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Questa memoria presenta i test sperimentali per la caratterizzazione termomeccanica del biopolimero acido polilattico e dei suoi compositi con farina di faggio o con nanorinforzo di montmorillonite modifcata, per uno studio di applicabilità nel settore automobilistico. Per la caratterizzazione meccanica e il confronto dei risultati vengono eseguiti prove di coppia e di trazione; i test dinamici vengono eseguiti per la caratterizzazione termomeccanica, determinando il modulo elastico e il fattore di perdita rispetto alla temperatura effettiva. This paper presents the experimental tests for the thermomechanical characterization of biopolymer polylactic acid, and its composites with beech flour or with nanoreiforcement of modifed montmorillonite, with the purpose of applicability in the automotive sector. Tests of torque and traction are executed for the mechanical characterization and the results comparison; dynamical tests are executed for the thermomechanical characterization, determining the elastic modulus and loss factor versus the actual temperature.

Questo lavoro contiene una rassegna dei metodi che sono usati per la previsione delle prestazioni del veicolo su strada, in dipendenza del motore installato. La prima parte mostra il calcolo delle resistenze al moto, cioè le forze che il veicolo deve vincere per avanzare sulle strade piane e in salita. Particolarmente interessante appare la parte che riguarda la resistenza aerodinamica, della quale si tratta di metodi sperimentali (galleria del vento), metodi empirici e metodi CFD. Si propone inoltre l’applicazione della norma CUNA sulla velocità per la determinazione dei consumi anche al calcolo dei coefficienti aerodinamici. La rassegna esclude la resistenza accidentale in curva perché non è essenziale per predire il comportamento del veicolo sulla strada. La seconda parte inizia con la caratteristica di potenza, la previsione dei diagrammi di trazione - velocità e velocità - potenza, il calcolo dei rapporti del cambio, e poi passando ai limiti, l'accelerazione stimata, i consumi e la distanza. Sono di un certo interesse le tecniche utilizzate per la costruzione dei diagrammi di accelerazione e derivati, e le tecniche che consentono di associare le curve di equiconsumo alle curve d’uso del veicolo, partendo dalla determinazione delle caratteristiche di coppia e di consumo al banco. Quando necessario sono riportati i riferimenti alla normativa internazionale. Si conclude con una sezione sulla guidabilità del veicolo, che presenta i vantaggi dei veicoli a quattro ruote sterzanti. This chapter deals with the forecast of the vehicle performance on the road, according to installed engine. It begins with a first part a) which shows the calculation of the resistance to motion, i. e. the forces that the vehicle must win to advance on the flat roads and uphill. The calculation excludes accidental resistance in curve because it is not essential for predicting the behavior of the vehicle on the road. The section b) begins with the power characteristic, the forecast by traction – speed and power speed diagrams, the calculation of gear ratios, and then passing to the limits to the estimated acceleration, features consumption and distance. It concludes with a section on the driveability of the vehicle, the report sets out the advantages of four-wheel drive ve

Le situazioni di impatto e la dinamica di ciclista e pedone sono le informazioni fondamentali per lo sviluppo di soluzioni efficaci per migliorare la protezione del pedone e del ciclista in caso di urto con autovetture. La casistica degli incidenti a Palermo, negli ultimi anni, avvenuti su strade urbane (84%) che coinvolgono adolescenti (6,4%), mostra che i ciclisti hanno in genere una posizione di impatto superiore rispetto al pedone, con una quota maggiore di lesioni per urti nella zona del parabrezza. In questo lavoro è eseguita la simulazione dinamica per lo studio delle lesioni alla testa e al torace dell’adolescente, tra una bicicletta generica e un modello di auto che presenta caratteristiche vantaggiose per la sicurezza del pedone o del ciclista. Il software SimWise (Visual Nastran) è stato usato per la simulazione multibody dell’impatto; il modello antropomorfo, l'auto e le biciclette sono quelli utilizzati in lavori precedenti. L'attenzione è su un ciclista adolescente, perché i relativi dati di lesione si trovano in letteratura con difficoltà. I dodici test d’impatto completo (auto contro ciclista) hanno come parametri principali: velocità del veicolo (20, 30, 40 e 50 km/h), con tre diverse posizioni del ciclista rispetto al veicolo: frontale, laterale e posteriore. La posizione di impatto della testa (sopra il cofano, nel parabrezza), determinato dalla prova di crash, mostra che la protezione del ciclista dovrebbe essere migliorata nella zona più alta del parabrezza, rispetto a quelle pedonali. La ferita alla testa viene analizzata utilizzando il parametro HIC e la ferita al torace è analizzata secondo il criterio dei 3 ms; viene calcolata la probabilità AIS 4 +, concludendo che la lesione alla testa è più pericolosa in caso di pedone adolescente, mentre la ferita della cassa toracica è più pericolosa nel caso di ciclista adolescente. Inoltre il ciclista adolescente ha una maggiore possibilità di sopravvivenza rispetto al ciclista adulto. Incidentologia e simulazioni mostrano che il parabrezza è una posizione di impatto frequente per testa e torace.

