Design method of wing arm tilting mechanism of tilt-rotor aircraft

Abstract

The application discloses a design method of a wing arm tilting mechanism of a tilt-rotor aircraft, and steps are as follows: combining a connecting rod mechanism principle, a tilting transition working condition rotor six force element and a tilting rudder torque threshold, transmission ratio design is completed; a distributed method and a topological optimization technology are adopted to obtain the best force transmission route and the optimal configuration of a motor support and an end frame support; a tilting transition and a peak torque working condition are taken as loads, and digital simulation and theoretical mechanics are combined to design static strength; a dynamics model is constructed based on vibration characteristics, a multi-rotor and a fixed-wing configuration wing arm vibration spectrum is taken as a load, and dynamic stress is superposed on static stress to design dynamic strength as a checking threshold. The application combines theoretical mechanics, vibration mechanics and digital simulation technology, provides a systematic design route, can realize high-G value resistance, lightweight, high stability and high reliability of the tilting mechanism design, guarantees reliable work of tilting, saves cost and shortens a development period.

Description

Technical Field

[0001] This invention relates to the field of mechanical technology, and in particular to a design method for a tilting arm mechanism of a tiltrotor aircraft. Background Technology

[0002] Tiltrotor aircraft not only have the vertical takeoff and landing capabilities of helicopters, but also the advantages of efficient cruise of fixed-wing aircraft. As the core system of tiltrotor aircraft, the tilt mechanism can realize multi-mode switching during flight, thereby achieving vertical takeoff and landing and efficient cruise. Therefore, the safety and reliability of the tilt mechanism directly affect the normal flight of the aircraft.

[0003] Patent CN112733276A discloses a dynamic optimization method and system for the tilt mechanism of a tilt-rotor UAV. The method analyzes the forces, torques and motion characteristics of the tilt mechanism during the tilting process; it analyzes the variation law and influence of relevant physical quantities of the tilt mechanism through multiphysics simulation based on finite element method, and corrects the theoretical model; based on the establishment of the theoretical model and the correction of the theoretical model by multiphysics simulation, an experimental platform for the tilt mechanism is built to verify the theoretical model.

[0004] This method constructs an accurate multiphysics model of the tilting mechanism using digital simulation technology, simulates the tilting process of the tilting mechanism, calculates the six rotor force elements of the tilting mechanism, and conducts experimental verification. This method has a certain accuracy in calculating the loads during the tilting process of the tilting mechanism, but it does not systematically report the design method of the tilting mechanism.

[0005] Based on the above defects and shortcomings, it is necessary to improve the existing technology and design a method for the tilting mechanism of the tilt rotor aircraft arm. Summary of the Invention

[0006] The main technical problem solved by this invention is to provide a design method for the tilt mechanism of the arm of a tiltrotor aircraft. It solves the technical difficulties of designing the transmission ratio of the tilt mechanism and designing for high G-force resistance, lightweight, and high reliability. By integrating multidisciplinary technologies, it provides a systematic design route to ensure the reliable operation of the tilt mechanism, while saving development costs and shortening the development cycle.

[0007] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: to provide a design method for the arm tilting mechanism of a tiltrotor aircraft, comprising the following steps: S1. The design of the transmission ratio of the tilting mechanism is achieved by applying the basic principle of the linkage mechanism and combining the six force elements of the rotor and the torque threshold of the tilting servo motor under the tilting transition condition. S2. The mechanism and structure design of the tilting mechanism adopts the distributed method of the tilting mechanism and obtains the optimal force transmission route and optimal configuration of the motor support and end frame support through topology optimization technology. S3. Static strength design of tilting mechanism: The tilting transition condition and peak torque condition are used as the load conditions for strength design, and the design adopts the integration technology of digital simulation and theoretical mechanics. S4. Dynamic strength design of tilting mechanism: Based on the vibration characteristics of tilting mechanism, a dynamic model of the basic excitation of tilting mechanism is constructed. The vibration spectrum of the boom of multi-rotor and fixed-wing configurations is used as the dynamic strength design load condition of tilting mechanism. Dynamic stress superposition with static stress is used as the dynamic strength check threshold. S5. Experimental design and verification of tilting mechanism.

