of the upper and lower rotor torque x As static load;

[0014] Calculate the static and dynamic loads on dangerous sections.

[0015] Furthermore, the dangerous section includes at least a first section with the smallest diameter and a second section with the largest load.

[0016] Furthermore, for the first section, the section axial force T is generated by the static load of the upper and lower rotor torques. S , Section torque N S As the static load of the first section; the section axial force T generated by the static and dynamic loads of the upper and lower rotor torques d , Section shear force Z d , Section bending moment M d and section moment N d is the dynamic load of the first section.

[0017] Furthermore, for the second section, the section torque generated by the static load part of the upper and lower rotor torques is the static load of the second section; and the section torque generated by the dynamic load part of the upper and lower rotor torques is the dynamic load of the second section.

[0018] Furthermore, the calculation formulas for static and dynamic loads include:

[0019]

[0020] N s =M z-ss +M z-xs ;

[0021]

[0022] N d =M z-sd +M z-xd ;

[0023] Among them, Mz-ss is the static torque transmitted by the upper rotor, M z-xs is the static torque transmitted by the lower rotor, M z-sd is the dynamic torque transmitted by the upper rotor, M z-xd is the dynamic torque transmitted by the lower rotor, M z-s is the total torque transmitted by the upper rotor, M z-x is the total torque transmitted by the lower rotor, and l is the axial distance between the gear meshing section and the first section.

[0024] Furthermore, the shaft intersection angle between the input bevel gear shaft and the rotor shaft is 90°.

[0025] Beneficial effects:

[0026] The present invention provides a fatigue strength analysis method for the input bevel gear shaft of a coaxial rotor transmission system, including aspects such as dangerous section selection, load processing, stress calculation, damage accumulation and life analysis. First, the dangerous section is selected according to the load analysis and structural characteristics of the input bevel gear shaft; the static and dynamic stresses of the section are obtained according to the resultant force of the upper and lower rotor meshing loads on the dangerous section, and then the equivalent dynamic stress of the section is obtained. Combined with the SN curve and Miner linear cumulative damage theory, the safe life considering high and low cycle fatigue under the calculated load spectrum is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the configuration principle of the coaxial counter-rotating transmission system;

[0028] Figure 2 It is a schematic diagram of the input bevel gear shaft structure and load;

[0029] Figure 3 It is a flow chart of the safety life analysis method.

[0030] 1-first section; 2-bearing connection part; 3-second section; 4-spline connection part. DETAILED DESCRIPTION

[0031] The following is an example of fatigue strength analysis of the input bevel gear shaft of the coaxial rotor transmission system. Figure 3 The present invention is described in further detail:

[0032] Step 1: A certain type of coaxial rotor transmission system configuration uses bevel gears as the basis to achieve coaxial reverse output, such as Figure 1 As shown. The input bevel gear shaft is right-handed and has a structure as shown Figure 2 As shown, the upper and lower rotors are meshed with each other through a pair of bevel gears to transmit torque. The tangential force F at the meshing point t , radial force F r and axial force F x Direction Figure 2 shown.

[0033] F t =2000M z / d m (1)

[0034]

[0035] Among them, M z Torque transmitted by the upper and lower rotors, d m is the mid-end pitch circle diameter of the input bevel gear shaft, α is the gear pressure angle, β is the gear helix angle, and δ is the gear pitch cone angle.

[0036] For the input bevel gear shaft, the external load is the meshing load at two locations. The combined force and bending moment of the external load are transmitted through the bearing radial force at the bearing connection, and the combined torque of the external load is transmitted at the spline connection. Combined with the structural characteristics of the input bevel gear shaft, the two dangerous sections can be determined as the first section with the smallest diameter and the second section with the largest load, such as Figure 2 shown.

[0037] Step 2: Since the two meshing load action points of the input bevel gear shaft remain unchanged relative to the reducer, but the input bevel gear shaft is a rotating part, the tangential force F in the meshing load generated by the static load part of the upper and lower rotor torque is t Radial force F r The relative load to the input bevel gear shaft is dynamic load, and the axial force F x It is a static load relative to the input bevel gear shaft, while the meshing load generated by the torque dynamic load part is a dynamic load relative to the input bevel gear shaft.

[0038] For the first section, the section load is a six-force factor synthesized by two meshing loads at the center of the section, among which the section axial force T is generated by the static load of the upper and lower rotor torques. S , Section torque N S is the static load; the section axial force T generated by the static and dynamic loads of the upper and lower rotor torques d , Section shear force Z d , Section bending moment M d and section moment N d is the dynamic load.

