Hao Dong

An effective dynamic wear prediction model for helical gear pairs considering tooth surface modification is established by deeply integrating the Archard wear model, the loaded tooth contact analysis (LTCA) model, and the lumped-parameter dynamic model of helical gear pairs. The dynamic contact stress can be obtained by introducing the dynamic mesh force into the LTCA model. By substituting the dynamic contact stress, relative sliding distance, and dynamic wear coefficient into the Archard wear model, the wear depth can be determined. A cyclic tooth-surface-updating strategy is employed during the wear prediction process. The impacts of input speed and input torque on contact stress and tooth surface wear distribution are discussed. The changes in mesh stiffness, dynamic contact stress, and dynamic responses of unmodified and modified helical gear pairs before and after wear are investigated.

1 IntroductionTo prevent gear transmission failure, improve transmission efficiency, and extend service life, Standard straight bevel gear transmission systems typically employ splash lubrication u...

This article investigates the multiphysics coupling mechanism among Dynamic Thermal Elastohydrodynamic Lubrication (DTEHL), Load Tooth Contact Analysis (LTCA), and system dynamics in a Closed Differential Herringbone Gear Transmission System (CDHGTS). Based on gear meshing theory, ring gear flexibility, and rough surface contact, a dynamic contact lubrication model is developed using thermoelastic fluid dynamic lubrication theory. A gear heat transfer model integrating heat transfer and flexible deformation is established to capture dynamic thermal variations at each ring gear node. By coupling the DTEHL model, heat transfer model, and LTCA model, a nonlinear dynamic model incorporating flexible-tribo coupling is constructed. The nonlinear dynamic response of the CDHGTS under DTEHL conditions is analyzed, focusing on the influence of ring gear flexibility on system vibration. Furthermore, nonlinear dynamic behavior induced by ring gear flexibility, friction coefficient, and damping coefficient is examined. The proposed model is validated through bench vibration experiments. The study refines dynamic modeling and analysis methods for herringbone gears, offering theoretical guidance for evaluating the impact of coupled engineering factors on gear dynamics.

To systematically clarify the migration and evolution mechanisms of metallic particles in the solid-liquid-gas three-phase flow field of a helicopter intermediate reducer under splash lubrication, this study innovatively develops a three-phase numerical model based on the CFD-DPM framework, and establishes a high-precision oil-churning visualization test rig for experimental validation via high-speed imaging technology. Under the baseline operating condition (gear rotational speed of 1500 r/min, dimensionless oil immersion depth λₕ=6.78), the effects of multiple hydrodynamic forces (gravity, pressure gradient force, virtual mass force, Magnus lift, and Saffman lift) on particle trajectories and dynamic responses are comprehensively evaluated. Meanwhile, comparative analyses are conducted to quantify the regulatory effects of particle density (intrinsic property variation) and initial release location (meshing region, spalling region, sidewall/bottom) on migration behavior. Numerical results reveal that the pressure gradient force and virtual mass force dominate macroscopic particle transport: the former prolongs the quasi-steady stage by 40%–50%, while the latter accelerates particle velocity decay to near-zero within 0.3–0.5 s. In contrast, the Saffman lift and Magnus lift play secondary roles, mainly inducing high-frequency velocity fluctuations (velocity perturbation amplitude ≤15% for Saffman lift) and exhibiting strong medium dependence (Magnus lift doubles particle migration distance in the gas phase but is negligible in the oil phase). Increasing particle inertia significantly weakens flow-following capability, and the particle velocity response intensity follows the order: meshing region > spalling region > sidewall/bottom. Visualization experiments verify a complete particle transport cycle inside the gearbox (extrusion from the meshing zone-airborne flight-wall collision-gravity-driven return), which is in good agreement with numerical predictions. Further experimental results show that increasing the rotational speed from 100 to 400 r/min significantly enhances oil splash height and particle adhesion on the top and side walls. At a high immersion depth (λₕ=11.86), intense turbulent splashing leads to global dispersion of the oil-particle mixture; at a low immersion depth (λₕ=1.70), particle motion is dominated by local entrainment with weak wall retention. Additionally, as the particle volume fraction increases from 0.1% to 1.0%, the oil-particle mixture exhibits a pronounced thickening effect, suppressing oil splashing and enhancing particle deposition. These findings provide robust theoretical support and technical guidance for the optimization of splash lubrication design and reliability assessment of helicopter transmission systems.

Elliptical gears are widely used in the fields of aerospace and automation equipment due to their excellent variable speed characteristics and compact structure. To reveal the control mechanism of phase angle on the motion characteristics of two-stage elliptical gear transmission system (TSEGTS) and improve its stability under variable speed loading, this paper proposes a modeling method that integrates two-dimensional tooth profile envelope method and image processing technology to extract tooth profile and analyze system motion characteristics. By introducing the fluctuation coefficient as a stability indicator, the system studied the effects of phase angle, input speed, and load torque on angular velocity, angular acceleration, and torque. The results indicate that the phase angle has a significant periodic modulation effect on the motion characteristics of the system. The angular velocity and acceleration of intermediate shaft B and output shaft C, as well as the torque of output shaft C, exhibit a distribution with 90° as the axis of symmetry within the range of 0°–180°. The average torque fluctuation coefficients of input shaft A and intermediate shaft B in the range of 0°–90° are 4.02 and 3.03, respectively, which are significantly higher than the 3.46 and 1.99 coefficients in the range of 90°–180°. As the input speed increases from 5π to 20π rad/s, the torque fluctuation coefficients of shafts A, B, and C increase from 2.87, 1.37, and 0.53 to 22.54, 14.19, and 8.43, respectively. When the load torque increases from 2 to 8 N·m, the fluctuation coefficients of the three axes decrease from 11.33, 7.12, and 4.22 to 3.51, 1.91, and 1.05, respectively. The increase in load torque effectively suppresses fluctuations and improves meshing stability. The experimental and simulation results are consistent, verifying the effectiveness of the model. The research results can provide theoretical basis for parameter optimization and dynamic performance control of TSEGTS.