Francesco Timpone

A physical-analytical model for a real-time local grip estimation of tyre rubber in sliding contact with road asperities

This paper deals with the frictional behaviour of a tyre tread elementary volume in sliding contact with road asperities. Friction is assumed to be composed of two main components: adhesion and deforming hysteresis. The target, which was fixed in collaboration with a motorsport racing team and with a tyre-manufacturing company, is to provide an estimation of local grip for online analyses and real-time simulations and to evaluate and predict adhesive and hysteretic frictional contributions arising at the interface between the tyre tread and the road. A way to approximate the asperities, based on rugosimetric analyses on a macroscale and a microscale, was introduced. The adhesive component of friction was estimated by means of a new approach based on two different models found in the literature, whose parameters were identified thanks to a wide experimental investigation previously carried out. The hysteretic component of friction was estimated by means of an energy balance taking into account the viscoelastic behaviour of rubber (which was characterized by means of appropriate dynamic mechanical analysis tests) and the internal stress–strain distribution (which was due to indentations of the road). The model results are finally shown and discussed, and the validation experimental procedure is described. The correct reproduction of the friction phenomenology and the model prediction capabilities are highlighted, making particular reference to the grip variability due to changes in the working conditions.

A combined use of phase plane and handling diagram method to study the influence of tyre and vehicle characteristics on stability

This paper deals with in-curve vehicle lateral behaviour and is aimed to find out which vehicle physical characteristics affect significantly its stability. Two different analytical methods, one numerical (phase plane) and the other graphical (handling diagram) are discussed. The numerical model refers to the complete quadricycle, while the graphical one refers to a bicycle model. Both models take into account lateral load transfers and nonlinear Pacejka tyre–road interactions. The influence of centre of mass longitudinal position, tyre cornering stiffness and front/rear roll stiffness ratio on vehicle stability are analysed. The presented results are in good agreement with theoretical expectations about the above parameters influence, and show how some physical characteristics behave as saddle-node bifurcation parameters.

Software-in-the-loop development and validation of a Cornering Brake Control logic

In this article, a logic for vehicle dynamics control during partial braking while turning a corner is presented, which only requires knowledge of the instantaneous speed of the four wheels. For this reason, the proposed control algorithm can be adopted on all ABS equipped cars. A scheme of the simulation program for logic validation is described, which is constituted by a loop of software models of the principal vehicle subsystems which are singly illustrated. The proposed logic has been tested both in closed and open-loop maneuvers. The results are provided in the form of time histories of the principal analyzed quantities. The analysis of the results confirms the goodness of the proposed control strategy.

Ph.An.Ty.M.H.A.: a physical analytical tyre model for handling analysis – the normal interaction

A new analytical–physical tyre model for which the paternity has to be ascribed to Professor Giuseppe Capone was developed at the Department of Mechanical Engineering for Energetics at Naples University ‘Federico II’ with the support of the Bridgestone Technical Centre Europe. The whole model allows to obtain the road–tyre interactions so it can be used in vehicle dynamic simulations. The model has been named Ph.An.Ty.M.H.A., acronym of ‘PHysical ANalytical TYre Model for Handling Analysis’ and it includes the normal, longitudinal and lateral tyre–road interaction. Considering that Ph.An.Ty.M.H.A. is an analytical ‘deductive’ model, it is necessary to develop it starting just from the normal interaction, described in this paper, and then the other ones will be described in future papers. In fact, the normal interaction, i.e. the relationship between the normal load and the normal deflection, influences the tangential (longitudinal plus lateral) one, which determines the vehicle handling behaviour. The parameters used in this model are physical and geometrical so they can be measured on the real tyre. This property allows to better understand the tyre–road interaction mechanism. The tyre behaviour is modelled by analytical expressions based on equilibrium conditions and geometrical relations. To reproduce the experimental normal interaction and the pressure distribution, once the tyre geometrical quantities are known, it is necessary to identify some parameters, related to the tyre structure, by a comparison with the experimental data. Moreover, the predictive ability of the whole model, combined with a vehicle model, is very careful in analysing the vehicle handling [J.C. Dixon, Tyres, Suspensions and Handling, Cambridge University Press, Cambridge, 1991].

TYRE - ROAD INTERACTION: EXPERIMENTAL INVESTIGATIONS ABOUT THE FRICTION COEFFICIENT DEPENDENCE ON CONTACT PRESSURE, ROAD ROUGHNESS, SLIDE VELOCITY AND TEMPERATURE

In this paper the results of an experimental activity carried out with the aim to investigate on the frictional behaviour of visco-elastic materials in sliding contact with road asperities is presented.Experiments are carried out using a prototype of pin on disk machine whose pin is constituted by a specimen of rubber coming from a commercial tyre while the disk may be in glass, marble or abrasive paper. Tests are performed both in dry and wet conditions.Roughness of the disk materials is evaluated by a tester and by a laser scan device. Temperature in proximity of the contact patch is measured by pyrometer pointed on the disk surface in the pin trailing edge, while room temperature is measured by a thermocouple. Sliding velocity is imposed by an inverter controlled motor driving the disk and measured by an incremental encoder. Vertical load is imposed applying calibrated weights on the pin and friction coefficients are measured acquiring the longitudinal forces signal by means of a load cell.As regards to the road roughness, the experimental results show a marked dependence with road Ra index.Dry and wet tests performed on different micro-roughness profiles (i.e. glass and marble) highlighted that friction coefficient in dry conditions is greater on smoother surfaces, while an opposite tendency is shown in wet conditions.Although affected by uncertainties the results confirm the dependence of friction on temperature, vertical load and track conditions.© 2012 ASME

