Optimization On Stiffness Model And Static Performance Of Thrust Foil Bearing

At present,the dynamic gas thrust foil bearing is more mature in some developed countries,and has been extensively used in aerospace,hydrogen fuel cell vehicles and other fields of highspeed rotating machinery.It gets the advantages that the traditional oil-lubricated sliding bearing and rolling bearing do not have.Therefore,it has a huge development prospect.However,the dynamic gas thrust foil bearing uses gas as lubricant,compared with the traditional bearing,so its axial load capacity is far lower than the traditional bearing.In addition,the theoretical model of the gas thrust foil bearing is more complex,and the theoretical prediction results usually deviate from the actual situation.Hence,improving the load capacity of gas thrust foil bearing and improving the prediction accuracy of theoretical model is focused in this paper.The specific research contents include the following aspects:The establishment of the theoretical model of the dynamic gas thrust foil bearing.The gas Reynolds equation,gas film thickness equation and foil deformation equation for thrust bearing are established based on the theory of gas dynamic lubrication.The calculation domain grid of sector foil is divided and the boundary conditions of numerical calculation of Reynolds equation are given.The gas Reynolds equation and the gas film thickness equation are solved by Newton iterative method,finite difference method and finite element method.The flow chart of theoretical numerical calculation is given.The establishment and verification of nonlinear stiffness model of bump foil.A test rig for measuring the static stiffness of bump foil is built and the static stiffness test of bump foil is carried out.The nonlinear equation between the stiffness of bump foil and the external load is obtained by using MATLAB fitting.The nonlinear stiffness equation of bump foil is considered in Newton iteration calculation.The test rig for testing thrust bearing is built and three thrust bearings with different taper inlet heights(20 ?m,70 ?m,114 ?m)are processed.The ultimate load capacity tests are carried out at different speeds.The results show that the load capacity predicted by the nonlinear stiffness model is closer to the test data than the constant stiffness model.Research on the influence of taper inlet height on the static characteristics of bearings.The nonlinear stiffness model is used to simulate and the thrust bearings are tested at different rotating speeds.The relationship between load capacity,friction torque and taper inlet height is studied.It is noted that there is an optimal taper inlet height,which maximize the bearing capacity while the friction torque is small.The load capacity increases sharply with the increase of taper inlet height when it is higher than the optimum taper inlet height;The load capacity decreases slowly with the increase of taper inlet height when it is lower than the optimum taper inlet height.Study on the influence of top foil sagging effect on the static characteristics of bearings.The relationship between the load capacity of thrust bearing with different pitch ratio and the thickness of top foil(0.075 mm ~ 0.2 mm)is analyzed by simulation.It is found that there is an optimal pitch ratio to maximize the bearing capacity,and the load capacity of the bearing with this pitch ratio hardly changes with the thickness of top foil.The load capacity decreases with the increase of top foil thickness when the bearing pitch ratio is less than the optimal pitch ratio;The load capacity increases with the increase of top foil thickness when the bearing pitch ratio is greater than the optimal pitch ratio.