Numerical Calculation For Adaptive Active Noise Control Of Engine Exhaust

Engine exhaust is main source of automobile noise. The exhaust noise has wide frequency band and its primary noise frequency is variable with engine working conditions. Traditional exhaust silencer can not match to the variable working conditions, thus it has difficulty to reduce noise substantially in all working conditions. Moreover, the traditional has the disadvantage of high resistance, high energy consumption and power dissipation. Active noise control can compensate above insufficiencies.Among active control techniques, adaptive feed-forward control technique is popular. But this method exists some difficulties when used to control exhaust noise, e.g., the selection of reference signal, the system identification for error acoustic path, the radiation power of secondary sound source, and the poor generality of AANC. Therefore it is necessary to check the parameters and select the reference signal by simulation before the experiment.The following problems are studied.1. Engine exhaust noise in various working conditions is recorded, then their frequency character is analyzed .It is indicated that energy of engine exhaust is concentrated in low frequency band and a good performance of ANC can be obtained in low frequency.2. Simulation program based on Filtered-XLMS algorithm is accomplished. Numerical simulation result shows that the performance of ANC alters with the reference signal. It is feasible to confine and optimize the scope of system parameters.3. The theory of system identification is introduced. On-line identification is compared with off-line identification. Simulation program using adaptive identification and adaptive filter is written . 4dB noise decrease in wide frequency band is influenced by on-line identification. This program can be transplanted to DSP.4. Vibration signal on the various positions of engine is acquired .The correlation between vibration signal and noise signal is studied. Simulation results show that the selection of reference signal depends not only on the correlation ,but also on the distribution of vibration energy, which can be used to guide the signal selection.