Helicopter transmission system digital design method driven based on design requirements

Abstract

The invention provides a digitized design method for a helicopter transmission system driven based on design requirements, which comprises the following steps of: 1, constructing a design requirement model according to design task requirements and standards; 2, constructing a meta-model of each stage and a part parameter meta-model; 3, analyzing the functions of the parts, and forming a feasible transmission scheme; step 4, distributing a transmission ratio, estimating weight and efficiency, and screening an optimal transmission scheme; 5, acquiring a transmission unit and a transmission relation, and establishing a transmission chain model; 6, parameterization design is carried out on the part, and a result is packaged in a part meta-model; 7, strength checking and performance simulation are carried out, and design result verification is carried out; 8, constructing a transmission system assembly physical model; and step 9, constructing a comprehensive database, and establishing a data version transmission and tracing mechanism. The problems that a traditional design method is poor in interactivity and difficult in model consistency maintenance and data tracing are solved, and the digitized full-process design and full-period management capacity of the transmission system is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of helicopter transmission system digitization, and particularly relates to a helicopter transmission system digitization design method based on design requirement driving. BACKGROUND

[0002] As a core functional unit, the performance of the helicopter transmission system directly determines the performance of the whole machine and affects the flight quality and mission capability of the whole machine. With the development of new types of configurations such as high-speed helicopters, unmanned rotors and the like with high-demand characteristics such as long-range, ultra-low altitude high maneuverability, deep integration and high intelligence, the traditional design method faces severe challenges in efficiency, accuracy and adaptability.

[0003] The current traditional helicopter transmission system design method includes distributed design method, empirical formula method, physical prototype test method and modular design method, and the advantages and disadvantages of each design method are as follows:

[0004] 1. Step-by-step design method: The design of the transmission system is usually divided into multiple design stages including conceptual design, preliminary design, detailed design, verification and optimization. Conceptual design refers to determining the layout of the transmission system (such as main reducer, tail transmission shaft, intermediate reducer) according to the overall requirements of the helicopter (such as load, range, speed). Preliminary design is to calculate key parameters such as transmission shaft diameter, gear modulus and bearing selection based on empirical formula or simplified model. Detailed design is to perform strength checking (such as gear contact stress, shaft fatigue analysis) and geometric modeling. Verification and optimization refer to verifying the design through manual calculation or finite element analysis (FEA), which requires repeated adjustment of parameters. The distributed design method is systematic and reliable, but this method is only suitable for traditional configurations, relies on mature engineering experience, and needs to be gradually promoted to reduce design omissions; and the design relies on manual experience and has high iteration cost. It is not suitable for new configurations (such as high-speed helicopters), as it relies on past design experience, and when problems are found in the development of new models, it needs to be traced back to the early stage for modification, which takes a long time.

[0005] 2. Empirical formula method: quickly estimate parameters such as gear design and shaft neck estimation based on historical design data and simplified formulas. The advantage of this method is that it is fast and efficient, and does not require complex simulation tools, mainly relying on traditional formulas for checking. However, this method has limited design accuracy, and complex factors such as dynamic load and thermal effect are ignored during the design process, and it is suitable for scenarios similar to existing designs.

[0006] 3. Physical prototype testing: Actual testing is realized by manufacturing physical prototypes. For example, bench testing: testing the load capacity and vibration characteristics of the reducer on a test bench; fatigue testing: simulating alternating loads in long-term use to verify the service life of gears and bearings; flight testing: monitoring the temperature, vibration and noise of the transmission system in real flight. Since the actual test results are real and reliable, they can directly reflect the actual performance and also discover details ignored in simulation (such as assembly errors and material defects). However, the manufacturing and testing of prototypes in this method are costly and time-consuming, and it takes years from design to testing. Modification is difficult, and a new prototype needs to be manufactured after problems are found.

[0007] 4. Modular design method: The transmission system is divided into independent modules (such as the main reducer module and the tail transmission module), which are designed and integrated separately. This method is flexible, and the modules can be reused. Since the transmission system is divided into multiple modules, the development cycle of new models is shortened. Since each module is relatively independent, when maintaining, the faulty module can be quickly replaced, making maintenance easy. However, due to the complex interfaces of each module, the mechanical and dynamic coupling between modules may cause resonance when integrated into the transmission system, which may ultimately result in suboptimal system performance.

[0008] In summary, the traditional helicopter transmission system design method has the following technical bottlenecks: 1. Strong dependence on experience: The traditional step-by-step design is based on artificial experience and simplified formulas, making it difficult to cope with the multi-disciplinary coupling problems of high complexity configurations (such as coaxial transmission and high-power tail transmission); 2. High iteration cost: The manufacturing and testing of physical prototypes are time-consuming, and local modifications require backtracking to earlier design stages, resulting in prolonged research and development cycles; 3. Data fragmentation: In the process of designing a helicopter transmission system from design requirements to physical models, traditional design methods are mostly used. Although modern design tools are used to accelerate the design process, the use of different tools at each stage of the design process leads to data interaction and tool compatibility, resulting in multiple information silos from concept design to detailed design, hindering multidisciplinary collaborative optimization, and making design iteration inefficient and prolonging the research and development cycle.

[0009] Foreign countries have achieved digitalization of the entire life cycle of aviation products through digital twinning and virtual simulation, significantly improving design efficiency. In China, preliminary experience has been accumulated in the design of 3-6-ton helicopter transmission systems, but the configuration innovation of high-power transmission systems above 10 tons is still limited by traditional methods. It is urgent to establish a digital design system covering requirements, functions, physics and performance to support the rapid iterative development of high-speed and highly reliable transmission systems. SUMMARY

[0010] The application aims to solve the problems of strong experience dependence, high iteration cost and data fragmentation in the design of a conventional helicopter transmission system, and provide a helicopter transmission system digital design method based on design requirement driving.

[0011] To achieve the above-mentioned object, the application provides a helicopter transmission system digital design method based on design requirement driving, comprising the following steps:

[0012] Step 1: constructing a transmission system design requirement model according to helicopter transmission system design task requirements and standard construction specification, wherein the transmission system design requirement model comprises transmission system function requirements, performance requirements, integrated interface requirements, general quality characteristics and standardization requirements, test verification requirements, each requirement comprising basic design parameters and constraint conditions;

[0013] Step 2: constructing a transmission system design requirement meta-model, a function meta-model and a performance meta-model according to the transmission system design requirement model, and establishing a component parameter meta-model of the transmission system according to the above meta-models, to generate a component parameter meta-model library, so as to realize integrated representation and transmission of component parameters; and constructing a design stage meta-model according to four stages of design requirement analysis-configuration design-performance evaluation-detailed design, and defining design files of each stage, which are used to transmit and trace the design data of each design stage of the transmission system;

[0014] Step 3: associating and mapping the design requirements in the transmission system design requirement model constructed in step 1 with each component in the transmission system, analyzing the function of each component, and combining the functions of the components to form multiple feasible transmission system schemes; and then constructing multiple transmission system component physical architectures according to the feasible transmission system schemes;

[0015] Step 4: first distributing the transmission ratio in the helicopter transmission system, estimating the weight and efficiency of the transmission system, excluding the transmission system schemes that do not meet the weight and efficiency index requirements of the transmission system according to the distribution results and the estimation results, and sorting the remaining transmission system schemes to select the optimal transmission system scheme;

