Research On The Vehicle Noise Signal Analysis And Abnormal Noise Diagnosis Technology

The diagnosis and optimization of abnonnal vehicle noise need to employ the combination of multiple testing methods,multi-body dynamics simulation and advanced signal processing technology,which is of great significance to enhance the NVH performance of vehicles.In this paper,two cases of abnormal noise in the idling and accelerating conditions are taken as examples to illustrate the source identification and the generated mechanism reasoning process of the abnormal sound source.Optimization schemes are also proposed.As to the idling abnormal noise,the initial source identification tests and modal simulation showed that the camshaft was the abnormal noise source.After excluding the possibility of the tappet and the high pressure pump plunger actuating the camshaft modality,VVT was certified as the excitation source by the test result of locking the relative rotation between the VVT stator and rotors.Combining the oil pressure test,the dynamic simulation of the valve train and the camshaft angular acceleration test,it was confirmed that the blade and the stator collided as abnormal sound occurred.Subsequent tests showed that the increase of the distance between the blade and the stator could avoid the collision,and the abnormal sound disappeared completely,which verified the correctness of the previous conclusions and provided a feasible solution to the abnormal sound.In order to get the time-frequency characteristics and sound source of the abnormal noise,basic sound and vibration tests,sound intensity tests and combustion tests were proceeded.The tests results revealed that the abnormal noise was radiated from every engine surface and had little connection with the combustion.Thus the crankshaft vibration was suspected to be the main cause of the abnormal noise.The torsional vibration tests of the crankshaft with different TVD were executed,the time-frequency contour maps of the torsional angle had similar characteristics with the abnormal noise,former suspect was affirmed.The simulation of the crankshaft torsional vibration was proceeded in order to find the optimum TVD,the TVD with operating frequency of 350Hz was verified to have the best vibration absorbing effect.Then the optimized TVD was manufactured and tested,and the indoor noise test result showed that the amplitude of 320?470Hz was attenuated dramatically and the abnormal noise was eliminated successfully.Finally,in order to provide an objective criterion for the coherence between noise and excitation source,EEMD was applied to decompose the signal.The IMF components including the abnormal noise and residuals were successfully separated.The coherence analysis between the angular acceleration signal and the noise with the residuals removed were proceeded.It was found that the peak of coherence in the abnormal noise frequency band was 0.78,while the coherence of the rest band was very low.The results objectively confirmed that the abnormal noise was caused by crankshaft torsional vibration.