Conference Paper

TIRE THERMAL CHARACTERIZATION: TEST PROCEDURE AND MODEL PARAMETERS EVALUATION

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Abstract

The TRT model, developed to accurately reproduce the tire thermal dynamics in all the vehicle working conditions, has to be physically characterized [1][2]. An appropriate non-destructive procedure, that allows to obtain the thermal diffusivity of completely different tire layers, is described. The heat is directly supplied on the tire tread surface trough a specifically powered laser, while two thermal cameras acquire temperatures reached on both the outer and the inner layers. Using the above instrumentation layout to acquire the tire radial and circumferential temperature gradients and a specifically developed mathematical TRTLab model based on the use of Fourier's equation of diffusion applied to a three dimensional domain, allows to estimate the tire thermal diffusivity.

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... Furthermore, the radial arrangement reduces fatigue and wear: being the sidewall thinner, the material is less subjected to hysteresis, occurring for shear between plies and generating heat to be dissipated. Radial tyres are characterized by better grip, more stability and a higher braking efficiency, acting as safer than conventional ones; they also allow greater energetic saving (increased durability and fuel economy) and a greater level of comfort (more shock absorption) (Allouis et al., 2016). The other type of structure, still used in some applications for trucks, trailers and farm implements, is called diagonal or bias because of the plies cross on the carcass being disposed according to proper inclinations respect to equatorial plane called "crown angles". ...
... The resultant couple M is simply the moment about the point O, but any other point could be selected. The traditional components of the magnitudes in equation set (4) have been already defined and are summarized in the following: F x is the longitudinal force, F y is the lateral force; F z is the vertical load (or normal force); M x is the overtuning moment, M y is the rolling resistance moment and M z is the self-aligning torque (Allouis et al., 2016). ...
... These expressions state that the vertical load depends on tyre deformations, whereas the longitudinal and lateral forces depend on the corresponding slip factors, longitudinal and lateral, respectively. In the following paragraphs, the longitudinal and lateral load will be briefly described; for more details about the tyre-road interaction, see the suggested references (Allouis et al., 2016;Batchelor, 2000). ...
Chapter
This chapter deals with tyre mechanics and it has a particular focus on thermal effects on its dynamical behaviour. In the first part the typical tyre structure is introduced together with the tyre mechanical/dynamical behaviour according to a classical approach, so recalling the main kinematic and dynamic quantities involved in tyre pure and combined interactions. The core of this chapter is the description of a physical-analytical tyre thermal model able to determine the thermal status in each part of the tyre useful for vehicle dynamics modelling and driving simulations in order to take into account thermal effects on tyre interactions and consequently on vehicle dynamical behaviour. Successively also the tyre wear modelling is faced, after a brief introduction to the different models available in literature some considerations are reported concerning the thermal effects on wear.
... Such complex structure is necessary for supporting the interaction forces with the road. In literature there are different models able to describe tyre behavior both based on an physical approach [1][2][3][4][5][6][7][8][9][10][11][12] and based on an empirical one [13][14][15][16] . In order to parametrize physical based models [1][2][3][4][5][6][7][8][9][10][11][12] , it is very significant the knowledge about the * Corresponding author. ...
... In literature there are different models able to describe tyre behavior both based on an physical approach [1][2][3][4][5][6][7][8][9][10][11][12] and based on an empirical one [13][14][15][16] . In order to parametrize physical based models [1][2][3][4][5][6][7][8][9][10][11][12] , it is very significant the knowledge about the * Corresponding author. E-mail address: v.pagliarulo@isasi.cnr.it ...
... thickness of the different tyre layers. This aspect is particularly important as it concerns the physical models describing the tyre thermal behavior [8][9][10] , the tyre grip behavior [1,2,6,7] and the tyre wear [11] . In this study two motorsport high performance tyres ( Fig. 1 ), one for automotive (Michelin S9H used in GT2 race) and the other for motorcycle applications (Pirelli Diablo Superbike used in superbike race) have been considered as test case. ...
