Abstract
Due to down-sizing phenomena, in designing and development of internal combustion engines the accent is put on turbocharging in order to maintain, or to raise the engine performances with less fuel consumption. From the most common methods of charging engines we mention the turbocharging using a turbocharger. Recent researches in the field of turbochargers show that specific models of turbochargers are capable, in some functioning conditions, of reaching rotational speeds over 250000 rot/min. Turbocharging always raised, from the very beginning, major problems related to noise and vibration traced to the turbocharger rotor. Due to high rotational speeds it is absolutely necessary to maintain a rigorous design and also to test the dynamical behavior of the turbocharger rotor. Classical solutions of turbochargers use hydrodynamic bearings, but modern turbochargers try to use hybrid rolling bearings with ceramic rolling elements. Also due to the friction and dilatation properties of the ceramic materials, the classical rolling bearings with steel rolling elements were replaced with bearings with ceramic rolling elements and steel raceways, in domains where it is necessary to maintain functioning at high speeds. In order to mount the rolling hybrid bearings on turbochargers shafts it is necessary to accomplish some modifications of the shaft. Two identical rotors one with hydrodynamic bearings, and one with rolling hybrid bearings, with same geometrical characteristics regarding the compressor and turbine, will not behave in the same way due to different shaft solutions. This paper is focused on showing the vibration behaviour of different types of turbocharges shafts in order to establish which solution is probably more fitted to reach a stable dynamic behaviour under vibrations (1). In order to present the aspects mentioned above it were made some simulations using software solutions and laboratory tests.
Keywords: Turbocharger, Vibration, Shaft, Modal analysis, Natural Frequencies, Mode Shapes