[0016] In M-Design, the optimal transmission system weight and efficiency index are distributed to the components in the transmission system, a index-component mapping matrix is constructed, the coupling relationship and design constraint of the components are determined, multiple transmission system index distribution schemes are obtained, and the transmission system index distribution schemes that meet the corresponding index requirements of the weight and efficiency of the components are reserved;

[0017] Step 5: According to the transmission system index allocation scheme obtained in step 4, the corresponding transmission system physical architecture is established, and the component parameter meta-model constructed in step 2 is mapped to the transmission system physical architecture, and a component unit library in the form of a graph element is formed synchronously; the SysML file corresponding to the transmission system component physical architecture is converted in format by using the DOM tree method, and the transmission units of the complete transmission system and the transmission relationship between the units are obtained; finally, the helicopter transmission system transmission chain model is established according to the graph theory method;

[0018] Step 6: According to the AGMA standard, the transmission ratio of each stage gear in the helicopter transmission system transmission chain model is allocated, and according to the helicopter transmission system transmission chain model, the transmission ratio allocation result, and the constraint conditions in the transmission system design requirement model, the parameters of each component of the transmission system are designed, including skeleton design, gear design, shaft diameter design, spline design, bearing selection, coupling selection, and clutch selection;

[0019] The parameterized design results are packaged in the transmission system component parameter meta-model;

[0020] Step 7: The transmission system dynamics model is constructed, and the dynamic characteristics, strength, and life of the transmission system are evaluated by using the transmission system dynamics model; if the evaluation results all meet the corresponding target values of the indexes, step 8 is executed; otherwise, step 6 is returned to re-parameterize the design of each component of the transmission system;

[0021] Step 8: According to the parameterized design results of each component of the transmission system, an initial skeleton model of the transmission system is established; based on the initial skeleton model, CATIA is developed to construct a function body of each component by using the design parameters of each component as an input file, to drive CATIA to build a transmission system entity model, and to obtain basic design parameters, hierarchical structure, assembly relationship, and constraint relationship of each component of the transmission system according to the data structure form in the transmission system component meta-model; parameterized modeling and assembly are performed from bottom to top, and the transmission system pre-assembly body model is formed according to the constraint relationship, the assembly relationship, through the parameterized parts, the basic components, and the sub-assembly body, and the helicopter transmission system assembly body physical model is obtained by adjusting the component parameters, assembly constraints, and / or spatial positions in the model according to the requirements;

[0022] Step 9: A comprehensive database is established, the data files of each design stage are stored in the database, the data transmission relationship between each design stage is built, and the forward data transmission and reverse tracing of each design stage are realized.

[0023] Further, in the step 1, the function requirements include rotating speed steering, power transmission, steering matching, lubrication cooling, accessory drive, state switching, rotor brake, high-power tail rotor and clutch. The performance requirements include power, transmission efficiency, weight, strength, vibration and working condition variation compensation capability. The integrated interface requirements include overall layout, main reduction interface, tail rotor reduction interface, skeleton model, mounting form and external dimensions. The general quality characteristics and standardization requirements include reliability, maintainability, supportability, testability, safety and environmental adaptability. The test verification requirements include structure verification, vibration noise, service life, safety factor, dry running and bulletproof

[0024] Further, in the step 3, the function of each component is analyzed by using a black box use case activity analysis method, and a plurality of different feasible transmission system schemes are obtained, including the following steps.

[0025] Step 3.1: According to the design experience and the helicopter transmission system design manual, a transmission system black box activity diagram is constructed in M-Design; the components corresponding to the function requirements of the transmission system are determined, and the interaction relationship between the components is established, and a transmission system-component white box activity diagram is constructed.

[0026] Step 3.2: Function analysis of components:

[0027] A component black box activity diagram is constructed, the functions of the components are determined, and the component part composition is obtained according to the component function analysis, and the number of component parts and the connection relationship are determined.

[0028] Step 3.3: According to the function analysis of all components in step 3.2, the system-component-part white box activity diagram is obtained by combining the analysis results of different functions.

[0029] Step 3.4: According to the hierarchical relationship of system, component and component part in the system-component-part white box activity diagram, a plurality of product structure trees are generated, and each product tree structure corresponds to a different feasible transmission system scheme.

[0030] Further, in the step 4, the power distribution process of the helicopter transmission system is as follows:

[0031] Firstly, according to the historical design experience, the power of the rotor, tail rotor and its accessories under the helicopter flight task state and engine working state is determined.

[0032] Then, the number of reducers in the helicopter transmission system is determined, the power transmission path of the helicopter transmission system is determined according to the number of reducers, and the transmission ratio is distributed according to the minimum weight method / equal strength method.

[0033] Finally, based on the power demand of the helicopter transmission system power transmission path, the rotor, the tail rotor and its accessories, and the estimated efficiency of each speed reducer, the input power of each speed reducer in the helicopter transmission system is obtained.

[0034] The estimated efficiency of each speed reducer is estimated by the following method:

[0035] First, estimate the gear precision grade in the speed reducer according to design experience or reference existing configuration; then, according to the gear precision grade, query the mechanical transmission design manual to determine the estimated value of the transmission efficiency corresponding to different gear trains; sort the estimated efficiency of the speed reducer according to the different combination types of the gear trains in the feasible transmission system scheme obtained in step 3, and sort the corresponding transmission system scheme.

[0036] Further, in step 5, all transmission units converted in step 5 are mapped one by one with the transmission units in the component unit library using the graph theory vertex model method, forming a helicopter transmission system transmission chain basic architecture file; finally, the helicopter transmission system transmission chain basic architecture file is converted into a helicopter transmission system transmission chain model file by an automatic layout method and MindFusion tool, and a helicopter transmission system transmission chain model is established according to the helicopter transmission system transmission chain model file.

[0037] Further, in step 6, according to the commonly used transmission ratio range of various gear transmissions, and based on the WILLIS weight estimation method, the transmission ratio of each stage of gears on the transmission chain is determined with the goal of minimizing weight.

[0038] Further, in step 6, the parameters of gears, shafts, splines, bearings, couplings and clutches are designed in the helicopter transmission system transmission chain model environment;

[0039] The transmission system skeleton model is constructed, and the spatial positions of each transmission unit are adjusted and determined in the skeleton model construction environment, and the strength of the shaft and bearing is checked.

[0040] Further, in step 7, in the process of evaluating the dynamic characteristics of the transmission system using the transmission system dynamics model, the operating condition parameters and the parameters of each component in the transmission system are input into the transmission system dynamics model as input conditions, and the excitations introduced by the operating conditions are considered as inertial excitations or load excitations, and the dynamic characteristics of the transmission system under different operating conditions are analyzed; wherein, the component parameters include gear basic parameters and structure parameters of each component.

[0041] Further, in step 7, when constructing the power transmission system dynamics model, first, based on the finite element theory and the working characteristics of each component in the power transmission system, the power transmission system is divided into gear unit, shaft unit, bearing unit and case unit. The dynamics model of the gear unit and the bearing unit is respectively established; the dynamics model of the shaft unit is established by using the Timoshenko beam theory; the dynamics model of the case unit is established based on the finite element substructure method;

[0042] According to the physical connection relationship of each unit, the mass matrix, the stiffness matrix and the damping matrix in each unit dynamics model are respectively assembled to obtain the coupled dynamics model of the helicopter power transmission system.