The study of the injury caused by the vehicle-teenage cyclist crash is presented in this paper. The vehicle is a SUV, with high frontal part, in order to compare the results with those obtained previously in the sedan- teenage cyclist crash and begin a study of the influence of the frontal shape of the vehicle. No variation is executed on the model of the teenage cyclist and the bike. Three different positions are analyzed: front, rear and lateral position. The injury on the cyclist head is examined by HIC criterion, in the way indicated in the rules. Correlation HIC – AIS is used to calculate the lethality of the injuries. The principal conclusion is done that the injury of the head is more dangerous for the SUV impact than the sedan, but only at the maximum speed (50 km/h). The injury to the chest is analyzed by 3 ms criterion; the injury is greater for the SUV impact than the sedan, but the entity is strongly dependent on the cyclist position. A comparison is executed with both the teenage and adult pedestrian concluding that the pedestrian is subjected to greater injury, because the bike absorbs a part of the energy in the front and side crash. The more dangerous injury is the telescoping. A further comparison show that the shape of the bonnet and the height of the frontal part have to be studied in an accurate way to reduce the injury to pedestrians and cyclists.

The research is carried out to improve passenger’s comfort to increase the vehicles stability in dynamic conditions. The literature available in the automotive engineering considers different topics for studying suspensions. An example represents mechanisms structure and analysis (synthesis, kinematics, and dynamics) under various operating conditions. These aspects have been approached before analytically, numerical. The current paper studies the influence of the lateral force on the contact patch of the wheel and the corresponding variations of vehicle stability parameters, such as camber angle and wheel rear track. The study is performed for a newer innovative rear suspensions mechanism which does not have a wheel track and camber angle variation, relative to the chassis, when the suspension components was considered rigid. A numerical solution is obtained through a virtual model on several commercial codes: MSC Adams, Patran, Nastran. Concerning the analysed parametes, their variation increases as the applied force is increased. Moreover, the largest variation corresponds to the case were elastic bushings and deformable links are considered.

In this work the data, obtained for the three vehicles (sedan, SUV and Pick Up), tested in previous works, are compared. Following the results found in the literature, particular emphasis is done on the speed of the teenager cyclist head at the instant of impact and the diagrams of the head speed and the chest obtained in the simulations are shown. The speed of the head is that absolute, and this is used for processing the data and the subsequent determination of the best values of the three geometric actual parameters identified in front of the vehicle. Absolute speed is preferred because using the relative speed respect to vehicle, some amounts that cannot be disregarded are omitted from the evaluation. The chosen speed is 30 km/h because higher values appear too dependent on the mass of the vehicle, while lower values may not result in serious injury and are therefore less attractive. The procedure, to obtain the optimal values of the height of the bumper, the height of the bonnet and of the inclination angle of the bonnet is illustrated in the case the side impact vehicle-teenager cyclist. The conclusion is made that analogous procedure can be applied to HIC values.

