Gear Structure Research Articles

Structural Design and Kinematic Modeling of Highly Biomimetic Flapping-Wing Aircraft with Perching Functionality

Birds use their claws to perch on branches, which helps them to recover energy and observe their surroundings; however, most biomimetic flapping-wing aircraft can only fly, not perch. This study was conducted on the basis of bionic principles to replicate birds’ claw and wing movements in order to design a highly biomimetic flapping-wing aircraft capable of perching. First, a posture conversion module with a multi-motor hemispherical gear structure allows the aircraft to flap, twist, swing, and transition between its folded and unfolded states. The perching module, based on helical motion, converts the motor’s rotational movement into axial movement to extend and retract the claws, enabling the aircraft to perch. The head and tail motion module has a dual motor that enables the aircraft’s head and tail to move as flexibly as a bird’s. Kinematic models of the main functional modules are established and verified for accuracy. Functional experiments on the prototype show that it can perform all perching actions, demonstrating multi-modal motion capabilities and providing a foundation upon which to develop dynamics models and control methods for highly biomimetic flapping-wing aircraft with perching functionality.

Effect of bionic texture on the lubrication efficiency and mechanical efficiency loss for rotating gears

In order to enhance lubrication effectiveness and transmission efficiency in gear transmission, it is imperative to minimize mechanical efficiency losses and frictional wear of the gears during the lubrication process. This paper proposes a bionic design scheme for the tooth surface structure of gears based on the surface texture of bay scallop shells, considering the operational conditions within the gearbox. Firstly, the microstructure of the bay scallop shell surface is analyzed, and a bionic gear mapping model based on the bay scallop shell surface is established. Meanwhile, the oil coverage rate and convective heat transfer coefficient of gear surfaces with different textures was analyzed using finite element analysis. The results showed that the oil coverage rate of gear tooth surfaces with bionic fringes surpassed that of conventional gear lubrication. Thirdly, based on the jet lubrication test calculation, it is proposed that the bionic gear exhibits a lower mechanical efficiency loss and wear mass compared to conventional gears, while the mechanical efficiency loss and wear mass of arc groove gear type lower than that of vertical groove gears. Finally, the optimal structure of the arc groove gear was predicted through orthogonal data analysis, and the validity of the data prediction was verified through experiments and simulations. The optimal combination of texture parameters for the arc groove gear is as follows: a texture depth of 225 μm, a texture width of 275 μm, a texture interval of 275 μm, and a texture length of 1600 μm. As a result, compared with the conventional gear, the lubrication efficiency of the optimized gear is increased by 41.98%, heat dissipation efficiency increased by 32.21%, and mechanical efficiency loss is decreased by 89.39%, the wear mass is reduced by 74.33%.

Research on the surface modification and microstructure evolution during gear profile grinding based on cellular automaton

The matrix structure of high-strength gears mainly comprises martensite with high stacking fault energy. The dominant mechanism of microstructure evolution in the surface layer during profile grinding is continuous dynamic recrystallization. However, the understanding of continuous dynamic recrystallization structure evolution during gear profile grinding remains limited. In this study, a predictive model based on cellular automaton for martensite structure evolution during gear profile grinding is proposed. Coupled with the finite element method, the microstructure evolution prediction of high-strength steel gears in profile grinding is conducted. The proposed model demonstrates good consistency with experimental data in calculating the proportion of low angle grain boundaries during grinding process. By combining experimental and theoretical prediction results, the mechanism of the influence of grinding depth on grain refinement in surface layer during gear profile grinding is elucidated. The dislocation density increases with the increase of grinding depth, leading to the generation and transformation of more subgrains. By analyzing the grain size and the proportion of subgrain boundaries, an optimal grinding depth threshold under dry grinding conditions is determined. This study provides valuable insights into the continuous dynamic recrystallization structure evolution during gear profile grinding process.