[0008] Furthermore, the transmission ratio design in step S1 includes the following steps: S1.1 Determine the motion envelope of the mechanism; S1.2 Preliminary scheme and parameters of linkage mechanism; S1.3, Calculate the transmission ratio i s ; S1.4 Determine the six force elements of the rotor under tilt transition conditions: thrust L, drag D, side force F, and counter-torque T. c Pitch moment Mp, roll moment M R ; S1.5, Calculation of tilt servo torque T; S1.6, If the tilt servo torque T <T max Then stop, to obtain the optimal transmission ratio i p Otherwise, return to step S1.2.

[0009] Furthermore, in step S1.3, the crank L at the output end of the servo motor... AB The generated driving torque M1 is: (1) In the formula: F B For link L BC The driving force generated at end B; θ1 is the crank L AB With connecting rod L BC The acute angle included; Output crank L EF The generated driving torque M3 is: (2) In the formula: F E For link L EC The driving force generated at end E; θ3 is the crank L EF With connecting rod L EC The acute angle included; The transmission ratio expression for the tilting mechanism is: (3) Substituting equations (1) and (2) into equation (3), we get: (4) According to the principle of two forces, we can obtain: (5) Substituting equation (5) into equation (4), we get: (6) Crank L CD The resulting driving torque M2 is: (7) In the formula: F C1 For link L BC The driving force generated at end C; θ2 is the crank L CD With connecting rod L BC The acute angle included; Another way to express M2 is: (8) In the formula: F C2 For link L CE The driving force generated at end C; θ4 is the crank L CD With connecting rod L CE The acute angle included; From equations (7) and (8), we can obtain: (9) Substituting equation (9) into equation (6), we get: (10) The above equation can be simplified to: (11) The above formula is the universal expression for the transmission ratio design of a series four-bar linkage.

[0010] Specifically, if the four-bar linkage ABCD is a parallelogram, then: (12) Substituting equation (12) into equation (11), we get: (13) This can be further simplified to: (14) In the formula: L FI For link L EF In force F E The projected length L DH For link L DC In force F C1The projection length is given by the formula above, which is the transmission ratio design method for a series four-bar linkage where the first four-bar linkage is a parallelogram and the second four-bar linkage is a general quadrilateral.

[0011] Furthermore, in step S1.5, the total torque M3 generated by the six rotor force elements at the tilting mechanism shaft EF is: (15) Where: M L M D and M F These are the moments generated at the pivot EF by the lift L, drag D, and lateral force F, respectively. Tilting servo torque T D The calculation expression is: (16) Substituting equations (11) and (15) into equation (16), we get: (17) The above formula is the universal expression for calculating the torque of the tilting servo motor in a series four-bar linkage mechanism; Specifically, substituting equations (14) and (15) into equation (16) yields: (18) The above formula is the torque calculation expression for a tilt servo motor in a series four-bar linkage where the first four-bar linkage is a parallelogram and the second four-bar linkage is a general quadrilateral.

[0012] Furthermore, the mechanism and structure design in step S2 includes the following steps: S2.1 Construct a static model of the motor support; S2.2 Determine the topology optimization variables for the motor bracket; S2.3, Construct topology optimization constraints: The displacement of the propeller disk's center of mass is less than its set initial displacement value, i.e., x. <x0; S2.4 Construct the topology optimization objective function: Minimize the volume fraction (min vf); S2.5, The six force elements of the rotor when the tilt angle θ = θ0 is applied to the center of the rotor disk; S2.6 Perform static calculations on the motor bracket; S2.7. Reconstruct the structure of the motor bracket after topology optimization to obtain the motor bracket structure with the optimal force transmission route.

[0013] Furthermore, mechanism and structural design also includes the following steps: S2.8 Construct a static model of the end frame support; S2.9 Determine the topology optimization variables for the end frame support; S2.10, Construct topology optimization constraints: Disk centroid displacement x <x0; S2.11, Construct the topology optimization objective function to minimize the volume fraction: min vf; S2.12 Extract the internal forces at the connection position in step S2.6. First, perform a static analysis on the motor bracket and extract the triaxial internal forces at the lower interface of the bracket as the input force of the end frame bracket connected to the aircraft, which is then applied to the connection hole. S2.12. Perform static calculations on the end frame support; S2.14. Reconstruct the structure of the end frame support after topology optimization to obtain the end frame support structure with the best force transmission route.