The study of the injury caused by Pick-up vehicle-teenage cyclist crash is presented in this paper. The vehicle has high frontal part, in order to compare the results with those obtained previously in the sedan and SUV - teenage cyclist crash. No variation is executed on the model of the teenage cyclist and the bike. Three different positions are analyzed: front, rear and lateral position. The injury on the cyclist head is examined by HIC criterion, in the way indicated in the rules. Correlation HIC – AIS is used to calculate the lethality of the injuries. A comparison is made between the results of the simulations for Pick up, SUV and sedan, concluding that the injury of the head is more dangerous for Pick-up impact than SUV and the sedan, but only at the maximum speed (50 km/h). This value of the speed can be considered critical, since HIC values are very high for all the three vehicles. The more dangerous injury is the side impact. A further comparison is done between the impact points of the three vehicles concluding that both the shape of the bonnet that the height of the front part must be studied carefully in order to reduce the damage to cyclists and pedestrians.

The purpose of this paper is to propose a useful method to implement active magnetic bearings (AMBs) on an existing rotating shaft which rotates on conventional bearings. This is feasible if AMBs can produce the same reaction loads of conventional ones and if the size of vane is large enough to host an AMB. As this substitution could offer some difficulties due to the different size between magnetic bearings and conventional ones, a set of equations are performed to show that a variation of some parameters can solve this problem. The journal ratio is the geometrical parameter introduced to develop the present analysis. The variation of journal ratio does not produce a variation of the pole’s surface so that the reaction load does not change. The results are analyzed by numerical analysis by mathematical relationships involving the design parameters, magneto-static simulations and dynamic simulation on shaft when it is tested by disturbance rejection and reference tracking input in order to analyze the differences on dynamic behavior of the shaft on its suspended sections. Results show that the displacement pattern of the suspended sections remains unchanged, confirming that the reaction load, produced by pole expansion, remains the same varying the journal ratio.

In this paper the results of experimental tests are shown, lead by extended method of measurement, on a tire for an off-road vehicle 175/82 R16, inserting Prescale paper at the contact with the ground. The experimental analysis of the pressures is lead, in cross-sectional direction, in 5 zones correspondents to the middle of the single dowels constituting the tread. The results are analyzed by means of software predisposed to the scope so as to go back easily to the value of the pressure. The obtained results are critically analyzed and the result are compared with those obtained by the formulas of Rowland and MacLaurin, and by the nominal pressure at ground, concluding that the expression of MMP for vehicles on wheels is simply to consider a pointer of the performances, in comparison with other vehicles or wheels, rather than a real prediction of the pressure on the ground. Besides a good agreement is found between the tire deflection calculated and measured experimentally.

The complex and highly non-linear phenomena involved during braking are primarily caused by friction materials’ characteristics. The final friction materials' characteristics are determined by their compositions, manufacturing, and the brake's operating conditions. Analytical models of friction materials' behaviour are difficult, even impossible, to obtain for the case of different brakes' operating conditions. That is why, in this paper, all relevant influences on the friction materials' cold performance have been integrated by means of artificial neural networks. The influences of 26 input parameters, defined by the friction materials' composition (18 ingredients), manufacturing (five parameters), and brake's operating conditions (three parameters), have been modelled versus changes of the brake factor C. Based on training and testing of 18 different architectures of neural networks with five learning algorithms, a total of 90 neural models have been investigated. The neural model (BR26841) trained by the two-layered neural network, with a Bayesian regulation algorithm, was found to reach the best prediction results. This neural model was able to generalize the friction materials' cold performance, for temperatures in the contact of the friction pair T>100°C, in the range of application pressure changes between 20 and 100bar, and for initial speed changes between 20 and 100km/h.

