EXPERIMENTAL INVESTIGATION OF THE VIBRATION-REDUCTION CHARACTERISTICS OF THE SHAFT COATING FOR A TURBOCHARGER

A turbocharger is a system that is fitted to automotive engines to increase performance and efficiency by taking air at atmospheric pressure, compressing it to a higher pressure and passing the compressed air into the engine via the inlet valves. A turbocharger consists of a turbine and a compressor impeller interconnected with a shaft supported in most cases by journal bearings. The shaft is one of most crucial components of a turbocharger system and it operates at high speed. The shaft vibrations are an inherent phenomenon and they are travelling to the surrounding structure, effecting the stability and reliability of the turbocharger system. The selection of the appropriate shaft-material property is a critical parameter among the parameters that affect the vibration of the system. This study focuses on exploring whether it is possible to reduce the shaft vibration using different types of coating materials, including aluminum chromium nitride (AlCrN), titanium nitride (TiN) and aluminum titanium nitride (AlTiN), each having thicknesses of (2, 4, and 6) mu m, for a shaft made of AISI 4140 alloy steel. The inherent natural vibration properties, such as the resonant frequencies, damping, and mode shapes of the turbocharger shaft with and without coating, were obtained by conducting an experimental modal analysis through measurements of the frequency-response function, which is about curve fitting the data using a predefined mathematical model of the turbocharger shaft. The results were validated numerically with the finite element method. From overall results, it was observed that the AlCrN, TiN, and AlTiN coating thicknesses have a small effect on the resonant frequencies, but a good damping effect. The resonant response of the turbocharger shaft at resonant frequencies was suppressed remarkably by the AlCrN and AlTiN coatings, especially those having a thickness of 6 and 4 mu m.