DEVELOPMENT OF A GRIP & THERMODYNAMICS SENSITIVE TYRE / ROAD INTERACTION FORCES ESTIMATION PROCEDURE EMPLOYED IN HIGH-PERFORMANCE VEHICLES SIMULATION

Abstract

The target of the activities described in the PhD thesis, fixed in collaboration with a motorsport racing team, with a high performance vehicle manufacturing company and with a tyre research and development technical centre is the development of a procedure able to estimate tyre interaction characteristics, reproducing them in simulation environments taking into account the fundamental friction and thermal phenomena concerning with tyre/road interaction.
A first tool, called TRICK, has been developed with the aim to process data acquired from experimental test sessions, estimating tyre interaction forces and slip indices. Once characterized the vehicle, filtering and sensors output correction techniques have been employed on the available data, creating a robust procedure able to generate as an output a "virtual telemetry" and, following a specifically defined track driving routine, to provide tyre interaction experimental curves.
TRICK virtual telemetry can be employed as an input for the second tool, TRIP-ID, developed with the aim to identify the parameters of a Pacejka Magic Formula tyre model. The advantage of this kind of procedure is the possibility to simulate the behaviour of a tyre without the bench characterizations provided by tyremakers, with the further benefit to reproduce the real interactions with road and the phenomena involved with it, commonly neglected in bench data.
Among such phenomena, one of the most important is surely the effect that temperature induces on tyre performances, especially in racing applications. For this reason a specific model, called TRT, has been realized and characterized by means of proper thermodynamic tests, becoming a fundamental instrument for the simulation of a tyre behaviour as close to reality as possible. One of the most useful features provided by the model is the prediction of the so called "bulk temperature", recognized as directly linked with the tyre frictional performances.
With the aim to analyse and understand the complex phenomena concerning with local contact between viscoelastic materials and rough surfaces, GrETA grip model has been developed. The main advantage to which the employment of the grip model conducts is constituted by the possibility to predict the variations induced by different tread compounds or soils on vehicle dynamics, leading to the definition of a setup able to optimise performances as a function of tyre the working conditions.
The described models and procedures can cooperate, generating a many-sided and powerful instrument of analysis and simulation; the main features of the available employment solutions can be summarised as follows:
 full geometric, thermodynamic, viscoelastic and structural characterization of tyres on which the analyses are focused;
 estimation of the tyre interaction characteristic curves from experimental outdoor test data;
 definition of a standard track driving procedure that employs tyres in multiple dynamic and thermal conditions;
 identification of Pacejka Magic Formula tyre models parameters on the basis of the estimated tyre interaction characteristic curves;
 estimation of surface, bulk and inner liner tyre temperatures for variable working conditions and real-time reproduction of tyre thermodynamic behaviour in simulation applications;
 correlation of tyre thermal conditions with friction phenomena observable at the interface with road;
 prediction of tyre frictional behaviour at tread compound and soil roughness variations;
 modelling of tyre interaction by means of MF innovative formulations able to take into account grip and thermodynamic effects on vehicle dynamics;
 definition of the optimal wheels and vehicle setup in order to provide the maximum possible performances improvement.