Sound Quality Evaluation And Research On Properties Of Noise And Vibration Of Automotive Door Closing

Major:Vehicle EngineeringWith the rapid development of auto industry in modern society, people demand more and more requirements on the NVH property of auto, but as an important part of the study of NVH of automobile, sound quality also becomes one of the main focus studied and cared by people about the car. Paying attention to the sound quality of automobile means that the traditional auto acoustics concerning the reduction of sound pressure level could not satisfied people with the requirements of acoustic comfort of automobile. Based on the objectivity of acoustic, the sound quality of automobile involves the person's subjective factors of psychology, so it can comprehensively reflect people's satisfaction on the auto acoustics. However, currently it is still not mature for the international to apply the sound quality on the field of design and manufacture, and its study results can not be completely applied in our country because of the differences of nation habit. Hence, in order to improve the research level of sound quality of automobile in our country, It needs more and more professional personage studying the sound quality of automobile to make the contribution on improving the sound quality of automobile which satisfies the comfort requirements of people in our country.Since 1980s, the problem of vibration and noise caused by the door of the car when it is closed is valued. This is because the closing sound quality of car has become one of the most important aspects affecting the sound quality of automobile. The closing sound of automobile could transfer a series of complex information to customer such as safety, comfort, luxury, reliable and faith and so on. The customer always deduce the quality and level of automobile through the closing sound by subjective evaluation, and even decide his or her purchase orientation. This paper is on the basis of a sub-project "automotive door closing sound quality and the characteristics of vibration and sound, which is cooperated through the combination car academy of vehicle engineering of jilin university and enterprise. By combining with the practice of automotive door closing of the automobile, the paper studies the assessment of the automotive door closing sound quality and the property of noise and vibration of the automobile, and it applies the subjective evaluation and objective evaluation of sound quality to the automobile door closing sound. Through the test of characteristics of automobile door closing vibration and sound, it finds out the noise source of automobile door closing sound by in-depth study of the sound in order to finally realize the improvement of automotive door closing sound quality and satisfied people with sweet-sounding of automobile which will be prepared for them.Firstly, it introduces some basic concepts of the sound quality, especially the four psychoacoustic evaluation parameters:loudness, sharpness, roughness and fluctuation which are widely used in sound quality. Based on the research of the automobile, this paper applies the objective evaluation and subjective evaluation of sound quality to its door closing sound quality. In the objective evaluation, it uses the software Test. Lab of LMS company to calculate the loudness and sharpness when the door of the automobile is closed. In the subjective evaluation, it applies subjective assessment to the automotive door closing sound in this research with another car and adopts contrast scoring and describes the main characteristics of the two automobiles.Secondly, this paper introduces the theories and methods of noise source identification, and it mainly introduces wavelet analysis used in this paper. The signal of automotive door closing vibration and sound belongs to the typical unsteady instantaneous pulse signal, and wavelet analysis is the only way to analysis it. Wavelet and wavelet packet decomposition theory of Wavelet analysis is based on the multi-resolution analysis of the signal and the signal can be decomposed into different frequency intervals. The correlative analysis of the signal of noise and vibration can be analyzed according to characteristic vector and correlation coefficient based on wavelet packet analysis, so it can identify the noise source of the unsteady signal.Finally, through the experiment and application of short-time Fourier transform and wavelet transform do this paper discuss the characteristics of automotive door closing vibration and sound and analyzes the temporal characteristics and time-frequency properties of automotive door closing vibration and sound. It obtain the main noise source of automotive door closing sound by the method of wavelet packet decomposition which finally provides the basis for the optimization of automotive door closing sound quality.