Turbocharger's Vibration Investigation Based On Experimental Modal Analysis

Turbocharger is a gas compressor that is used for forced-induction of an internal combustion engine. Turbocharger has a broad application on the engine because it can improve the performance of an engine by compressing more air into the cylinders, making fuel burn more efficiently and helping the engine generate more power. As the turbocharger is always installed on the engines, low frequency, with respect to engine's running speed, large deflection vibrations are easily transferred from the engine to the turbocharger rotor through the hydrodynamic bearings,which influences turbocharger's performance. Therefore, it is necessary to analysis and monitor turbocharger's vibration. However, under real working condition, due to the limitation of measurement conditions and costs, it is impossible to monitor the response of any point on the turbocharger. Hence, this master thesis aims at predicting vibration responses which are hard to measure based on vibration responses which are easy to measure. Firstly, the transmissibility function from center housing to compressor housing is measured by the experimental modal analysis. Secondly, the acceleration vibration responses are measured on the vibration shaker by the simulation of engine's base excitation. Meanwhile, with the help of FFT algorithm, center housing's vibration response can be multiplied by the transmissibility function in frequency domain, which turns out to be the prediction of compressor housing's vibration response. The comparison result demonstrates that the predicted vibration response matches the measured one. Thirdly, this method is applied to the engine and turbocharger system under engine's real working condition. The result of the experiment and calculation proves the validation of the method. Finally, due to the fact that it is difficult to measure displacement vibration responses under the real measurement condition whereas acceleration vibration responses are easy to measure, an integral algorithm is adopted in this thesis in order to calculate displacement vibration responses based on acceleration vibration responses. The calculation result shows the integral algorithm possess relatively high accuracy.