Transfer Path Analysis And Control Of Light Bus Low-Frequency Structural-Acoustic Coupling Noise

With the development of the automobile technology and the improvement of living standard,a higher demand for automobile riding comfort has emerged.Noise,vibration,and harshness(NVH)performance is an important indicator of riding comfort.As an important part of the vehicle NVH development,the inner low-frequency noise problem of automobile is complicatedly generated and transferred due to its frequency characteristics,making it difficult to analyze the noise source and influencing factors.Therefore,the immediate determination of the source of low-frequency structural-acoustic coupling noise,a more accurate determination of the main components that affect the noise,a more relevant control plan proposal,the application of accurate prediction during the product development stage,and the analysis of low-frequency structural-acoustic coupling noise in automobiles have become the main research focus of various major vehicle manufacturers and research institutions.In this study,through an in-depth research on the transfer path analysis of the low-frequency structural-acoustic coupling noise of a light bus,a set of theoretical and technical methods and procedures were established which can be used to rapidly and accurately predict,analyze,and control the low-frequency structural-acoustic coupling noise,thereby enriching the transfer path analysis(TPA)theory and method.In this paper,the research and control methods for low-frequency structural-acoustic coupling noise are summarized and analyzed.The research development trend of TPA and the basic concept of this paper are determined.The theoretical basis of the TPA of low-frequency structural-acoustic coupling noise is systematically introduced,that is,the theory of transfer function and its unbiased estimation are deduced and the three kinds of work load identification methods andtheir scope of application are specifically introduced.The use of the singular-value decomposition method to solve the generalized inverse matrix was discussed in detail.In addition,in accordance with the characteristics of the TPA model of low-frequency structural-acoustic coupling noise presented in this paper,the multi-reference TPA was introduced.The TPA model for low-frequency structural-acoustic coupling noise was constructed based on the domestic light bus.This model consists of multiple transfer paths with the power train mount,the front and rear suspensions and the transfer shaft mount support at the excitation side,and the human ear side as the response point.On the basis of this model,the TPA of the low-frequency structural-acoustic coupling noise was performed.The structural path transfer function was tested for multiple transfer paths with the noise beside the ears of the driver and passengers on the second and fifth rows as the response points.The inverse matrix method was used to obtain the working load at the passive end of elastic components under various working conditions.Before the TPA,a brief in-vehicle NVH level analysis was conducted in accordance with the target point data in the working condition test.By combining the subjective evaluation and the objective data,the noise problem was determined to occur beside the ears of the driver and passengers on the fifth row while the bus is running below 70 km/h.In addition,the subjective feelings about the noise was specifically described in detail.The TPA was conducted in accordance with the main problematic positions under this working condition.A contribution evaluation method of noise transfer path was proposed by comprehensively considering the factors of sound pressure level,amplitude,and phase.This method was used to recalculate each mount further.The contribution of each suspension path was calculated,and the path with major influence on each position was initially determined.To conduct an in-depth analysis of the generation mechanism and characteristics of low-frequency noise problem,a structural-acoustic coupling finite-element model was constructed,which included the vehicle body,frame,door,and window.The finite-element model of the frame and body-in-white were gradually constructed,thesimulation and tested modal frequency were proven consistent,and the modal shape was also consistent.Furthermore,the finite-element model of the door and window was constructed and linked with the correct connection and constraint method,and the full vehicle model with the door and window closed was obtained.On the basis of the full vehicle finite-element model,the finite-element acoustic cavity model was constructed with the consideration of chairs.The full-vehicle structural-acoustic coupling model was constructed,and the acoustic cavity and the structural model before and after coupling were compared and analyzed.The absorption characteristic and structural damping was obtained through a test,and was added to the model.To verify the low-frequency structural-acoustic coupling model,the hybrid TPA of the vehicle inner noise was performed,and its result was compared with the result of the TPA test.An accurate low-frequency structural-acoustic coupling model was obtained.To reflect the superiority of TPA further in terms of analysis,prediction,and application during the early stage of research and development,a full-vehicle multi-dynamics model was constructed,which included the running gear and B-level road.By combining this model with the structural-acoustic coupling model,the virtual TPA model for full-vehicle structural-acoustic coupling noise was constructed.On the basis of the result of virtual TPA for low-frequency structural-acoustic coupling noise,a comprehensive contribution analysis method was proposed for noise transfer path within the vehicle,which comprehensively considers multiple frequencies,reference points,and working conditions,and the transfer path with high contribution to the light bus inner low-frequency structural-acoustic coupling noise was determined.The three different TPA methods were further analyzed based on the theoretical basis,analysis results,and subsequent optimization.The advantage of virtual TPA was proved.For the path with the biggest contribution,single-stage and secondary TPA were performed.By applying the single-stage TPA,the transfer characteristic was determined as the factor that needs to be optimized,and the plate was determined as the main link that needs to be optimized.The secondary TPA was performed for the plate link,and the improved coefficient algorithm for plate acoustic contribution wasproposed considering multiple frequencies,multiple reference points,multiple working conditions,and the relative relation.On the basis of this method,the concept of plate acoustic influence coefficient was proposed,and its definition was introduced.Through this method,the secondary TPA was performed intensively.Finally,the plates that needed to be controlled were determined based on the analysis result,the damping noise reduction measure was proposed,and the noise suppression effects were verified by simulation and testing.The test proved that the series of theories and methods proposed in this paper can be used to accurately,effectively,and rapidly analyze,control,and predict low-frequency structural noise.