Research On Characteristic Of Micro Multileaf Gas Foil Bearing

Power microelectromechanical systems(PowerMEMS)are growing rapidly as a power source.The PowerMEMS with high requirements of power density and efficiency extremely need a stable rotor-bearing system.The traditional rolling element bearings cannot work at such extremly high temperature.The magnetic bearings are interfered by electromagnetic field easily.The external aid gas supply is necessary for hydrostatic bearings.Micro gas foil bearings,a kind of bearing with flexible support structure,have wide range of potential applications in the field of PowerMEMS due to their low friction,good stability,high tolerance to shaft misalignment,and without the need for aid gas supply.The research of domestic and abroad mainly focused on micro rigid gas bearings.However,the research on micro gas foil bearings is very limit and almost still in preliminary experiment and numerical calculation status.There are little research reports on micro gas foil bearings to now,especially in the domestic.In this study,a novel micro multileaf foil bearing(MLFB)is proposed and analyzed.The elastic foundations of MLFB are designed with piecewise stiffness,which can help to reduce the friction during the start-up effectively without weakening the load capacity significantly during the operation.Meanwhile,the large friction area between elastic foundations and top foil can provide the MLFB with enough damping to enhance stability.Based on the proposed structure of MLFB,the MLFB is fabricated by using ultraviolet lithography technology.In this study,equations governing the foil deformation are derived using Castigliano's theorem.The results solved from the foil deformation equation show agreement with the results obtained from the ANSYS Workbench.Compressible Reynolds equation is coupled with equations governing the foil deformation to generate hydrodynamic lubrication equation.Some of numerical methods,including finite difference method,Newton-Raphson method and low relaxation method,are used to solve hydrodynamic lubrication equation to predict the static performance of MLFB.In this study,the effects of operation parameters,structure parameters of elastic foundations and reserved clearance between adjacent foils on bearing performance are investigated.The small perturbation method is applied in dynamic Reynolds equation to obtain the perturbation equation which can be solved by using numerical method to obtain the dynamic stiffness and damping coefficients.In addition,with aim to micro gas foil bearing,a kind of structure of PowerMEMS is proposed in this study.Through the XL-rotor software,rotordynamic performance including Campbell and damping ratio diagrams is predicted using the calculated bearing dynamic coefficients.The research mainly focuses on the effect of reserved clearance on stability of rotor-bearing.Based on the structure of designed PowerMEMS,a test rig of micro bearing-rotor system is set up preliminarily.