[0014] Furthermore, the static strength design in step S3 includes the following steps: S3.1 Construct a static model for the tilting transition condition; S3.2. Load the rotor six force elements under tilt transition conditions and extract the stress under different conditions; S3.3 If the stress in the tilting transition condition is less than the tensile strength of the material, i.e., σ tran <σ b If the tilt transition condition verification is successful, then return to step S3.1; otherwise, return to step S3.1. S3.4 Analyze the tilt transition load condition and determine the configuration that is most severely subjected to the peak torque condition; S3.5 Construct a static model for the peak torque condition; S3.6, Axial force corresponding to peak torque loading condition, if the calculated stress σ tran <σ b If the peak torque condition tilt mechanism passes the verification, then return to step S3.1; otherwise, return to step S3.1. S3.7 Extract the internal forces of the connecting holes under tilt transition conditions and peak torque conditions; S3.8. Check the connection strength between the tilt transition condition and the peak torque condition. If the connection strength is less than the allowable strength of the material, i.e., σ c If the value is less than σ, the connection strength check passes; otherwise, return to S3.1.

[0015] Furthermore, the dynamic strength design in step S4 includes the following steps: S4.1 Construct a dynamic model of the tilting mechanism; S4.2, Loading the center of mass and moment of inertia of the rotor system and motor assembly; S4.3 Calculate the yaw frequency f of the tilting mechanism based on modal analysis. yaw and pitch frequency f pit ; S4.4, Yaw frequency f yaw >f excor f pit >f exc If the condition is met, return to step S4.1; otherwise, continue to the next step, where f exc The excitation frequency; S4.5, Vibration spectrum of loaded multi-rotor configuration; S4.6 Extracting the dynamic stress σ of the tilting mechanism dD ; S4.7 Calculate the total dynamic stress σ of the tilting mechanism. ZD =σ dD +σ tran ; S4.8, If the total stress σ ZD <σ s If yes, proceed to the next step; otherwise, return to step S4.1. S4.9 Vibration spectrum of a fixed-wing configuration under load; S4.10, Extracting dynamic stress σ dG ; S4.11 Calculate the total dynamic stress σ of the tilting mechanism. ZG =σ dG +σ tran ; S4.12. If the total dynamic stress is less than the yield stress of the material, i.e., σ ZG <σ s If yes, proceed to the next step; otherwise, return to step S4.1. S4.13, Physical test verification.

[0016] Furthermore, the experimental design and verification in step S5 includes the following steps: S5.1 Design the vibration test mounting base for the tilting mechanism and the simulated motor and rotor assembly. The weight and moment of inertia of the center of gravity of the assembly should be consistent with the actual values, with an error of no more than ±10%. S5.2 Install the tilting mechanism mounting base, tilting mechanism, and motor and rotor assembly simulation component on the vibration table; S5.3. Two accelerometers are deployed on the upper interface of the tilting mechanism and the end frame of the tilting mechanism respectively, and sinusoidal frequency sweep tests are carried out in the Z and Y directions. Two-point averaging control is adopted, the frequency sweep bandwidth is 5-500Hz, and the vibration value is 0.5g. S5.4. Take the frequency corresponding to the peak value where the quality factor Q of the frequency response curve is greater than twice as the resonance point, and record the first two resonance points. S5.5. Using the sensor deployment method in step S5.3, and the control mode is four-point average control, a random vibration test is conducted on the tilting mechanism. The test spectrum is broadband random plus narrowband sine and broadband random plus narrowband random. The vibration value is 6G, the bandwidth is 15~2000Hz, and the vibration time is 1h. S5.6 After the test, check whether the tilting mechanism structure has failed and whether the bolts are loose.

