Modelling Interfacial Details in Tyre/Road Contact — Adhesion Forces and Non-Linear Contact Stiffness

Doktorsavhandling, 2005

Rolling resistance, noise generation, and wear are all determined by the interaction process between the rolling automotive vehicle tyre and the road. A deep understanding of the interaction process is needed for optimisation aiming at reducing these effects. Details in the tyre/road contact interface are considered in the presented work; non-linear contact stiffness and adherence forces at the interface are investigated and modelled. A description of the tyre structure and especially its tread layer is required for contact modelling. The dynamic responses of smooth and patterned passenger-car tyres are experimentally investigated. Experimental results are used to validate a high-frequency tyre model based on the elastic field equations, which includes the local deformation of the tread. The separation process when tyre tread blocks are rapidly separated from road surfaces is investigated in an experiment. This process is described with the aid of the total contact force and noise generation. Based on the experimental results, a model for the adherence force as a function of load, load duration, and unloading rate is proposed. Optimisation of the tyre/road interaction including interfacial details requires time-domain contact models including a wide range of length-scales. The strategy is to divide the contact problem into different ranges of length-scales. A model based on statistical description of the contact geometry is used on the smallest length-scales. A tread block in contact with the road surface is modelled on intermediate length-scales, and on the largest length-scales is a contact model of the complete tyre structure rolling over the road surface. The two latter models use a numerical time-domain contact formulation with a discretised contact geometry. These three models are connected via constitutive relations between contact pressure and relative displacements, incorporated as non-linear springs between the contact elements. The modelling approach is still under development but preliminary results are presented.