This chapter deals with the forecasting of vehicle performance on the road, according to the installed engine. It begins with Section 1, which shows the calculation of the resistance to motion, that is, the forces that the vehicle must overcome to advance on flat roads and uphill. The calculation excludes accidental resistance in curves because it is not essential for predicting the behavior of the vehicle on the road. Section 2 begins with the power characteristic, the forecast by traction–speed and power–speed diagrams, calculation of gear ratios, and then passing to the limits to the estimated acceleration, feature consumption, and distance. This chapter concludes with a section on the drivability of the vehicle, and sets out the advantages of four-wheel-drive vehicles. Keywords: motion resistances; inertia coefficient; performance forecast; power characteristic; torque characteristic; traction–speed diagram; power–speed diagram; consumption diagram; maneuverability; handling

The vehicle-bicyclist impact is studied in this paper. After analysis of the accidents in Palermo in the last years, the multibody simulation of the crash is executed by making use of Visual Nastran. Dummy, car and bicycle are those used in previous works. The attention is on a teenage cyclist, because the data on this argument are found in literature with difficulty. The impact is simulated at four different speeds until 50 km/h, with three different positions of the cyclist relative to the vehicle: frontal, side and rear. In particular the injury of the head is analyzed using the parameter HIC and the chest injury is analyzed by 3 ms criterion; the likelihood AIS 4+ is calculated, concluding that head injury is more dangerous in the case of teenage pedestrian, while chest injury is more dangerous in the case of the cyclist.

The paper aim is the investigation of optimal damping constant of a quarter car shock absorber that is performed in the frequency domain. The optimal damping constant refers to the value that minimizes the acceleration of all connected bodies characterizing a two degree of freedom system sketching a quarter car. The connected bodies are sprung and unsprung mass respectively for quarter of chassis and tire, the last one maintain the contact with the ground and it is connected with the sprung mass through a shock absorber characterized by spring and fluid damper. Optimal damping constant was determined by imposing analytical conditions on the expression of acceleration of two masses. Afterwards, the variation of acceleration and position in function of frequency for the obtained value of damping constant is plotted numerically in two ways using Wolfram Mathematica and MSC Adams software.

A simplified theory on the vehicle stability in curve is explained in this paper; it allows the calculation of the force on the wheels during the motion in curve, supposing unchanging the position of the rolling centre; moreover it does not take in account the turn of the wheels and the behaviour of the tires, so that the theory can be applied to 2WS and 4WS vehicles for vertical loads calculation. The virtual simulations of 2WS and 4WS vehicles are executed, extracting all the data interesting the vehicle stability; it needs the distinction between manoeuvrability and handling. The simulations of two different tests are executed: the elk test like manoeuvrability test and a similar one at low speed as handling test. The values of vertical forces are compared one another and with the results by the simplified theory of the above. The results of horizontal (longitudinal and transversal) forces and the self alignment moment are compared with those obtained by magic formulae of Pacejka. All the comparisons are very satisfactory for both 2WS and 4WS vehicles, indicating that 4WS vehicle has a greater stability in curve, in every situation and that the theoretical formula of the weight displacement gives good results. Moreover the better performances of 4WS vehicle in terms of the slip angle, of the weight displacement and of the forces give in general a substantial contribute to the safety of the vehicles, well as an increase of driveability. 4WS has lower yaw-rate in high speed, smaller slip angle and lateral acceleration, so it has better robustness. Besides2WS loses stability in advance when steering angles of front wheels are greater.

This paper presents the optimization process of MR – magnetorheological brake in order to define its configuration, and to reach the requested vehicle braking torque. FEM analysis previously carried out, concerning structural sizing of such a brake, showed that both braking torque and brake mass did not satisfy the requirements. Due to the necessity of limitation on the suspended mass of a motor vehicle, the optimization of the form of MR brake stator has been executed, including determination of its contribution to the total mass of the brake. Thus a percentage reduction of approximately 40% was obtained. In order to estimate the brake temperature which results from the transformation into heat of a vehicle kinetic energy during brake application, a thermal Finite Element Analysis is carried out. In particular a fade braking test composed of snub braking, i.e. repeated cycles of acceleration and consecutive braking applications is performed.