Vibration Analysis of the Double Row Planetary Gear System for an Electromechanical Energy Conversion System

Electromechanical energy conversion systems (EECSs) are widely used in vehicles to combine the double-row planetary gear system (DRPGS) with high transmission efficiency and high-performance motors. The integrated structure of the ring gear and motor rotor have put forward higher demands for the vibration performance of the DRPGS. This paper establishes a multibody dynamic model of the DRPGS for an EECS. Based on the kinetic relationship between the gear pairs and bearing components, the dynamic equations of the DRPGS are derived. The DRPGS model is simulated under different operating conditions. The results are compared to reveal the relationships between the system vibration and the operating speed and load torque. The typical conditions are selected to study the effectiveness of the structural parameters in reducing the DRPGS vibrations. The structural parameters, including the bearing clearance, the ball numbers, the gear tooth modification amount, and length, are comprehensively discussed. Several suggestions for the low-vibration design of the DRPGS for the EECS are provided.

Vibration Qualification Campaign on Main Landing Gear System for High-Speed Compound Helicopter

Vibrations in helicopters have strong implications for their performance and safety, leading to the increased fatigue of components and reduced operational efficiency. As helicopters are designed to land on several types of surfaces, the landing gear system dissipates the impact on the ground and maintains stability during landing and take-off. These vibrations can arise from a variety of sources, such as aerodynamic loads, mechanical imbalances, and engine instabilities. In the present work, the authors describe the vibration qualification process of the main landing gear tailored to fast helicopters within the Clean Sky 2 Racer program. The method entails devising preliminary load sets that deform the structure in its key excited mode shapes to assess stresses and address the experimental campaign. A full-scale prototype model is then tested for sine sweep and random vibrations as per the Airbus Helicopter requirements in order to reach the final qualification and acceptance stage. Although the discussion centers on a landing gear structure, the described process could be extended to other critical equipment as well.

Research on the Hobbing Processing Method of Marine Beveloid Gear

Due to the particular structure of the beveloid gear, it cannot be directly hobbed by an ordinary gear hobbing machine. The existing processing method is complex and has a high cost. Therefore, the mass production and industrialization of beveloid gears are limited. To improve the machining efficiency and accuracy of processing beveloid gears, we proposed a hobbing method via the modification of ordinary hobbing machines. At first, we completed the derivation and calculation of the relevant processing parameters of the beveloid gear based on the study of the structural characteristics of the beveloid gear and the principle of hobbing machining. Then, we proposed and designed a beveloid gear hobbing method, and the modification of the ordinary hobbing machine was completed by using a hanging wheel mechanism in synchronous belt type. Finally, we completed the actual hobbing of the beveloid gear, and the feasibility of the proposed method was verified. After that, we analyzed the machining error of the trial-produced beveloid gear; the results showed that the accuracy of the trial-produced beveloid gear met the 6-level standard, which also verified the accuracy of the proposed method.

Gear error control and response of electric vehicle transmission gearing based on gear trimming

The lightweight development of electric vehicle motors is a prominent future trend, with the challenge of transmission vibration and noise acting as a key bottleneck that limits the enhancement of power and speed in electric vehicle drive systems. The noise generated by electric vehicle transmissions is primarily associated with the transmission system and gear structure. In line with this, the present study proposes an analysis of transmission error and response mechanisms through gear modifications. The research delves into the analysis of gear deformation and error generation characteristics. It further investigates methods for parametric equation modeling, tooth profile modification, deformation imprint analysis, and vibration response modeling to examine excitation response analysis and noise reduction techniques pertaining to transmission errors. The findings demonstrate that, under 40 % torque, the shaped gear exhibited a maximum reduction in transmission error of 34.2 %, resulting in an overall error improvement of over 5.7 %. Moreover, the maximum error difference after tooth profile and tooth direction shaping exceeded 2 %. The gear-shaping-based electric vehicle transmission showcased favorable economic and technical performance, while its excitation response mechanism provided valuable guidance for mass production. Overall, these results highlight the significance of analyzing transmission errors through gear modifications in achieving lightweight electric vehicle motors. By addressing transmission vibration and noise issues, this research contributes to overcoming limitations and promoting advancements in power and speed within electric vehicle drive systems.

