Tire testing is a fundamental process in the automotive industry. The thesis is focused on the MoLAS, an innovative moving laboratory able to characterize a wide range of tires (from 15" to 24") in testing scenarios that represent real working environments. The laboratory is a semi-trailer in which some actuators make it possible to modify running conditions such as camber angle, steering angle, vertical load and also torque input thanks to a dedicated internal combustion engine (that provides traction torque) and an electromagnetic retarder (for braking torques). The aims of this thesis were multiple: designing a system able to directly measure the side slip angle of the vehicle during its motion, and the development of a digital twin of the driveline that connects the already cited motor and brake to the wheel under measurements. Concerning the first aim, the design process started with the study of the system requirements and the verification of the spacial constraints. Two different solutions were developed in parallel, both based on a ready-to-use bicycle frame: a CAD design was done. Then, a study on the forces acting on the structure was performed and the outputs were used for the FEM analysis of the solutions. In both cases the results were satisfying, as the two structures were far from their limit and showed very little deformations. Finally a comparison between the two solution is presented, where pros and cons are analyzed. Regarding the second goal of the thesis, the process started by debugging the SWIFT model developed by other authors. After numerous attempts, good results were obtained by adding low-pass filters to the output signals. The whole powertrain model was implemented by means of both Simulink and Simscape blocks, in which the inertia, torsional stiffness and damping values of all the mechanical components of the driveline were inserted. Many simulations were performed imposing braking and traction torques, and camber and steering angle variations to test the functioning of the model. In the final stages of the work, an optimization script was created on MATLAB to derive the main tire parameters from the available experimental data: these parameters were then used as input to the model to perform a first validation. In most of the cases the results given by the digital twin are meaningful and close to the experimental case.This thesis had mainly two purposes: the first one was to complete the development of a digital twin. Concerning this the first step was a complete debug process, ended with the addition of filters whose cut-off frequency can be modified in order to obtain proper results. Then, the whole powertrain model was implemented by means of Simulink and Simscape blocks: this helped to take into consideration also the inertias, stiffnesses and damping of the system during the simulations. Simulations that were performed and whose outputs are presented and described. Variation of camber angle, steering angle and response to both positive and negative torque inputs were tested. Finally a preliminary optimization script was created on MATLAB to derive the tire parameters from the experimental data: these parameters were then used as input to the model to verify if the obtained outputs were comparable with the experimental tests results in the same testing conditions, i.e. with the same velocity profile. The second aim of the thesis was to design a measuring system for the semi-trailer drift angle: the presence of a tire to be tested in fact affects the motion of the whole truck, generating certain drift angle. Consequently the measures on the tested tire must be adjusted taking into consideration that, and to do so this angle must be computed at every time instant. Two alternative solutions were developed, both defined by a structure attached to the back of the truck and built around a bicycle frame free to rotate around its vertical axis. Both the systems were validated with FEM analysis to verify their deformations and stresses and confronted to understand pros and cons of each one.
Testare gli pneumatici è un processo fondamentale nell’industria automotive. La tesi è focalizzata sul MoLAS, un innovativo laboratorio mobile capace di caratterizzare un ampio range di gomme (da 15" a 24") in scenari di prova che rappresentano le reali condizioni operative. Il laboratorio è un rimorchio sul quale alcuni attuatori permettono di modificare parametri quali angolo di camber, di sterzo, carico verticale e coppia alla ruota grazie a un motore a combustione interna dedicato (che fornisce coppie positive) e a un freno elettromagnetico. Gli obiettivi di questa tesi erano molteplici: progettare un sistema capace di misurare direttamente l’angolo di deriva del veicolo durante il moto, e sviluppare un modello virtuale della linea di trasmissione che collega il motore e il freno sopra citati con lo pneumatico testato. Riguardo il primo punto, la progettazione è iniziata con lo studio dei requisiti di sistema e la verifica dei limiti spaziali. Sono state sviluppate due soluzioni, entrambe basate su un telaio di bicicletta pronto per essere usato: un disegno CAD è stato effettuato. Successivamente, è stato fatto uno studio sulle forze agenti sulla struttura e i risultati sono stati usati per condurre un’analisi FEM. In entrambi i casi queste hanno restituito risultati soddisfacenti essendo le due soluzioni lontane dal loro limite strutturale e con deformazioni ridotte. Infine è stato effettuato un confronto critico, analizzando pro e contro. Per quanto riguarda lo sviluppo del modello si è partiti con un processo di debug del modello SWIFT sviluppato da altri autori. Dopo numerosi tentativi, risultati soddisfacenti sono stati ottenuti aggiungendo filtri passa-basso ai segnali in output. L’intero powertrain è stato modellato utilizzando Simulink e Simscape, nel quale sono stati inseriti i valori di inerzia, rigidezza torsionale e smorzamento. Diverse simulazioni sono state effettuate imponendo coppie di trazioni e di frenatura e variazioni di angolo di camber e di sterzo per verificare il funzionamento del modello. Nelle fasi finali della tesi uno script di ottimizzazione è stato sviluppato su MATLAB per ricavare i principali parametri della gomma partendo da dati sperimentali: questi sono poi stati usati come input al