Tyre modelling for rolling resistance

Increased efficiency in road vehicle is a demand in today’s society in the view of rising fuel cost and emission regulation. An important source for losses in road vehicles is tyre rolling resistance. For tyres with rolling resistance coefficient of 0.012, the fuel consumption due to tyre rolling resistance losses can amount to 20% - 30% of total consumption depending on the drive cycle, according to the study ‘the tyre: rolling resistance and fuel savings’ by Michelin, 2003. This study investigates mathematical models based on physical understanding and literature reviews of tyre rolling resistance phenomena. The work aims to develop a tyre model that explains the influence of tyre inflation pressure, tyre size, velocity and normal load on the rolling resistance coefficient. The model is based on free rolling condition without taking the longitudinal slip into account. The consideration of the model developed includes vertical tyre stiffness with geometrical belt constraint accounting for tyre vertical deflection and counter-deflection, tyre viscous and coulomb damping effect and rotational aerodynamic drag effect. The vertical stiffness model accounts for tyre geometry indirectly by means of constants in the model. The stiffness model and the simple lumped damping model together takes into account various hysteresis losses.\n\nThe tyre model developed for rolling resistance gives results which are in very good agreement with the experimental data. For example an 8.3% increase in tyre outer radius from 60 cm to 65 cm, the proposed model predicts a reduction of 4.8% in tyre rolling resistance coefficient compared to 5% suggested by experimental data. Furthermore, a change to low rolling resistance tyre in LeanNova’s energy simulation model corresponds to a reduction in the average energy consumption by 3.8% for a NEDC run in an electric vehicle and a reduction of 1.3% in average fuel consumption for a NEDC run in a conventional vehicle. Through these findings and the proposed tyre model that calculates rolling resistance by taking a limited number of tyre parameters into consideration, a foundation for physical understanding of tyre rolling resistance phenomena is established.