Modeling and simulation of coefficient of friction on gear teeth contacts

Okşayan, Yeliz
Friction is defined as the resistance to motion between two dry or lubricated contacted surfaces. The contact load, contact geometry, surface speeds, surface roughness parameters and oil properties affect the lubrication condition or regime. The purpose of this thesis is to develop a mixed EHL (Elastohydrodynamic Lubrication) model that is capable of calculating the variation of friction coefficient between gear teeth contacts. Gear systems operate commonly in mixed EHL regime where the elastic deformations of the surfaces are in the order of the film thickness. In this regime, metal to metal asperity contact and hydrodynamic film thickness occurs together. In the model, the effects of deformation of surface asperities, oil viscosity change with pressure, slide to roll ratio, surface roughness parameters are taken into account. The model is capable of plotting the Stribeck curve that specifies the regimes with friction coefficient and Lubrication number. For higher loads, due to the shift on the Stribeck curve, lower coefficient of friction is observed for the same Lubrication number. In the present study, the model is adopted to non-Gaussian asperity height distributions since the surfaces do not always have Gaussian distributions in practice. vi Applying the Weibull distribution, the mixed EHL model is modified with the contact pressure calculation that is load carried by asperities. The effect of load and surface roughness parameters on the Stribeck curve is analyzed. The effect of Skewness and Kurtosis parameters on the mixed EHL regime is investigated and for comparison, the Stribeck curves are plotted for both Gaussian and non-Gaussian asperity height distributions. Eventually, the mixed EHL model for non-Gaussian surfaces is applied to a spur gear pair to determine the frictional power loss. For smaller Sk values and for higher Ku values than the Gaussian values, the friction coefficient values are lower giving low power loss than the Gaussian asperity summit distribution. Therefore, the gear tooth surfaces are to be machined giving smaller Sk than zero and Ku value that is higher than 2.72.
Citation Formats
Y. Okşayan, “Modeling and simulation of coefficient of friction on gear teeth contacts,” M.S. - Master of Science, Middle East Technical University, 2014.