Questo lavoro ha come obiettivo principale lo studio teorico e con supporto di software F.E.M. di un dispositivo che consenta recupero energetico da una sospensione automobilistica. In sostituzione allo smorzatore viscoso, che dissipa l’energia cinetica del veicolo a seguito dell’attraversamento di strade sconnesse o ostacoli più marcati, si è usato uno smorzatore elettromagnetico che svolga le funzioni dello smorzatore viscoso consentendo un recupero di energia elettrica. Lo smorzatore elettromagnetico è di tipo a magneti permanenti e il suo funzionamento si basa sul fenomeno dell’induzione elettromagnetica. Il modello matematico descrive il funzionamento dello smorzatore, restituendo i valori delle grandezze elettriche e meccaniche in funzione della velocità relativa tra stelo e statore. Si è valutato il recupero energetico considerando una minicar elettrica che transita su una strada mediamente sconnessa. La potenza elettrica recuperata ha un valore complessivo di circa 250 W

Dopo un’accurata ricerca bibliografica sui fluidi magnetoreologici, il loro comportamento ed impiego, si è passati alla progettazione di una frizione magnetoreologica per autoveicoli. Considerando le caratteristiche di coppia trasmessa e potenza, il dispositivo è stato dimensionato tenendo presente i vincoli di ingombro del veicolo preso in esame. Sottoponendo il dispositivo ad analisi magnetostatica agli elementi finiti, si è determinato l’andamento delle linee di flusso del campo magnetico nel meato di fluido e nelle zone di maggior interesse, calcolando la coppia teoricamente trasmessa dall’innesto.È stato anche eseguito il confronto delle prestazionifra una frizione MR ed una frizione tradizionale, evidenziando che la frizione MR presenta tempi di risposta più brevi con un elevato risparmio energetico. Lo studio effettuato mostra che il dispositivo si adatta bene ad un veicolo con cambio automatico o robotizzato o comunque con tempi di risposta molto brevi, ma necessita di un sistema di controllo per l’avviamento del veicolo.

The purpose of this paper is the study of the shape of catamaran with asymmetrical hulls by both experimental and numerical viewpoint. The experimental study is based on the towing tank tests on a catamaran hulls shape obtained from previous works, showing that the wave resistance is very low produces a lower energy loss and a greater effectiveness. The hulls shape is optimized by the CFD application by force of commercial software, which shows that the reduction of wasted energy is very sensitive to make some changes; in particular three different width of the catamaran are tested and their performances are compared.

This paper reports the results of multi-body numerical simulation of a vehicle crash with a teenager pedestrian. A previous technique utilized for adult pedestrian impact is applied. The work starts with the determination of the masses for the various segments of the body of a teenager with a total mass of 45 kg and then switches to the construction of the dummy and the middle-class vehicle in the Visual Nastran environment. Simulations are performed for both frontal impacts and lateral impacts, when the vehicle is travelling at a constant speed and when the vehicle is braking, following the Euro NCAP rules on the subject. The results are analysed by calculating the values of the head injury criterion for the head and the values of the thoracic trauma index and 3 ms criterion for the chest; the injuries are assessed according to the current interpretation. Abbreviated injury scale curves are used to determine the dangerousness of the impact. Finally, the results are close to those obtained by applying the same technique to an adult pedestrian and other available data in the literature for an adult or a child.

This work steps from a bachelor thesis, joining the results of a study about the dynamic loads to evaluate the comfort loss in the motorcycle during the usage, with the potentiality of a modern FEM software. The goal is the development of a new methodology for structural optimization of motorcycle’s frame. In many of cases the success of the structural optimization is linked with a two factors combination: the software and the strength of the engineer to condition the mathematical problem, defining parameters domain and technological constraints. A good alternative to the traditional load hypothesis linked to historical data or instrumental measurements is focused in this paper. Consistent with the tendency to hyper-specialization, the machine has to fit the final user, with his anthropometric characteristics and a neutral riding style, in order to save calculation time, physical driving test and finally saving metal-weight and money

Si è considerata una piastra forata di materiale ferromagnetico opportunamente accoppiata da bobine di filo di rame smaltato alimentato da un alimentatore DC a 30V. Essa è stata analizzata agli Elementi Finiti e successivamente sono state eseguite sperimentazioni per la validazione dei risultati ottenuti. Dopo aver levigato la piastra sono stati installati due estensimetri per misurare la deformazione lungo l’asse x e lungo l’asse z. Si sono ottenuti i valori di deformazione di 5µm in direzione z e -2µm in direzione x. Il confronto numerico-sperimentale mostra che i risultati di laboratorio sono più bassi di quelli numerici, mentre segni e ordini di grandezza sono gli stessi. Si conclude che i risultati dell’analisi FEM possono essere considerati accettabili a causa dell’ortogonalità del piano delle spire rispetto al piano della piastra e a causa del coefficiente di impacchettamento del rame.

