Friction coefficient between gear teeth in mixed film lubrication

摘要

A mixed film elastohydrodynamic (EHD) lubrication model was developed for the evaluation of normal and shear contact stress fields. The mixed film pressure field is obtained combining an elastic pressure field (dry contact between rough surfaces, considered similar to boundary lubrication) with an EHD pressure field (isothermal EHD rough contact in full film lubrication), through a normal load share function. The mixed film shear stress field is also obtained combining a boundary film shear stress field with the shear stresses in the lubricant film (including thermal effects and viscoelasto-plastic rheological behaviour in full film lubrication), using a tangential load share function. The mixed film lubrication model was used to extract the lubricant rheological parameters from the experimental traction curves of a gear mineral oil obtained in a twin-disk machine. In this case, full film EHD lubrication is predominant but the surface roughness of the disks is taken into account. The mixed film lubrication model was also applied to the contact between gear teeth. The results obtained were correlated with experimental values measured by Hoehn et al. and the corresponding values for normal load share function and for the friction coefficient in boundary film lubrication were determined.