An experimental characterization of the friction coefficient of a wind turbine gearbox lubricant

Abstract

In this study, a method to predict the contact friction coefficients at the rolling‐sliding contacts of isotropic superfinished and axially ground gear and bearing surfaces in wind turbine gearboxes is proposed. A two‐disc test rig was used to measure friction coefficient values within a slide‐to‐roll ratio range of −0.8 to 0.8, rolling velocities of 2 to 12 m/s, at oil temperatures of 50°C, 70°C, and 100°C and Hertzian contact pressures of 1.2, 1.6, and 2.0 GPa. A polyalphaolefin (PAO) International Standards Organization (ISO) viscosity grade (VG) 320 was the lubricant. Data from 90 individual friction coefficient tests were combined to develop two closed‐form friction coefficient formulae. A multivariable linear regression analysis was used to derive the regressed formulae. Using the developed regressed formulae, the predicted friction values follow the trend of measured values at all of the operating conditions. The results show that the regressed formulae are close to experimental friction coefficient values. The friction coefficient predictions confirm that the regressed formulae are capable of simulating contact friction values for the lubricated contact conditions considered.