This paper shows a comparison about dynamic behavior of a rotating shaft when it is suspended by 4-axis radial active magnetic bearing system. The active magnetic suspension is obtained by two different controllers which realize the robust stability and robust performance. The control systems used are µ-synthesis and loop shaping design procedure. Each of these controllers is characterized by fourinput and four output signals and the introduction of uncertainties on displacement gain and current gain is justified by the simple fact that during the time the component which constitutes these gains can be subjected to torn and worn which can lead the entire system to instability phenomena. The inputs are the feedbacks of four displacement components relative to the four axis of radial active magnetic bearing while the outputs are the control current injected in the plant in order to provide the control of position of two section under the monitoring of ideal sensors. An ideal sensor here is meant to be able to capture small displacements and without presence of noise. The advantages of a four input controller is the absence of velocity components which are present in the state vector such that no observer and speedsensors are need to build a feedback. The comparison of the performances is made through the introduction of same weighting function for the two control system. The weighting functions are introduced in order to define the required performances for the position and control signals. The results are produced by simulations tracking of reference and disturbance rejection are tested in order to provide elements useful to implement the goal of this paper. All simulations and results are performed by MATLab.

This paper shows the influence on dynamic behavior of the car when it is equipped with magneto-rheological dampers controlled by a feedback. The feedback is built up in two ways; the first is implemented by a switch on/off control that is characterized by the injection of magnetic field with a constant value. It happens when a certain value of relative speed between the sprung and unsprung mass is exceeded. The second feedback is characterized by the H-infinity control which is based on the relative displacement in order to vary the magnetic field signal in a continuous manner. At the same time the H-infinity control of vehicle is maintained by taking into account the exceeding of speed signal in order to consider the substantial differences with the switch on/off control. These differences are evaluated in terms of relative displacement and speed between the unsprung and sprung mass. The exogenous excitation is the road disturbances which are introduced as a square wave input in order to emulate those that are commonly encountered on the road. All simulations and results are performed by MATLab-Simulink and Mathematica.

After an initial study of the characteristics of magnetorheological fluids based on a thorough search in literature, a preliminary configuration of MR brake is proposed. It comes from the evaluation of the main factors influencing the design of an appropriate magnetic circuit, and then the performance obtained in terms of brake torque. The analytical study of the brake has allowed a first preliminary sizing. Through the subsequent execution of an electromagnetic finite element model, created in ANSYS, it was possible to assess more accurately the distribution of the magnetic field inside the MR fluid and hence the resistance to relative motion between rotor and stator. The work needs an accurate optimization due to insufficient value of the braking torque and high mass of the device.

The paper presents firstly an introduction discussing: the problem’s statement emphasizing the actual problem of research of passenger car suspension to improve driving comfort and dynamic of the vehicle movement; aspects regarding the studies of car suspension mechanisms; the paper’s aims and objectives showing that a new configuration of suspension mechanism having in structure mobile frame and an actuator offering some important operational advantages is proposed. After this, the innovative concept is presented. The motions of mechanism elements and actuator and kinematic displacements are largely presented. The simulation using modern software (MSC Patran 2007, MD R2 Nastran and MSC ADAMS/View) accentuates the actuality of the results, which are presented and discussed for an application. Final conclusions are given.

