Power dissipation in car tyres

Traffic is a major source of green house gases. The transport field stands for 32 % of the energy consumption and 28 % of the total CO2 emissions, where road transports alone causes 84 % of these figures. The energy consumed by a car traveling at constant speed, is due to engine ineffiency, internal friction, and the energy needed to overcome resisting forces such as aerodynamic drag and rolling resistance.Rolling resistance plays a rather large role when it comes to fuel economy. An improvement in rolling resistance of 10 % can yield fuel consumption improvements ranging from 0.5 to 1.5 % for passenger cars and light trucks and 1.5 to 3 % for heavy trucks. The objective of this thesis is to estimate the power consumption in the tyres. To do this a car tyre is modeled with waveguide finite elements. A non-linear contact model is used to calculate the contact forces as the tyre is rolling on a rough road. The contact forces combined with the response of the tyre is used to estimate the input power to the tyre structure, which determines a significant part of the rolling resistance. The tyre model accounts for: the curvature, the geometry of the cross-section, the pre-stress due to inflation pressure, the anisotropic material properties and the rigid body properties of the rim. The model is based on design data. The motion of the tyre belt and side wall is described with quadratic anisotropic, deep shell elements that includes pre-stress and the motion of the tread on top of the tyre by quadratic, Lagrange type, homogenous, isotropic two dimensional elements. To validate the tyre model, mobility measurements and an experimental modal analysis has been made. The model agrees very well with point mobility measurements up to roughly 250 Hz. The eigenfrequency prediction is within five percent for most of the identified modes. The estimated damping is a bit too low especially for the antisymmetric modes. Above 500 Hz there is an error ranging from 1.5 dB up to 3.5 dB for the squared amplitude of the point mobility. The non proportional damping used in the model is based on an ad hoc curve fitting procedure against measured mobilities. The contact force predictions, made by the division of applied acoustics, Chalmers University of Technology, are based on a non-linear contact model in which the tyre structure is described by its flexibility matrix. Topographies of the surface are scanned, the tread pattern is accounted for, and then the tyre is ’rolled’ over it. The contact forces are inserted into the tyre model and the response is calculated. The dissipated power is then calculated through the injected power and the power dissipated within each element. Results are promising compared to literature and measurements.QC 20101112</p