TURBOCHARGER NONLINEAR RESPONSE WITH ENGINE-INDUCED EXCITATIONS: PREDICTIONS AND TEST DATA
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Turbochargers (TCs) aid to produce smaller and more fuel-efficient passenger vehicle engines with power outputs comparable to those of large displacement engines. This paper presents further progress on the nonlinear dynamic behavior modeling of rotor-radial bearing system (RBS) by including engine-induced (TC casing) excitations. The application concerns to a semi-floating bearing design commonly used in high speed turbochargers. Predictions from the model are validated against test data collected in an engine-mounted TC unit operating to a top speed of 160 krpm (engine speed = 3600 rpm). The bearing model includes non-cylindrical lubricant films as in a semi-floating ring bearing with an anti-rotation button. The nonlinear rotor transient response model presently includes input base motions for the measured TC casing accelerations for increasing engine load conditions. Engines induce TC casing accelerations rich in multiple harmonic frequencies; amplitudes being significant at 2 and 4 times the main engine speed. FFT post-processing of predicted nonlinear TC shaft motions reveals a subsynchronous whirl frequency content in good agreement with test data, in particular for operation at the highest engine speeds. Predicted total shaft motion is also in good agreement with test data for all engine loads and over the operating TC shaft speed range. The comparisons validate the rotor-bearing model and will aid in reducing product development time and expenditures.
