A Engine Noise Source Identification And Control

On the one hand,the current automobile market increases lacking and competition is more heated;on the other hand,with the continuous improvement of living standards,consumers demand for more in automobile comfort performance.The performance of automobile NVH is a key factor for consumers to choose a car.So,the enterprises have to pay more attention to control NVH which stands for noise vibration and hashness in order to win a place in the fierce market competition.In the vehicle,engine noise is the most prominent.Therefore,it's very important for the engine noise source identification a nd controlFirst,this paper expounds the significance of engine noise control and introduce some basic parameters of acoustic with its concept,and the relationship between parameters.Commonly used octave,wave equation,etc are displayed in this paper.This paper also describes all kinds of engine noise and its cause,and proposed some appropriate measures according to different kinds of noise.Then outlined some basic principle of the engine noise source identification methods and their respective advantages and disadvantages,finally determine the acoustic array technology is adopted to improve the engine noise source identification.The experiment in this paper is based on an engine noise improvement projects from a motorcycle enterprises.Firstly collected the acceleration noise spectrum of the motorcycle,conclude a conclusions that 6700 RPM is the working condition of sound source localization experiment.In half free sound field with drum,collect acoustic data of a motorcycle through 3560 D device made in the Bruel & Kj?r in driving and another condition,then found that the noise sources are concentrated in the engine cylinder head,flywheel cover and sprocket cover these three places.Engine cylinder head is the only noise source and no obvious change in spectrum after remove flywheel cover and sprocket cover,thus we confirmed that the main engine noise source is in the engine cylinder head preliminary.Found that the noise source is rich of harmonic which is similar to the noise of engine mechanical noise that may be caused by the piston slap through the spectrum analysis.Use the exclusive method,finally confirmed the piston slap is the main cause of the engine noise.An improved scheme for modifying the shape of the piston skirt and the piston top structure is proposed.Calculated the stress and deformation of the new piston,and the maximum stress of the material is in accordance with the design requirements.Collected acoustic data of a motorcycle with the new piston,found that the total sound power level of the improved engine on the right sid had reduced 1.6 d B in driving condition,and the engine vibration acceleration amplitude at 3500 RPM also have obvious drop,subjective evaluation is acceptable,the piston slap phenomenon largely disappeared,has obtained the good improvement...