Approaches of estimating the stiffness and damping coefficients of journal bearings

Turbocharging of internal combustion engines plays an important role in providing the appropriate quality and efficiency. The requirement of long-term reliable operation imposes on modern turbocharging systems and this fact has determined the widespread use of journal bearings as supports for the rotor assembly. An assessment of the stability of the turbocharger rotor must be carried out at the design step considering the characteristics of the supports. Nowadays, in engineering practice, the available feature for analyzing the dynamics of a rotor on journal bearings is limited and, as a rule, requires a prior knowledge of the stiffness and damping coefficients. The main purpose of this article is to review the methods offered by present software systems and scientists in evaluation the dynamic characteristics of sliding bearings. Modern turbochargers, even when operating in steady-state modes, can be subject to shock loads, vibrations with large amplitudes, which inevitably entail large rotor deflections that do not advise the assumption of small orbits around the equilibrium position. This circumstance raises the question of a different approach to determining the stiffness coefficients, which can be based on a combination of linearization of the force in the equilibrium position and an additional mathematical model describing the region of large displacements, which will correlate with the results of nonlinear analysis.