[0043] Further, the step 9 comprises the following sub-steps:

[0044] Sub-step 9.1: a three-level data table is established, and the data files of each design stage are stored in the corresponding data table; wherein: the first-level data table comprises a design prototype model table, which is used for the basic data information management of the top model; the second-level data table comprises a design requirement model table, a function model table, a performance model table, a physical model table and a meta-model library table, which are used for storing the model file data of each design stage; and the third-level data table comprises a meta-model library, which is used for storing the design result data of the components, including the design parameters, geometric size parameters, material parameters and performance parameters of the component instances.

[0045] Sub-step 9.2: a version ID is set for the first-level data table, which is used for data management and design version tracing; and a foreign key ID is set for all the data tables, which is used for associating the data tables at all levels, so as to realize the forward data transmission of the design requirement model-component parameter meta-model-parameter design result-power transmission system physical model.

[0046] Sub-step 9.3: a reverse tracing mechanism is established based on the foreign key ID, so that the power transmission system physical model can be traced back to the original design requirement, and historical scheme query is supported.

[0047] The advantages of the application are:

[0048] The application presents a fragmentation phenomenon based on the existing helicopter transmission system digital design method, and most researches focus on performance model and physical model, without considering the design requirement model and function model. A helicopter transmission system digital prototype forward design method is proposed, which integrates "expression and mapping, coupling and transmission, modeling and optimization, verification and evaluation". The application adopts the model-based system engineering thought, uses the design requirement model to drive the whole design process of the transmission system, realizes the design requirement driven helicopter transmission system function-performance-physical model construction and iterative verification, and establishes the model driven transmission system forward design process based on the transmission system integrated design parameter representation technology of the meta model, solves the problems of low integration, poor interactivity, inconvenient model consistency maintenance, complex model dependency relationship and difficult data tracing in the transmission system design process, and improves the transmission system digital full-process design and full-cycle management capability. Specifically, the following advantages are included:

[0049] 1. Design quality improvement

[0050] (1) Precise demand mapping: in steps 1 to 4, the index-component mapping matrix is established according to the design requirements, ensuring that each design parameter meets the top-level demand (such as transmission efficiency ≥ 98%), avoiding the performance not meeting the standard caused by experience deviation in the traditional design using experience method.

[0051] (2) Parameterized collaboration: based on the linkage of gear parameterized design (step 6) and CATIA secondary development (step 8) based on AGMA standard, the size tolerance is automatically inherited, the assembly interference is detected in real time, and the assembly precision is improved by 40%.

[0052] 2. Multidisciplinary collaborative optimization

[0053] SysML and graph theory modeling (step 5): use SysML to describe the physical architecture, combine graph theory to build the transmission chain model, realize mechanical-electrical-control multidisciplinary coupling analysis, and reduce the time-consuming problem of cross-professional collaboration in traditional method.

[0054] Dynamics closed-loop verification: in step 7 of the application, the transmission system multi-body dynamics model is further established to realize the synchronous evaluation of vibration, thermal load and fatigue life, and improve the recognition rate of complex failure modes which cannot be covered by traditional single-point analysis method.

[0055] 3. Data-driven iteration

[0056] Parameter meta-model reuse (steps 2, 6 and 9): in the traditional method, the repeated modeling workload accounts for as high as 60%, while the component meta-model (such as gear, bearing) constructed in the application supports cross-project reuse, shortening the design cycle of new projects.

[0057] Version tracing (step 9): the database constructed in the application records the data files of each design stage in each iteration design, and establishes a reverse tracing mechanism, which can quickly locate the root cause of design defects, and overcomes the defects of traditional backtracking needing manual screening of logs and low efficiency.

[0058] In summary, the helicopter transmission system digital design method based on design requirement driving provided by the application realizes the paradigm shift from experience guidance to scientific decision making through model driving, data penetration and scheme optimization.

[0059] Additional aspects and advantages of the application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0060] The above and / or additional aspects and advantages of the application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0061] Figure 1 is a flow chart of a helicopter transmission system digital design method based on design requirement driving according to the application;

[0062] Figure 2 is a use case activity diagram of the cruise and hover black box constructed in step 3 of the application;

[0063] Figure 3 is a schematic diagram of the physical architecture and transmission chain model file conversion in step 5 of the application;

[0064] Figure 4 is Figure 3 a schematic diagram of the transmission system physical architecture in the application;

[0065] Figure 5 is a flow chart of transmission ratio optimization distribution of the transmission system in step 6 of the application;

[0066] Figure 6 is a schematic diagram of the helicopter transmission system dynamic characteristic evaluation process in step 7 of the application;

[0067] Figure 7 is a schematic diagram of the transmission system assembly input file form in step 7 of the application;

[0068] Figure 8 is an ER diagram of the comprehensive database constructed in step 9 of the application. DETAILED DESCRIPTION

[0069] The embodiments of the present application are described in detail below, which are exemplary and intended to explain the present application, and cannot be understood as a limitation of the present application.

[0070] Referring Figure 1 The embodiment provides a helicopter transmission system digital design method based on design requirement driving, and comprises the following steps.

[0071] Step 1, according to the helicopter transmission system design task requirement (i.e. transmission system type design requirement) and the helicopter transmission system design standard file (including but not limited to GJB2350, GJB70 and airworthiness standard), the function, performance, general quality characteristic requirement-transmission system design index system is formed, and the basic parameters and constraint conditions are provided for the transmission system scheme design. The specific method of step 1 is as follows:

[0072] Firstly, according to the transmission system design task requirement and the helicopter transmission system design standard, the helicopter transmission system design requirement model is constructed by means of DOORS, MDesign and other requirement modeling tools. The transmission system design requirement model mainly comprises: 1, function requirement: rotating speed steering, power transmission, steering matching, lubrication cooling, accessory transmission, state switching, rotor brake, high-power tail push, clutch and the like; 2, performance requirement: power, transmission efficiency, weight, strength, vibration, working condition variation compensation capacity and the like; 3, integrated interface requirement: overall layout, main reduction interface, tail push reduction interface, skeleton model, installation form, size and the like; 4, general quality characteristic and standardization requirement: reliability, maintainability, supportability, testability, safety and environmental adaptability; 5, test verification requirement: structure verification, vibration noise, life, safety coefficient, dry running, bulletproof and the like.

[0073] In the modeling process of the design requirement, the operation condition of the transmission system needs to be analyzed, the design requirement is decomposed according to the hierarchical relationship of the structure, the mapping relationship between the requirement entries and the corresponding verification indexes is established, the interface relationship between the transmission system and other components and the interface relationship between the internal parts of the transmission system are designed.

[0074] Step 2, according to the transmission system design requirement model, the transmission system design requirement meta-model, the function meta-model and the performance meta-model are constructed, and the parameter meta-model of each component in the transmission system is established according to the transmission system design requirement meta-model, the function meta-model and the performance meta-model, the component meta-model library is generated, so as to realize the integrated representation and transmission of the component parameters; and according to the design requirement analysis-configuration design-performance evaluation-detailed design four stages, the design stage meta-model is constructed, the design files of each stage are defined, and the design data of each design stage of the transmission system is transmitted and traced back. The specific method of step 2 is as follows:

[0075] (1) Constructing design phase meta-model: used to define the design files of each design phase, the basic identification parameters of each meta-model are defined, including design name, design number, design personnel, design date, and other basic identification information, and the data file format is defined, including SysML model file, semi-structured.Xml file, CAD / E model file of parts, and bill of materials table.

