Investigations on the Effect of Bearing Clearance in Turbocharger Fully Floating Hydro-Dynamic Bearing System

Abstract

Turbocharger technology helps in achieving reduced emissions, increased performance and downsizing of automobile engines. The rotor system of the TC is supported with the help of hydrodynamic fully/ rotating floating ring (RFRB) bearing systems. Hydro-dynamic bearing systems are more sensitive to inner and outer clearances. The possibility of maintaining nominal clearance in the mass produced turbocharger is limited to manufacturing capabilities and constrains. The inner and outer bearing clearances are always in the controlled range. This range creates four different combination of clearances which need to be validated to ensure safe shaft motion, which incurs huge development & testing cost and time. In hot gas stand, using NVH Data Acquisition System (DAQ) with frequency analyzers and eddy current displacement sensors, rotor shaft motion behavior was studied for the nominal bearing clearances. Numerical simulation model was created for the nominal clearances case. In numerical simulations, multi-body dynamics (MBD) of flexible rotor and housing structures are coupled with Elasto-hydrodynamics (EHD) of the inner and outer oil films. The energy equation is considered for calculation of oil film temperature in EHD using thermal boundary conditions obtained from 3D FE simulation. Simulation and tested results are compared and correlated. With this validated simulation methodology, investigation is conducted for the four different combination of clearances and results are discussed in this paper.