No 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 sub-synchronous 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 240 krpm, and for lubricant inlet pressure of 4 bar at 150°C. Linear and nonlinear rotordynamic models reproduce very well the test data for synchronous response to imbalance. The nonlinear results show two sub-synchronous 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.

The rotor/stator configurations considered are washer-shaped laminate stack (WL), tape-wound laminate stack (TL), U-shaped laminate stack (UL), solid metal (S), and solid wedge pieces. Since preloading reduces rotor vibration, the effects of preloading a WL rotor and TL stator system on the flux density/input current transfer function magnitude and phase are determined from tests. Since eddy currents result in power loss and phase lag, tests are performed on four rotor/stator pairs, i.e., WL/TL, TL/TL, TL/UL, and S/S, to find the one with minimal eddy currents. For S/S, the test results are compared with those obtained from a two-dimensional finite element analysis, for Silicon-Iron and Hiperco-27. Since overhanging the rotor beyond the stator is a common practice, the effect of this on the fringing of magnetic flux is studied using finite element analysis.

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.

Passenger vehicle turbochargers (TCs) offer increased IC engine power and efficiency. TCs operate at high rotational speeds and use engine oil in their bearing support system comprising of inner and outer lubricant films acting in series. The hydrodynamic bearings induce instabilities, i.e. subsynchronous shaft motions over wide operating speed ranges [1]. Yet, the motions are well bounded limit enabling the TC continuous operation [2, 3]. Due to the lack of accurate and efficient predictive nonlinear tools, turbocharger rotordynamic design followed, until recently, costly test stand iteration [3]. Presently, a rotordynamics model coupled to a bearing lubrication model calculates the nonlinear motions of TCs and delivers predictions of TC shaft dynamic response for practical conditions [4–6]. The software emulates a virtual laboratory, effectively aiding to design better TC products with increased reliability in a shorter cycle time. Predictions of the nonlinear model compare well with recorded TC shaft motions, both in amplitude and frequency content. The benchmarking lends credence to the validity of the integrated computational model.