Online detection and classification of changing harmonic signal content are common issues in vehicle control, both regarding mechanical and electrical oscillations. This paper presents an overview of the most recent patents. In particular it shows an invention in which a fast and numerically efficient method is used. The well known signal correlation principle is applied to detect, in real time operation, instantaneous dominant oscillations in a time-varying (temporally-variant) harmonic signal. © 2011 Bentham Science Publishers Ltd.