An elastohydrodynamic lubrication model for helicopter high-speed transmission components

This thesis describes a deterministic approach to analyze elastohydrodynamic lubrication (EHL) of helicopter transmission gear surfaces with asperities.; Thermal, Newtonian or non-Newtonian models are used to study the mechanisms of film generation, pressure distribution and temperature distributions within the fluid and on the surface, for an EHL line contact. A two-slope viscosity-pressure model is used to avoid overestimation of the viscosity of the lubricant under heavy loads. The three-dimensional roughness description of an actual gear tooth surface is measured using a non-contact surface profilometer. Detailed analysis of the fluid parameters and the surface roughness influences are presented. Five different types of lubricants are studied in order to determine which one best corresponds to the operating conditions. The pressure distribution, fluid film thickness distribution and the temperature rise at the contact surface are predicted as a function of the gear operating conditions including normal load, lubricant temperature and rolling/sliding speed. A new numerical method, used to solve the Reynolds equation, is employed in order to maximize the computational speed.; The numerical developments described for EHL lubrication are extended then to incorporate metal-to-metal contact. A mixed-elastohydrodynamic lubrication model is presented in order to analyze helicopter transmission gears. A parametric analysis is performed in order to determine explicitly the metal-to-metal contact effects on the viscosity, and implicitly on the pressure, fluid film generation, and temperatures for both fluid and surfaces.