Modal Properties of Rotating Shafts with Order-Tuned Absorbers

Abstract

We consider the properties of torsional vibration modes of rotating shafts fitted with centrifugally driven pendulum vibration absorbers. These systems feature interesting modal behavior that arises from the coupling of constant-stiffness elements, namely the shaft torsional modes, and engine-order-based elements, namely the absorbers. These models are relevant to automotive crankshafts fitted with pendulum absorbers, which are being considered for reducing vibrations in a number of advanced technology engines. The coupled system modes exhibit frequency veering as the rotor speed varies, and when the system is subjected to engine-order excitation the resonances depend in a non-trivial manner on the system parameters. The absorbers are typically tuned to suppress shaft torsional vibrations, and proper tuning of the absorbers requires a thorough understanding of this resonance behavior. In this paper we describe the manner in which natural frequencies depend on rotor speed and how this influences the overall frequency response of the rotor. We also discuss how to tune absorbers to achieve the desired vibration reduction, and we consider some examples that demonstrate the rich response behavior of these systems.