Research On Unbalance Vibration Characteristics Of The Turbocharger Rotor System With Floating Ring Bearings

High-speed turbocharger rotors are easy to cause random u nbalance phenomena due to the heterogeneity of multiple parts material, manufacturing and assembly errors, running wear in impeller and uneven carbon deposition of turbine. Under the condition of allowable residual unbalance, the manufacturing tolerance of floating ring bearings(FRBs) causes different inside and outside limits clearance for the same batch bearings and leads to the inner and outer oil film dynamic characteristics coefficient change, which will induce excessive rotor vibration and noise for the same type of turbocharger, then affects the quality of automobile turbocharger itself and the whole machine's NVH performance. To master the turbocharger rotor unbalance vibration rule, therefore, the unbalance vibration characteristics of turbocharger rotor-FRBs system are investigated to control or reduce the rotor v ibration and ensure safe and efficient operation. The main content of this paper is as follows:1) The structure characteristics of the high-speed turbocharger are introduced, and the current state research on unbalance vibration characteristics of turbocharg er rotor is analyzed. A realistic turbocharger of gasoline engine is taken as a research object, the rotordynamic equations of motion under the condition of unbalance are derived by applied unbalance force and nonlinear oil film force of FRBs. The finite element model of turbocharger rotor-bearing system is modeled which includes the unbalance excitation and nonlinear FRBs. The critical speed and mode shapes, steady state synchronous response analysis and the nonlinear transient analyses of turbocharger rotor are performed based on the rotor FE model. The result shows that the normal rotor and unbalance rotor are characterized by linear characteristics at low speed, while shows obvious nonlinear features at high speed. A certain unbalance can suppress the nonsynchronous vibration components and reduce rotor vibration.2) Aiming at the problem of the turbocharger's complex unbalance vibration characteristics and the limit manufacturing tolerance clearances of FRBs, the finite element method is applied to investigate the influence law of unbalance imposed location, unbalance magnitude, unbalance phase difference, in-phase and out-of-phase unbalance, and the bearing manufacturing tolerance clearances on the rotordynamic characteristics of turbocharger. The turbocharger rotor vibration and nonsynchronous vibration components can be effectively reduced or suppressed in the design and manufacture process by controlling the unbalance imposed location, unbalance magnitude, unbalance phase and the bearing manufacturing tol erance clearance reasonably.3) In view of the problem of double overhung rotor structure feature of turbocharger and the existence of random unbalance in impeller, the double overhung rotor experimental rig is designed and built. The unbalance vibration response characteristics of double overhung rotor with oil film bearings are investigated by using the run-up and constant speed measurement methods, and the speed is across two critical speed. The result shows the unbalance is a key parameter for the system response of double overhung rotor, it should pay more attention to the influence of unbalance location in design. The research provides reference and guidance for the reasonable unbalance parameter design and staggering the high frequency resonance area of double overhung rotor as much as possible.4) Turbocharger rotor test rig is established in actual working condition and the experiment verification of unbalance vibration characteristics. The turbocharger rotor test rig is designed and established which the rotor speed up to 25000r/min. The rotor unbalance vibration characteristics of turbocharger within 25000r/min are researched. The B&K system is adopted to test the turbocharger vibration under four kinds of unbalance magnitude. The time-frequency characteristics of each measuring point are obtained by analyzing the initial vibration data. The experimental results are basically identical with the simulation results. The conclusions will provide definite reference value to the production-manufacturing, dynamic design, fault diagnosis and vibration control of the high-speed turbochargers...