Investigation into nonlinear dynamics of rotor-floating ring bearing systems in automotive turbochargers

As a high speed rotating device, a modern turbocharger rotor is commonly supported by floating ring bearings (FRBs), owing to their cost effectiveness for mass production and good damping performance. Thanks to the rapid growth of the power of the modern computer, rotordynamic analysis of turbocharger rotor-bearing systems becomes feasible, and it is closely related to the healthy operation and noise generation of turbochargers. The work in this thesis is concerned with the nonlinear rotordynamic modelling, simulation and analysis in the rotor-FRB system of turbochargers. The conventional linear eigenvalue analysis is shown first in a gradually deepening manner to provide a deeper insight into the results from nonlinear simulations and reported experimental results. It is subsequently found the onset of first two nonlinear jumps can be effectively predicted by the linearized FRB model, although the rotordynamic characteristics at higher rotor speeds can hardly be linearly predicted. The desired oil-film forces for nonlinear simulations are calculated from a newly proposed analytical method, which is extended from the Capone’s journal bearing model. Stationary simulations under the perfectly balanced condition show two major subsynchronous components throughout the considered speed range, while the inclusion of in-phase unbalance places a considerable effect on the rotor response at relatively low speed and delays the occurrence of oil-film instability. However, at higher rotor speeds, the lower subsynchronous component can still establish the dominance. The engine induced vibrations are also considered, and it is seen the rotor response over the lower end of the speed range will be considerably affected, whereas, at higher rotor speeds, the engine induced vibrations can be suppressed by the dominant lower subsynchronous vibrations. Through carrying out many run-up and run-down simulations, the FRB outer clearance is found to be a critical parameter of the rotordynamic performance of the investigated TC rotor-FRB system, since distinct frequency maps are obtained with varying FRB outer clearances. The nonlinear effects of unbalance are also investigated, and it is observed the rotor response can be considerably affected by the amount and distribution of the imposed unbalance.