Modelo de contacto neumático-calzada a baja velocidad

Las fuerzas generadas en el contacto neumático-calzada influyen de manera importante en las características dinámicas del vehículo. Es, por este motivo, que resulta fundamental el desarrollo de modelos de neumáticos precisos para el estudio del comportamiento de un vehículo automóvil. La mayor parte de estos modelos han sido desarrollados y optimizados para elevadas velocidades, solicitaciones combinadas, etc. Sin embargo, los vehículos automóviles durante gran parte de su vida útil circulan a velocidades bajas (inferiores a 60 km/h) y en condiciones estacionarias. Además, en pruebas de inspección y mantenimiento realizadas en vehículos automóviles, como pueden ser las del sistema de dirección o del sistema de frenos, se miden las fuerzas transmitidas por los neumáticos. La totalidad de estas pruebas tiene lugar a baja velocidad. Por estos motivos resulta interesante desarrollar un modelo de contacto neumático-calzada específico para baja velocidad, sin la complejidad de modelos desarrollados para un amplio rango velocidades y con mayor precisión a bajas velocidades. La placa dinamométrica ha demostrado ser un equipo de ensayo idóneo para la caracterización del contacto neumático-calzada a baja velocidad. Su capacidad para realizar ensayos en todo tipo de neumáticos montados en los propios vehículos permite operar con gran flexibilidad y rapidez. Es por ello que se ha seleccionado como equipo de medida. En la presente Tesis Doctoral se presenta el desarrollo de un modelo de contacto neumático-calzada a baja velocidad basado en la medida de esfuerzos longitudinales y laterales. El estudio experimental realizado mediante placa dinamométrica ha permitido establecer relaciones entre las variables de influencia y las fuerzas longitudinal y transversal en el contacto neumático-calzada a baja velocidad en régimen estacionario. A partir del estudio de sensibilidades se ha comprobado que las variables que m¶as influyen sobre las fuerzas en el contacto neumático-calzada son la presión, la fuerza vertical y el ángulo de convergencia. Por el contrario, la influencia de la temperatura y el ángulo de caída ha resultado ser mucho menor en las condiciones fijadas para el desarrollo del modelo. Para llevar a cabo los ensayos experimentales, se ha propuesto una metodología de ensayo que permita realizar los ensayos de un modo sistemático y controlado en placa dinamométrica. Asimismo, se propone un nuevo procedimiento de inspección del sistema de dirección basado en la aplicación del modelo desarrollado mediante placa dinamométrica. A partir de la medida de fuerzas longitudinales, transversales y verticales se proponen límites de rechazo para dicho procedimiento de inspección. Dichos límites han sido evaluados experimentalmente a partir de un número estadísticamente significativo de vehculos. _____________________________________________The behaviour of the tyre plays an important role in the vehicle handling. Thus for the analysis of vehicles and road safety it is necessary to take into account the forces and moments generated at contact patch. An accurate tyre model that estimates these forces and moments it is highly essential for the studies of vehicle dynamics and control. Most of the tyre models have been developed for high speed, combined forces, etc. But, usually, automobile vehicles run at low speeds during an im- portant part of their operating life (less than 60 km/h) and in steady state conditions. Furthermore, during vehicle inspection and maintenance of the steering and brake system, the forces transmitted by the tyres are measured. All of these inspections are carried out at low speeds. Therefore, it is particularly interesting to develop a model of the contact patch tyre-pavement for low speeds without the complexity of models that cover a wide speed range but with a bigger precision at low speeds. The dynamometer plate has proved to be an appropriate test equipment to characterise the tyre-pavement contact patch at low speed. It has the feature of being able to carry out tests for any type of tyre allowing to test with a great flexibility and operating speed. For this reason, the dynamometer plate has been chosen as test equipment. In this Thesis a contact model between tyre and pavement at low speed, based on the measurement of longitudinal and lateral forces, is presented. The experimental tests carried out by means of the dynamometer plate have allowed to establish a relationship between influence variables and the longitudinal and lateral forces in the contact patch for steady state low speeds. A sensibility study has shown that the most influential variables in the forces of the contact patch are the pressure, the vertical force and the toe angle. However, the influence of temperature and camber angle are lower for the defined model conditions. A test methodology that allows to carry out the experimental tests in a systematic and controlled way in the dynamometer plate is suggested. Likewise, a new procedure to inspect the steering system based on the developed model on the dynamometer plate, is proposed. From the measurement of longitudinal, lateral and vertical forces a reject value for the inspection procedure is suggested. These reject values have been evaluated by means of experimental tests over a statistically significant number of vehicles

A Strain-Based Method to Detect Tires' Loss of Grip and Estimate Lateral Friction Coefficient from Experimental Data by Fuzzy Logic for Intelligent Tire Development

