The Acoustic Cavity Mode and the Effects of Modal Coupling and Rotation on Force Transmission to the Hub

Concerns about tire noise radiation arise partly from city traffic planning, environmental protection and pedestrian safety standpoints, while from the vehicle passengers\u27 perspective, noise transmitted to the vehicle interior is more important. It is the latter concern that is addressed in this presentation. In particular, a tire’s internal, acoustical cavity resonance contributes significantly to tire-related structure-borne noise near 200 Hz, and it can easily be perceived by passengers. That acoustic mode can be suppressed by adding an absorptive lining to the tire’s interior. However, apart from the additional cost and weight of such tires, there are concerns with durability, and there is also an increased complexity when repairing them because of the need to avoid damaging the absorptive lining. In that light, modifying the design of the tire-rim and suspension system to decrease the cavity noise influence without the addition of sound absorbing material has a clear benefit. To that end, fully-coupled, structural-acoustic finite element tire models have been developed to study the force transmission to the hub, and how the force transmission is affected by the coupling of the acoustic mode with circumferential structural modes of the treadband. In the case of a static, loaded tire, for example simulation results have indicated that when the frequency of the vertical cavity mode matches with an odd-numbered, circumferential flexural mode of the treadband, the vibration levels transmitted from the tire to the hub and hence the vehicle’s suspension increase significantly. This situation is further complicated by effects of rotation which cause the modal frequency splits due to loading to increase with increasing speed, thus altering the modal coupling. These effects will be demonstrated in this presentation and compared with experimental results. Ultimately, if these coupling effects are clearly understood, it may be possible to to minimize the coupling between the acoustic and structural modes in specific speed ranges by altering structural mode locations through the adjustment of tire stiffness properties, for example, hence eliminating the need for the insertion of absorptive materials within the tire