modello per effettuare una prima validazione. Nella maggior parte dei casi i risultati ottenuti sono stati significativi e vicini ai risultati sperimentali.Questa tesi ha avuto due scopi: il primo era quello di completare lo sviluppo di un modello virtuale. Il primo passo è stato effettuare un processo di debug culminato con l'aggiunta di filtri la cui frequenza di taglio può essere modificata per ottenere risultati corretti. Poi, l'intero powertrain è stato modellato tramite blocchi Simulink e Simscape: questo ha permesso di tenere in considerazione tutte le inerzie, rigidezze e smorzamenti del sistema durante le simulazioni. Simulazioni che sono state effettuate e i quali output sono qui presentati e descritti. Variazioni di angolo di campanatura, angolo di sterzo e risposta sia a coppie positive che negative sono state testate. Successivamente un primo abbozzo di software di ottimizzazione è stato sviluppato su MATLAB con l'obiettivo di derivare i parametri delle gomme, derivati da risultati sperimentali: questi parametri sono stati poi usati come input del modello per verificare se i risultato ottenuti fossero comparabili con gli output dei test sperimentali in uguali condizioni di prova, ovvero imponendo lo stesso profilo di velocità. Il secondo scopo della tesi è stato di progettare un sistema di misura per l'angolo di deriva del rimorchio: la presenza infatti di uno pneumatico da testare influenza il moto del camion intero, generando un certo angolo di deriva. Quindi le misure effettuate sulla gomma devono essere aggiustate tenendo conto di questo fenomeno e quindi tale angolo deve essere continuamente monitorato. Due soluzioni alternative sono state sviluppate, entrambe definite da una struttura collegata alla parte posteriore del veicolo e costruite a partire da un telaio di bicicletta libero di ruotare attorno all'asse verticale. Entrambi i sistemi sono stati validati tramite analisi FEM per verificare deformzioni e sforzi e confrontate per comprendere vantaggi e svantaggi di ognuna.
Development of a unique moving laboratory for tire testing : side slip angle measuring system and driveline digital twin
Zacconi, Matteo;DAGONI, MATTIA
2021/2022
Abstract
Tire testing is a fundamental process in the automotive industry. The thesis is focused on the MoLAS, an innovative moving laboratory able to characterize a wide range of tires (from 15" to 24") in testing scenarios that represent real working environments. The laboratory is a semi-trailer in which some actuators make it possible to modify running conditions such as camber angle, steering angle, vertical load and also torque input thanks to a dedicated internal combustion engine (that provides traction torque) and an electromagnetic retarder (for braking torques). The aims of this thesis were multiple: designing a system able to directly measure the side slip angle of the vehicle during its motion, and the development of a digital twin of the driveline that connects the already cited motor and brake to the wheel under measurements. Concerning the first aim, the design process started with the study of the system requirements and the verification of the spacial constraints. Two different solutions were developed in parallel, both based on a ready-to-use bicycle frame: a CAD design was done. Then, a study on the forces acting on the structure was performed and the outputs were used for the FEM analysis of the solutions. In both cases the results were satisfying, as the two structures were far from their limit and showed very little deformations. Finally a comparison between the two solution is presented, where pros and cons are analyzed. Regarding the second goal of the thesis, the process started by debugging the SWIFT model developed by other authors. After numerous attempts, good results were obtained by adding low-pass filters to the output signals. The whole powertrain model was implemented by means of both Simulink and Simscape blocks, in which the inertia, torsional stiffness and damping values of all the mechanical components of the driveline were inserted. Many simulations were performed imposing braking and traction torques, and camber and steering angle variations to test the functioning of the model. In the final stages of the work, an optimization script was created on MATLAB to derive the main tire parameters from the available experimental data: these parameters were then used as input to the model to perform a first validation. In most of the cases the results given by the digital twin are meaningful and close to the experimental case.This thesis had mainly two purposes: the first one was to complete the development of a digital twin. Concerning this the first step was a complete debug process, ended with the addition of filters whose cut-off frequency can be modified in order to obtain proper results. Then, the whole powertrain model was implemented by means of Simulink and Simscape blocks: this helped to take into consideration also the inertias, stiffnesses and damping of the system during the simulations. Simulations that were performed and whose outputs are presented and described. Variation of camber angle, steering angle and response to both positive and negative torque inputs were tested. Finally a preliminary optimization script was created on MATLAB to derive the tire parameters from the experimental data: these parameters were then used as input to the model to verify if the obtained outputs were comparable with the experimental tests results in the same testing conditions, i.e. with the same velocity profile. The second aim of the thesis was to design a measuring system for the semi-trailer drift angle: the presence of a tire to be tested in fact affects the motion of the whole truck, generating certain drift angle. Consequently the measures on the tested tire must be adjusted taking into consideration that, and to do so this angle must be computed at every time instant. Two alternative solutions were developed, both defined by a structure attached to the back of the truck and built around a bicycle frame free to rotate around its vertical axis. Both the systems were validated with FEM analysis to verify their deformations and stresses and confronted to understand pros and cons of each one.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/209080