[0076] (2) Constructing design requirement meta-model: including semi-structured files (.xml) of itemized requirements, physical architecture model, and design constraint requirements.

[0077] Constructing functional meta-model: including transmission chain model, transmission system design parameters, parts design parameters, and multi-scheme evaluation data file.

[0078] Constructing performance meta-model: including constructing physical meta-model, mainly including detailed design model file, parts instantiation meta-model, and bill of materials; data composition realizes data flow between modules on the platform.

[0079] Based on the information of the constructed design requirement meta-model, performance meta-model, and functional meta-model, the parameter meta-model of each part in the transmission system is established, and the parameter integration representation and transmission of parts are realized. In the establishment process, the design parameters of each part of the transmission system are sorted out one by one according to the existing design standards of the helicopter transmission system. The inheritance method is adopted to avoid repeated definition of part attributes, and the part attributes are classified and summarized, such as geometry, material, and processing, so as to abstract the top-level base class describing the characteristics of the transmission system parts. The inheritance method is used to derive each level of part class, and the corresponding verification rules are written for each part class. The verification includes integrity verification and correctness verification. The integrity verification is used to constrain the attribute set that each part meta-model should contain; the correctness verification is used to limit the value range of each attribute in the attribute set. Finally, the interface for reading and writing part parameter meta-model is encapsulated for calling by other modules.

[0080] Based on the above process, the parameter meta-model library of various typical parts (such as gears, shafts, and bearings) of the helicopter transmission system is generated. In the process of digital design of the helicopter transmission system, the required part parameter meta-model can be directly queried from the part parameter meta-model library, and the encapsulated parameter meta-model reading and writing interface is used to complete the encapsulation, transmission, and analysis of the design parameters.

[0081] Step 3, according to the functional analysis of the helicopter transmission system design requirements in step 1, a plurality of feasible transmission system schemes are formed according to the functional combination of parts, and a physical architecture of the transmission system is constructed based on the M-Design tool to form a modularized expression of the transmission system parts composition diagram. The specific method of step 3 is:

[0082] The design requirements in the transmission system design requirement model are associated and mapped with each functional unit (such as cylindrical gear, double helical gear, bevel gear, planetary gear train, face gear, shaft, radial bearing, thrust bearing, coupling, clutch). The core of the functional analysis stage is to determine the functional decomposition and the relationship of each function, including the following sub-steps:

[0083] Step 3.1: According to the design experience and the helicopter transmission system design manual, build the transmission system black box activity diagram in M-Design. Then determine the corresponding components of each functional requirement of the transmission system, analyze the interaction between the components, and build the transmission system-component white box activity diagram.

[0084] Step 3.2: Functional analysis of components: first build the component black box activity diagram, determine the function of the component, then analyze the parts composition of the component according to the characteristics of the functional unit, from black to gray, further determine the number of parts and the connection relationship, realize from gray to white.

[0085] Step 3.3: According to the process of step 3.2, perform functional analysis on all components, and combine the analysis results of different functions to obtain the white box activity diagram of system-component-parts;

[0086] Step 3.4: According to the hierarchical relationship of system-component-parts in the system-component-parts white box activity diagram, build multiple traditional system architecture physical diagrams (product structure trees), such as Figure 4 As shown. Different analysis results and combination methods correspond to different transmission system architectures, and according to each transmission system architecture, multiple different feasible transmission system schemes are obtained.

[0087] The following is a specific example to illustrate the process of analyzing the function of each component using the black box use case activity analysis method. Guided by the system functional requirements, the cruise and hover top-level use cases are decomposed, and the system black box use case activity diagram is constructed, as shown in Figure 2The system is shown. First, determine if the system is malfunctioning, in normal working condition, engine input power, transmission system after deceleration and reversing drive main rotor, tail rotor and accessories (including generator, rotor speed sensor, etc.), the pilot controls the acceleration of the aircraft, steering flight, to the target point gradually reduce power transmission, and finally stable power transmission, hover delivery of goods and return. In the fault state, the type of fault needs to be analyzed, for example, if there is a vortex ring, the pilot needs to operate the aircraft to make the rotor generate greater tension, and at the same time, the pilot needs to operate the aircraft to make the rotor generate greater tension. The sinking trend in the vortex ring state is overcome by side flight or rear flight; After the tail rotor is hit by a bullet, the pilot stabilizes the heading by precise rudder operation. Redundant design can be adopted in the design, and backup link control can be used when the main control link is damaged; Gear tooth breakage, bearing overheating, transmission shaft fracture and other faults can be set up safety protection devices in the transmission system, such as friction clutch, which automatically cuts off power transmission when the gear tooth breaks, preventing the fault from spreading to the engine and other transmission components. Ensure that the functional units can cover the functional requirements, and new system requirements may be generated in this process, which needs to be iterated to complete the analysis of the functional units.

[0088] From the above analysis, the transmission system undertakes the functions of deceleration and reversing, power adjustment and distribution, driving accessories, safety protection, etc. In the subsystem use case, the functional units can be further refined, such as the transmission system main reducer, which undertakes deceleration and torque transmission. According to the positions of the engine and the rotor, the transmission form and the number of transmission stages are determined. Multiple engines realize power convergence and distribute power to the main rotor, tail rotor and accessories, etc. The final determination of the functional units usually needs multiple use cases to be iterated to complete the functional analysis, so as to cover all functional requirements of the helicopter transmission system. Since the cruise and hover use cases are the main operating scenarios of the helicopter transmission system, they are used to cover the functional requirements of the transmission system. The same functional requirement may correspond to multiple components, such as the reversing function corresponding to bevel gear set or face gear set. Therefore, multiple feasible transmission system schemes can be formed in the functional analysis stage.

[0089] Step 4, adopt the minimum weight method / equal strength method to distribute the transmission ratio, estimate the weight and efficiency of the transmission system; According to the distribution results and estimation results, exclude the transmission system schemes that do not meet the weight and efficiency indicators of the transmission system, and sort the remaining transmission system schemes, select the optimal transmission system scheme; Then assign the weight and efficiency indicators of the optimal transmission system scheme in M-Design to the components in the transmission system, construct the indicator-component mapping matrix, determine the coupling relationship and design constraints of the components, and obtain multiple transmission system indicator distribution schemes. The weight and efficiency of the components meet the corresponding indicator requirements. The specific process of step 4 is as follows:

[0090] The transmission system indicator allocation is to decompose different indicator types (quantitative indicators and qualitative indicators) using corresponding decomposition methods to form the overall technical indicators of the transmission system, and then conduct more fine-grained technical indicator decomposition to form a complete indicator tree for the transmission system from the overall, components to parts.

[0091] The power distribution method and process of the transmission system are as follows: first, analyze the helicopter flight mission and engine operating status, and determine the power of the rotor, tail rotor and its accessories under various conditions based on design experience; second, determine the basic structure of the helicopter transmission system, whether it is two reducers or three reducers; then, preliminarily analyze the power transmission path of the helicopter transmission system, and distribute the transmission ratio according to the minimum weight method; finally, based on the power transmission path, the power requirements of the rotor, tail rotor and other parts, and the efficiency of each reducer, the input power of each reducer can be decomposed.

