Dynamic analysis of turbochargers with thermo-hydrodynamic lubrication bearings Abstract

The use of a turbocharger in a downsized engine has become the current practice in all vehicle categories, to reduce engine emissions. Typically, the turbocharger is supported by hydrodynamic bearings, namely, fully or semi-floating ring bearings in radial direction, and double-acting thrust bearing in the axial direction. Given the high rotational speeds a typi-cal automotive turbocharger can achieve, description of the shaft motion is a computation-ally expensive task, as the lateral oscillations are highly nonlinear and the phenomenon of oil whirl/whip is particularly strong in this type of rotating system. Moreover, axial motion is also crucial to be considered, as the thrust bearing may affect the shaft lateral oscil-lations. This work presents the development of a turbocharger rotor dynamic model, ac-counting for lateral and axial vibrations and cross-coupling bearing effects, to analyze run down or run up dynamic response. Thermal variations of the oil films are included in the modeling, accounting for temperature increases in both the radial and axial bearings. Two experiments enable to measure the turbocharger nonlinear oscillations in both run down and run up transients. Numerical results are compared with experimental responses lead-ing to a previous tuning of the unbalance levels of the turbine and compressor wheels, as well as the floating rings residual unbalance. Besides, axial-lateral coupling occurs from the runner tilt regarding the thrust bearing. Predictions show a fair agreement with test data in frequency domain and temperature estimates, especially for higher rotational speeds, wherein eventual foundation effects are negligible. (c) 2021 Elsevier Ltd. All rights reserved.