Effects of Coulomb friction in foil structure on foil journal bearing performance

The Coulomb friction model of foil structure of bump foil journal bearing was developed by using finite element method. Through changing friction coefficients between top foil and bump foil, bump foil and bearing housing, the stiffness of foil strucure of Coulomb friction model and linear spring model from literatures were compared under various load distributions, and the effects of Coulomb friction on stiffness of bump foil were studied. Then, by using finite element mothod and finite difference method, the compressible gas lubricated Reynolds equation and the film thickness equation were solved together. Predictions of the minimum gas film thickness on bearing mid-plane for increasing static loads and load capacity versus eccentricity ratio at two speeds were obtained. The numerical results of this finite element model were compared with those of linear spring model and rigid surface gas bearing, and the predicted film thickness was also compared with test data. The results indicate that Coulomb friction force can enhance the stiffness of bump foil. With the increase of friction coefficient, the stiffness of bump foil and number of bump foil with both ends fixed are also increased, so the surface of foil bearing is made to be hard, and static performance of bearing is similar to that of rigid bearing. Moreover, when the bearing load capacity is fixed, the minimum film thickness decreases with the increase of foil friction coefficient.