Hubert Sar

Investigation of the tyre characteristics under non-steady-state conditions on the basis of road tests

This paper presents a method of identifying the dynamic characteristics of tyres for non-steady-state conditions on the basis of road measurements on a vehicle. The side force acting on the tyre is presented as a function of not only the slip angle but also the slip angle derivative (i.e. the velocity of the change in the slip angle). Hence, the influence of the manoeuvre dynamics on the tyre characteristics and the difference between the characteristics obtained for steady-state conditions and the characteristics for non-steady-state conditions are shown. Also the results of computer simulations prepared for different types of tyre characteristics are presented in this paper. It is evident from the presented graphs that applying dynamic non-linear tyre characteristics for computer simulations instead of steady-state characteristics enables us to describe the real motion of a vehicle better.

Investigation of adhesion characteristics of different tyre types in different weather conditions

Tyre-to-road adhesion has a great influence on transmitting forces between wheels and road surface and in the consequence on the safety of automobile motion. It plays significant role in vehicle motion modelling, especially for the needs of traffic accidents reconstruction and the development of active safety systems in automobiles. Simultaneously, the knowledge about tyre-to-road adhesion is limited, especially in case of the differences between anti-slip properties of summer and winter tyres. In the paper, method of the measurement of tyre-to-road adhesion coefficient is presented. The measurement system SRT-4 consists of special dynamometer trailer, towing vehicle and test-measuring equipment. It was designed for the needs of road engineering and further developed in the Institute of Vehicles of Warsaw University of Technology. It enables to obtain adhesion characteristics, i.e. graph of adhesion coefficient as a function of wheel slip ratio. In the article, examples of tyre-toroad adhesion characteristics and velocity characteristics of peak adhesion coefficient for different types of tyres (summer, winter) in different weather conditions are presented. Differences in characteristics courses caused by tyre type and weather conditions are discussed. For instance, in case of winter tyres it was noticed that their peak value of adhesion coefficient was reached for higher values of slip ratio than it was observed for summer tyres.