Article
In this work is exploited the possibility to use two optical techniques and combining their measurements for the 3D characterization of different tyres with particular attention to the tyre's section. Electronic Speckle Pattern Interferometry (ESPI) and Laser Scanner (LS) based on principle of triangulation have been employed for investigating and studying the tyre's section and 3D shape respectively. As case studies two different racing tyres, Michelin S9H and Pirelli Diablo respectively, have been considered. The investigation has been focused at the aim to evaluate and measure the section's components in order to add to the 3D model obtained by Laser Scanning accurate information about the different layers along through the tyres sections. 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 and even with the LS. Here we demonstrate that the different layers can be easily highlighted and identified by mean of the ESPI.
... In particular, the thermodynamic non-linear characteristics of different materials have been estimated employing the testing non-destructive methodology described in [44], allowing to estimate the diffusivity characteristics of the tyre tread starting from the acquisitions of the temperature gradients on the tyre external and internal surfaces established as a consequence of the application of a known heating power source and its propagation through the internal layers. The procedure requires two thermal cameras pointed on the opposite sides of the tyre tread, external surface and internal innerliner, acquiring the temperatures in radial and circumferential directions. ...
... The procedure requires two thermal cameras pointed on the opposite sides of the tyre tread, external surface and internal innerliner, acquiring the temperatures in radial and circumferential directions. The non-linear diffusivities are determined applying boundary conditions of a specifically designed testing procedure [44], solving a minimization iterative problem between the model temperature outputs and the experimentally acquired ones. Since the material diffusivity parameters are not constant, but they deeply depend on the model thermal state, the diffusivity of each node in each direction of interest will be different per each step: for this reason, the transient phase is particularly important due to higher thermal gradients within the composite structure to accurately identify the tyre node intrinsic characteristics. ...
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Article
The characterization and reproduction of tyre behaviour for vehicle modelling is a topic of particular interest both for real-time driver in the loop simulations and for offline performance optimization algorithms. Since the accuracy of the tyre forces and moments can be achieved by the accurate physical modelling of all the phenomena concerning the tyre-road interaction, the link between the tyre thermal state and the tyre frictional performance turns into a crucial factor. An integrated numerical methodology, allowing to couple the full 3D CFD (Computational Fluid Dynamics) flux within the internal chamber of the tyre with an equivalent discrete 3D structure model, is proposed with the aim to completely represent the tyre thermodynamic convective behaviour in the steady-state operating conditions. 3D CFD model enables the evaluation of the internal distribution of the gas temperature and of the thermal powers exchanged at each sub-wall in detail. This allows to increase the reliability of the tyre thermodynamic modelling with a particular reference to the proper managing of the aero-thermal flow of the brake disc impact on the rim temperature and therefore on the internal gas dynamics in terms of temperature and pressure, being able to optimize the tyre overall dynamic performance in both warm-up and stabilized thermal conditions. The steady RANS (Reynolds Averaged Navier-Stokes) simulations have been performed employing the 3D CFD model in a wide range of angular velocities with the aim to calculate the convective thermal flux distributions upon rim and inner liner surfaces. The simulation results have been then exploited to derive the convective heat transfer coefficients per each sub domain to be employed within the real-time tyre physical thermal model, with the peculiar advantage of an enhanced model reliability for thermal characteristics. To validate the proposed methodology, the tyre thermal model outputs, in terms of temperatures of internal and external layers, have been validated towards the acquired ones within the specific routine performed on tyre force and moment test bench, confirming an excellent agreement with the experimental data in the entire range of operating conditions explored.
... The tire structure was lacking of sidewalls and so the model was not able to reproduce the temperature distribution in all the parts of the system, losing important elements influencing the tire behavior. In any case, the availability of the bulk temperature in the TRT allowed to identify the compound optimal thermal range [11], starting from the polymer thermal characteristics, appropriately evaluated by means of indoor test procedures and a specifically developed version of the model for laboratory activities (TRT LAB) [12][13]. ...
... The sidewall nodes, called surface (in yellow) and bulk (in red), are respectively in contact with the external air flux and with the inner gas contained inside the wheel chamber. In order to properly describe the heat conduction phenomena, the entire discretized volume has to be physically characterized, evaluating the material thermal and inertial properties [12][13]. ...
