Modelling of an Automotive Turbocharger Bearing System within GT-SUITE Environment

The introduction of severe emissions regulation and the demand for a more sustainable mobility foreseen in the upcoming years have led car manufacturers to adopt innovative technologies to improve the efficiency and reduce vehicles emissions. In such a framework, the combined use of downsizing and turbocharging raised as one of the most promising solutions to improve the engine fuel economy, avoiding any lack of performance. Therefore, to maximize the effectiveness of this approach, a design of the turbocharger capable not only to optimize the aerodynamics, but also to minimize the mechanical losses seems to be crucial. As a result, this thesis aims to develop, within the GT-SUITE environment, a predictive model for the center housing of an automotive turbocharger, in order to forecast the oil flow of the system and the frictional power loss due to hydrodynamic effects. Two different center sections were modelled, one characterized by a semi-floating radial bearing with integrated thrust bearings and the other characterized by full-floating radial bearings with separated thrust bearings. A non-Newtonian pseudoplastic behavior of the oil was implemented in the model, since, in automotive turbochargers, the high revolution speed implies the lubricating oil to operate in an environment where shear thinning phenomenon may occur. The model validation has been conducted with a database of experimental data measured on a dedicated test bench designed by a large European OEM. The impact of different boundary conditions has been investigated, involving not only several oil inlet pressure and temperature levels, but also the influence of the thrust force levels. Furthermore, since both heat transfer and friction effects are typically included in the turbocharger operating maps measured at the hot gas stand, a thrust force-dependent friction prediction provides a more precise methodology to correct the experimental data and to assess the quality of the turbocharger aerodynamics. Finally, the possibility to predict not only the overall frictional power loss, but also its distribution between the radial and axial components can be of crucial importance in bearing system design and development.