[0092] Transmission Weight Estimation Process: The power-to-weight ratio (PWR) is often used as a performance metric to evaluate helicopter transmission system performance. This ratio is the ratio of the transmission system's input power to its weight. Given the same input power, a higher PWR indicates better transmission system performance. Understanding the impact of changes in design parameters on weight is crucial during the design process to minimize transmission weight. Similar to the transmission ratio decomposition process, the overall weight requirement is the control unit's requirement for the transmission system. Based on the established power-to-weight ratio ranges for each reducer, the weight of each reducer and shaft is estimated.

[0093] Given that the transmission components had not yet been parametrically designed, parameters such as the module, number of teeth, and shaft diameter were unknown. The RTL weight estimation method was used to estimate the transmission system mass. The RTL formula estimates weight based on the power transmission ratios between various components in the transmission system and the corresponding speeds. The weight of the shaft and reducer were estimated separately, and then the total weight of the entire transmission system was estimated.

[0094] Among them, the total weight prediction formula of the reducer is:

[0095] W gb =100.6T mrgb 0.7693 T trgb 0.079 n gb 0.1406

[0096] Where W gb is the total weight of the reducer, in kg; T mrgb =HP ttrmr / rpm tr The ratio of the power delivered to the main rotor to the rotor speed (dimensionless); T trgb =100(HP ttr / rpm tr ) is the ratio of the power delivered by the tail rotor to its rotational speed (dimensionless); n gb is the number of reducers.

[0097] The total weight of the transmission shaft is predicted by the formula

[0098] W dsh = 3.88 x 10 -3 T mrgb 0.4265 T trgb 0.0709 L dr 0.8829 n dsh

[0099] In the formula, W dsh is the total weight of the transmission shaft, in kg; L dr is the horizontal distance between the rotor hubs, in mm; and n dsh is the number of transmission shafts other than the rotor shaft.

[0100] The total weight of the transmission system is the sum of the weights of the reducers and the transmission shafts, and is calculated by the formula

[0101] W ds = W gb + W dsh

[0102] Transmission system efficiency estimation process: The efficiency of the transmission system depends on many factors, including lubricating oil, speed, gear geometry and surface roughness, bearing type, installation accuracy, and housing design. The efficiency of the transmission system is an important indicator of the transmission system, and the efficiency of the traditional system can be decomposed into the efficiency of each reducer.

[0103] Considering that the efficiency formula cannot be used at this stage, when estimating the efficiency, the designer needs to estimate the gear precision grade based on design experience or reference to existing configurations, and then find the estimated values of spur gears, helical gears, bevel gears, planetary gear trains, and other different transmission combination types through the mechanical transmission design manual. According to the transmission system efficiency corresponding to different combination types in the transmission system scheme, the corresponding transmission system scheme is sorted. Here, the efficiency is a preliminary estimate when the scheme is initially selected, and is not the true design value. The efficiency in the subsequent performance evaluation is derived according to the mechanical transmission design manual efficiency calculation formula.

[0104] According to the above allocation results and estimation results, transmission system schemes that do not meet the weight and efficiency indicators of the transmission system are excluded, and the remaining transmission system schemes are sorted to select the optimal transmission system scheme to re-allocate indicators. The weight and efficiency indicators of the transmission system are allocated to the corresponding components to construct an indicator-component mapping matrix, determine the coupling relationship and design constraints of the components, and obtain multiple transmission system indicator allocation schemes. According to the indicator accessibility, a reasonable and feasible transmission system indicator allocation scheme is formed. The indicator accessibility refers to the fact that the overall system indicators meet the design requirements, but after the transmission system weight and efficiency indicators are allocated to specific components, the design results of the components do not meet the corresponding indicator requirements. Such allocation schemes cannot be used for subsequent design and need to re-allocate the indicators of the transmission system to the components. The indicators include but are not limited to weight, reliability, efficiency, and life allocated to the components by the design requirements.

[0105] Step 5, first, according to the transmission system indicator allocation scheme obtained in step 4, a corresponding transmission system physical architecture is established, and the component parameter meta-model constructed in step 2 is mapped to the transmission system physical architecture to form a component unit library in the form of a graph element. The SysML file corresponding to the transmission physical architecture is parsed using the DOM tree method, where SysML is the language used by the M-Design tool at the bottom layer. Finally, a helicopter transmission system transmission chain model is established according to the graph theory method.

[0106] The transmission system physical architecture and the transmission chain model file format and form are as shown in Figure 3 The specific process of parsing the SysML file corresponding to the transmission physical architecture in step 5 is as follows:

[0107] Step 5.1: First, create a file and get the root node model of the file.

[0108] Step 5.2: In the directory structure, get the set of graph information through the root node, and find the part of the graph information with the type of internal block diagram in the set.

[0109] Step 5.3: In the labels contained in the graph information, find the bank+ID existing in the graph information obtained in step 5.2 by searching the pakeelement label set, and match the attributes in the label to find the information contained in the corresponding graph.

[0110] Step 5.4: According to the block label found in step 5.3, find the labels with umi:type as port, part, and connector as the containers, blocks, and connections in the output file.

[0111] Step 5.5: Match the first root node of type file, traverse to find other umitype as data id, position of port and textbox. According to the id, match the xmi:id value in the directory structure to find the corresponding name and type type, and according to the type, match the value of xmi:id in the pageelement tag to find the value of the current type type as the guid value in the container tag.

[0112] Step 5.6: Find the value of the tag of type part, traverse the tags of type part, port and textbox under this tag, and find the content of text in the textbox tag as the name of the reference content. Find the content with xmi:id attribute under the part tag, traverse the Owen tag with xmi:type attribute of part in the directory structure, find the type, id, name in this tag and construct the corresponding blocks object; traverse the next layer node under the xmi:type port tag, find the value corresponding to xmi:id, traverse the value corresponding to xmi:id in the root node, find the pageelement tag, find the tag with xmi:type attribute of port in the Owen tag as the params parameter information in the block.

[0113] Step 5.7: Find the tag of type connector, traverse the first node under this node with id information, traverse the root node of the file to find the value of type connector and connect tag, match to the appropriate node, get all the appropriate nodes and traverse the information in all the appropriate nodes, and take the node containing isconfig=true as the terminal connection, otherwise as the starting connection; according to the starting connection and the terminal connection, establish the connections object.

[0114] Step 5.8: According to the above process, find the points contains, connections and blocks object, and write a new xml file as an intermediate file.

[0115] The conversion of the intermediate format is realized through the above steps, so that the complete transmission unit, the inter-unit containing relationship and the connection relationship are obtained. By using a graph theory vertex model method, all transmission units are mapped with the transmission units in the part unit library one by one, to form a helicopter transmission system transmission chain basic architecture file. Since the transmission chain basic architecture file is constructed by using the SysML language, the parts and the connection relationship are expressed by using the ID and the field, and it is necessary to convert the transmission chain basic architecture file into a graph element form, so as to intuitively express the transmission chain basic architecture. In the embodiment of the application, the helicopter transmission system transmission chain basic architecture file is converted into a tsconf file required for constructing a transmission chain model by using an automatic layout method and a MindFusion tool, and the helicopter transmission system transmission chain model is established according to the tsconf file.

[0116] Step 6: According to the AGMA standard, the parameterized design of the transmission system parts (cylindrical gears, bevel gears, splines, shafts) is performed, and the selection of standard parts such as bearings and shaft couplings is performed. The design and selection results are packaged in the part meta-model, and the part parameters are transmitted and expressed through the instantiation of the meta-model. The specific process of step 6 is as follows:

[0117] According to the commonly used transmission ratio range of various gear transmission types, the transmission ratio is optimally distributed with the minimum weight as the target and based on the WILLIS weight estimation method, so as to determine the transmission ratio of each level of gear transmission on the transmission chain. Specifically, the optimization mathematical model of the transmission ratio distribution method is as follows:

[0118]

[0119] In the objective function, f(x) represents the transmission quality of each level of the main reducer, and x represents the transmission ratio of each level of the main reducer.

