Concept tire model for noise, vibration and harshness analysis

Noise, Vibration and Harshness (NVH) analysis is largely used in the automotive industry to simulate the interior noise and comfort of the vehicles in driving conditions. Modern tire models when coupled to a suspension and vehicle body model can correctly predict the interior noise for frequency up to 300 Hz. A limitation of this tire models is that there is no direct relationship between model parameters and tire physical parameters. LMS has developed a concept tire model, whose parameters have a direct relation with tire physical properties such as geometry, mass and stiffness of the tread band and sidewall. The concept model is a Finite Elements (FE) model with a certain number of parameters that have to be identified through an optimization process based on modal comparison. The existing concept tire model can simulate the tire road noise phenomena up to 180 Hz and presents an important amplitude error in the 80-180 Hz frequency range. Furthermore the optimization process requires a large amount of data that have to be experimentally acquired and processed that require a strong time effort. A new concept tire model and a new parameter identification process has been designed in this master thesis. The new model is constituted by shell and springs elements modeling the tire and the rim and by brick elements modeling the tire air cavity. The new optimization process is based on a direct comparison of model FRFs with test FRFs. The new model has been optimized both with the modal method and with the new method showing strong differences in the final correlation with test FRFs for the two cases. The new concept model optimized with the new method shows very good correlation up to 240 Hz and is capable to simulate the tire air cavity resonance. The total time of the parameters identification, with the new method, has been reduced by twice. The new concept model and process have been validated on three different tires with different geometrical characteristics and hence different frequency response functions. The validation has shown that the new model optimized with the new process can simulate the tire FRFs relevant for NVH applications with very low amplitude error up to 240 Hz. The new tire model has been coupled through Frequency Based Substructuring (FBS) to a vehicle model identified with Transfer Path Analysis (TPA) methods to generate a full vehicle model. Using operational accelerations measured on the knuckle and the full vehicle model, an inverse road surface identification has been performed that has been used as input for the full vehicle model. The target responses (noise and vibrations in the cabin) have been predicted by the full vehicle model with low amplitude error with respect to the measured operational responses. Eventually a sensitivity analysis has been performed to study the influence of tire physical characteristics (such as tire mass and belt stiffness) on vehicle interior noise by changing the tire model equivalent parameters and predicting the target response, i.e. the interior noise.