Article
Vehicle performances, especially in motorsport, are deeply affected by tire behavior and in particular by tire compound proper working conditions. In this research activity, a series of innovations have been introduced on the Thermo Racing Tire (a physical-analytical tire thermal model, based on Fourier’s law of heat transfer applied to a three-dimensional domain) in order to take into account all the main aspects actively involved in the thermal behavior of the tire, as the presence of exhausted gases eventually impacting at the rear axle and the inhomogeneous distribution of local variables (pressure, stress and sliding velocity) within the contact patch, caused in example by the tire camber angle. The new model developed considers the presence of the sidewalls, actively involved in the convective heat exchanges, respectively, with the external airflow and the inner gas fluid, located inside the inflation chamber. The aim of the new version of the tire thermal model is a better physical comprehension of all the phenomena concerning the contact with the asphalt and the prediction of the link between the thermal state and the frictional performance, crucial for the definition of an optimal wheel and vehicle setup.
... Modeling the behaviour of the tire at the race conditions 1 is interesting both to optimise the grip with the asphalt of the road and to optimise its wear resistance. 2 For doing that, the assessment of the thermophysical properties of the tires is mandatory. In this work the density, specific heat and thermal conductivity are measured. ...
... Further, Motorsport racing teams use to face with the restrictions due to the employment of confidential tires and not available to invasive testing. Therefore, an innovative procedure for the acquisition of the data for tire viscoelasticity characterization within the working thermal range could be very useful for vehicle setup optimization and definition of vehicle simulation tools [8] [9]. ...
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Chapter
The evaluation of the viscoelastic properties is a key topic for the analysis of the dynamic mechanical behaviour of polymers. In vehicle dynamics field, the knowledge of the viscoelasticity of tread compound is fundamental for tire-road contact mechanics modelling and friction coefficient prediction for the improvement of vehicle performance and safety, i.e. motorsport field. These properties are usually characterised by means of Dynamic Mechanical Analysis, which implies testing a compound sample obtained by destroying the tire of interest or a slab manufactured in different conditions respect to the final product provided by tiremakers. In this scenario, the non-destructive procedures are an advantageous solution for the analysis of the tread viscoelasticity, without affecting the tire integrity, allowing a great number of tests in the shortest possible time. For this reason, the authors propose an innovative instrument, called VESevo, for viscoelasticity evaluation by means of non-destructive and user-friendly technique. The purpose of the following work is the preliminary analysis of the dynamic response of the tires tested employing the VESevo in order to determine viscoelastic behaviour indexes for mechanical properties evaluation.
... Hence, a real-time compounds characterization, which could be performed by means of a portable device [2], allows engineers to analyse directly the effects due to tire heating and cooling [3,14,15], tread wear [16,17], aging or winter and summer season compound choice on road so that the safety and handling performances can be improved by taking into account tire viscoelastic behaviour in friction coefficient evaluation for vehicle dynamics onboard algorithms. ...
Full-text available
Chapter
The knowledge of tires tread viscoelastic behaviour plays a fundamental role in automotive to optimize vehicle performance and safety. These properties are usually characterized by means of Dynamic Mechanical Analysis [1] which implies the testing of compound sample that can be obtained by destroying the tire of interest or manufactured in different condition respect to the final product provided by tiremakers. Nowadays, the non-destructive analysis procedures are an attractive solution. These techniques are essentially advantageous for being employed in testing the whole tire, allowing the analysis of a great number of them without affects costs. The purpose of this work is the experimental analysis of the tire tread response, in different working condition, evaluated by a commercial dial indicator [2] considering the measured displacement values of the device. Experimental tests have been carried out on different tread compounds and, being the tire performance strictly affected by the working temperature, additional tests have been performed by heating and cooling each sample in a range of interest [3, 4]. Moreover, the effects of aging on a tire has been studied. The comparison of the testing activity results shows the reliability of the dynamic dial indicator to capture the tires tread different behaviour within the operating condition of interest. These encouraging results lead to next step of the research activity which will focus on the evaluation of properties characterizing the hysteretic behaviour of tires.
... A fundamental starting point is the knowledge of the rubber viscoelastic properties [7,8] because of the asperities of the surface generate oscillating forces causing energy dissipation in the rubber bulk. Moreover, the rubber friction is function of the temperature being the rubber viscoelastic properties largely influenced from this parameter [8,9]. ...
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Chapter
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.