Nel lavoro è investigato il comportamento a fatica di lastre forate in lega di alluminio. In particolare è valutata l‟influenza combinata dell‟espansione a freddo dei fori e dell‟indentazione sul miglioramento della vita a fatica. A tal fine sono state condotte diverse prove di fatica aventi lo scopo di valutare il numero di cicli a rottura e la conseguente curva di Wöhler. I risultati sperimentali sono stati confrontati con quelli ottenuti senza la realizzazione di alcun processo di espansione e di espansione-indentazione. Lo studio ha permesso di concludere che il processo di espansione ed indentazione anulare determina un ritardo nella nascita della cricca e della conseguente rottura a fatica.

The purpose of this work is the achievement of an anthropomorphic model for the virtual simulation of pedestrian – vehicle crash test. “Dummy” construction in Visual Nastran room does possible the preparation of crash test with several vehicle models. Its three-dimensional geometry is implemented by video animation software, extracting the geometry element for element, and its characteristics are in keeping with EURONCAP protocol. Every bodily segment properties are determined using the reference material on the movement biomechanics. At last fall tests from three different heights are simulated for the “Dummy” validation, obtaining a reliable result.

Nel lavoro è valutato il comportamento di carrelli per serramenti in condizioni di carico variabile al fine di valutarne l’usura. Le prove dinamiche sono state condotte su una macchina di semplice concezione appositamente realizzata e adatta a garantire un moto alterno sotto carico. Per la valutazione dell’usura è stata eseguita una scansione molto accurata della geometria delle rotelle (prima e dopo aver effettuato le prove dinamiche) attraverso un sistema di rilevazione a luce strutturata COMET V STEINBICHLER. Il processo di scansione ha permesso di digitalizzare le rotelle con un’accuratezza dell’ordine di 5µm. I dati della scansione hanno evidenziato un aumento pressoché uniforme del diametro del foro. E’ stato inoltre effettuato un raffronto dei risultati sperimentali con la teoria dell’usura zero: In particolare, è stato valutato il carico massimo fino al quale si ha usura zero per un determinato numero di cicli (20000) nel contatto rotella–asse e rotella– guida. I valori ottenuti sono stati confermati dalle elaborazioni dei risultati sperimentali.

The performance of 1,6 l four-valve Otto cycle engines is examined in this paper from the point of view of excessive consumption of lubricating oil. Three failure bands were recognized, at low, medium, and high distance traveled, each one obtained from a sample of 15 vehicles. A “Weibull model in bands” was applied; we obtained a satisfactory result from the point of view of reliability and applied the method to several types of motor vehicle. FMEA analysis of a sample permitted identification of the principal causes of unevenness in cylinder surfaces and an evaluation of the methods of machining required to correct this unevenness. Finishing of cylinders with a flexible smoothing tool is a low-cost technique for restoring vehicles to a suitable reliability level.

Il presente lavoro ha come scopo quello di mettere in mostra le sostanziali differenze rilevate nel comportamento dinamico di un rotore supportato da cuscinetti radiali in levitazione magnetica attiva. Sono stati rilevati sia gli spostamenti radiali che la risposta in frequenza controllando il rotore dapprima con una legge di ottimo tempo variante e successivamente con una di tipo sub-ottimo, ricavata dalla precedente rendendola stazionaria rispetto alla velocità angolare. È mostrato come la presenza del controllo sub-ottimo annulla la dipendenza del segnale di controllo dalle componenti di spostamento non interessate dal sensore e riduce sensibilmente l’entità degli spostamenti radiali.

The purpose of this paper is the simulation of vehicle – pedestrian crash test, executed by Visual Nastran. The evaluation of the damage caused to pedestrian is obtained following the EURONCAP directive. The vehicle virtual model, DIMA, follows closely the characteristics of a saloon car belonging to the small cars category. A total of 16 simulation tests are conduced; each characterized by different initial conditions. The vehicle advances with several speeds, at constant speed and in braking. The anthropomorphic model Dummy impacts with the vehicle in lateral or perfectly frontal position with respect to the front of the vehicle.

