Nonlinear Rotordynamics of Automotive Turbochargers: Predictions and Comparisons to Test Data

Abstract

Passenger vehicle turbochargers (TCs) offer increased engine power and efficiency in an ever-competitive marketplace. Turbochargers operate at high rotational speeds and use engine oil to lubricate fluid-film-bearing supports (radial and axial). However, TCs are prone to large amplitudes of subsynchronous shaft motion over wide ranges of their operating speed. Linear rotordynamic tools cannot predict the amplitudes and multiple frequency shaft motions. A comprehensive nonlinear rotordynamics model coupled to a complete fluid-film-bearing model solves in real time the dynamics of automotive turbochargers. The computational design tool predicts the limit cycle response for several inner and outer film clearances and operating conditions including rotor speed and lubricant feed pressure. Substantial savings in product development and prototype testing are the benefits of the present development. The paper presents predictions of the linear and nonlinear shaft motion of an automotive turbocharger supported on a semi-floating ring bearing. The shaft motion predictions are compared to measurements of shaft motion at the compressor nose for speeds up to 240krpm, and for lubricant inlet pressure of 4bar at 150°C. Linear and nonlinear rotordynamic models reproduce very well the test data for synchronous response to imbalance. The nonlinear results show two subsynchronous whirl frequencies whose large magnitudes agree well with the measurements. A large side load predicted for this turbocharger must be considered for accurate prediction of the rotordynamic response.

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

“…TC rotors supported on engine oil lubricated bearings produce time-varying responses that are rich in subsynchronous whirl motions, i.e. having one or more subsynchronous frequencies and with large amplitudes of rotor motion at the turbine and compressor ends that could touch (rub) against their housings [25,28]. The nonlinearity arises from the hydrodynamic character of the fluid film bearings supporting the rotor, the flexible nature of the slim rotor and heavy end inertias (turbine and compressor), and the exceedingly large operating speeds of the rotating shaft, many times above the lowest (rigid body) natural frequencies of the rotor-bearing system.…”

“…San Andrés et al (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) developed increasingly complex physical and numerical models for evaluation of the TC dynamic response [12,13,[25][26][27][28]. The rotordynamics model integrates a fluid film bearing analysis program that calculates the mechanical element reaction force vector as a function of the current state (rotor position and velocity).…”

Stability Effects of Non-Circular Geometry in Floating Ring Bearings

“…Tian et al [11] and Schweizer [1,12] carried out thorough nonlinear analyses by means of run-up and coast-down simulations, putting in evidence the influence of the unbalance distribution within the TC rotor and giving particular emphasis to the character of the whirling modes and the phenomenon of total instability. The dynamical behavior of TC rotor on semi floating ring bearings, which differ from FRBs because the locking of the bush rotation was also studied by Bonello [13] and San Andrés et al [14]. The effect of adopting a non-circular geometry for the bearing clearance, in place of the common circular one, remained though practically neglected in the research literature about FRBs.…”

Wire Mesh Dampers for Semi-Floating Ring Bearings in Automotive Turbochargers: Measurements of Structural Stiffness and Damping Parameters

“…See Refs. [4,5] for comprehensive review of relevant literature on rotordynamic behavior of automotive TCs supported on SFRBs (as well as fully FRBs).…”

“…SFDs in SFRBs enable acceptable limit cycle operation without failure even with persistent large amplitude subsynchronous whirl motions since SFDs introduce support flexibility and damping in the bearing structure [2,4,5]. In TCs, forced dynamic responses of the SFRBs strongly rely on viscosity of engine oil and thermal expansion of SFRB and bearing housing (BH) [6].…”