Research On Recognition Method Of Noise Source In BMW 3 Series

Excessive interior noise will affect the experience of drivers and passengers,which not only makes drivers easy to fatigue but also has adverse effects on the physical and mental health of passengers.Therefore,reducing interior noise has always been the focus of automobile production.In order to design a car more in line with the concept of consumers,automobile manufacturers will study and analyze the noise sources of new cars.In order to improve the noise quality in the car,it is very important to develop a complete and effective method for noise source identification.Firstly,based on the theory of partial coherence analysis,the interference between the measuring points is removed by conditional power spectrum density function,and the model of a 6-input single output sound source system is established.The scale parameter adaptive model is adopted,and the scale range of continuous wavelet transform is automatically adjusted by a multi-scale differential operator.The difficulty of setting scale parameters manually is solved and the recognition ability of signal features is improved.Secondly,a method of noise source identification based on the subjective evaluation and acoustic vibration measurement is proposed based on BMW Brilliance 3 series.The experienced automobile engineer makes a preliminary subjective evaluation on the interior noise of the vehicle under different working conditions,and then determines the working conditions of the vehicle road test and the layout of sensors.The DH5902 data acquisition equipment is used to collect the test data,and then the collected signals are processed by continuous wavelet transform and partial coherence analysis.The results show that the influence of structure noise is more than the air noise on the interior noise,the largest contribution to the interior noise is the noise of the panel frame,which accounts for 32.15%,thus the low-frequency noise is the most important factor to the noise in the vehicle.In order to study the cause of low-frequency noise inside the car,the contribution of the car body panel was studied.In order to determine the vibration measuring points of the panels,the frequency response function curve of each body panel is collected by the hammering method.Under the same working conditions,the vehicle road test is carried out again and the data are collected.The partial coherence analysis method is used to process the data.It is clear that the panel with the largest contribution to the interior noise is the left front leaf panel,which is 19.2%.Finally,in order to study the vibration source of the body parts,the wavelet partial coherence method is proposed to analyze the transmission path of the vibration source of the body parts,and the feasibility of this method is verified by the simulation analysis of the analog signal.The sensor position is determined according to the transmission path of the excitation source and wavelet partial coherence analysis is used to process the collected signal.The results show that the road excitation causes the vibration of the front suspension lower control arm and the front suspension shock absorber.The vibration is transmitted to the sub-frame through the connection between the front sub-frame mounting point and the body,and the sub-frame transmits the vibration to the vehicle body,causing the vibration of the left front leaf plate.The noise source of the transmission path is improved,and the improved vehicle is tested and analyzed again.The results show that there is no obvious partial coherence relationship between the improved left front vane and the interior noise.It is proved that the interior noise is obviously improved and the overall sound pressure level is reduced by 3d B,which further verifies the accuracy of the proposed noise identification method.To sum up,the whole set of noise source identification methods proposed in this article can accurately identify the location of the car's noise,which provides an efficient and accurate identification method for future vehicle NVH(Noise,vibration and harshness)improvement.