Elastohydrodynamic lubrication analysis of meshing conjugate face-gear pairs for pericyclic transmissions

This paper investigates the Elastohydrodynamic Lubrication (EHL) characteristics of the meshing conjugate face-gears used in the Pericyclic Transmission (PVT) and predicts the PVT mesh efficiency. Initially, the meshing face-gear teeth are modeled and the unloaded meshing kinematics is simulated. Next, Hertzian contact characteristics of the meshing face-gear pair are investigated analytically by two different geometric models. The first model is developed to capture the nominal contact behavior of the meshing face-gears. The details of the contact characteristics of the meshing face-gear pair are captured by the second model. The established Hertzian contact deformation area, contact deflection and contact stress along with the rolling velocity are used in the calculation of the iso-thermal non-Newtonian EHL film thickness. By considering the effects of lubricant, shear strain, shear stress and pressure-viscosity relations in the contact zone, the friction coefficient is calculated. Lastly, the PVT efficiency is calculated as a function of friction coefficient, mesh loads and mesh kinematics. The Hertzian contact behavior, film thickness and friction coefficient values are simulated for an example fixed axis face-gear pair rotating with 1000 rpm at 34kN-m torque. The contact stress ranges from 1.5GPa to 4GPa through the meshing cycle this study. The EHL film thickness ranges from 0.1 μm to 0.25 μm. The average friction coefficient is predicted as 0.05. Moreover, the efficiencies of three different 24:1 reduction ratio PVT designs are investigated for a 760HP level conceptual in helicopter transmission system. The minimum and maximum efficiency in the given design space are 97% and 98.7%, respectively. The effects of gear diameter and number of teeth on the efficiency are demonstrated in this investigation.