This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain 2017Tires are a key sub-system of vehicles that have a big responsibility for comfort, fuel consumption and traffic safety. However, current tires are just passive rubber elements which do not contribute actively to improve the driving experience or vehicle safety. The lack of information from the tire during driving gives cause for developing an intelligent tire. Therefore, the aim of the intelligent tire is to monitor tire working conditions in real-time, providing useful information to other systems and becoming an active system. In this paper, tire tread deformation is measured to provide a strong experimental base with different experiments and test results by means of a tire fitted with sensors. Tests under different working conditions such as vertical load or slip angle have been carried out with an indoor tire test rig. The experimental data analysis shows the strong relation that exists between lateral force and the maximum tensile and compressive strain peaks when the tire is not working at the limit of grip. In the last section, an estimation system from experimental data has been developed and implemented in Simulink to show the potential of strain sensors for developing intelligent tire systems, obtaining as major results a signal to detect tire's loss of grip and estimations of the lateral friction coefficient

Influence of camber angle on tire tread behavior by an on-board strain-based system for intelligent tires

Tires are a key sub-system of vehicles that have a big responsibility in comfort, fuel consumption and traffic safety. Nevertheless, current tires are just passive rubber elements which do not contribute actively to improve the driving experience or the vehicle safety. The lack of information that tires provide during driving is the main reason to develop an intelligent tire, which could provide useful information to other systems and become an active safety system. In this paper, an experimental tire strain-based system is used to measure tire tread deformation by means of strain gauges. Tests under different working conditions such as vertical load or slip angle considering a certain camber angle have been carried out using an indoor tire test rig. The results prove that the camber angle has a significant effect on strain signal, so it should be considered for tire working conditions estimation purposes.We acknowledge the University of Birmingham for the test facilities and the Universidad Carlos III de Madrid for the financial support to acquire the testing equipment

A Strain-Based Method to Estimate Slip Angle and Tire Working Conditions for Intelligent Tires Using Fuzzy Logic

Tires equipped with sensors, the so-called "intelligent tires", can provide vital information for control systems, drivers and external users. In this research, tire dynamic strain characteristics in cornering conditions are collected and analysed in relation to the variation of tire working conditions, such as inflation pressure, rolling speed, vertical load and slip angle. An experimental tire strain-based prototype and an indoor tire test rig are used to demonstrate the suitability of strain sensors to establish relations between strain data and lateral force. The results of experiments show that strain values drop sharply when lateral force is decreasing, which can be used to predict tire slip conditions. As a first approach to estimate some tire working conditions, such as the slip angle and vertical load, a fuzzy logic method has been developed. The simulation and test results confirm the feasibility of strain sensors and the proposed computational model to solve the non-linearity characteristics of the tires' parameters and turn tires into a source of useful information

A Constrained Dual Kalman Filter Based on pdf Truncation for Estimation of Vehicle Parameters and Road Bank Angle: Analysis and Experimental Validation

Vehicles today are equipped with control systems that improve their handling and stability. Knowledge of road bank angle and vehicle parameters is crucial for good behavior in this type of control. This paper develops a new method for estimating different states, such as vehicle roll angle, road bank angle, and vehicle parameters. This method combines a dual Kalman filter with a probability density function truncation method to consider the parameter physical limitations. Experimental results show the effectiveness of the proposed method and demonstrate that the incorporation of parameter constraints improves its estimation accuracy. The proposed method provides an estimation of the parameters and the states' physical meaning and the stable values within the real boundary limits in contrast to other estimation methods.This work was supported by Project TRA2013-48030-C2-1-R from the Spanish Ministry of Economy and Competitiveness. The Associate Editor for this paper was P. Kachroo

Development and experimental validation of a real-time analytical model for different intelligent tyre concepts

In recent years, the ever-increasing interest in intelligent tyre technology has led to the formulation of different empirical models correlating deformation measurements provided by the sensors with tyre dynamics. In this paper, a real-time physical model, suitable for describing the dynamics of intelligent tyres based on measurements of strains and/or displacements of the tyre carcass, is presented. The proposed flexible ring model can reproduce the tyre dynamics for both concentrated and distributed forces by introducing a discrete approach that also allows to analyse the longitudinal dynamics of the tyre in real-time. The analytical description of the problem allows to obtain solutions in closed form and to quickly identify model parameters from experimental data. The comparison between the simulated results and the ones provided by indoor tests of two intelligent tyre concepts highlighted that the proposed tyre model can estimate with an acceptable precision both the carcass deformations and the forces acting on the tyre

A real-time physical model for strain-based intelligent tires

In recent years, a large amount of research has been focused on intelligent tire technology. Several systems have been developed based on different sensors installed on tires. Nowadays one of the major research problems for intelligent tire development is how to correlate measurements provided by sensors to the tire dynamics. The methods mostly presented in literature are based on empirical correlations between measurements and tire working conditions obtained with extensive experimental activities which are expensive and time consuming. In this paper, a real-time physical model suitable to describe the longitudinal dynamics of strain-based intelligent tires is described. The mathematical tire model consists of a flexible ring on a viscoelastic foundation. The solution of the model dynamics has been obtained in closed form and the model parameters have been identified from experimental data. The comparison between the simulated strains and the ones provided by an intelligent tire prototype highlighted that the proposed tire model can estimate with an acceptable precision the tire deformations for several operative working conditions

