Analysis and Control for the Intake Noise of a Vehicle

Abstract

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. To understand the mechanism and solve this problem, the finite element model of the entire intake system is established to calculate the acoustic mode. Meanwhile, the 1D computational fluid dynamics (CFD) model integrating the intake/exhaust system with the engine is constructed to predict the intake noise. The modal analysis results demonstrate that the natural frequency of the intake system is close to the frequency of the 2nd-order periodic pressure pulsation noise at around 2250 rpm. The resonance of the air column is the main cause of the above-mentioned problem. The results of 1D-CFD simulation agree well with the experiment. Based on the analysis results and considering the constrains of engine cabin space, three kinds of control measures are proposed, which include changing the length of intake dirty pipe, changing the length of the clean pipe and installing the Helmholtz resonator. The simulation results are as follows: (1) By increasing the length of intake dirty pipe appropriately, the 2nd-order noise is reduced at low engine speed, while increased at high engine speed. (2) The length of the intake clean pipe has obvious influence on the acoustic mode of the intake system, but little influence on the total noise, and the 2nd-order noise attenuation is not obvious. (3) Helmholtz resonator can attenuate the total noise and the 2nd-order noise in most of engine speed range. Therefore, the Helmholtz resonator is used for the solution. The acoustical characteristics of the intake noise and the vehicle sound quality are improved.