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention integrates theoretical mechanics, vibration dynamics and digital simulation technology to systematically provide a design technical route for the tilt mechanism of the arm of a tilt rotor aircraft. This method ensures the reliable operation of the tilt mechanism during the tilting process, saves costs and shortens the product development cycle; (2) By applying the basic principle of linkage mechanism and combining the six force elements of rotor and the torque threshold of tilt servo motor in tilt transition condition, the transmission ratio design of tilt mechanism was realized, which ensured the stable operation of tilt mechanism in tilt process. (3) By adopting the distributed method of tilting mechanism and topology optimization technology, the optimal force transmission route and optimal configuration of motor bracket and end frame bracket were obtained, which can quickly carry out the optimal transmission route and lightweight design of the structure. (4) Taking the tilting transition condition and peak torque condition as the load conditions for strength design, the static strength of the tilting mechanism was designed by adopting the integration technology of digital simulation and theoretical mechanics, which provides static strength support for the reliable operation of the structure during the tilting process. (5) Using digital simulation and modal analysis technology, the excitation frequency and harmonic frequency generated by the multi-rotor system and propeller system are used as frequency avoidance design constraints to ensure that the structure will not be coupled with the environmental excitation frequency and provide dynamic strength support for the reliable operation of the structure during tilting. (6) Based on the vibration characteristics of the tilting mechanism, a dynamic model of the basic excitation of the tilting mechanism is constructed. The vibration spectrum of the boom of the multi-rotor and fixed-wing configurations is used as the dynamic strength design load condition of the tilting mechanism. The dynamic stress superimposed on the static stress is used as the dynamic strength check threshold. The dynamic and static strength of the tilting mechanism during the tilting process is comprehensively evaluated, providing strength support for the reliable and safe operation of the tilting mechanism. Attached Figure Description

[0018] Figure 1 This is the main flowchart of the present invention.

[0019] Figure 2 This is a flowchart illustrating the transmission ratio design of the present invention.

[0020] Figure 3 This is a schematic diagram of the dynamic ratio design principle of the present invention.

[0021] Figure 4 This is a flowchart of the topology optimization process for the motor bracket of the present invention.

[0022] Figure 5 This is a flowchart of the end frame topology optimization process of the present invention.

[0023] Figure 6This is a flowchart of the static strength design method of the present invention.

[0024] Figure 7 This is a flowchart of the dynamic strength design method of the present invention. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0026] Please see Figures 1 to 7 The embodiments of the present invention include: A design method for the boom tilting mechanism of a tiltrotor aircraft, comprising the following steps: S1, Tilting mechanism transmission ratio design, combined with Figure 2 This includes the following steps: S1.1 Determine the motion envelope of the mechanism; S1.2 Preliminary scheme and parameters of linkage mechanism; S1.3, Calculate the transmission ratio i s ; S1.4 Determine the six force elements of the rotor under tilt transition conditions: thrust L, drag D, side force F, and counter-torque T. c Pitch moment Mp, roll moment M R ; S1.5, Calculation of tilt servo torque T; S1.6, If the tilt servo torque T <T max Then stop, to obtain the optimal transmission ratio i p Otherwise, return to step S1.2.

[0027] Furthermore, combined Figure 3 In step S1.3, the crank L at the output end of the servo motor (input end of the transmission mechanism) AB The generated driving torque M1 is: (1) In the formula: F B For link L BC The driving force generated at end B; θ1 is the crank L AB With connecting rod L BC The acute angle included; Output crank L EF The generated driving torque M3 is: (2) In the formula: F E For link L EC The driving force generated at end E; θ3 is the crank LEF With connecting rod L EC The acute angle included; The transmission ratio expression for the tilting mechanism is: (3) Substituting equations (1) and (2) into equation (3), we get: (4) According to the principle of two forces, we can obtain (5) Substituting equation (5) into equation (4) yields (6) Crank L CD The resulting driving torque M2 is: (7) In the formula: F C1 For link L BC The driving force generated at end C; θ2 is the crank L CD With connecting rod L BC The acute angle included; Another way to express M2 is: (8) In the formula: F C2 For link L CE The driving force generated at end C; θ4 is the crank L CD With connecting rod L CE The acute angle included; From equations (7) and (8), we can obtain: (9) Substituting equation (9) into equation (6), we get (10) The above equation can be simplified to obtain (11) The above formula is the universal expression for the transmission ratio design of a series four-bar linkage.

[0028] Specifically, if the four-bar linkage ABCD is a parallelogram, then: (12) Substituting equation (12) into equation (11), we get: (13) This can be further simplified to: (14) In the formula: LFI For link L EF In force F E The projected length L DH For link L DC In force F C1 The projection length is given by the formula above, which is the transmission ratio design method for a series four-bar linkage where the first four-bar linkage is a parallelogram and the second four-bar linkage is a general quadrilateral.

