Development of methodologies and their applications on the improvement of vehicle NVH performance

In today's competitive automotive industry, analyzing the noise level inside a passenger compartment and determining the contributors to the interior noise level has become more important due to opportunities for improvement. Finding opportunities for improvement to provide customers with a more refined vehicle in terms of passenger compartment noise level provides an advantage to the automotive manufacturer over its competitors. In the first phase of our study, integration of Acoustic Source Quantification (ASQ) and SEA methodologies is aimed to model the interior noise level inside the passenger compartment. The ASQ Direct Method, briefly explained in theory part of section 2, has been used to perform Panel Contribution Analysis (PACA), in order to investigate regions with panels that contribute primarily to the interior noise level and to determine opportunities for refining the interior noise levels within vehicles. To determine the airborne contributions of engines, the ASQ Indirect Method, briefly explained in theory section, has been applied. Creating a contribution model using MATLAB (PACA and Engine ASQ), the interior noise level of the vehicle has been calculated and correlated with the test results. By performing further analysis on the interior noise contribution model and focusing on the panel contributions, the regions with the most contributing panels have been determined and interior noise refining actions have been applied. By applying interventions, which are the refining outputs of the panel acoustic contribution analysis, an improvement of up to 3 dB(A) for a few engine speed ranges has been obtained for the overall noise level of the vehicle. In addition to the panel contribution analysis, which is the primary focus of this study, thickness optimization of the inner dash isolator has been performed for a correlated SEA model, which confirms that no performance loss occurred in the acoustic transfer functions from the engine to the passenger compartment. The physical prototype of the optimized inner dash isolator has been assembled in the vehicle during the panel contribution analysis validation tests. The integration of the ASQ (direct & indirect) and SEA techniques may be offered as a unique method that can be applied in the refinement phase of product development when the physical vehicle is available, to release refined and lower weight vehicles. In the second phase of our work, we have developed an analytical model of a multilayer porous material based on the transfer matrix method to predict the absorption behavior at plane wave incidence. The aim of this study is to modify/tune the sound absorption coefficient of a felt to obtain an improved absorbing performance in the mid frequency range without increasing its weight. To achieve this target, the developed model has been used to find the best combination of each layer type and thickness. The analytical results were validated by test results. The second section consists of three parts. First, we describe the analytical model based on the transfer matrix method of a multilayer porous material to predict the sound absorption coefficient subjected to plane waves with a rigid backing boundary condition. Second, the sound absorption coefficient calculation result of the model for a multilayer material has been presented to obtain more absorbing performance in the mid frequency range without increasing its weight, which is the main objective of this study. Generally, the mid-frequency range sound absorption performances of felts are low compared to their performance in the relatively high frequency range. There may be some cases where one may want to increase the mid-frequency absorption performance of a felt without increasing its weight. In such cases, according to the experimental results shown in this section of our study, one can modify the sound absorption curve characteristic of a felt using elastic films and the air gap without increasing or decreasing its weight. Finally, the model results have been validated with the experimental results. There is a good agreement between the analytical and experimental results in terms of the amplitude of the sound absorption coefficient in most of the frequency range and the tendency of the behavior of the curve comparing different configurations. In conclusion, compared to the initial condition, with 12% less weight, one can gain 35% in the absorption performance in the relatively mid-frequency range with a loss (20%) in the relatively high frequency range. In the third phase of our work, we have developed an analytical model that uses the transfer matrix method to predict the transmission loss (TL) of a resonator system with a helical side branch duct connected to the main duct. The resonator system is tuned to a proper frequency range to be applied on vehicle in order to decrease the air intake pipe radiated noise of the selected passenger car below 1000 Hz. In order to fulfill the packaging requirements, the developed resonator does not require an additional volume. The designed helical resonator is a tunable resonator and can be tuned to the required frequency range by adjusting the dimensions. Resonator in our study is tuned to mainly 300 Hz – 600 Hz frequency range to decrease the noise level of the selected passenger car of which's air intake pipe radiated noise in the specified frequency range is high. Developed helical resonator has been analyzed numerically, the analytical results are first validated with the numerical ones, and the prototype part has been produced with rapid prototyping technique. Finally, the prototype part has been tested on a 1.6 l Gasoline Engine Vehicle. Our numerical calculations show that the 1D analytical approach yields satisfactorily accurate approximations in the 0 to 1000 Hz. The physical verification test results are well correlated with the numerical analysis results for both the pressure drop and the sound transmission loss. The developed tunable resonator shows significant improvement in the noise radiated from the AIS pipe between 300 and 600 Hz. This improvement resulted in a quieter passenger compartment. Considering these results, the designed tunable helical resonator is a solution for high AIS radiated noise in vehicles, especially those vehicles with small volume engine compartments where strict packaging requirements are necessary. The application of these resonators may become widespread with the further development of rapid prototyping techniques.