... An original non-destructive technique to evaluate the thermal diffusivity by means of a specifically developed TRT_lab model, sharing with TRT the same tire structure module, differing only in the boundary conditions package, is illustrated in detail in Allouis et al. 19 The test procedure is performed on the whole tire acquiring the temperature distribution in all the directions of heat propagation from the point of the heat supply on the tread surface. ...
Article
The tire and vehicle setup definition, able to optimise grip performance and thermal working conditions, can make the real difference as for motorsport racing teams, used to deal with relevant wear and degradation phenomena, as for tire makers, requesting for design solutions aimed to obtain enduring and stable tread characteristics, as finally for the development of safety systems, conceived in order to maximise road friction, both for worn and unworn tires. The activity discussed in the paper deals with the analysis of the effects that tire wear induces in vehicle performance, in particular as concerns the consequences that tread removal has on thermal and frictional tire behaviour. The physical modelling of complex tire–road interaction phenomena and the employment of specific simulation tools developed by the Vehicle Dynamics UniNa research group allow to predict the tire temperature local distribution by means of TRT model and the adhesive and hysteretic components of friction, thanks to GrETA model. The cooperation between the cited instruments enables the user to study the modifications that a reduced tread thickness, and consequently a decreased SEL (Strain Energy Loss) and dissipative tread volume, cause on the overall vehicle dynamic performance.
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In this work, a combined numerical/experimental analysis is performed for an automotive tyre. A preliminary experimental activity is realized on examined tyre to measure the temperatures of its layers under various operating conditions. In a second stage, a 3D CFD model of tyre is developed in a commercial code and steady RANS simulations are performed in the full range of angular velocity with the aim to refine the prediction of convective thermal power and heat transfer coefficient. CFD simulation results are passed to a user-defined 3D thermodynamic model to furnish a detailed and reliable tyre thermal output with the advantage of a low computational time. Tyre thermodynamic model, enhanced by CFD-related thermal characteristics, demonstrates the capability to properly forecast the measured temperature of tyre layers in a wide range of investigated operating conditions. The proposed numerical approach represents a valuable tool supporting the optimization of tyre behavior and the development of advanced control rules for optimal tyre management.
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Viscoelastic contacts are present in countless industrial components including tires, dampers and rubber seals. The effective design of such components requires a full knowledge of viscoelastic contact mechanics in terms of stresses, strains and hysteric dissipation. To assess some of these issues, this paper describes a series of experiments on the contact area and penetration in a rolling contact between a nitrile rubber ball and a glass disk. The experimental results are compared with the theory proposed by Carbone and Putignano1 showing close agreement at low speeds. However, discrepancies arise at speeds above 100 mm/s because of the frictional heating. In order to evaluate this effect, the temperature of the sliding interface is measured for different rolling speeds using infrared microscopy. Thermal results showed that interfacial temperature remained constant at low rolling speeds before rising significantly when speeds above 100 mm/s were reached. These temperature effects are incorporated into the numerical simulations by means of an approximated approach, which corrects the viscoelastic modulus based on the mean measured temperature in the contact. The result of this approach is to extend the region of agreement between experimental and numerical outcomes to higher speeds.
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In the paper a new physical tyre thermal model is presented. The model, called Thermo Racing Tyre (TRT) was developed in collaboration between the Department of Industrial Engineering of the University of Naples Federico II and a top ranking motorsport team. The model is three-dimensional and takes into account all the heat flows and the generative terms occurring in a tyre. The cooling to the track and to external air and the heat flows inside the system are modelled. Regarding the generative terms, in addition to the friction energy developed in the contact patch, the strain energy loss is evaluated. The model inputs come out from telemetry data, while its thermodynamic parameters come either from literature or from dedicated experimental tests. The model gives in output the temperature circumferential distribution in the different tyre layers (surface, bulk, inner liner), as well as all the heat flows. These information have been used also in interaction models in order to estimate local grip value.
