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.

Increasingly stringent emission norms place tougher challenges on the efficiencies of a turbocharger. Higher efficiency requirement on turbocharger translates into tighter tolerances on the various geometrical dimensions. While this is applicable for all the components, in this study, the focus is on the compressor wheel. Compressor wheels are either cast or milled and variations are possible in either of the processes. Even small changes in the dimensions of compressor wheel (like diameter, angle distribution, thickness distribution, axial length and blade width etc.), cause the performance losses in Turbo charger. Loss in Performance of turbocharger affects Low-end torque, power rating, fuel economy as well as increasing compressor exit temperature. It is therefore important to understand and quantify the impact of the variation in blade geometry on pressure ratio, choke flow and efficiency. In this paper, a few case studies of manufacturing variations in blade thickness, blade height and axial length are shown based on gas stand tests as well as 3D CFD simulations. A process for extracting real geometry from white light scan data obtained from the manufactured wheel is shown which helps to compare the differences with the design intent geometry. Flow simulations with the real geometry show the impact on performance. Subsequently a systematic analysis of the variations is carried out to quantify the performance impact.

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