[0029] In step S1.5, the total torque M3 generated by the six rotor elements at the tilting mechanism shaft EF is: (15) Where: M L M D and M F These are the moments generated at the pivot EF by the lift L, drag D, and lateral force F, respectively. Tilting servo torque T D The calculation expression is: (16) Substituting equations (11) and (15) into equation (16), we get: (17) The above formula is the universal expression for calculating the torque of the tilting servo motor in a series four-bar linkage mechanism; Specifically, substituting equations (14) and (15) into equation (16) yields: (18) The above formula is the torque calculation expression for the tilt servo motor of a series four-bar linkage where the first four-bar linkage is a parallelogram and the second four-bar linkage is a general quadrilateral. T D For a series-type four-bar linkage, there are no special requirements, making it more universally applicable. De For T D Special circumstances.

[0030] The present invention is illustrated by taking a tilting mechanism of a series four-bar linkage in which the first four-bar linkage is a parallelogram and the second four-bar linkage is a quadrilateral as an example.

[0031] The six rotor force elements of the tilting mechanism are shown in Table 1; the characteristic parameters of the tilting mechanism are shown in Table 2; the peak torque is 1600 N·m, and the safety factor is 1.5; the tilting mechanism is made of aluminum alloy 7050, and the material parameters are shown in Table 3; the frequency avoidance range of the tilting mechanism is 12-15 Hz and 22-25 Hz; the vibration spectrum of the multi-rotor configuration is a broadband + narrowband sine wave with a bandwidth of 15-2000 Hz and a vibration magnitude of 6G; the vibration spectrum of the fixed-wing configuration is a broadband + narrowband random wave with a bandwidth of 15-2000 Hz and a vibration magnitude of 6G.

[0032] Table 1. Six rotor force elements for tilt transition of the tilt mechanism.

[0033] Table 2 Characteristic parameters of tilting mechanism

[0034] Table 3 Mechanical properties of metallic materials

[0035] Table 4 Mass characteristics of the combination of electrical equipment and rotor system or propeller

[0036] Based on the known parameters in Tables 1 and 2, the transmission ratio of the tilting mechanism and the design torque of the servo motor are calculated according to formula (18), as shown in Table 5. The transmission ratio of the tilting mechanism is between 1.12 and 1.43, which can achieve stable tilting transition; the maximum design torque T of the servo motor is... De =1541.899 N·m < 1600 N·m, proceed to the next step.

[0037] Table 5 Characteristic parameters of tilting mechanism

[0038] Step S2, tilting mechanism and structural design, combined with Figure 4 This includes the following steps: Step S2.1: Construct a static model of the motor support; Step S2.3: Determine the topology optimization variables for the motor bracket; Step S2.3, construct topology optimization constraints: propeller disk centroid displacement x < 5mm; Step S2.4, construct the topology optimization objective function: minimize the volume fraction (min vf); Step S2.5: Apply the six rotor forces at a tilt angle θ = 80° to the center of the rotor disk, namely drag 711.99 N, side force 150.66 N, thrust 7676.70 N, roll moment 19130 N·m, pitch moment 1203.15 N·m, and motor anti-torsion moment 1979.91 N·m.

[0039] Step S2.6: Perform static calculations on the motor bracket; Step S2.7: Reconstruct the structure of the motor bracket after topology optimization to obtain the motor bracket structure with the optimal force transmission route.

[0040] Combination Figure 5 It also includes: Step S2.8: Construct the static model of the end frame support; Step S2.9: Determine the topology optimization variables for the end frame support; Step S2.10, topology optimization constraint: propeller disk centroid displacement x < 3mm; Step S2.11, the objective function of topology optimization is to minimize the volume fraction, i.e., min vf; Step S2.12: Extract the internal forces at the connection positions from step 2.6. First, perform a static analysis on the motor bracket and extract the triaxial internal forces at the lower interface of the bracket, which will be used as the input force for the end frame bracket connected to the aircraft and applied to the connection hole. Step S2.13: Perform static calculations on the end frame support; Step S2.14: Reconstruct the structure of the topology-optimized end frame support to obtain the end frame support structure with the optimal force transmission route.

