Research On Active Noise Control Method Of Automobile Engine

As people's requirements for automotive products continue to increase,in-vehicle noise has become one of the important indicators for evaluating the comfort of a car.Most of the traditional passive noise reduction technologies such as vibration isolation,sound insulation,noise reduction,and sound absorption are used.These noise reduction techniques have good effects on medium and high frequency noise,but are not ideal for low frequency noise control.The noise inside the car is mainly low frequency noise,and the control method for low frequency noise is active noise reduction technology.Active noise reduction technology has only been developed in recent years.It uses the principle that the acoustic wave interference involves mutual cancellation.The generated secondary acoustic wave has the same amplitude and phase difference as the original noise,thus achieving the purpose of noise reduction.Based on this,the engine sound signal is used to construct the secondary sound source reference signal,and the FXLMS algorithm's interior noise feedforward active control system is simulated.The improved algorithm is proposed for the specific sound field environment in the car.For better results,the noise reduction can reach 20 dB at some frequencies.The source of interior noise and the characteristics of engine noise are analyzed.It is concluded that the main component of interior low frequency noise is engine noise,and the peak frequency of interior noise always appears at the first three frequencies of engine speed.The single channel FXLMS algorithm and multi-channel FXLMS algorithm are theoretically and simulated.The results show that the single channel control system is more suitable for local noise reduction than the single channel of the multi-channel system,and the multi-channel system is more suitable for full-space noise reduction because of the need to use multiple secondary sources in large-scale noise control.In order to improve the stability and noise reduction of the system,a module that compensates for the frequency offset is added to the system to cope with the frequency offset problem within 10%.The simulation compares the sinusoidal step size algorithm and the normalization algorithm,and proposes an improved algorithm for the time-varying noise signal in the car.The algorithm uses the normalization algorithm to replace the parameter of the control step size range in the sine variable step size algorithm.It not only has the advantages of fast convergence and small steady-state error of the sinusoidal step-size algorithm,but also has the advantage that the normalization algorithm adapts to the characteristics of the time-varying reference signal and the parameters are easy to select.In the active noise control system,the location of secondary sound sources has a great influence on the noise reduction effect and space.In order to find a method for the distribution of secondary sound sources with larger noise reduction,the finite element model of automobile acoustic cavity is simulated by LMS Virtual.lab acoustic software.By placing the secondary sound source near the head of the main driver's seat,the average sound pressure level near the head before and after placing the secondary sound source is compared,and the local noise reduction effect of 13.86 dB is achieved.Three kinds of secondary sound source location layout schemes are proposed for the whole space noise reduction of the car interior,and the noise reduction amount of the three layout schemes is compared.It is concluded that the noise reduction can be achieved at the same height as that of the human head in the inner wall of the car.In this scheme,we study several frequencies,and calculate that it can reduce at least 7.4dB in the range of 50Hz-800 Hz.