[0120] Design variables: x = [x1, x2, …, x i , x n ] represent the set of transmission ratios of each level;

[0121] Transmission ratio distribution constraint conditions:

[0122] Bevel gear: 1 < x i < 5

[0123] Cylindrical gear: 1 < x i < 5

[0124] Planetary gear: 2 < x i < 5

[0125] Double planetary gear: 5 < x i < 14

[0126] And, the first stage transmission ratio: 1 < x1 < 4, the second stage transmission ratio is greater than the first stage transmission ratio: x1 < x2.

[0127] According to the optimization mathematical model of the above transmission ratio distribution method, a main reducer transmission ratio distribution flow chart is drawn, as shown in the figure, so as to obtain the transmission ratio distribution result of the transmission system. Figure 5

[0128] According to the transmission chain model and the transmission ratio distribution result, the component parameterization design is carried out, which includes skeleton design, gear design, shaft diameter design, bearing selection, coupling selection and clutch selection. Among them, the gear design, shaft diameter design, spline design checking and bearing selection are preliminarily completed in the transmission chain modeling environment, and then the skeleton model is constructed, and the spatial position of each transmission unit is adjusted and determined in the skeleton model construction environment, and the strength of the shaft and the bearing and other transmission units is checked.

[0129] The basic parameter design criterion of the cylindrical gear is to ensure the tooth root bending fatigue strength condition to prevent tooth breakage, to ensure the tooth surface contact fatigue strength condition to prevent tooth surface pitting, and to ensure the anti-gluing ability of the gear to prevent tooth surface gluing.

[0130] The spline design object is involute spline, and rectangular spline is not considered. The basic method of cylindrical straight tooth involute spline parameter design is to select the modulus according to the reference diameter, and then calculate the involute spline parameters and the spline bearing capacity, and determine the final design parameters by judging whether the group of data meets the strength checking.

[0131] The bearing selection is to traverse the database according to the input parameters (installation shaft outer diameter D, rotating speed n) to filter out the bearing type that meets the condition, and then the user selects the appropriate type from the bearing type that meets the condition displayed on the software interface according to experience, and saves the selected type to the file.

[0132] The coupling selection is to traverse the database according to the input parameters (installation shaft outer diameter D, torque T, rotating speed n) to filter out the coupling type that meets the condition, and then the user selects the appropriate type from the coupling type that meets the condition displayed on the software interface according to experience, and saves the selected type to the file.

[0133] The above cylindrical gear design, spline design, bearing selection and coupling selection process are all known methods, and those skilled in the art can refer to the corresponding standard manual for design or selection.

[0134] ​Step 7: Construct a transmission system dynamics model and evaluate the dynamic characteristics, strength, and life of the transmission system. If the evaluation results meet the target values ​​(i.e., quantitative indicators) in the design requirements, perform parametric assembly and detailed design; if not, return to the parametric design stage for iterative design. The specific process of Step 7 is as follows:

[0135] The dynamic characteristics of the transmission system are analyzed using operating conditions and basic parameters of the transmission system components as input. When analyzing the system's dynamic characteristics under different operating conditions, the excitations introduced by the operating conditions need to be considered as inertial excitations or load excitations. Basic component parameters include gear parameters and transmission component structural parameters. To effectively simulate the coupling relationship between the transmission system and flexible components such as the casing, the transmission system is first divided into gear units, shaft units, bearing units, and casing units based on generalized finite element theory and the operating characteristics of each component. Force analysis is then performed on the gears and bearings, and corresponding dynamic models are established. A shaft unit model is established using Timoshenko beam theory, and a casing dynamic model is established using the finite element substructuring method. The mass, stiffness, and damping matrices in the unit dynamic models are assembled according to the physical connections between the units to obtain a rigid-flexible coupled dynamic model of the high-speed helicopter transmission system.

[0136] Specifically, the technical approaches for evaluating the dynamic characteristics of helicopter transmission systems are as follows: Figure 6 As shown in the figure, the main components include meshing stiffness and transmission error calculation, system dynamics modeling, and solution. First, during modeling, information about the shaft segments, gears, bearings, couplings, and operating conditions is obtained. Based on the established unit partitioning rules, the system's finite element node and element information is generated. Subsequently, the corresponding matrices and load vectors for each element are established, assembling the overall system stiffness, mass, and damping matrices, as well as the nodal load vectors.

[0137] Finally, by comprehensively considering the macro- and micro-geometric parameters of each gear pair, the dynamic meshing excitation of each gear pair is solved based on the tooth surface load contact analysis model. The Fourier series fast solution method is used to obtain the vibration response of the gear pair in the system, including the dynamic meshing force, tooth surface contact stress, dynamic load coefficient, bearing dynamic load, and vibration acceleration spectrum. Based on the finite element method, combined with the material properties of the gear components and the probabilistic distribution of failure forms, the influence of bearing parameters and gear meshing impact on the gear component life, bending safety factor, contact safety factor, bending stress, contact stress, and gear overlap is considered to explore the stress distribution on the gear tooth surface and realize the strength verification of the gear component tooth surface of the transmission system. Based on the finite element method, the force load conditions are obtained through the rigid-flexible coupling model of the helicopter transmission system and substituted into the finite element model of the shaft system and the finite element model of the casing. The bending stress, torsional stress, combined stress, safety factor, maximum deformation, and maximum stress are calculated to realize the strength verification analysis of the shaft system and the casing.

[0138] The shaft and gear fatigue strength calculation process includes the following three steps:

[0139] (1) Obtain the load spectrum. In the case of constant load, only the stress load spectrum needs to be calculated. The load spectrum of the load or stress is counted using the rainflow counting method, which converts the random load into a regular load segment.

[0140] (2) Obtain the S-N curve. The obtained stress load spectrum is imported into the finite element analysis software ANSYS or other software for fatigue life calculation to obtain the S-N curve of the part.

[0141] (3) Fatigue life analysis. Using the Miner theory, the fatigue life of each stress distribution under a certain load is first accumulated, then the total fatigue life of the part is obtained by superimposing the fatigue damage of multiple segments, and finally the fatigue strength is verified according to the design index or the corresponding standard.

[0142] According to the performance evaluation of the part design result parameters, if the evaluation result is satisfied, proceed to detailed design, design the spoke structure, tooth shape, etc. of the gear, the chamfer, relief groove, etc. of the shaft; if not, return to step 6 for iterative design according to the index-part mapping relationship.

[0143] Step 8, parameterized modeling and assembly through CATIA secondary development, convert the semi-structured parameterized file (part parameter result encapsulated in step 6) into an editable three-dimensional model file, and the designer can perform detailed design on the part details in CATIA. The specific method of step 8 is:

[0144] The first step of converting the transmission chain topology model to a spatial model is to establish an initial skeleton model. The initial skeleton model refers to the shafting that has not been completely adjusted in space through gear meshing, and at this time it cannot be called a spatial model of the transmission system. The generation of the initial skeleton model is the beginning of the completion of the entire spatial model design. The purpose of establishing the initial skeleton model is twofold. One is to meet the positioning constraints of the main rotor and tail rotor of the helicopter transmission system and the coaxial shafting constraints. The second is to visualize all the shafting and the transmission units on the shafting, making it easy to interactively layout the shafting in space to generate a complete transmission system spatial model. The coordinates of the main rotor and tail rotor positioning points are given in the design parameter stage, i.e. the default main rotor direction is vertical and the tail rotor shaft direction is x-axis.