[0041] Step S3, static strength design of the tilting mechanism, combined with Figure 6 This includes the following steps: Step S3.1: Construct a static model of the tilting transition condition; Step S3.2: Apply the six force elements of the rotor under tilt transition conditions and extract the stress under different conditions; Step S3.3, the maximum stress σ in the tilt transition condition tran =161MPa<σ b If so, the tilt transition condition verification is passed; Step S3.4: Analyze the tilt transition load condition and determine the configuration with the most severe peak torque condition. Step S3.5: Construct a static model for the peak torque condition; Step S3.6, apply the axial force corresponding to the peak torque condition, if the calculated stress σ c =503MPa<σ b If so, the tilt mechanism under peak torque condition verification is passed; Step S3.7: Extract the internal forces of the connecting holes for the tilt transition condition and the peak torque condition; Step S3.8, the minimum safety margin of the connection strength between the tilt transition condition and the peak torque condition is checked and found to be 1.1 > 0, the connection strength check is passed; Step S4, dynamic strength design of the tilting mechanism, combined with Figure 7 This includes the following steps: Step S4.1: Construct the dynamic model of the tilting mechanism; Step S4.2: Load the center of mass and moment of inertia of the rotor system and motor assembly according to Table 5; Step S4.3: Calculate the yaw frequency f of the tilting mechanism based on modal analysis. yaw For 30Hz and pitch frequency f pit It is 29Hz; Step S4.4, yaw frequency f yaw and pitch frequency f pit Both are greater than the frequency avoidance range of the tilting mechanism, which is 12-15Hz and 22-25Hz; Step S4.5: Load the vibration spectrum of the multi-rotor configuration, i.e., broadband + narrowband sine wave, with a bandwidth of 15 to 2000 Hz and a vibration value of 6 G. Step S4.6: Extract the dynamic stress σ of the tilting mechanism. dD =135 MPa; Step S4.7, calculate the total dynamic stress σ of the tilting mechanism. ZD =σ dD +σ tran= 135 + 161 = 296 MPa; Step S4.8, if the total stress σ ZD =296MPa<σ s =470MPa; Step S4.9: Load the vibration spectrum of the fixed-wing configuration. The vibration spectrum of the fixed-wing configuration is broadband + narrowband random, with a bandwidth of 15 to 2000 Hz and a vibration value of 6 G. Step S4.10, extract dynamic stress σ dG =141MPa; Step S4.11, calculate the total dynamic stress σ of the tilting mechanism. ZG =σ dG +σ tran =141+161=302MPa; Step S4.12, if the total stress σ ZG =302MPa <σ s =470MPa; Step S4.13: After the physical test, the structural strength of the tilting mechanism meets the design requirements.

[0042] Step S5: Experimental design and verification of the tilting mechanism.

[0043] This method integrates theoretical mechanics, vibration dynamics, and digital simulation technology to systematically present the design technology route for the tilt mechanism of tiltrotor aircraft arms. It can realize the design of tilt mechanism for tiltrotor aircraft with high G-force resistance, lightweight, high stability, and high reliability, ensuring the reliable operation of the tilt mechanism during the tilting process, saving costs, and shortening the product development cycle.

[0044] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A design method for a tilting arm mechanism of a tiltrotor aircraft, characterized in that: Includes the following steps: S1. The design of the transmission ratio of the tilting mechanism is achieved by applying the basic principle of the linkage mechanism and combining the six force elements of the rotor and the torque threshold of the tilting servo motor under the tilting transition condition. S2. The mechanism and structure design of the tilting mechanism adopts the distributed method of the tilting mechanism and obtains the optimal force transmission route and optimal configuration of the motor support and end frame support through topology optimization technology. S3. Static strength design of tilting mechanism: The tilting transition condition and peak torque condition are used as the load conditions for strength design, and the design adopts the integration technology of digital simulation and theoretical mechanics. S4. Dynamic strength design of tilting mechanism: Based on the vibration characteristics of tilting mechanism, a dynamic model of the basic excitation of tilting mechanism is constructed. The vibration spectrum of the boom of multi-rotor and fixed-wing configurations is used as the dynamic strength design load condition of tilting mechanism. Dynamic stress superposition with static stress is used as the dynamic strength check threshold. S5. Experimental design and verification of tilting mechanism.

