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

For most modern cars at normal driving speeds, tyre/road interaction is a major source tothe exterior as well as interior vehicle noise. The interaction between a tyre and a roadsurface generates tyre structure vibrations, leading to sound radiation into the surroundingair, and to dynamic forces acting on the wheel hub. These forces are transmitted via thesuspension 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 understandingis required of the physics involved in the excitation, transmission and radiationof tyre structure vibrations. The focus of this thesis is on modelling of the vibrationson a rolling tyre and their relation to the sound radiation and the forces acting on thewheel 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 tyreresponsible for the radiation of sound during rolling. It was found that in the critical frequencyrange around 1000 Hz, where maximum radiation occurs, the radiation is mainlydue to low-order modes. These modes are not the ones with the strongest excitationaround 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 connectionwith the contact model to simulate the forces acting on a blocked hub duringrolling. It was found that the transmission is strongly influenced by three modes: theradial semi-rigid body mode on the tyre, the first mode inside the fluid cavity and a wheelmode. 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 existingcontact model for tyre/road interaction to encompass the tangential contact forces. Themodel 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 contactforce

A waveguide finite element aided analysis of the wave field on a stationary tyre, not in contact with the ground

Although tyre/road noise has been a research subject for more than three decades, there is still no consensus in the literature as to which waves on a tyre are mainly responsible for the radiation of sound during rolling. Even the free vibrational behaviour of a stationary (non-rotating) tyre, not in contact with the ground, is still not well understood in the mid- and high-frequency ranges. Thus, gaining an improved understanding of this behaviour is a natural first step towards illuminating the question of which waves on a rolling tyre contribute to sound radiation. This is the topic of the present paper, in which a model based on the waveguide finite element method (WFEM) is used to study free wave propagation, on a stationary tyre, in the range 0-1500 Hz. In the low-frequency region (0-300 Hz), wave propagation is found to be rather straightforward, with two main wave-types present. Both have cross-section modes involving a nearly rigid motion of the belt. For higher frequencies (300-1500 Hz) the behaviour is more complex, including phenomena such as 'curve veering' and waves for which the phase speed and group speed have opposite signs. Wave-types identified in this region include (i) waves involving mainly sidewall deformation, (ii) belt bending waves, (iii) a wave with significant extensional deformation of the central belt region and (iv) a wave with a 'breathing' cross-section mode. The phase speed corresponding to found waves is computed and their radiation efficiency is discussed, assuming free-field conditions. In a future publication, the tyre model will be used in conjunction with a contact model and a radiation model to investigate the contribution of these waves to radiated sound during rolling. (C) 2010 Elsevier Ltd. All rights reserved