Upgrade of a Turbocharger Speed Measurement Algorithm Based on Acoustic Emission

The present paper is about the rotational speed measurement of an automotive turbocharger, obtained starting from the analysis of acoustic emission produced by an engine, which have been acquired by a microphone placed under the vehicle hood. In the first part of the paper several upgrades to increase the overall performance of the speed extraction algorithm are presented and discussed, starting from the basic algorithm that has already demonstrated the methodology capability in a previous paper. In particular it has been considered a different signal sampling rate in order to extend the applicability of the methodology to a wider range of engines. Also a new processing procedure has been defined to increase the capability of the algorithm to tune on the frequency signal. A possible calibration procedure has been evaluated in order to set-up a threshold value in the algorithm procedure, based on a off-line analysis of the acoustic signal acquired with the engine running during a typical acceleration phase from idle up to the upper gear shift. In the results section, a new graphic representation of the algorithm performance has been introduced in order to obtain a sufficient clear idea of the performance of the rotational speed reconstruction algorithm. The trend of the percent error versus time and also an evaluation of the algorithm performance in every single second of the test are proposed. The results obtained demonstrate that the methodology is ready to be introduced in the ECU to enhance new strategies for the turbocharger control.