Estructura monocasco de plásticos reforzados con fibra de carbono (CFRP) para coches de Formula Student

Formula Student es una competición internacional de ingeniería en que las universidades compiten para crear el monoplaza más rápido, barato y fiable. Para cumplir este objetivo, los equipos trabajan duro en sus diseños, fabricación y pruebas a fin de mejorar el comportamiento de su vehículo en la pista, de modo que el consumo de combustible y el coste se reduzcan mientras la velocidad, dinámica lateral y longitudinal y aerodinámica mejoren. Una forma directa de obtener estos resultados es reduciendo el peso del coche tanto como sea posible. Es importante utilizar estructuras ligeras en términos de rendimiento del vehículo, lo que generalmente implica estructuras monocasco basadas en materiales de alta relación resistencia-peso, como matrices poliméricas reforzadas con fibra de carbono (CFRP). En este estudio se ha propuesto una estructura monocasco formada por paneles tipo sándwich fabricados con una lámina superior e inferior de fibra de carbono con matriz epoxi y un núcleo de espuma colocado entre ellos, aumentando el momento de inercia del área de la estructura y mejorando la resistencia del panel. La rigidez torsional del chasis final se ha evaluado utilizando un Modelo de Elementos Finitos (MEF), así como ensayos físicos representativos de los paneles laminados para cumplir con los requisitos de las normas de Formula Student Germany y para garantizar la seguridad de los pilotos.Formula Student is an international engineering competition on which Universities compete to create the fastest, cheapest, and most reliable single-seated and open-wheeled car. In order to fulfill this objective, teams work hard on their designs, manufacturing and testing in order to improve the behaviour of their Formula Student cars on the track so the fuel consumption and cost reduces while velocity, lateral and longitudinal dynamics, and aerodynamics improves. A direct way to get that is by reducing the weight of the car as much as possible. Lightweight structures are important in terms of vehicle performance, and that usually implies monocoque structures based on high strength-to-weight ratio materials as Carbon Fiber Reinforced Plastics (CFRP). In this study, it has been proposed a monocoque structure based on sandwich composite panels made of an upper and a lower facesheet of epoxy reinforced carbon fiber with a foam core placed between them, increasing the area moment of inertia of the structure and improving the strength of the panel. Torsional stiffness of the final chassis has been evaluated by using FEM as well as physical representative tests of the laminated panels to fulfill the requirements of Formula Student Germany rules and to ensure safety for the drivers

Characterization of the loss of grip condition in the Strain-Based Intelligent Tire at severe maneuver

The early detection of the instantaneous tire–road condition enables the control systems to react against the risk of the vehicle's loss of control. This situation usually occurs when the phenomena of stick–slip is not present in the tire–road interaction yielding the full slip of the tire (the whole contact patch is gliding). The relation between the friction force and the vertical load of the tire can be used as an indicator of this loss of grip when it is higher than the maximum capacity of friction used for the surfaces in contact. Nonetheless, this limit of friction is currently unknown. This study proposes the development of the tire as an active sensor able to provide all this information. Previous studies have shown that the Strain-based Intelligent Tire enables the monitoring of the forces in the tire–road interaction, the wheel load, the effective radius, the contact length, and the wheel velocity in the contact patch. These parameters affect the tire–road friction characterization. Therefore, it is proposed the integration of the LuGre model with the achievements of the Strain-Based Intelligent Tire in order to estimate the adherence limit. To show the effectiveness of the methodology proposed it is used the CarSim™ simulation software. The validation process is carried out monitoring the limit of adherence with a set of vehicle’s severe maneuvers, where the dynamic behavior of the vehicle highlights its influence in the operational condition of the tire in order to expose the wheels to full slip.Publicad

Estimation of tire-road contact forces through a model-based approach employing strain measurements

The employment of intelligent tires to test the vehicle performances is ever-increasing in the last years. Many research activities have been made to correlate measurements provided by sensors to the tire dynamics. In this paper, a novel tire-road forces estimation technique is presented. The developed estimator is based on an approximation of the well-known Flexible Ring Tire Model (FRTM) and therefore, it is suitable for real-time normal and tangential forces identification. Only the tread band strain measurements are employed in the developed algorithm which can estimate the tire-road forces at every wheel revolution. The tool is validated through both numerical and experimental tests. The results indicate that the developed estimation algorithm, obtained by a mathematical inversion of the FRTM, can be employed as a monitoring tool for tires and vehicles.Open access funding provided by Università degli Studi di Napoli Federico II within the CRUI-CARE Agreement