Excitation of Tyre Vibrations due to Tyre/Road Interaction

Doctoral thesis, 2004

Tyre/road noise is the main contributor to road traffic noise at speeds above 40 km/h for passenger cars and above 70 km/h for heavy trucks. Research has been carried out during the last thirty years in order to understand and quantify the generation mechanisms responsible for tyre/road noise. However, there is still substantial work remaining until tyre/road noise can be reduced substantially if at all. The work presented in this thesis concerns the modelling the tyre/roads interaction and the resulting vibrations of the tyre structure. The model is supposed to calculate the time varying forces when the road roughness is indenting the tyre tread during rolling. To achieve this, a contact model is developed, implemented and validated against measurements. The contact model is formulated in the time domain and considers a three-dimensional contact. An elastic half-space is used as a tool to describe the deformation of the tyre tread, and an iterative algorithm is utilised in order to solve the contact problem for each time step of the calculation. In parallel, an alternative quasi-three-dimensional contact model is also presented. Good agreement of calculated and measured tyre vibrations is found for different tyres and road surfaces. Additionally to the tyre vibrations air-pumping is included in the model in the form of the local deformations of the tyre tread due to road roughness indenting at the contact patch. The local deformation is believed to be a main contributor to tyre/road noise about 1 kHz. In this work, the local deformation is calculated from the deformation of the elastic half-space used for the contact problem. Preliminary qualitative results shows that the sound radiated due to local deformation dominates above 1-2 kHz whereas the sound radiated by the tyre structure vibrations dominates below 1-2 kHz. The model developed in this thesis is used to study the coupling between vibration pattern on the tyre and radiated sound. It is shown, that mainly the low order modes are contributing to the radiation and that the coupling between modes with respect to the radiated sound is essential.