Abstract
Recently active control techniques have received an increasing attention, since they provide an effective way for vibration suppression and noise reduction of thin-walled structures. In active noise reduction smart materials are attached to structures as actuators and sensors connected by a control unit which enable the system to reduce the structural vibrations with the objective to reduce simultaneously also the sound radiation caused by structural vibrations. Piezoelectric materials are widely used as actuators and sensors, because they provide large forces, operate in high frequency regimes and can be easily bonded on or imbedded into conventional structures. Active control methods are usually employed in applications where the frequency range of interest is between 50 Hz and 1200 Hz. This is also an important frequency region in engine acoustics. Considering passenger cars, the power train represents one of the main noise sources where the engine oil pan contributes significantly to the noise emission. The aim of the present paper is to design a smart car oil pan with surface-mounted piezoelectric actuators for active vibration and noise reduction of a stripped car engine.
At first numerical FEM-BEM simulations of the stripped car engine are performed in order to investigate the general noise reduction potential of the piezoelectric patch actuators as well as to calculate optimal actuator locations. Based on these results a demonstrator of a stripped car engine is developed, built and experimentally investigated. The demonstrator is excited with a white noise and also with real engine spectra resulting from diesel engine measurements. The experimental setup developed enables measurements of controlled and uncontrolled structural vibrations as well as radiated sound fields. The vibrations can be recognized by surfaceattached acceleration sensors and by surface-mounted patches. The sound field is measured with the help of a microphone-array. The focus of the paper is the design and the verification of a suitable control strategy. Feedback controllers are proposed and applied to reduce noise radiation of the stripped car engine. An adaptive control formulation is analyzed with respect to random variations of real engine parameters in which neuro-fuzzy networks are included for the controllers design.
The paper presents the main results of the investigations and concludes with an outlook to ongoing research activities.
Keywords: Stripped car engine, Piezoelectric patches, FEM, BEM, Feedback control