Modeling and Study on Static Performance of the Double-Top-Foil Air Foil Journal Bearing for Air Compressors in Fuel Cell Vehicles

Air foil bearings are gradually applied in air compressors in fuel cell vehicles for the advantages of high speed, oil-free and non-contact. Advanced air foil bearings with different structures are used to improve the performance of air compressor. Accurate modeling of the complex structures in air foil bearings has become a research hotspot in recent years. This paper presents a theoretical model for a double-top-foil air foil journal bearing (DAFJB) for centrifugal air compressors used in fuel cell vehicles. The foil structure is modeled by finite element method (FEM) using shell elements. Coulomb law and penalty function method are applied to model the tangential and normal behavior of the contact areas. The local contact between the middle top foil and the bump foil, the bump foil and the bearing sleeve are modeled using node-to-segment contact method. The large-area contact behavior between two layers of top foils is modeled by simplified surface-to-surface contact scheme. The hydrodynamic air film is modeled by two-dimensional isothermal compressible Reynolds equation, and the fluid-structure coupling calculation is carried out within the foil and the rotor. Results show that the DAFJB has better static characteristics than the first-generation air foil bearing, because the double-layer structure increases the thickness of the foil and introduces additional friction between the two layers of top foil. Greater stiffness results in less foil deformation, so its hydrodynamic film distribution is more uniform, so the load-carrying characteristics are improved. The DAFJB can be applied in more complex and high-load working conditions, also improve the stability of rotor.