The Influence of Tyre Rotation on the Vertical Tyre Force Transmission and Tyre Kinematics

Development and validations of safety relevant vehicle dynamics control systems and automated driving functions are increasingly done on hardware- and driver-in-the-loop test systems such as driving simulators. Tyre models that are used in these test systems have to be numerically efficient. Semi-physical tyre modelling approaches prove their worth in this field of advanced vehicle handling dynamics. To enhance the transferability of test system behaviour to real-life operation, effects that are influencing the tyre behaviour have to be considered, such as tyre temperature or transient effects.
Conventional empirical and semi-physical tyre models do not yet fully consider the influence of the tyre rotation on the tyre behaviour. Thus, the present thesis deals with a detailed experimental investigation and semi-physical modelling of the influence of the tyre rotational speed on the vertical tyre stiffness, the free unloaded, the static loaded and the effective (dynamic) tyre radius which are crucial quantities for an accurate description of tyre kinematics such as slip computation and of tyre force transmission.
An extensive and detailed tyre testing series on an indoor tyre test rig with two types of radial ply tyres was carried out to quantify the influence of tyre rotation and identify the rotational speed induced effects and mechanisms. The rotational speed dependent behaviour of both test tyres was investigated by means of two specifically designed measurement manoeuvres in a wide travelling velocity range from 0 to 180 km/h at several different operating conditions. The tested tyres show a distinct rotational speed dependent behaviour. In detail, a nearly linear rotational speed induced increase of vertical stiffness and a non-linear progressive increase of the unloaded radius. The static and effective radius also react progressively due to the non-linear progressive variation of the unloaded radius.
Based on the semi-physical TMeasy 5 handling tyre model and the findings of the experimental investigation, an enhanced modelling approach is presented which is able to consider the identified rotational speed dependent tyre behaviour in an effective semi-physical and numerically efficient manner.
A final validation by means of measurement data shows that the presented enhanced semi-physical modelling approach for the vertical tyre force transmission and tyre kinematics is qualified to approximate the rotational speed dependent behaviour of tyre stiffness and tyre radii with sufficient accuracy from the engineering point of view.