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Prediction of the friction coefficient between gear teeth using a mixed film lubrication model

DOI: 10.1016/s0167-8922(03)80173-6
  • Mathematics


The experimental results found in literature for the friction coefficient between gear teeth cannot be predicted from the lubricant traction curves obtained in twin disc machine tests under full film lubrication regime. A numerical model was developed to simulate the linear contact between rough surfaces in mixed film lubrication. The model is based on the pressure distributions of a full film EHD rough contact and of the corresponding dry contact, from which the pressure distribution in the mixed film lubrication regime is obtained using a load share function. This load share function is based on failure probability curves for lubricated gears, depending on the specific lubricant film thickness and on the gear pitch live velocity. The mixed film pressure distribution is used to evaluate the corresponding contact deformed geometry, the lubricant film shear stresses, the lubricant and surfaces temperatures and the contact friction coefficient. The model admits the non-Newtonian behaviour of the lubricant and a local distribution of the temperature inside the contact. It was used to predict the friction coefficient along the meshing line of a FZG type C gear. The numerical results obtained are compared with results extrapolated from twin disc machine lubricant traction curves and with results obtained from real gear tests. The correlation between numerical and experimental gear results is quite good, putting into evidence the need to consider mixed film lubrication, surface roughness, lubricant non-Newtonian behaviour and contact temperature in order to predict realistic values of the friction coefficient between gear teeth.

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