2. The design method for the arm tilting mechanism of a tiltrotor aircraft according to claim 1, characterized in that: The transmission ratio design in step S1 includes the following steps: S1.1 Determine the motion envelope of the mechanism; S1.2 Preliminary scheme and parameters of linkage mechanism; S1.3, Calculate the transmission ratio i s ; S1.4 Determine the six force elements of the rotor under tilt transition conditions: thrust L, drag D, side force F, and counter-torque T. c Pitch moment Mp, roll moment M R ; S1.5, Calculation of tilt servo torque T; S1.6, If the tilt servo torque T <T max Then stop, to obtain the optimal transmission ratio i p Otherwise, return to step S1.

2.

3. The design method for the arm tilting mechanism of a tiltrotor aircraft according to claim 2, characterized in that: In step S1.3, the crank L at the output end of the servo motor AB The generated driving torque M1 is: （1） In the formula: F B For link L BC The driving force generated at end B; θ1 is the crank L AB With connecting rod L BC The acute angle included; Output crank L EF The generated driving torque M3 is: （2） In the formula: F E For link L EC The driving force generated at end E; θ3 is the crank L EF With connecting rod L EC The acute angle included; The transmission ratio expression for the tilting mechanism is: （3） Substituting equations (1) and (2) into equation (3), we get: （4） According to the principle of two forces, we can obtain: （5） Substituting equation (5) into equation (4), we get: （6） Crank L CD The resulting driving torque M2 is: （7） In the formula: F C1 For link L BC The driving force generated at end C; θ2 is the crank L CD With connecting rod L BC The acute angle included; Another way to express M2 is: （8） In the formula: F C2 For link L CE The driving force generated at end C; θ4 is the crank L CD With connecting rod L CE The acute angle included; From equations (7) and (8), we can obtain: （9） Substituting equation (9) into equation (6), we get: （10） The above equation can be simplified to: （11） The above formula is the universal expression for the transmission ratio design of a series four-bar linkage.

4. The design method for the arm tilting mechanism of a tiltrotor aircraft according to claim 3, characterized in that: If the four-bar linkage ABCD is a parallelogram, then: （12） Substituting equation (12) into equation (11), we get: （13） This can be further simplified to: (14) In the formula: L FI For link L EF In force F E The projected length L DH For link L DC In force F C1 The projection length is given by the formula above, which is the transmission ratio design method for a series four-bar linkage where the first four-bar linkage is a parallelogram and the second four-bar linkage is a general quadrilateral.

5. The design method for the arm tilting mechanism of a tiltrotor aircraft according to claim 4, characterized in that: In step S1.5, the total torque M3 generated by the six rotor elements at the tilting mechanism shaft EF is: (15) Where: M L M D and M F These are the moments generated at the pivot EF by the lift L, drag D, and lateral force F, respectively. Tilting servo torque T D The calculation expression is: (16) Substituting equations (11) and (15) into equation (16), we get: （17） The above formula is the universal expression for calculating the torque of the tilting servo motor in a series four-bar linkage mechanism; Specifically, substituting equations (14) and (15) into equation (16) yields: （18） The above formula is the torque calculation expression for a tilt servo motor in a series four-bar linkage where the first four-bar linkage is a parallelogram and the second four-bar linkage is a general quadrilateral.

6. The design method for the arm tilting mechanism of a tiltrotor aircraft according to claim 1, characterized in that: Step S2, the mechanism and structure design, includes the following steps: S2.1 Construct a static model of the motor support; S2.2 Determine the topology optimization variables for the motor bracket; S2.3, Construct topology optimization constraints: The displacement of the propeller disk's center of mass is less than its set initial displacement value, i.e., x. <x0; S2.4 Construct the topology optimization objective function: Minimize the volume fraction (min vf); S2.5, The six force elements of the rotor when the tilt angle θ = θ0 is applied to the center of the rotor disk; S2.6 Perform static calculations on the motor bracket; S2.

7. Reconstruct the structure of the motor bracket after topology optimization to obtain the motor bracket structure with the optimal force transmission route.

7. The design method for the arm tilting mechanism of a tiltrotor aircraft according to claim 6, characterized in that: It also includes the following steps: S2.8 Construct a static model of the end frame support; S2.9 Determine the topology optimization variables for the end frame support; S2.10, Construct topology optimization constraints: Disk centroid displacement x <x0; S2.11, Construct the topology optimization objective function to minimize the volume fraction: min vf; S2.12 Extract the internal forces at the connection position in step S2.