[0039]

[0040] N s =M z-ss +M z-xs (5)

[0041]

[0042] N d =M z-sd+M z-xd (9)

[0043] Among them, M z-ss is the static torque transmitted by the upper rotor, M z-xs is the static torque transmitted by the lower rotor, M z-sd is the dynamic torque transmitted by the upper rotor, M z-xd is the dynamic torque transmitted by the lower rotor, M z-s is the total torque transmitted by the upper rotor, M z-x is the total torque transmitted by the lower rotor, and l is the axial distance between the gear meshing section and the first section.

[0044] For the second section, since the forces and bending moments generated by the meshing loads at two locations are transmitted to the casing through the bearings, the section load only has torque, so the static loads of the upper and lower rotor torques generate a section torque N S is the static load; the section torque N generated by the dynamic load of the upper and lower rotor torque d is the dynamic load. The calculation formula of section torque is the same as (5) and (9).

[0045] Step 3: According to the geometric dimensions of the dangerous section, obtain the cross-sectional area A and bending modulus W z , torsional modulus W tor And the tensile stress concentration factor K tT , bending stress concentration factor K tM , Torque stress concentration factor K tN , combined with the section load, the section stress is obtained.

[0046] For the first section:

[0047]

[0048] σ eq =σ d / (1-(σ s / σ 02 ) 2 ) (12)

[0049] Among them, σ 02 is the material yield limit, σ s is the section static stress, σ d is the cross-sectional dynamic stress, σ eq is the equivalent dynamic stress of the section.

[0050] For the second section:

[0051] σ s =K tN N s / W tor (13)

[0052] σd =K tN N d / W tor (14)

[0053] σ eq =σ d / (1-(σ s / σ 02 ) 2 ) (15)

[0054] Step 4: Based on the material high-cycle safety SN curve and the upper and lower rotor torque spectra, the high-cycle fatigue damage in each state can be obtained:

[0055] lgN i =a0-b0×lg(σ eqi -σ ∞ ) (16)

[0056]

[0057] Among them, a0 and b0 are material parameters, σ ∞ is the material safety fatigue limit corresponding to an infinite number of cycles, n i is the frequency corresponding to the i-th state per hour, N i is the equivalent dynamic stress σ eqi The number of damages under action, D Hi is the high-frequency damage in the i-th state.

[0058] According to the low-cycle safety SN curve of the material and the upper and lower rotor torque extremes, the low-cycle fatigue damage can be obtained:

[0059]

[0060] Among them, k m , σ m is the material low-cycle safety SN curve parameter, n L is the number of ground-air-ground cycles per hour corresponding to the low frequency, N L is the equivalent dynamic stress σ generated by the extreme torque eqL The number of damages under action, D L It is a low frequency injury.

[0061] Step 5: According to Miner's linear cumulative damage theory, combined with high and low cycle fatigue damage, the safe fatigue life of the input bevel gear shaft is obtained:

[0062]

[0063] Among them, m is the load level in the torque spectrum, f is the low-cycle fatigue life dispersion coefficient, and L is the safe fatigue life.

[0064] Furthermore, the input bevel gear shaft is a typical moving part of an aircraft, and its material is generally structural steel, specifically: 20Cr2Ni4A structural steel, 9310 structural steel, 15-5PH structural steel, etc.

[0065] Furthermore, the shaft intersection angle between the input bevel gear shaft and the rotor shaft is 90°.

[0066] Furthermore, the input bevel gear shaft in step one can also be left-rotating.

[0067] Furthermore, the pitch circle diameter of the middle end of the gear in step one is obtained according to gear parameters, including the number of teeth, module, tooth width, etc.

[0068] Furthermore, in step 4, the frequency number n i , where the dynamic stress part generated by the static load of the rotor torque is 1 times the rotation frequency, and the dynamic stress part generated by the dynamic load of the rotor torque is consistent with the main frequency component of the dynamic load of the rotor torque, which is generally a high-order frequency.

