Research On Vehicle Interior Adaptive Active Noise Control System Based On Engine Rotation Speed

The interior noise in automotive cabin has been one of the important indexes used to evaluate the ride comfort, as a result of the increasing requirements of automotive performances. Now, the traditional passive reduction noise measures in automobile, such as noise elimination, sound absorption, vibration and sound isolation, etc, have good effect on reducing the middle and high frequency noise, but little effect on low frequency. The adaptive active noise control(AANC)developed in the recent years is effective on decreasing low frequency interior noise in automotive cabin, so an active noise control method using engine rotation speed to construct reference signal of the initial secondary noise source in vehicle is proposed in this paper.After measuring and analyzing interior noise characteristics in a minibus, an adaptive active noise control system based on engine rotation speed is established on the basis of the full simulation research. Then the active noise control experiments in the minibus are carried out in laboratory and on roads, and the results are satisfying. The main research works completed in this paper are as follows:At first, the measure experiment of interior noise in a minibus is finished, after analyzing the generant mechanism and propagation path of the interior noise in automotive cabin and engine noise. The investigation shows that the low frequency noise produced by engine plays a vital role in the vehicle interior noises, and the frequencies of main noise peak value points are directly correlative with the engine rotation speed. Therefore, the engine rotation speed can be used to construct reference signal of the initial secondary noise source in vehicle, and the expression between the rotation speed and reference signal is presented. The active noise control can be done based on the above method.The derivation of LMS and FXLMS adaptive algorithm indicates that sound time delay problem can be resolved by estimating transfer function of error acoustic path. According to the requirement of real-time active noise control, a method identifying error acoustic path with LMS adaptive algorithm is proposed, and computer simulation analysis indicates its feasibility. Besides, some control parameters of FXLMS algorithm, such as order of Filter and convergence factor, are confirmed by simulation analysis with MATLAB/Simulink toolbox.The next work is finishing a simulation model of adaptive active noise control system based on Simulink Toolbox, then the simulation research is carried out with the data of vehicle interior noise experiment. The results prove that the active noise control method using engine rotation speed to construct reference signal of the initial secondary noise source is feasible.On the basis of the above-mentioned simulation analysis, a real-time adaptive active noise control system based on engine rotation speed in a minibus is established. The input of the system is the engine rotation speed signal, and output is sound wave signal generated by loudspeaker. FXLMS adaptive filter algorithm works in a digital signal processor (DSP) to realize interior noise control. Weight coefficients of FXLMS algorithm are adjusted according to feedback of residual error sound signal at the position of driver's ear.Finally, the AANC experiments are carried out in laboratory and on roads by means of the AANC system developed. The experiment results show that the developed AANC system can effectively reduce the low frequency noise in automotive cabin, the sound pressure level at the position of driver's ear is reduced 9—13dB(Lin) under different engine rotation speeds in laboratory, and 8—9 dB(Lin) under different vehicle travel speeds on roads. The AANC system is of the better stability and satisfactory convergence speed, and it is able to satisfy the requirement of the real-time noise control.