This paper investigates the transient elastohydrodynamic lubrication (EHL) characteristics of steel- polyamide involute short-tooth profile-shifted gears. A novel gear structure combining tooth shortening with positive profile modification is proposed to eliminate tip interference, enhance load-carrying capacity, and improve lubrication stability. A transient EHL numerical model is developed considering the real tooth geometry and time-varying meshing conditions. The model couples the generalized Reynolds equation and the elastic deformation equation, and employs the finite difference method combined with a multigrid iterative algorithm to achieve efficient convergence and accurately capture the transient pressure and film thickness distribution within the contact zone. Validation against the Dowson-Higginson empirical formula shows that the relative error of the minimum film thickness remains between 1.87% and 5.89%, confirming the model's accuracy and numerical stability.
An isothermal transient EHL analysis is carried out for the steel-polyamide standard gear pair to study the influence of rotational speed, applied load, and pressure angle on the minimum film thickness and the maximum pressure. Furthermore, the lubrication characteristics are comparatively analyzed under four different transmission configurations: positive drive, negative drive, standard gear drive, and equivariant profile shifted gear drive. For the short-tooth positive profile-shifted gear, transient analyses are conducted at three key meshing positions: the approach point, pitch point, and recess point. The results indicate that at the pitch point, where single-tooth contact occurs, the Hertzian half-width increases significantly, leading to the highest peak pressure. Although the short-tooth design reduces the nominal contact length, it increases the gradient between the inlet and outlet clearances, thereby forming a stronger wedge-shaped hydrodynamic effect that enhances oil film generation and raises the overall film thickness. The positive profile modification further enlarges the equivalent radius of curvature, enhances lubricant entrainment at the inlet, and reduces local stress concentration, leading to a smoother pressure transition and more stable lubrication film formation. The parametric analysis reveals that as the rotational speed increases, the oil film thickness increases while the maximum pressure decreases; as the load increases, the film thickness decreases and the pressure rises; and with an increasing pressure angle, the oil film exhibits improved stability and uniformity. Comparative investigations among the standard gear, short-tooth gear, and short-tooth profile-shifted gear show that the short-tooth positive profile-shifted gear exhibits the largest minimum film thickness and the lowest maximum pressure throughout the meshing cycle, indicating the best overall lubrication performance among all configurations. The study demonstrates that the coupling of tooth shortening and positive profile modification fundamentally alters the inlet geometric convergence ratio and the combined curvature radius, thereby strengthening the hydrodynamic wedge effect and promoting more effective oil film formation. This coupled mechanism mitigates the adverse influence of reduced contact length and ensures stable lubrication performance even under transient loading conditions.
In conclusion, the research elucidates the mechanism by which the interaction between short-tooth geometry and positive profile modification enhances the EHL behavior of steel-polyamide gear pairs. The developed transient numerical model provides a reliable theoretical and computational foundation for the design and optimization of non-standard polymer-metal gears. The findings offer valuable insights for the application of steel-polyamide short-tooth profile-shifted gears in high-speed, lightweight, and space-constrained transmission systems, where efficient lubrication and wear resistance are critical.
Key words
polymer /
steel-polyamide /
short-tooth profile shifted gear /
transient elastohydrodynamic lubrication /
load- carrying capacity
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Funding
National Natural Science Foundation of China (52575216)
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