[0069] The key points of the present invention are:

[0070] (1) The present invention aims at analyzing the fatigue strength of the input bevel gear shaft of the coaxial rotor transmission system, and proposes a method for analyzing the strength of the input bevel gear shaft by taking into account the fact that the torques of the upper and lower rotors are not completely offset and the actual torque spectrum loads of the upper and lower rotors, which can more truly reflect the structural strength;

[0071] (2) In view of the fact that the torque dynamic load amplitude is greater than the static load under special configurations, the present invention provides a fatigue strength analysis of the input bevel gear shaft under high and low cycle loads, which can provide a safe fatigue life taking into account high and low cycle damage.

[0072] At present, when analyzing the load of the input bevel gear shaft of the coaxial rotor transmission system, it is assumed that the torques of the upper and lower rotors are equal in magnitude and opposite in direction, and the tangential force and radial force of the input bevel gear shaft at the upper and lower meshing points are completely offset, without considering the different power requirements of the upper and lower rotors and the influence of the downwash of the upper rotor on the lower rotor. The fatigue strength analysis method of the input bevel gear shaft of the coaxial rotor transmission system provided by the present invention takes all the meshing loads of the upper and lower rotor gears into consideration, and then performs strength assessment based on the calculated torque spectrum of the complete real state. Compared with the previous analysis methods, it can more truly reflect the load characteristics of the input bevel gear shaft and ensure the integrity of the input load during the strength analysis.

[0073] The present invention is widely used in coaxial rotors that drive upper and lower rotor shaft branches through two pairs of bevel gears meshing. The present invention provides a strength analysis method for the input bevel gear shaft taking into account high and low cycle fatigue damage, which can truly reflect the load characteristics of the structure throughout its life cycle and obtain the true calculated safe life. At the same time, it can be widely used in fatigue assessment of rotating parts of various types of coaxial rotor reducers and in anti-fatigue design and analysis of various types of coaxial aircraft transmission system structural parts.

Claims

1. A fatigue strength analysis method for the input bevel gear shaft of a coaxial rotor transmission system, characterized in that: include: Determine the dangerous section based on the coaxial rotor reducer configuration, input bevel gear shaft load analysis and structural characteristics; According to the meshing load of the upper and lower rotors and the relative motion relationship between the meshing load input bevel gear shaft, the static and dynamic loads of the dangerous section are determined; According to the static and dynamic loads of the dangerous section, the static and dynamic stresses are obtained, and then the equivalent dynamic stress of the section is obtained; According to the material SN curve and torque spectrum, the fatigue damage in each state is obtained; According to Miner's linear cumulative damage theory, the safe fatigue life of the input bevel gear shaft is obtained.

2. The method according to claim 1, characterized in that According to the meshing load of the upper and lower rotors, and the relative motion relationship between the meshing load and the input bevel gear shaft, the static and dynamic loads of the dangerous section are determined, including: Assuming the motion state of the input bevel gear shaft is relatively static, the dynamic load includes the meshing load generated by the torque dynamic load part and the tangential force F in the meshing load generated by the torque static load part of the upper and lower rotors. t and radial force F r All are regarded as dynamic loads; determine the axial force F in the meshing load generated by the static load part of the upper and lower rotor torque x As static load; Calculate the static and dynamic loads on dangerous sections.

3. The method according to claim 2, characterized in that The dangerous sections include at least a first section with the smallest diameter and a second section with the largest load.

4. The method according to claim 3, characterized in that For the first section, the section axial force T is generated by the static load of the upper and lower rotor torques. S , Sectional torque N S As the static load of the first section; the section axial force T generated by the static and dynamic loads of the upper and lower rotor torques d , Section shear force Z d , Section bending moment M d and section moment N d is the dynamic load of the first section.

5. The method according to claim 3, characterized in that: For the second section, the section torque generated by the static load part of the upper and lower rotor torque is the static load of the second section; the section torque generated by the dynamic load part of the upper and lower rotor torque is the dynamic load of the second section.

6. The method according to claim 4 or 5, characterized in that: The calculation formulas for static and dynamic loads include: N s =M z-ss +M z-xs ; N d =M z-sd +M z-xd ; Among them, M z-ss is the static torque transmitted by the upper rotor, M z-xs is the static torque transmitted by the lower rotor, M z-sd is the dynamic torque transmitted by the upper rotor, M z-xd is the dynamic torque transmitted by the lower rotor, M z-s is the total torque transmitted by the upper rotor, M z-x is the total torque transmitted by the lower rotor, and l is the axial distance between the gear meshing section and the first section.

7. The method according to claim 6, characterized in that The shaft angle between the input bevel gear shaft and the rotor shaft is 90°.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 7 is implemented.

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