Analysis Prediction And Control Of The Mid-high Frequency Noises For Commercial Vehicle Cab

The level of vehicle interior noise is an important evaluation index of vehicle ride comfort performance. Predicting and controlling the interior noise successfully in the early stage of product development is significant to improve product design and shorten the development cycle and reduce development costs. Finite element method (EFM) and boundary element method (BEM) have got great success in prediction and control of low-frequency interior noise so far. However, these methods can't be used to study the mid-high frequency problem of the complex acoustic-vibration system. Because of the characteristics of the context of high modal density, high modal overlap and short wavelength features in complex mid-high frequency acoustic-vibration system, and with large-scale calculation it is very difficult to solve. In this case, the statistical energy analysis (SEA) will come into being. Because these limitation factors of FEM and BEM applications in the mid-high frequency range of factors are prerequisite for application of SEA methods.This paper is based on the research of cab noise analysis and control, a subproject of National 863 Program (2006AA110104) "High-quality integrated development of advanced technology for heavy commercial vehicles". In this paper, a fully equipped commercial vehicle cab of statistical energy analysis model was established based on statistical energy analysis principles. In the modeling project, the principles of subsystem division, determining the performance parameters of the model and getting the incentive of the model were deeply studied. The cab SEA model was validated by experiments. Through the SEA model the energy transfer path analysis and noise control method are studied, and a number of practical noise reduction measures were put forward. The results showed that cab noise levels in the mid-high frequency were significantly lowered by taking noise reduction measures. It is proved that statistical energy analysis method for the analysis of the car's mid-high frequency noise prediction and control is feasible. The research completed in this paper as follows: First, the principle of statistical energy analysis is discussed, and the principle of subsystem division is summarized. According to these principles the cab acoustic-vibration system is divided into 116 structure subsystems and 8 acoustic cavity subsystems. These subsystems are connected with points,lines and surfaces. Finally the SEA model of a fully equipment cab is established.SEA model includes three major performance parameters—Modal density, Internal loss factor and Coupling loss factor. In order to determine these parameters, this paper studied the numerical calculation,experimental measurement and theoretical analysis aspects in-depth, and proposed a virtual test method for determining the complex sub-structure modal density. The method can be used to determine the the complex sub-structure modal density at the early stage of product design withno physical sample.Through the road test based on GB/T18697-2002, excitations from the road surface roughness vibration, engine vibration and the acoustic radiation, the cab suffered in various operating conditions, can be obtained. And also the interior noise level which is used to validate the SEA modal. Interior noise spectrum analysis shows that the amplitude of sound pressure level is higher in the 100Hz~1000Hz frequency range. It is the main focus band of noise energy.The performance parameters and excitations are involved in the calculation for the interior noise. Comparing the measure results with the calculate results in different work conditions show the validity of the SEA model.In order to improve interior noise prediction accuracy of the cab SEA model, this paper analysis the division method for cab acoustic subsystem and finally, determine a sub-division method.Then, using the SEA model tested by experiments, considering the driver's head acoustic cavity subsystem as study object for the energy transfer path analysis and find the main path of energy transfer. In the 200Hz~6300Hz frequency range, the dominant source of energy passed into the driver's head acoustic cavity subsystem is located that the energy was transmitted from the driver's bottom and rear acoustic cavity subsystem. This has important significance for noise control.Through the experimental research on leak and sound isolation of vehicle cab using a simple measurement method, the weak link of the cab is located. According to the"Equal Through Acoustic Volume"principle of soundproof hood design, the optimization design of the weak link isolation structure is achieved.Staring from the energy balance equation of statistical energy analysis model, with the basic principles of sensitivity analysis, a method for determining the layout of the damp panal in auto-body is derived. Damping material should be laid in the subsystems having the largest modal energy, instead of the subsystems with having the largest response.Noise control schemes are used to the SEA model and calculate the response of the interior noise. The results showed that the interior noise of cab is reduced 2.13dB(A) by taking above schemes, achieving the expected goals. Finally, the forward design method of forecast and control of the mid-high frequency noise for commercial vehicle cab is applied to new product development.