[0145] First, the number and spatial positioning coordinates of the main rotor and tail rotor need to be obtained and visualized. In this embodiment, a red ball represents the input shaft end positioning point of the main rotor, and an arrow represents the power output direction of the system. The shafting of the main rotor and tail rotor: the main reducer shafting and the tail rotor shaft shafting belong to fixed shafting,

[0146] Secondly, the fixed shaft system and the transmission units on the shaft system are visualized according to the positioning constraints of the main rotor and the tail rotor and the coaxial system constraint. The components on the main reducer shaft satisfy the coaxial system constraint by ensuring that the x and y coordinates of each transmission unit on the shaft system are equal. The order of the transmission units on the shaft system is ensured by specifying the z coordinate, and no interference occurs between the transmission units. After the visualization of the fixed shaft system, the fixed shaft system is placed in the positioned shaft system list, and the remaining shaft system is placed in the unpositioned shaft system list.

[0147] Finally, the unpositioned shaft system is continuously looped and traversed, and the initial position of the unpositioned shaft system is gradually determined according to the gear meshing relationship with the positioned shaft system. The unpositioned shaft system is placed in the same plane (parallel to the XOY plane) as the positioned shaft system. Until all unpositioned shaft systems become positioned shaft systems, the generation of the initial skeleton model is completed, and the initial skeleton model serves as the basis for subsequent assembly.

[0148] Through secondary development of CATIA, automatic drawing of three-dimensional models is realized. First, the function body of different components is constructed with design parameters as input, and the constructed function body is used to drive CATIA to complete the construction of the solid model. According to the transmission chain model file obtained in step 5, the assembly relationship between each component of the transmission system is parsed, Figure 7 The assembly input file represents the assembly of a certain type of transmission system. The file format is consistent with the data structure of the transmission system, and the text file format is adopted. By parsing the assembly input file, the program can obtain the basic design parameters, hierarchical structure and assembly constraint relationship.

[0149] A bottom-up method is used for parametric modeling and assembly. According to the constraint relationship and assembly relationship, the parametric parts, basic assemblies and sub-assemblies are formed to form the transmission system assembly body model. Adjust the parameters in the transmission system assembly body model or the incomplete assembly constraints of the components. The spatial position is adjusted through interactive commands until the adjustment meets the design requirements, and the physical model of the helicopter transmission system assembly is obtained.

[0150] Step 9, establish a comprehensive database to store the data files of each design stage in the database, build the data transmission relationship between each design stage, realize the forward transmission and reverse tracing of the data of each design stage, and facilitate the design version management and tracing; the database has basic add, delete, modify and query functions. The specific method of step 9 is:

[0151] Substep 9.1: Establish a three-level data table to store the data files of each design stage in the corresponding data table, and set a version ID for the first-level data table to facilitate data management and design version tracing; set a foreign key ID for each level of data table. As shown in Figure 8 Each data table includes:

[0152] The first-level data table includes a design prototype model table, used for top model basic data information management. The main storage is the basic information management of the top model of the transmission system design. The version ID is the unique identification of the design prototype model table and is also the unique identification of the current design version. The purpose is to realize the search of multiple versions of the same design through the version ID, and to determine the design sequence by the version number.

[0153] The second-level data table includes a design requirement model table, a function model table, a performance model table, a physical model table, and a meta-model library table, used for storing design model file data at each stage,

[0154] The third-level data table includes a meta-model library, used for storing the design result data of the parts, including the design parameters, geometric size parameters, material parameters, and performance parameters of the part instances.

[0155] Sub-step 9.2: The data tables at each level are associated through the foreign key ID to realize the forward data transmission of the design requirement model-meta model-parameter design-physical model. The data at each stage is associated through the foreign key ID;

[0156] Sub-step 9.3: The reverse tracing mechanism is established based on the foreign key ID, so that the transmission system physical model can be traced back to the original design requirement, and the historical scheme query is supported. The designer can directly trace back to the original design requirement (such as querying the historical scheme through the version ID) according to the obtained transmission system assembly physical model.

[0157] Based on the above process, a comprehensive database covering the whole life cycle data of the helicopter transmission system is constructed, efficient data transmission, version control and tracing are realized, and the design collaboration efficiency and reliability of the helicopter transmission system are significantly improved.

[0158] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any skilled person in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application.

Claims

1. A digital design method for helicopter transmission system driven by design requirements, characterized by: The following steps are involved: Step 1: Based on the helicopter transmission system design task requirements and standards, standardized items are constructed to build a transmission system design requirement model. The transmission system design requirement model includes transmission system functional requirements, performance requirements, integration interface requirements, general quality characteristics and standardization requirements, and test and verification requirements. Each requirement includes basic design parameters and constraints. Step 2: Based on the transmission system design requirement model, construct the transmission system design requirement metamodel, function metamodel, and performance metamodel. Based on this, establish the transmission system component parameter metamodel and generate a component parameter metamodel library to achieve integrated component parameter representation and transmission. In addition, a design phase meta-model is constructed according to the four stages of design requirements analysis - configuration design - performance evaluation - detailed design, and the design documents of each stage are defined to transfer and trace the design data of each design stage of the transmission system; Step 3: Associate and map the design requirements in the transmission system design requirement model constructed in Step 1 with the components in the transmission system, analyze the functions of the components, and form multiple feasible transmission system solutions based on the component functions. Then, construct multiple physical architectures of the transmission system components based on the feasible transmission system solutions. Step 4: First, allocate the transmission ratios in the helicopter transmission system and estimate the transmission system weight and efficiency. Based on the allocation and estimation results, eliminate the transmission system solutions that do not meet the transmission system weight and efficiency index requirements, and sort the remaining transmission system solutions to select the optimal transmission system solution. In M-Design, the optimal transmission system weight and efficiency indicators are allocated to the transmission system components. An indicator-component mapping matrix is ​​constructed to determine the component coupling relationships and design constraints. Multiple transmission system indicator allocation schemes are obtained, and only those with component weight and efficiency that meet the corresponding indicator requirements are retained. Step 5: First, based on the transmission system indicator allocation scheme obtained in Step 4, the corresponding transmission system physical architecture is established. The component parameter metamodel constructed in Step 2 is mapped to the transmission system physical architecture, and a component unit library represented by graphic primitives is simultaneously formed. The SysML file corresponding to the transmission system component physical architecture is converted using the DOM tree method to obtain the transmission units of the complete transmission system and the transmission relationships between each unit. Finally, a transmission chain model of the helicopter transmission system is established using graph theory methods. Step 6: Assign the transmission ratios of each gear in the helicopter transmission system transmission chain model according to the AGMA standard. Based on the helicopter transmission system transmission chain model, the transmission ratio assignment results, and the constraints in the transmission system design requirement model, perform parametric design of each transmission system component, including frame design, gear design, shaft diameter design, spline design, bearing selection, coupling selection, and clutch selection. Encapsulating the parametric design results in a parametric meta-model of the transmission system components; Step 7: Construct a transmission system dynamics model and use the transmission system dynamics model to evaluate the dynamic characteristics, strength, and life of the transmission system; if the evaluation results meet the corresponding indicator target values, proceed to step 8; Otherwise, return to step 6 and re-parameterize the design of each component of the transmission system; Step 8: Based on the parametric design results of each component of the transmission system, an initial skeleton model of the transmission system is established; based on the initial skeleton model, secondary development is carried out using CATIA, and the design parameters of each component are used as input files to construct the function body of each component. The constructed function body drives CATIA to build a transmission system solid model, and according to the data structure form in the transmission system component metamodel, the basic design parameters, hierarchical structure, assembly relationship and constraint relationship of each component of the transmission system are analyzed and obtained; a bottom-up approach is used for parametric modeling and assembly, and according to the constraint relationship and assembly relationship, a pre-assembly model of the transmission system is formed through parametric parts, basic components and sub-assemblies. The component parameters, assembly constraints and / or spatial positions in the model are adjusted as needed to obtain the physical model of the helicopter transmission system assembly; Step 9: Establish a comprehensive database, store the data files of each design stage in the database, build a data transfer relationship between each design stage, and realize the forward transfer and reverse tracing of data in each design stage.

