Numerical and Experimental Investigations on the Lubrication Regime Transition Characteristics of Journal Bearings Used in Wind Turbine Gearboxes

Abstract Planetary gear journal bearings (PGJBs) are a promising alternative to rolling bearings for large-scale wind turbine gearboxes due to their high power density and low failure rates. However, the lubrication regime of PGJBs converts frequently between the hydrodynamic and mixed lubrication regimes with the fluctuation in wind speed, which brings challenges to the long life of gearboxes. Decreasing the critical speed of the lubrication regime transition can help PGJBs expand the wind speed range operating under the hydrodynamic lubrication and reduce bearing friction and wear, thereby extending their service life. To accurately evaluate the bearing performance under mixed and hydrodynamic lubrication regimes, a mixed-TEHD model considering the influences of the elastic–plastic asperity contact, axial misalignment, bearing deformation, and thermal effects is developed in this article. A full-size test rig for PGJBs is built to simulate the transition process of the lubrication regimes by conducting a variable rotational speed experiment. The measured friction torque curve agrees well with the predicted one, which verifies the accuracy of the presented model. Furthermore, the effects of bearing clearance ratio, aspect ratio, composite roughness, and helix angle on the lubrication regime transition characteristics of PGJBs are explored. The results indicate that the PGJB with a smaller clearance ratio, a larger aspect ratio, and a smaller composite roughness can reduce the critical speed of the lubrication regime transition. This research can provide some references for further investigation of the surface optimization and structure design of PGJBs.