Nonlinear Transient Modeling and Design of Turbocharger Rotor/Semi-Floating Bush Bearing System

This work presents the bearing design and analysis of radial semi-floating bush oil lubricated bearings for a typical industrial turbocharger configuration. Initially, the stability analysis for a linear rotor/bearing system is evaluated through eigenvalues and eigenvectors. The stiffness and damping coefficients of the inner oil film are obtained for the linear modeling process. The operating speed range of the turbocharger is high enough, at 21,000 to 24,000 rpm, to be unstable, indicating that the analysis should be and is carried out with nonlinear transient modeling. The nonlinear transient analysis evaluates the rotor and bush limit cycle orbits, rotor dynamics, the forces acting on the rotor and semi-floating bush surfaces, the oil flow through the bearing, the oil temperatures, and the power loss of the two oil films. The optimum design of a set of semi-floating bush bearings for this application depends strongly upon the clearances of the bush and squeeze film damper, usually expressed as the non-dimensional clearance to radius ratio. A typical clearance is evaluated to determine the bearing performance in terms of orbit size, forces acting on the bush and squeeze damper surfaces, oil flow through the bearing, power loss, and thermal heating. The nonlinear transient orbit values are evaluated for frequency content using the FFT to determine which orbits show both the synchronous and sub-synchronous vibration components and the associated rotor modes excited. These results are compared to the linear analysis over the operating speed range. The oil flow through the bearing component is much larger than the squeeze film damper. The forces acting on the bush and squeeze damper surfaces are related to the fatigue life of the bearing