On the Dynamic Stability of Automotive Turbochargers: Case Studies with Various Bearing Configurations

Abstract

The present study introduces a finite element structural rotor dynamic model to predict the stability of automotive turbochargers (TCs) supported on simple rigid geometry fluid film bearings (2-axial groove bearings or multi-lobe bearings or offset-half bearings). The turbocharger finite element (FE) structural model for linear analyses include lumped masses for compressor wheel, and turbine wheel. The free-free mode shapes and natural frequencies of a rotor are measured and compared with predictions. Stability of the TC rotor-bearing system is largely related to bearing dynamic coefficient (stiffness and damping coefficients). Rotordynamic predictions are conducted with a commercial TC rotor model from 10 krpm to 200 krpm. By comparing the bearing force coefficients of various configuration bearings, the results show the relationship between bearing configurations and rotor-bearing system stability. The higher offset provides higher direct stiffness and damping force coefficients of multi-lobe bearing when the bearings are preloaded. The higher pad angle provides higher direct stiffness and damping force coefficients of the multi-lobe bearings. The 3 lobe bearings provide higher direct dynamic coefficients than the 4 lobe bearings, offset-half bearings, and 2-axial groove bearings. Furthermore, the eigenvalue analysis show significantly different stability results among the 2-axial groove bearings, 3 lobe bearings, 4 lobe bearings, and offset half bearings.