Tyre-Road Adherence Conditions Estimation for Intelligent Vehicle Safety Applications

It is well recognized in the automotive research community that knowledge of the real-time tyre-road friction conditions can be extremely valuable for intelligent safety applications, including design of braking, traction, and stability control systems. This paper presents a new development of an on-line tyre-road adherence estimation methodology and its implementation using both Burckhardt and LuGre tyre-road friction models. The proposed strategy first employs the recursive least squares to identify the linear parameterization (LP) form of Burckhardt model. The identified parameters provide through a Takagi-Sugeno (T-S) fuzzy system the initial values for the LuGre model. Then, it is presented a new large-scale optimization based estimation algorithm using the steady state solution of the partial differential equation (PDE) form of LuGre to obtain its parameters. Finally, real-time simulations in various conditions are provided to demonstrate the efficacy of the algorithm.

Multibody Model to Evaluate Quality Grasping of an Underactuated Mechanical Finger

A multibody model to analyse the gripping quality of an underactuated mechanical finger operated with tendon is described. To study the gripping ability of the finger a contact model that can simulate the interaction with the object to be taken has been developed. In the last section, some results related to the gripping of a spherical object, are described.

A Physical Analytical Model to Study the Elasto-Kinematic Behaviour of a MacPherson Suspension

This paper describes a physical analytical model able to characterize the elasto-kinematic behaviour of a MacPherson suspension for automotive applications. The presented model allows to determine the position and the orientation of the wheel upright as a function of the generalized three-dimensional loads applied to the center of the tire-road contact patch, and consequently to determine the variation of the characteristic suspension parameters of main interest: wheel base, track, camber and toe. All the steps carried out to build the model are described, starting from the kinematic analysis, ongoing with the static and finally with the elasto-kinematic ones, describing how compliance has been taken into account in equilibrium conditions. The kinematic and static analyses have been validated by comparing the results with the ones of a multibody model. In order to obtain the desired elasto-kinematic curves it is possible to act both on the geometry of the suspension, and on the stiffness of the bushings and of the arms, which cause compliance, modifying the positions of the various elements of the suspension and ultimately of the hub. By means of the proposed model it is possible to rapidly evaluate the effects of these variations. Numerical examples relative to a suspension for the front axle of a vehicle are presented.

A real-time approach to robust identification of tyre–road friction characteristics on mixed-μ roads

ABSTRACT The interaction between the tyre and the road is crucial for understanding the dynamic behaviour of a vehicle. The road–tyre friction characteristics play a key role in the design of braking, traction and stability control systems. Thus, in order to have a good performance of vehicle dynamic stability control, real-time estimation of the tyre–road friction coefficient is required. This paper presents a new development of an on-line tyre–road friction parameters estimation methodology and its implementation using both LuGre and Burckhardt tyre–road friction models. The proposed method provides the capability to observe the tyre–road friction coefficient directly using measurable signals in real-time. In the first step of our approach, the recursive least squares is employed to identify the linear parameterisation form of the Burckhardt model. The identified parameters provide, through a T–S fuzzy system, the initial values for the LuGre model. Then, a new LuGre model-based nonlinear least squares parameter estimation algorithm using the proposed static form of the LuGre to obtain the parameters of LuGre model based on recursive nonlinear optimisation of the curve fitting errors is presented. The effectiveness and performance of the algorithm are demonstrated through the real-time model simulations with different longitudinal speeds and different kinds of tyres on various road surface conditions in both Matlab/Carsim environments as well as collected data from real experiments on a commercial trailer.

Tyres shoulder section characterization by means of ESPI

In this work is exploited the possibility to use Electronic Speckle Pattern Interferometry (ESPI) for the characterization of different tyres with particular attention to the tyres shoulder section. Tyres characterization is of fundamental importance for vehicle dynamics modelling, since they are the main responsible of vehicles dynamical behaviour and thanks to their ability to deform, they allow to drive a vehicle generating the appropriate interaction forces at the interface with the road. Their behaviour is a consequence to their very complex structure. Two different racing tyres, one for car and other for motorcycle, have been considered. The investigation has been focused at the aim to evaluate and measure the section’s components in order to get accurate information about the different layers along through the tyres shoulder section. Here we demonstrate that the different layers (rubber, nylon, steel) can be easily highlighted and identified by mean of the ESPI that, thanks to its high sensitivity, is capable to estimate the different out of plane displacement of the different layers that respond in a different way (i.e. with a different deformation) to a thermal stimulus highlighting the layers themselves. Moreover, we introduce a de-noising step in the reconstruction process: in particular we enhance the wrapped phase information by using a suitable algorithm called SPADEDH. It is important to note that the assessment about the different layers along the section is a very difficult task to obtain by visual inspection or classical microscopy. In fact, the condition of the cutted surface, or rather the strong inhomogeneity and the roughness make impossible to obtain good images especially in the shoulder area.