Some torsional stiffness and damping characteristics of a small pneumatic tyre and the implications for powertrain dynamics

Abstract

Torsional vibration modelling of powertrains is hindered by the lack of understanding of tyre low-frequency torsional stiffness and damping characteristics. Torsional here means rotation about the wheel (spin) axis so that the rotation of the wheel hub is different from that of the periphery of the tyre. This paper explains a simple, practical test rig design that can be used to determine a tyre's torsional characteristics via simple modelling. The model assumes a complex stiffness that allows the damping type to be determined as a function of the frequency. The measurement of some torsional stiffness and damping characteristics of a small pneumatic tyre while under load and rolling is presented. The tyre was excited torsionally and, from the results obtained, the tyre's torsional stiffness and damping characteristics were calculated. The investigations were concerned with the low-frequency characteristics. It was found that there was a large torsional vibration associated with the tread pattern. Over the frequency range tested (10–50Hz), it was found that the damping is more accurately represented as hysteretic and not viscous when lightly loaded. The effects of rotational speed, preload, and inflation pressure on the stiffness and damping were also investigated. The damping type for the tyre (hysteretic or viscous) was found to vary depending on the loading and excitation. Tyre properties were then included in a lumped-inertia, frequency-domain powertrain model and the steady-state response predicted. The results indicated that the viscous or hysteretic damping assumption has significant effects on the predicted frequency response of the powertrain. The need for further studies investigating the damping characteristics of automotive tyres in torsion is therefore recommended.