The investigation performed by the Authors represents the most recent development of a research presented in [1] and [2], in which the geometrical solutions of the hull have been obtained through an optimization process, made by using the CFD numerical methods. The most important result of this optimization was the wave resistance reduction, which arrived up to 20% of the total initial resistance. In this further process the hull catamaran model has been built and tested at the towing tanks of the Universities of Naples and Trieste. The results obtained in the numerical process have been compared with the experimental ones and the reliability of the numerical results will be proved. Then the numerical investigation has been extended further on, through a numerical process made by using the linear theories of the wave resistance and a general comparison between the results has been made

The cold-expansion process is widely used to enhance the fatigue life of structures with fastener holes. Various studies assert that the cold-expansion improves the fatigue strength of fastener holes; however, the improvement of fatigue life is difficult to quantify. The influence on fatigue life of cold-worked hole in a 6061-T6 alluminum allosy was studied by numerical and experimental tests. Fatigue crack growth tests were carried out to find the crack length and growth rates of crack propagating from hole edge. Thus, the cold-expansion process was modeled with a Lagrangian implicit code for metal forming to obtain the residual stress field. Progressive crack growth along the observed fatigue path was simulated as part of the analysis to observe the residual stress redistribution due to the crack propagation. The behavior of a fatigue crack in the presence of the hoop residual stress is discussed.

The purpose of this work is the description of the phenomenology of driving behaviour of a production car characterized by a hybrid powertrain and a continuously variable transmission (CVT), along with a theoretical study of consumption that provides results in agreement with the experimental ones obtained and reported by the Car Maker.

V clanku je predstaven vyvoj metodiky pro vypocet dynamiky mechanismu motoroveho rozvodu. Vyuzity jsou techniky simulaci vicehmotovych soustav; pouzit byl software AVL/Tycon. Objektem vyzkumu byl vliv pracovnfho rezimu motoru na dynamiku retezoveho rozvodu s jednim (SOHC) a dvema (DOHC) vackovymi hndeli v hiave motoru. Analyza obsahuje dukaz, ze retezovy prevod zavadi (di'ky kinematickemu zaberu) vysokou frekvenci s velmi malou amplitudou v porovnani s harmonickymi frekvencemi od externi sil. Metodika umozhuje urdt zati'zeni vstupni'ho a pomocnych hridelu, zatizeni na strukturu motoru indukovane pres operne a napmaci kladky. Diky tomu se predstavena metodika stava vyznamnym nastrojem pro predvidani zatizeni; a navic umoznuje i detailni vypocet trecich ztrat v jednotlivych castech retezoveho rozvodu. The purpose of the present work is the development of a methodology to study the dynamic behavior of the drive distribution system, based on the techniques of multi-body numerical simulation using AVL/Tycon code. Chain drive systems with both single cam shaft (SOHC) and double cam shaft (DOHC) are studied to investigate how the dynamic behavior varies with the engine working rate. The analysis includes evidence that the chain transmissions introduce a high frequency due to kinematic engagement (polygon effect), with a very low amplitude with regard to the harmonics of external forces. The methodology permits the evaluation of the loads on the drive shaft, on the distribution shafts, and loads acting on the engine structure through the supports and constraint points. It represents an important forecasting tool; moreover, it also permits the detailed calculation of the friction lost in the interaction between the chain components.

The difference between the stress value calculated by a two-dimensional finite element model of spur gears and those obtained by the rules in ISO 6336 was evaluated. Hertz theory, which provides information on the extension of the contact area and the maximum value of the contact pressure, was used to choose the dimensions of the elements. The mesh was created using the stress analytical solution relative to a model consisting of two cylinders in contact. Analogous optimization was executed for the mesh of the teeth feet; a mesh of 15 elements was considered optimum, because it minimized the difference to 0.5 per cent in the bending stress calculation. Stress values, obtained using the finite element method (FEM), are generally lower than those obtained with the ISO rules. Hence, this approach yields a conservative determination of the effective material strength. In all the examined cases, the difference was less than 2.5 per cent. The set FEM technique gives a result accuracy of better than 1 per cent; the difference between the stress obtained by FEM and those obtained by ISO 6336 is less than 2.5 per cent, so that the FEM confirmed, consistent with the ISO rules, that correction of the profile results in significant benefits with respect to determination of the mechanical resistance of spur gears.