Session: 25-07 Bearings and Dampers

Paper Number: 79386

79386 - A Nonlinear Rotordynamics Model for Automotive Turbochargers Coupled to a Physical Model for a (Semi) Floating Ring Bearing System 

Automotive turbochargers (TCs) use an engine oil lubricated bearing system to produce acceptable performance (as per the engine volumetric efficiency) and proven reliability. However, the bearings also cause TC rotordynamic responses that are rich in subsynchronous whirl motions though reaching stable limit cycles. The paper describes the lubrication model for a finite length semi-floating ring bearing (SFRB) system and its coupling to the rotor and ring structure models for prediction of both linear and nonlinear system responses and their characterization in terms of motion amplitudes and whirl frequency content. The SFRB model includes a thermal energy transport network for the inner and outer films in both radial bearings and the thrust bearings located on the end sides of the ring. The large temperature difference between the hot shaft and a cold housing induces a three-dimensional thermal gradient in the fluid films and the floating ring, further exacerbated by the heat generated from drag power losses in the inner films adjacent to the rotor. The temperature gradients affect the lubricant viscosity and the bearing system operating clearances. The numerical integration of the rotor and bearing system (RBS) equations of transient motion accounts for the SFRB nonlinear forces and starts from a static equilibrium position, if existing. Analysis of the transient response of a commercial TC for operation at increasing shaft speeds, from 500 Hz (30 krpm) to 4,000 Hz (240 krpm), and for particular mass imbalance conditions, shows dominant subsynchronous whirl motions with frequencies ranging from approximately ¼ to ~ ½ of shaft speed and a transition from conical to cylindrical-bending rotor mode shapes. The model predictions of nonlinear behavior are accurate when benchmarked to a set of measurements procured in a gas stand test rig. The analysis also investigates the influence of bearing physical dimensions (length and clearance), oil viscosity, and rotor mass imbalance distribution on the onset, persistence and severity of subsynchronous whirl rotor motions. The results of the parametric analysis aid to identify physical parameters that could ameliorate, even eliminate, sub synchronous multi-frequency rotor motions. Some recommendations could deteriorate the thermo-mechanical performance of the TC system, while others oppose current practice and environmental restrictions on the viscosity of the lubricant. The analysis thus offers a concerted insight to the bearing dimensions and operating conditions affecting a TC nonlinear rotor response.
 

Presenting Author: Wonbae Jung KeyYang Precision Co., Ltd.

Presenting Author Biography: Wonbae Jung is a Senior Research Engineer in KeyYang Precision Company.<br/>Wonbae completed his PhD degree at Texas A&amp;M University (TAMU) with research addresses to the flow of energy in automotive turbochargers and envisions ways to make it more efficient with operation supporting high temperature gradients and super-fast shaft speeds (&gt; 4 kHz).<br/>Wonbae completed a MS degree at TAMU, with research related to testing gas foil bearings toward assess the effect of top foil coatings on bearing power losses and dynamic force coefficients.

Authors:

Wonbae Jung KeyYang Precision Co., Ltd.
Luis San Andres Texas A&M University Turbomachinery Laboratory
Jungbae Kim KeyYang Precision Co., Ltd.