Automotive turbocharger rotordynamics: Interaction of thrust and radial bearings in shaft motion simulation

Abstract

The analysis of turbocharger rotordynamics has been conducted so far focusing solely on the effect of radial bearings on the non-linear oscillations of the rotor-bearing system. It is well known that the oil-film concentrated in the rotor's journal bearings is the root cause of the system's occurring nonlinear vibrations. Nevertheless, the rotor-assembly requires to be supported in the axial direction as well in order to compensate the various thrust load effects occurring during operation. This paper investigates the influence of hydrodynamic thrust bearings on the nonlinear oscillations and bifurcations of the rotor system in terms of the thrust- and radial bearing interaction during run-ups. For that purpose the conventional rotordynamics environment is extended by integrating a nonlinear hydrodynamics thrust bearing model suited for transient run-up simulations. Focus is set on the impact of two major parameters that drive the virtual prototype process of new rotor-assemblies: the shaft diameter and the thrust bearing's position along the shaft. It is shown that for a given set of boundaries the thrust bearing's position along the shaft can have either positive, neutral or negative influence on shaft motion. Furthermore, certain combinations of shaft diameter and thrust bearing positions could occur that may have a negative impact on the thrust bearing itself, for example by means of the associated load capacity. In this regard, it is demonstrated that simulating the thrust and radial bearing interaction during run-ups is mandatory not only for shaft motion purposes, but for designing a robust thrust bearing as well. Finally, with the help of correlation coefficients and response surface methods, trends are identified that set guidelines while designing a new turbocharger center section.