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A new technique for the determination of the thermal diffusivity of a tyre compound is proposed. The diffusivity is defined as the ratio between the thermal conductivity and the product of the specific heat and density. This technique is based on infrared measurement and successive analysis of the tyre cooling. Tyre samples were heated up by a laser at constant power rate and the heating and the next cooling of the tyres were registered versus time by mean of thermocouples and infrared cameras. Determination of the thermal diffusivity was thus estimated by mean of home-made model. The research activity was carried out in the laboratories of the department of Mechanics and Energetics of the University of Naples Federico II, in cooperation with the Combustion Institute of the CNR in Naples.
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We present a simple theory of crack propagation in viscoelastic solids. We calculate the energy per unit area, G(v), to propagate a crack, as a function of the crack tip velocity v. Our study includes the non-uniform temperature distribution (flash temperature) in the vicinity of the crack tip, which has a profound influence on G(v). At very low crack tip velocities, the heat produced at the crack tip can diffuse away, resulting in very small temperature increase: in this "low-speed" regime the flash temperature effect is unimportant. However, because of the low heat conductivity of rubber-like materials, already at moderate crack tip velocities a very large temperature increase (of order of 1000 K) can occur close to the crack tip. We show that this will drastically affect the viscoelastic energy dissipation close to the crack tip, resulting in a "hot-crack" propagation regime. The transition between the low-speed regime and the hot-crack regime is very abrupt, which may result in unstable crack motion, e.g. stick-slip motion or catastrophic failure, as observed in some experiments. In addition, the high crack tip temperature may result in significant thermal decomposition within the heated region, resulting in a liquid-like region in the vicinity of the crack tip. This may explain the change in surface morphology (from rough to smooth surfaces) which is observed as the crack tip velocity is increased above the instability threshold.
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The thermomechanical behavior of pneumatic tires is a highly complex transient phenomenon that, in general, requires the solution of a dynamic nonlinear coupled thermoviscoelasticity problem with heat sources resulting from internal dissipation and contact and friction. This highly complex and nonlinear system requires in-depth knowledge of the geometry, material properties, friction coefficients, dissipation mechanisms, convective heat transfer coefficients, and many other aspects of tire design that are not fully understood at the present time. In this paper, a simplified approach to modeling this system that couples all of these phenomena in a straight forward manner is presented in order to predict temperature distributions in static and rolling tires. The model is based on a one-way coupling approach, wherein the solution of mechanical rolling contact problem (with friction and viscoelastic material properties) provides heat source terms for the solution of a thermal problem. The thermal solution is based on the thermodynamics of irreversible processes and is performed on the deformed tire configuration. Several numerical examples are provided to illustrate the performance of the method.
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A finite element-based method is demonstrated to predict tire rolling resistance and temperature distributions. Particular attention is given to the material properties and constitutive modeling as these have a significant effect on the predictions. A coupled thermomechanical method is described where both the stiffness and the loss properties are updated as a function of strain, temperature, and frequency. Results for rolling resistance and steady state temperature distribution are compared with experiments for passenger and radial medium truck tires. An extension of the method for transient temperature predictions is also demonstrated.
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A simplified three-dimensional model has been developed to predict the temperature distribution in a tyre during rolling or skidding, allowance being made for cooling. Calculated temperatures are shown to be in reasonable agreement with surface temperature measurements obtained during the running of a tyre against a rotating drum. The analysis is also used to investigate the effects of varying certain parameters and operating conditions.
An Evolved Version of Thermo Racing Tyre for Real Time Applications
  • F Farroni
  • A Sakhnevych
  • F Timpone
F. Farroni, A. Sakhnevych, and F. Timpone, "An Evolved Version of Thermo Racing Tyre for Real Time Applications", Lecture Notes in Engineering and Computer Science: Proceedings of The World Congress on Engineering 2015, 1-3 July, 2015, London, U.K., pp 1159-1164
The results of two tests for the same tire at different power values are shown. The simulated temperatures are with continuous lines while the acquired data are with dotted ones
  • Fig
Fig. 9. The results of two tests for the same tire at different power values are shown. The simulated temperatures are with continuous lines while the acquired data are with dotted ones. In order to handle properly the infrared measurements, the both tire surfaces emissivity has been set constant equal to 0.95.
Principles of Heat Transfer
  • F Kreith
  • R M Manglik
  • M S Bohn
F. Kreith, R. M. Manglik and M. S. Bohn, "Principles of Heat Transfer". 6 th ed. Brooks/Cole USA, 2010.