2. The method for digital design of a helicopter transmission system driven by design requirements according to claim 1, characterized in that: In step 1, the functional requirements include speed steering, power transmission, steering matching, lubrication and cooling, accessory transmission, state switching, rotor braking, high-power tail thrust and clutch; The performance requirements include power, transmission efficiency, weight, strength, vibration and working condition variation compensation capability; The integration interface requirements include overall layout, main reduction interface, tail thrust reduction interface, skeleton model, installation form and overall dimensions; The general quality characteristics and standardization requirements include reliability, maintainability, security, testability, safety and environmental adaptability; The test verification requirements include structural verification, vibration and noise, life, safety factor, dry operation, and ballistic resistance.

3. The method for digital design of a helicopter transmission system based on design requirements according to claim 1 or 2, characterized in that: Step 3 uses a black box use case activity analysis method to analyze the functions of each component to obtain multiple different feasible transmission system solutions, including the following steps: Step 3.1: Based on design experience and the helicopter transmission system design manual, construct a black-box activity diagram for the transmission system in M-Design. Identify the components corresponding to the functional requirements of the transmission system and establish the interaction relationships between the components. Based on this, construct a white-box activity diagram for the transmission system components. Step 3.2: Perform functional analysis on the components: Construct component black box activity diagrams, determine the functions of each component, analyze the component functions, obtain the component components, and determine the number of components and their connection relationships; Step 3.3: Perform functional analysis on all components according to the process in step 3.2, and obtain the system-component-part white box activity diagram based on the combination of different functional analysis results; Step 3.4: Based on the hierarchical relationship of systems, components, and parts in the system-component-part white box activity diagram, generate multiple product tree structures, each of which corresponds to a different feasible transmission system solution.

4. The method for digital design of a helicopter transmission system driven by design requirements according to claim 3, characterized in that: In step 4, the power distribution process of the helicopter transmission system is as follows: First, based on historical design experience, determine the power of the rotor, tail rotor and its accessories under the helicopter's flight mission status and engine operating conditions; Then, the number of reducers in the helicopter transmission system is determined, the power transmission path of the helicopter transmission system is determined based on the number of reducers, and the transmission ratio is allocated according to the minimum weight method / equal strength method; Finally, based on the power transfer path of the helicopter transmission system, the power requirements of the rotor, tail rotor and its accessories, and the estimated efficiency of each reducer, the input power of each reducer in the helicopter transmission system is decomposed and obtained. The estimated efficiency of each reducer is estimated using the following method: First, estimate the gear accuracy level in the reducer based on design experience or reference to existing configurations; then, query the mechanical transmission design manual based on the gear accuracy level to determine the estimated transmission efficiency corresponding to different gear trains; rank the estimated efficiency of the reducer based on the different combinations of gear trains in the feasible transmission system solutions obtained in step 3, and rank the corresponding transmission system solutions.

5. The method for digital design of a helicopter transmission system driven by design requirements according to claim 4, characterized in that: In the step 5, all the transmission units converted in the step 5 are mapped one by one with the transmission units in the component unit library using the graph theory vertex model method to form a basic architecture file of the helicopter transmission system transmission chain; finally, the helicopter transmission system transmission chain basic architecture file is converted into a helicopter transmission system transmission chain model file through the automatic layout method and the MindFusion tool, and a helicopter transmission system transmission chain model is established based on the helicopter transmission system transmission chain model file.

6. The method for digital design of a helicopter transmission system driven by design requirements according to claim 2, characterized in that: In step 6, the transmission ratios of the gears at each level in the transmission chain are determined with the goal of minimizing weight according to the commonly used transmission ratio ranges of various gear transmission types and based on the WILLIS weight estimation method.

7. The method for digital design of a helicopter transmission system based on design requirements as claimed in claim 6, characterized in that: In step 6, parametric design is performed on gears, shaft diameters, splines, bearings, couplings, and clutches in the helicopter transmission system transmission chain model environment; Construct a transmission system skeleton model, adjust and determine the spatial position of each transmission unit in the skeleton model construction environment, and check the strength of the shaft and bearings.

8. The method for digital design of a helicopter transmission system driven by design requirements according to claim 7, characterized in that: In step 7, in the process of evaluating the dynamic characteristics of the transmission system using the transmission system dynamics model, the operating condition parameters and the parameters of each component in the transmission system are input into the transmission system dynamics model as input conditions, and the excitation introduced by the operating condition is considered as inertia excitation or load excitation to analyze and obtain the dynamic characteristics of the transmission system under different working conditions; wherein, the component parameters include basic gear parameters and structural parameters of each component.

9. The method for digital design of a helicopter transmission system driven by design requirements according to claim 8, characterized in that: In step 7, when constructing the transmission system dynamics model, the transmission system is first divided into a gear unit, a shaft unit, a bearing unit, and a casing unit based on finite element theory and the working characteristics of each component in the transmission system; The dynamic models of the gear unit and the bearing unit are established respectively; the dynamic model of the shaft unit is established using the Timoshenko beam theory; The dynamic model of the casing unit is established based on the finite element substructuring method; According to the physical connection relationship of each unit, the mass matrix, stiffness matrix and damping matrix in the dynamic model of each unit are assembled respectively to obtain the coupled dynamic model of the helicopter transmission system.

10. The method for digital design of a helicopter transmission system based on design requirements as claimed in claim 9, characterized in that: Step 9 includes the following sub-steps: Sub-step 9.1: Create a three-level data table and store the data files of each design stage in the corresponding data table; where: The first-level data table includes the design prototype model table, which is used for basic data information management of the top-level model; The secondary data tables include the design requirement model table, function model table, performance model table, physical model table and meta-model library table, which are used to store model file data at each stage of design. The third-level data table includes a meta-model library, which is used to store component design result data, including design parameters, geometric size parameters, material parameters and performance parameters of component instances; Sub-step 9.2: Set a version ID for the primary data table for data management and design version traceability. Set foreign key IDs for all data tables to link data tables at all levels, enabling forward data transfer from the design requirement model to the component parameter metamodel, to the parameter design results, and finally to the transmission system physical model. Sub-step 9.3: Establish a reverse traceability mechanism based on the foreign key ID so that the transmission system physical model can be traced back to the original design requirements and support historical solution queries.

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