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.
Stockholm: KTH , 2006. , 17 p.