Research On Noise Control Of The Automobile Intake System

The sound quality of a vehicle equipped with an inline four-cylinder engine is poor at around 2250 rpm with characteristic of prominent pure tone.The experimental results indicate that the second?2nd?order intake noise has a peak at this engine speed,which was the main cause of the phenomenon.In order to explore the mechanism of the phenomenon,firstly,the finite element model of the entire intake system was established.The acoustic modes of the air intake system with and without the air filter were calculated,and the acoustic responses were analyzed.The modal analysis results demonstrated that the intake noise was amplified since the acoustic modal frequency of the pipe coincided with the 2nd order noise frequency.At the same time,a one-dimensional Computational Fluid Dynamics?1D-CFD?model of coupling the intake and exhaust systems with the engine was built to simulate the intake noise,and compared it with the experimental values to verify the accuracy of the model.Secondly,based on the 1D-CFD model,the influences of the length of the intake pipe on the acoustic mode and intake noise were discussed.The results showed that the acoustic mode of the air intake system was related to the length of the intake clean pipe.The attenuation of 2^nd order noise was not obvious,but it could change the low-frequency peak corresponding to the engine speed by increasing the length of the intake clean pipe.The influence on the acoustic mode of the dirty pipe was small,and the engine speed where the peak noise occurred in the 2^nd order noise was not changed.The 2^nd order noise in the low-speed range could be reduced,but increased in the high-speed.Increasing the lengths of the two pipes simultaneously,the effects on the acoustic mode and the 2^nd order peak were the superposition of the effect when the dirty pipe and the clean pipe were separately extended.The study on the acoustic modes of the intake system and the effects on the 2^nd order noise further validated that the peak noise was caused by the resonance of the air column,when the frequency of the pipe acoustic mode was close to the frequency of the 2^nd order periodic pressure pulsation noise.Finally,considering the layout space of the engine cabin,the Helmholtz muffler was designed based on the theoretical formula and the finite element method.The parameters of the resonance frequency and the acoustic performance were explored.The designed muffler was installed on the main pipe of the intake system to simulate the intake noise.The results showed that the total and the 2^nd order noise were reduced.Then the actual Helmholtz muffler was install on the intake pipe to test intake noise.The results showed that both the total and 2^nd order noise were attenuated almost throughout the entire engine speed range.The 2^nd order SPL was reduced by 2.8 dB?A?at 2250 r/min after installing the Helmholtz muffler.The pure tone had been eliminated effectively,and the sound quality had been improved in the interior of the vehicle.