Dynamic contact stiffness and air-flow related source mechanisms in the tyre/road contact

Licentiate thesis, 2013

Two aspect of phenomena occurring in, and in the vicinity of the contact patch formed by a tyre rolling on a road are here investigated: 1. A detailed numerical time domain contact model is used to evaluate approximations of the tread response that are commonly embraced in tyre/road interaction models. 2. A statistical approach is applied in the search to quantify the contribution from air-flow related source mechanisms to the total tyre/road noise. Effects of inertia and material damping when the tread is locally deformed are often neglected in many tyre/road interaction models. How the dynamic features of the tread affect contact forces and contact stiffness is here assess by simulating the detailed contact between an elastic layer and a rough road surface. The dynamic case, with an elastic layer impulse response extending in time, is compared with the case where the corresponding quasi static response is used. The results indicate that the significant effect of material damping may approximately be included as an increased stiffness in a quasi static tread model if not very detailed processes are to be predicted. There are at least two main tyre/road noise generation mechanisms: tyre vibrations and air-flow related source mechanisms (commonly referred to as air-pumping). This study investigates the importance of air-flow related noise sources by employing the fact that their vehicle speed dependence differs from the noise produced directly by tyre vibrations. Results show that air-flow related sources are significant contributors to measured tyre/road noise. A comparison with results from calculated rolling noise indicates that tyre vibrations in/close to the contact may lead to noise with air-flow characteristics.