Effect of Static Load on Critical Speeds of a Shaft Supported by Two Symmetrically Arranged Bump-Foil Bearings in a Turbocharger

Abstract

AbstractWorking as a self-acting bearing without lubrication, foil bearing has shown its potential applications into high-speed machines, including turbochargers. Numerous studies on various types of foil bearings have been conducted but bump-foil bearings have drawn the most attention. The role of bump-foil bearing in shaft performance has been analyzed through evaluating structural and technological parameters such as foil dimensions, nominal clearance, shaft weight… However, external parameters including static load have not been concerned in evaluating the shaft performance in a turbocharger. Therefore, in this theoretical study, a turbocharger shaft supported by two bump-foil bearings were investigated under the effect of an external static load at different positions on the shaft. Finite difference was employed to transform the governing equations, and then the system of ordinary differential equations was solved to obtain orbit of the shaft center, while Newton-Raphson algorithm was applied to investigate the shaft stability at equilibrium state. The results indicate significant influences of the load values as well as acting points on the critical speeds of the shaft. The research is believed to make further contribution to not only structural design for turbocharger shaft through load effect presented as bushes, shaft collars, … but also shaft stability control through load control using piezoelectric material.KeywordsFoil-air bearingReynold’s equationShaft stability