Lubrication film monitoring of the pitch bearing in a wind turbine

Due to the roller curvature and the narrow contact area in roller-type pitch bearings, it remains challenging to accurately extract contact signals and achieve high resolution in ultrasonic film thickness measurement. The acoustic finite element simulation is carried out to investigate sonic wave propagation in the roller–ring tribo-pair. The echo signals from the contact area are extracted exactly, considering the scattering of the roller’s surface. Subsequently, the conventional ray model is modified by a correction factor relevant to both working conditions and the dimensional parameters size. Eventually, the film thickness in the contact area can be obtained accurately. Referring to the theoretical results from classical Elasto-Hydrodynamic Lubrication (EHL), the modified ray model has a higher simulated measurement accuracy up to 38.2 % over the conventional model. An industrial pitch-bearing fatigue test is carried out for verification. The results indicate that the measured lubrication film thickness falls within the bearing’s design range. Moreover, the reversal moments are identified from the amplitudes of echo waves. These findings support the lubrication design and condition monitoring of pitch bearings.