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The understanding of tire’s adherence with a rough surface is a common goal for several fields in the automotive sector. In fact, grip is synonym of safety and performance, playing a decisive role for braking distance and vehicle stability, fuel consumption, wear rate [1], noise generation and for the vehicle dynamics control system (e.g. ABS, TCS, AYC and other) [2]. This paper deals with tire tread grip experimental investigation and evaluation under different conditions that influence it during the sliding contact [3]. In this regard the test campaign involves the use of different tire compounds (in terms of viscoelastic characteristics), tested in several conditions: different contact pressure, sliding speed, temperature, sliding contact length and road surface. The test bench employed by the UniNa Vehicle Dynamic Research Group is an upgrade of the British Pendulum, an instrument for outdoor tribological tests on road sections. The principal sensors installed on the test bench are an encoder, for the evaluation of the sliding speed of the tire specimen, and a load cell, for the measurement of the force arising at tire/road interface in the longitudinal and vertical directions [4]. In fact, the grip shall be determined as the ratio of the longitudinal force and corresponding load on the tire. The paper's aim is the description of the experimental campaign after an accurate introduction on the test setup and an illustration of the equipment. Finally, the preliminary results and the methodologies used to process the acquired data are described.

This paper investigates the capability of the fraction derivative Maxwell model to reproduce the mechanical behaviour of advanced viscoelastic materials, that are designed to be able to dissipate energy in an extended range of frequency than traditional viscoelastic materials and present a more complex shape of strain-stress frequency response. Fraction derivative models, compared to traditionally used generalized Maxwell model, can reproduce the material behaviour with a smaller number of parameters, reducing the utilization complexity and the computational burden.

The implementation of a tire model in a simulation environment is fundamental to characterize the vehicles and to predict the dynamic behaviour during the design phase, e.g. to test automotive control systems like ADAS [1] or different parameters or working conditions like tire compound, pressure, and speed. Moreover, the output of a tire model can be employed also to predict its temperature distribution [2]. This paper deals with the comparison between different Pacejka formulations, differing for the sensitivity to physical factors, like inflation pressure and slight analytical variations. Since the discussed tire models are different version of the same formulation, the microparameters concerning specific physical effects have been zeroed, in order to make the comparison more reliable. In particular, a Pacejka’s MF 5.2 has been compared towards the MF 6.1 tire model employing a tire vehicle in specific dynamic manoeuvres. Some longitudinal (braking and acceleration) and lateral manoeuvres (spiral, steering pad, fishhook, line change, constant speed curve) have been adopted to compare the results of the implemented tire model influence on the overall vehicle dynamics. Finally, to evaluate the effect of different tire configurations, a sensitivity test was carried out.

The numerical prediction of rubber friction properties is a great challenge from the modelling point of view. In many applications such as tyres, sealing systems, conveyor belts, the observed friction process arises from complex mechanisms occurring at the interface rubber/substrate [1]. During the sliding contact between two deformable bodies, the friction main contributions can be accountable in adhesive and hysteretic causes [2]. The adhesive contribution is related to the formation and breaking of the adhesive bridges in the real contact points inside the nominal contact region, instead the hysteretic contribution is related to the deformation cycles that result in energy losses due to the viscoelastic behaviour of the bodies. Due to these mechanisms, a frictional force is generated during the relative sliding between two bodies. As concerns the hysteretic contribution, previous studies [3] showed that even in the absence of adhesion in the contact region, the contact pressure is distributed in a non-symmetrical manner causing a force of resistance that opposes the motion. In this paper, a physical-analytical model is developed to calculate the friction hysteretic component of a tyre tread elementary volume in sliding contact with road asperities. In this study, the road macroscale is only considered. The shape of the asperity is modelled as the osculating sphere [4]. The model is based on the energy balance between the work done by the friction force component and the energy dissipated in the material due to hysteresis. The compound viscoelastic properties are defined in terms of storage and loss moduli by means D.M.A. experimental tests. The internal dissipated energy is evaluated considering the stress and strain field calculated by Hamilton formulation [5]. Finally, some consideration about further model improvements are made regarding the introduction of a complete road spectrum (PSD) and the material modelling by fractional derivative algorithms.

In recent years, autonomous vehicles and advanced driver assistance systems have drawn a great deal of attention from both research and industry, because of their demonstrated benefit in reducing the rate of accidents or, at least, their severity. The main flaw of this system is related to the poor performances in adverse environmental conditions, due to the reduction of friction, which is mainly related to the state of the road. In this paper, a new model-based technique is proposed for real-time road friction estimation in different environmental conditions. The proposed technique is based on both bicycle model to evaluate the state of the vehicle and a tire Magic Formula model based on a slip-slope approach to evaluate the potential friction. The results, in terms of the maximum achievable grip value, have been involved in autonomous driving vehicle-following maneuvers, as well as the operating condition of the vehicle at which such grip value can be reached. The effectiveness of the proposed approach is disclosed via an extensive numerical analysis covering a wide range of environmental, traffic, and vehicle kinematic conditions. Results confirm the ability of the approach to properly automatically adapting the inter-vehicle space gap and to avoiding collisions also in adverse road conditions (e.g., ice, heavy rain).