Design and Optimization of Halbach Magnetic Gear

This article proposes a new structure to enhance the torque and torque density of permanent magnet gears. The outer magnet is designed with a dual-layer permanent magnet configuration, where the first layer adopts a Halbach array, and the other layer utilizes a conventional radial magnetization structure. With the optimization objectives defined as maximum torque and torque density, and guided by parameter sensitivity, optimization analysis was conducted using response surface method and multi-objective genetic algorithm. The optimized parameters were determined, and finite element simulations were performed to validate the optimization results. The result indicate a 22.22% increase in torque and a 27.42% increase in torque density compared to the previous the traditional magnet gear. The performance of the proposed new structure of magnetic gear has shown significant improvement.

Modeling of a Ti/NiTi spring-blade gear for space micro–vibration isolation

Space pointing mechanisms are crucial in space scientific experiments and observations. Since the precision of such mechanisms is highly susceptible to micro–vibrations due to environmental disturbances and inherent defects, isolating micro–vibrations is important. A low rotational stiffness spring-blade gear installed on the output shaft of the stepper motor can isolate micro–vibrations due to the motor’s discontinuous rotation. However, a quantitative performance description is still lacking. In this paper, a rotational stiffness model for the spring-blade gear made of titanium and nickel–titanium-based shape memory alloy is established and experimentally validated. A vibration transmissibility model is developed, revealing the relationships among the layout, material properties, structural parameters, external loads, rotational stiffness, and vibration transmissibility of the spring-blade gear. This paper can be used to design and optimize the spring-blade gear, predicting the isolation and suppression capability against micro–vibrations at different frequency ranges. The optimal gear structure can be obtained according to vibration isolation requirements, load, and installation constraints to achieve the predetermined vibration isolation effect. This study can ensure the space pointing mechanisms operate with high precision and stability by attenuating space micro–vibrations effectively, improving the quality of signal acquisition and observation accuracy.

Gear walk instability caused by brake-disc friction characteristics

A multi-body dynamic rigid-flexible coupling model of landing gear is established to study the gear walk instability caused by the friction characteristics of the brake disc. After validating the model with the experimental results, the influence of the landing gear structure and braking system parameters on gear walk is further investigated. Among the above factors, the slope of the graph for the friction coefficient of the brake disc and the relative velocity of brake stators and rotors is the most influential factor on gear walk instability. Phase trajectory analysis verifies that gear walk occurs when the coupling of multiple factors causes the system to exhibit an equivalent negative damping trend. To consider a more realistic braking case, a back propagation neural network method is employed to describe the nonlinear behavior of the friction coefficient of the brake disc. With the realistic nonlinear model of the friction coefficient, the maximum error in predicting the braking torque is less than 10% and the effect of the brake disc temperature on gear walk is performed. The results reveal that a more negative friction slope may contribute to a more severe unstable gear walk, and reducing the braking pressure is an effective approach to avoid gear walk, which provides help for future braking system design.

Large gear structure assembly method based on uncalibrated image visual servo guidance.

The reliability of the transmission system hinges significantly on the assembly quality of its main component, the large gear structures. However, the traditional approach of employing manual lifting presents a host of challenges, such as high assembly complexity and lowered efficiency, rendering the overall assembly process notably arduous. In this study, a large gear structure assembly method based on uncalibrated image visual servo guidance is proposed. Comprising three modules, the approach involves constructing a task function for projective homography, estimating the image Jacobian matrix, and designing an adaptive servo controller. This methodology facilitates the mapping of changes in gear images to the motion of the end-effector in the parallel mechanism. Consequently, the system dynamically guides the end-effector to achieve the required attitude adjustments in the gear assembly in response to changes in the image features. Experimental results demonstrate that the method proposed surpasses alternative approaches, simultaneously exhibiting a significant enhancement in assembly efficiency. The method has a wide application prospect in the field of automated assembly of large gear structures.

