Recent experimental results have shown that the vibration induced by the tire air cavity resonance is transmitted into the vehicle cabin and may be responsible for significant interior noise. The tire acoustic cavity is excited by the road surface through the contact patch on the rotating tire. The effect of the cavity resonance is that results in significant forces developed at the vehicle's spindle, which in turn drives the vehicle's interior acoustic field. This tire-cavity interaction phenomenon is analytically investigated by modeling the fully coupled tire-cavity systems. The tire is modeled as an annular shell structure in contact with the road surface. The rotating contact patch is used as a forcing function in the coupled tire-cavity governing equation of motion. The contact patch is defined as a prescribed deformation that in turn is expanded in its Fourier components.The response of the tire is then separated into static (i.e. static deformation induced by the contact patch) and dynamic components due to inertial effects. The coupled system of equations is solved analytically in order to obtain the tire acoustic and structural responses. The model provides valuable physical insight into the patch-tire-acoustic interaction phenomenon. The influence of the acoustic cavity resonance on the spindles forces is shown to be very important. Therefore, the tire cavity resonance effect must be reduced in order to control the tire contribution to the vehicle interior. The analysis and modeling of two feasible approaches to control the tire acoustic cavity resonances are proposed and investigated. The first approach is the incorporation of secondary acoustic iii cavities to detune and damp out the main tire cavity resonance. The second approach is the addition of damping directly into the tire cavity. The techniques presented in this dissertation to suppress the adverse effects of the acoustic cavity in the tire response, i.e.forces at the spindle, show to be very effective and can be easily applied in practice.iv

Different numerical sub-structuring techniques for the representation of tire modal behavior have been developed in the past 20 years. By using these numerical techniques reduced dynamic models are obtained which can not only be used for internal studies but also be provided to the automobile industry and linked to reduced dynamic vehicle models in order to optimize the coupled vehicle-tire response for noise vibration and harshness purposes. Two techniques that have been developed in a custom-made finite element code are presented: 1) the component mode synthesis type models for which the wheel center interface is free and 2) the Craig and Bampton type models for which the wheel center interface is fixed. For both techniques the interface between the tire and the ground is fixed. The choice of fixed or free wheel center boundary condition is arbitrary. In this paper we will compare the formulation of these two numerical methods, and we will show the equivalency of both methods by showing the results obtained in terms of frequency and transfer functions. We will show that the two methods are equivalent in principle and the reduced dynamic models can be converted from one to the other. The advantages-disadvantages of each method will be discussed along with a comparison with experimentally obtained results.

A series of tests were conducted to measure the dynamic stiffness transfer functions between the wheel center of a rim-mounted tire and the contact patch. Of particular interest was the interaction between the tire acoustic cavity mode and the modes of the tire/rim system. By varying the concentration of helium gas within the tire, it was possible to sweep the acoustic resonance through a group of rim/tire resonances. These results showed that there is relatively weak interaction between the cavity modes and the tire/rim modes. It was found that the resonance frequency of the cavity shifts downward with increasing tire load, and that only the z-direction dynamic stiffness is affected by load. Changes in inflation pressure were found to have no effect on the cavity resonance frequency, and increases in inflation pressure led to significant changes only in the x-direction dynamic stiffness. A simple analytical model of a coupled structural/acoustic system was found to produce results similar to those observed in the tire testing.