6. First, perform a static analysis on the motor bracket and extract the triaxial internal forces at the lower interface of the bracket as the input force of the end frame bracket connected to the aircraft, which is then applied to the connection hole. S2.

12. Perform static calculations on the end frame support; S2.

14. Reconstruct the structure of the end frame support after topology optimization to obtain the end frame support structure with the best force transmission route.

8. The design method for the arm tilting mechanism of a tiltrotor aircraft according to claim 1, characterized in that: The static strength design in step S3 includes the following steps: S3.1 Construct a static model for the tilting transition condition; S3.

2. Load the rotor six force elements under tilt transition conditions and extract the stress under different conditions; S3.3 If the stress in the tilting transition condition is less than the tensile strength of the material, i.e., σ tran <σ b If the tilt transition condition verification is successful, then return to step S3.1; otherwise, return to step S3.

1. S3.4 Analyze the tilt transition load condition and determine the configuration that is most severely subjected to the peak torque condition; S3.5 Construct a static model for the peak torque condition; S3.6, Axial force corresponding to peak torque loading condition, if the calculated stress σ tran <σ b If the peak torque condition tilt mechanism passes the verification, then return to step S3.1; otherwise, return to step S3.

1. S3.7 Extract the internal forces of the connecting holes under tilt transition conditions and peak torque conditions; S3.

8. Check the connection strength between the tilt transition condition and the peak torque condition. If the connection strength is less than the allowable strength of the material, i.e., σ c If the value is less than σ, the connection strength check passes; otherwise, return to S3.

1.

9. The design method for the arm tilting mechanism of a tiltrotor aircraft according to claim 1, characterized in that: Step S4, dynamic strength design, includes the following steps: S4.1 Construct a dynamic model of the tilting mechanism; S4.2, Loading the center of mass and moment of inertia of the rotor system and motor assembly; S4.3 Calculate the yaw frequency f of the tilting mechanism based on modal analysis. yaw and pitch frequency f pit ; S4.4, Yaw frequency f yaw >f exc or f pit >f exc If the condition is met, return to step S4.1; otherwise, continue to the next step, where f exc The excitation frequency; S4.5, Vibration spectrum of loaded multi-rotor configuration; S4.6 Extracting the dynamic stress σ of the tilting mechanism dD ; S4.7 Calculate the total dynamic stress σ of the tilting mechanism. ZD =σ dD +σ tran ; S4.8, If the total stress σ ZD <σ s If yes, proceed to the next step; otherwise, return to step S4.

1. S4.9 Vibration spectrum of a fixed-wing configuration under load; S4.10, Extracting dynamic stress σ dG ; S4.11 Calculate the total dynamic stress σ of the tilting mechanism. ZG =σ dG +σ tran ; S4.

12. If the total dynamic stress is less than the material's yield stress, i.e., σ ZG <σ s If yes, proceed to the next step; otherwise, return to step S4.

1. S4.13, Physical test verification.

10. The design method of the arm tilting mechanism for a tiltrotor aircraft according to claim 1, characterized in that: Step S5, the design and verification of the dynamic experiment, includes the following steps: S5.1 Design the vibration test mounting base for the tilting mechanism and the simulated motor and rotor assembly. The weight and moment of inertia of the center of gravity of the assembly should be consistent with the actual values, with an error of no more than ±10%. S5.2 Install the tilting mechanism mounting base, tilting mechanism, and motor and rotor assembly simulation component on the vibration table; S5.

3. Two accelerometers are deployed on the upper interface of the tilting mechanism and the end frame of the tilting mechanism respectively, and sinusoidal frequency sweep tests are carried out in the Z and Y directions. Two-point averaging control is adopted, the frequency sweep bandwidth is 5-500Hz, and the vibration value is 0.5g. S5.

4. Take the frequency corresponding to the peak value where the quality factor Q of the frequency response curve is greater than twice as the resonance point, and record the first two resonance points. S5.

5. Using the sensor deployment method in step S5.3, and the control mode is four-point average control, a random vibration test is conducted on the tilting mechanism. The test spectrum is broadband random plus narrowband sine and broadband random plus narrowband random. The vibration value is 6G, the bandwidth is 15~2000Hz, and the vibration time is 1h. S5.6 After the test, check whether the tilting mechanism structure has failed and whether the bolts are loose.

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