Design and Analysis of a Novel Wave Energy Harvester

A novel wave energy harvester (WEH) that can recover energy in the direction of heave, sway, and surge is designed under the background of low recovery efficiency and complex installation of the existing wave energy harvester. The harvester consisted of four main components: energy input module, energy transfer module, energy conversion module, and energy store module. In the paper, to convert more wave energy into electrical energy and improve the energy conversion efficiency of WEH, the motion transfer module is divided into vertical and horizontal motion transfer modules, which are used to harvest vertical and horizontal wave energy, respectively. The vertical motion transfer module combined with the ball screw structure, planetary gear structure, and one-way gear units ensure the generator has high speed. The horizontal motion transfer module is mainly composed of three uniformly distributed one-way gear units, ensuring collect the wave energy in all horizontal directions. The dynamic model of the harvester is established, and the simulation experiment is carried out under wave conditions with periods of 2 s, 2.5 s, and 3 s, respectively. The simulation results show that when the wave period is 2[Formula: see text]s, 2.5 s, and 3 s, the corresponding energy conversion efficiency of the WEH is 66.7%, 60.9%, and 57.1%, respectively. The proposed study provides a theoretical reference for modeling similar WEHs and can effectively balance energy supply and demand and further support the global agenda of UN-2030 for sustainable development, especially SDG-7.

The Effect of Landing Gear Dimension Variation on the Static Strength and Dynamic Response of Unmanned Aerial Vehicle (UAV)

This research discusses the static and dynamic analysis of the landing gear structure of an unmanned aerial vehicle (UAV). The dimensional study is conducted to investigate the effect of landing gear dimension variation on UAVs’ static strength and dynamic response. Static analysis was performed with Finite Element Method (FEM) software. The dynamic response of the UAV is analyzed using a single-degree-of-freedom vibration model. Based on the static analysis results, the landing gear stiffness and strength can be increased by increasing the width and decreasing the height, radius, and length of the landing gear structure. The energy dissipation in the dynamic analysis is described by hysteresis and viscous damping model. The dynamic response simulation results show that the increase in the stiffness of the landing gear leads to an increase in force transmission and acceleration of the UAV. Furthermore, the UAV response using the viscous damping model can accurately predict the system’s response with the hysteretic damping model for small damping conditions. However, the deviation was observed for large damping conditions.

Effect of Metallic Coatings on the Wear Performance and Mechanism of 30CrMnSiNi2A Steel.

The finger lock structure of aircraft landing gear is prone to wear and failure during repeated locking and unlocking processes, which is disastrous for the service safety of the aircraft. At present, the commonly used material for finger locks in the industry is 30CrMnSiNi2A, which has a short wear life and high maintenance costs. It is crucial to develop effective methods to improve the wear resistance of 30CrMnSiNi2A finger locks. This work explores the wear resistance and wear mechanisms of different metallic coatings such as chromium, nickel, and cadmium-titanium on the surface of a 30CrMnSiNi2A substrate. The effects of load and wear time on the wear behavior are also discussed. The results indicated that the wear resistance of the chromium coating was the maximum. When the load was 80 N and 120 N, the wear mechanisms were mainly oxidation and adhesive. For greater loads, the wear mechanism of the coating after failure was mainly abrasive and oxidation, and the wear was extremely severe. When the load was 80 N, for a greater loading time, the wear mechanisms were mainly oxidation and adhesive.

Transmission Scheme Design of Gearbox for 15MW Offshore Semi-direct-driven Wind Turbine

In order to further improve the reliability of wind turbine operation, reduce manufacturing, installation and maintenance costs, and make the size of the gearbox further reduced, in this paper, the gear box design of 15MW offshore semi-direct-driven wind turbine is studied. First, analyze the development trend and demand, draw up the basic transmission plan, then, carry on the gear structure design, use the software modeling, the motion analysis and carry on the check, the life analysis, finally, the design of sealing mode, design box, end cover structure, determine the fastener, connection, design of dust-proof program and design of lubrication. This reduces the weight and volume of the main engine of the medium-speed transmission mechanism of the wind turbine. The obvious benefits are lower overall load, lower difficulty in manufacturing, transportation and installation, lower cost and controllable technology, the market prospects are broad and competitive.

