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.

Automotive engines are facing increased design focus towards downsizing, higher performance and lower emissions, in the process, challenging turbocharger (TC) technology to their limits. Downsizing of the engine needs smaller compressor and turbine wheels to achieve the critical flow requirements that leads to very high TC operating speeds of more 300k rpm. In general, TC rotor is most commonly supported by hydrodynamic fully floating (RFRB) or semi-floating bearing (SFRB) systems. For such high-speed applications, SFRB could be preferred bearing system where inner and outer bearing clearances act as a plain journal bearing and a squeeze film damper. These hydrodynamic bearings, exhibit non-linear oil whirl/whip phenomena in the inner bearing that leads to higher sub-synchronous vibration and overall deflection of the shaft. Sub-synchronous behavior of the SFRB is evaluated both numerically and experimentally (hot gas stand) for two design variants and results are published in this paper. TCs were run up in hot gas stand and were recorded using NVH Data Acquisition System (DAQ) with frequency analyzers and eddy current displacement sensors. 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 condition obtained from 3D FE simulation. Detailed numerical investigation was conducted using EHD joint definitions in the above bearing system. Good agreement was obtained between test and prediction, and finer source characterization was achieved using simulation.

No abstract