Power dissipation in car tyres
Sammanfattning: Traffic is a major source of green house gases. The transport fieldstands for 32 % of the energy consumption and 28 % of the totalCO2 emissions, where road transports alone causes 84 % of these figures. The energy consumed by a car traveling at constant speed, isdue to engine ineffiency, internal friction, and the energy needed toovercome 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 fuelconsumption improvements ranging from 0.5 to 1.5 % for passengercars and light trucks and 1.5 to 3 % for heavy trucks.The objective of this thesis is to estimate the power consumptionin the tyres. To do this a car tyre is modeled with waveguide finiteelements. A non-linear contact model is used to calculate the contactforces as the tyre is rolling on a rough road. The contact forces combinedwith the response of the tyre is used to estimate the input powerto the tyre structure, which determines a significant part of the rollingresistance. The tyre model accounts for: the curvature, the geometry of thecross-section, the pre-stress due to inflation pressure, the anisotropicmaterial properties and the rigid body properties of the rim. The modelis based on design data. The motion of the tyre belt and side wall isdescribed with quadratic anisotropic, deep shell elements that includespre-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 experimentalmodal analysis has been made. The model agrees very wellwith point mobility measurements up to roughly 250 Hz. The eigenfrequency prediction is within five percent for most of the identifiedmodes. The estimated damping is a bit too low especially for the antisymmetric modes. Above 500 Hz there is an error ranging from 1.5 dBup to 3.5 dB for the squared amplitude of the point mobility.The non proportional damping used in the model is based on an adhoc curve fitting procedure against measured mobilities.The contact force predictions, made by the division of appliedacoustics, Chalmers University of Technology, are based on a non-linearcontact model in which the tyre structure is described by its flexibilitymatrix. Topographies of the surface are scanned, the tread pattern isaccounted for, and then the tyre is ’rolled’ over it. The contact forcesare inserted into the tyre model and the response is calculated. Thedissipated power is then calculated through the injected power and thepower dissipated within each element. Results are promising comparedto literature and measurements.
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