Risk Prediction Of Automobile Door Of Rattle Noise

Squeak & Rattle is an abnormal short-lived noise perceived by the user,which is one of the main factors affecting the perceived NVH performance of a vehicle.Years of research and the spread of electric vehicles have greatly reduced the overall noise level of a vehicle,making these intermittent,anomalous noises even more pronounced.Rattle is an acoustic phenomenon caused by a impact,which is a relative movement between components with a brief loss of contact.The traditional "find-and-fix" approach to addressing rattle issues is often time-consuming and costly,and the tools and methods available for predicting rattle issues during the forward development phase of a vehicle are not yet mature.Therefore,this paper proposes a fast prediction method for the rattling noise problem of any complex continuous elastic body structure,and applies the method to the risk prediction of the rattling noise of a passenger car door.In this paper,the mechanism and characteristics of abnormal rattling sound are firstly analyzed,and the rattling force of continuous elastic body structure is regarded as the secondary excitation force outside the system,and the linear characteristic of the main system is preserved.To obtain the rattling secondary excitation force,it is assumed that the pulse waveform of the rattling force is a half-cycle sine wave,and the Hertz contact model and the origin transfer function of the contact point are used to express the contact mechanical properties and structure of the rattling material pair.Based on the impedance properties of the striking part,the equivalent impact force model of a single continuous elastic body colliding with a fixed block and two continuous elastic bodies impacting with each other was deduced.To verify the equivalent impact force model,a impact experiment of a cantilever beam impacting with a fixed hammer was designed,and 48 experimental conditions were set up with three material pairs,different harmonic excitation frequencies and initial gaps.The experimental results show that the peak value and impulse of the impact force predicted by the equivalent impact force model are in good agreement with the experimental values,while the predicted duration is shorter than the experimental value;Therefore,a correction method of the percussive force pulse waveform is proposed.The corrected force pulse waveform is closer to the measured waveform,so that the duration of the predicted force pulse is also very close to the measured value.According to the local nonlinear characteristics of the impacting vibration,combined with the equivalent impact force model proposed in this paper,the nonlinear link of the impact system is treated as the feedback link of the main linear system,and a feedback calculation method for rapidly predicting the impact vibration response is proposed.The effectiveness of the method is verified by experiments.To improve the efficiency of risk assessment of abnormal noise,the surface normal vibration characteristic quantity ANVL is proposed to characterize the sound radiation of the structure,and then to classify and evaluate the risk level of rattle noise.The relationship between cantilever beam vibration characteristic quantity ANVL and reference point radiation sound pressure level is studied by means of virtual experiments.The results show that there is an obvious linear correlation between the two,and the correlation coefficient reaches 0.9995.Finally,the equivalent impact force model,the feedback calculation method and the rattle noise risk assessment method are applied to the risk prediction of a passenger car door rattling noise.The rattle noise evaluation standard of the door is researched and formulated,the ANVL of the door is predicted to be 53.4d B under a certain working condition,and the risk level of rattle noise is evaluated as serious,which is consistent with the evaluation result of the simulation calculation of the radiated sound field of the car door.The degree of freedom scale of the finite element model of the door reaches959,990,and it takes 11,076 seconds to complete the risk assessment of rattle noise by using an ordinary microcomputer.The practical application shows that the risk prediction method of door rattle noise proposed in this paper can meet the needs of practical engineering applications in terms of efficiency and accuracy.