Modelling the vibrations on a rolling tyre and their relation to exterior and interior noise

Doctoral thesis, 2011

For most modern cars at normal driving speeds, tyre/road interaction is a major source to the exterior as well as interior vehicle noise. The interaction between a tyre and a road surface generates tyre structure vibrations, leading to sound radiation into the surrounding air, and to dynamic forces acting on the wheel hub. These forces are transmitted via the suspension system to the car body, resulting in sound radiation into the passenger compartment. To reduce the exterior and interior noise produced by rolling tyres, a deep understanding is required of the physics involved in the excitation, transmission and radiation of tyre structure vibrations. The focus of this thesis is on modelling of the vibrations on a rolling tyre and their relation to the sound radiation and the forces acting on the wheel hub. To be specific, state-of-the-art simulation tools, involving a tyre model, tyre/road contact model and radiation model, are used to first identify the modes on a tyre responsible for the radiation of sound during rolling. It was found that in the critical frequency range around 1000 Hz, where maximum radiation occurs, the radiation is mainly due to low-order modes. These modes are not the ones with the strongest excitation around 1 kHz, but have high enough radiation efficiency to dominate the sound radiation. The tyre model is then modified to incorporate the air-cavity and wheel, and used in connection with the contact model to simulate the forces acting on a blocked hub during rolling. It was found that the transmission is strongly influenced by three modes: the radial semi-rigid body mode on the tyre, the first mode inside the fluid cavity and a wheel mode. Further, the spectra of the hub forces are concentrated to the low-frequency range (up to say 250 Hz). Finally, the thesis is also concerned with the extension of an existing contact model for tyre/road interaction to encompass the tangential contact forces. The model is first validated towards an alternative contact formulation found in the literature. Thereafter, a minor parametric study is conducted to see the influence of rolling speed, road surface roughness and longitudinal slip ratio on the total radial and tangential contact force.