Dynamic characteristics of the ring gear structure of two-stage plastic planetary reducers

Dynamic characteristics of the ring gear structure of two-stage plastic planetary reducers

Fiber Bragg Grating Bonding Characterization under Long-Period Cyclic Loading

The Smart Landing Gear system to be developed in the framework of the ANGELA project provides the strain measurements on landing gear structure at landings, and this system should be maintained efficiently under operational conditions. It is intended to assess the relevance of Fiber Bragg Gratings for in-flight testing. To assess the capabilities of the FBG bonding and to analyze the strain transmission conditions from the host structure to the FBG through the bonding layer during the operational phases of landing gears, a long-period cyclic loading test campaign on the bonding layer itself was performed. The primary objective of this fatigue-like test was to prove the ability of FBG sensors to withstand the operational life-cycle of landing gear while providing the same strain transfer function throughout the entire cycle; the secondary objective was to select the most suitable fiber-coating and bonding agents for this application. This document describes the execution and results of the fatigue-like test, intended as a preparatory test campaign to support the preliminary design activities of the Smart Landing System.

Research on the calculation method of windage power loss of aviation spiral bevel gear and experiment verification

This paper proposes a method for calculating windage power losses of spiral bevel gears by dividing the losses into the sum of windage effects on tooth surface, toe/heel, conical surface, and circumferential surface, according to the gear structure. A calculation model for each component of windage losses is established based on the basic equation of fluid dynamics. Subsequently, a windage loss measurement test bench is developed, and a windage moment measurement method is proposed for experimental spiral bevel gears. The individual contributions of each windage loss component are calculated. The results of the calculations indicate that the gear speed is the primary factor that impacts windage losses, with the windage power loss being proportional to the 2.96th power of gear speed. Gear geometry parameters and the jet flow impacting the tooth surface are also significant factors, followed by the hub and spoke values in the wheel body parameters. The findings also show that an increase in lubricating oil content in oil-gas two-phase flow can significantly increase windage losses. Finally, a comparison between the dimensionless windage calculation values and the experimental measurement values demonstrates good agreement. This paper provides theoretical guidance for future research aimed at reducing windage power loss and improving the efficiency of aviation gear transmission.

A Self-Attention Integrated Learning Model for Landing Gear Performance Prediction.

The landing gear structure suffers from large loads during aircraft takeoff and landing, and an accurate prediction of landing gear performance is beneficial to ensure flight safety. Nevertheless, the landing gear performance prediction method based on machine learning has a strong reliance on the dataset, in which the feature dimension and data distribution will have a great impact on the prediction accuracy. To address these issues, a novel MCA-MLPSA is developed. First, an MCA (multiple correlation analysis) method is proposed to select key features. Second, a heterogeneous multilearner integration framework is proposed, which makes use of different base learners. Third, an MLPSA (multilayer perceptron with self-attention) model is proposed to adaptively capture the data distribution and adjust the weights of each base learner. Finally, the excellent prediction performance of the proposed MCA-MLPSA is validated by a series of experiments on the landing gear data.

Crack propagation life of high-speed aviation gear

The most common fault in aviation power transmission systems is the fatigue fracture of gears, which seriously affects the reliability and safety of the structure. The aim of this study is to analyze the crack propagation path (CPP) to predict the crack propagation life (CPL) of gears. The location of crack initiation is determined by statics analysis and building a gear pair model in ANSYS software. A FEM model of the gear pair with a crack is created, the Stress Intensity Factor (SIF) at the crack tip is calculated, and the influence of the initial state of the crack on the SIF is analyzed. FRANC3D is adopted to obtain the CPP and CPL. Based on the obtained results, the impact of gear structure parameters on CPL is discussed. With the reduction of flange thickness, web thickness, and root radius, the CPL gradually decreases.