Smart materials and vehicle efficiency. Design and experimentation of new devices.

In this dissertation the activities carried out during the PhD are comprehensively described. The research mainly focused on the development of novel smart devices aimed at disengaging auxiliaries in internal combustion engine vehicles. In particular, the activities dealt with modeling, design, manufacturing and testing different fail-safe magnetorheological clutch prototypes, in the framework of a project funded by Regione Toscana, which involved two departments of the University of Pisa and Pierburg Pump Technology - Stabilimento di Livorno. After an extended literature review, several concepts of the clutch were proposed, which led to the design of the first magnetorheological prototype. An intensive experimental campaign was conducted, which involved several prototypes. A particular attention was focused on the measurement and analysis of the torque transmitted by the clutch in different operating conditions and new indices were proposed to objectively analyze the performances of magnetorheological clutches in general. On the basis of the results of the first experimental phase, the limits of the first design were analyzed and a novel prototype was developed, which succeeded in fulfilling all the design specifications. Further analyses were carried out in order to develop a clutch model starting from the experimental results. The effect of clutch heating was considered and a complete model of the clutch based on neural networks was proposed. The model was capable of taking into account the effect of the main parameters influencing the torque characteristic and may be used in a vehicle simulator or in a hardware-in-the-loop bench. Finally, an additional component to be connected to the clutch, which made use of shape memory alloys, was developed and tested during the visiting period at the University of Toledo (OH), USA

A new formulation of the understeer coefficient to relate yaw torque and vehicle handling

The handling behaviour of vehicles is an important property for its relation to performance and safety. In 1970s, Pacejka did the groundwork for an objective analysis introducing the handling diagram and the understeer coefficient. In more recent years, the understeer concept is still mentioned but the handling is actively managed by direct yaw control (DYC). In this paper an accurate analysis of the vehicle handling is carried out, considering also the effect of drive forces. This analysis brings to a new formulation of the understeer coefficient, which is almost equivalent to the classical one, but it can be obtained by quasi-steady-state manoeuvres. In addition, it relates the vehicle yaw torque to the understeer coefficient, filling up the gap between the classical handling approach and DYC. A multibody model of a Formula SAE car is then used to perform quasi-steady-state simulations in order to verify the effectiveness of the new formulation. Some vehicle set-ups and wheel drive arrangements are simulated and the results are discussed. In particular, the handling behaviours of the rear wheel drive (RWD) and the front wheel drive (FWD) architectures are compared, finding an apparently surprising result: for the analysed vehicle the FWD is less understeering than for RWD. The relation between the yaw torque and the understeer coefficient allows to understand this behaviour and opens-up the possibility for different yaw control strategies

Geometry optimization of a magnetorheological clutch operated by coils

Magnetorheological fluids are smart materials responsive to magnetic field, widely applied in dampers and shock absorbers but also in clutches and brakes. The magnetorheological fluid gap shape is a very important topic in the design of clutches, since it directly influences the transmissible torque and the power loss. In this paper, an approach to magnetorheological fluid clutch design based on optimization is proposed and tested on four different layouts. Starting from a given available volume, two magnetorheological fluid gap shapes, namely single cylinder and multi-disc, and two coils positions, i.e. internal or external, were considered. A lumped parameter model was developed to analytically compute the magnetic flux along the clutch magnetic circuit and to calculate the transmissible torque of the clutch. The optimal geometry of the clutch for maximum transmissible torque, in terms of number and dimensions of the coil sectors, was determined for each shape and coil configuration and the results were validated by finite element models

Caratterizzazione oggettiva dell'handling di autovetture con un nuovo approccio

Lo studio della dinamica laterale è di fondamentale importanza per coloro che si occupano di dinamica del veicolo. L'argomento è solitamente trattato attraverso un approccio strettamente legato all'analisi sperimentale, mentre le definizioni teoriche risultano limitate e alle volte confuse. Con questa tesi si vuole impostare un'analisi oggettiva della dinamica laterale, cercare di riprendere e rivedere concetti classici quali il fin troppo noto gradiente di sottosterzo, e proporre degli indici attraverso i quali poter analizzare il comportamento di un veicolo. Grazie alla collaborazione con il Centro Ricerche Fiat, è stato possibile validare l'analisi proposta a partire dai dati relativi a modelli monotraccia di alcuni veicoli e confrontare i risultati ottenuti con i giudizi solitamente adottati dal CRF per giudicare il comportamento dei veicoli stessi

Smart materials and vehicle efficiency. Design and experimentation of new devices.

In this dissertation the activities carried out during the PhD are comprehensively described. The research mainly focused on the development of novel smart devices aimed at disengaging auxiliaries in internal combustion engine vehicles. In particular, the activities dealt with modeling, design, manufacturing and testing different fail-safe magnetorheological clutch prototypes, in the framework of a project funded by Regione Toscana, which involved two departments of the University of Pisa and Pierburg Pump Technology - Stabilimento di Livorno. After an extended literature review, several concepts of the clutch were proposed, which led to the design of the first magnetorheological prototype. An intensive experimental campaign was conducted, which involved several prototypes. A particular attention was focused on the measurement and analysis of the torque transmitted by the clutch in different operating conditions and new indices were proposed to objectively analyze the performances of magnetorheological clutches in general. On the basis of the results of the first experimental phase, the limits of the first design were analyzed and a novel prototype was developed, which succeeded in fulfilling all the design specifications. Further analyses were carried out in order to develop a clutch model starting from the experimental results. The effect of clutch heating was considered and a complete model of the clutch based on neural networks was proposed. The model was capable of taking into account the effect of the main parameters influencing the torque characteristic and may be used in a vehicle simulator or in a hardware-in-the-loop bench. Finally, an additional component to be connected to the clutch, which made use of shape memory alloys, was developed and tested during the visiting period at the University of Toledo (OH), USA

A multilevel finite element-multibody approach to design the suspension system for the road transportation of SSR1 cryomodule

Cryomodules (CM) represents edge-frontier assemblies in particle physics research field. The road transportation of CM is a critical phase during which the structures can be subjected to significant dynamic loads. It is therefore necessary to design a Transportation Tool (TT) equipped with an appropriate suspension system. This work describes the approach adopted for the design of the TT for the CM PIP-II SSR1 (Proton Improvement Plan-II – Single Spoke Resonators 1), which is firstly introduced in the CM research field. Initially a Finite Element (FE) model was developed, considering the main sub-assemblies of the CM. However, this model was not suitable for the design of the TT due to the high computational burden. For this reason the model was exported as a Modal Neutral File and imported into a MultiBody software (MB) where the remaining components were modeled as concentrated stiffnesses or rigid bodies. The MB model thus obtained has drastically reduced the calculation time, proving to be fundamental in the TT iterative design phase, which involves the use of Helical Isolators (HI) performing the function of mechanical filters. To validate the effectiveness of TT in reducing dynamic loads, a 3D acceleration profile measured during the transport of a similar cryomodule (Linear Coherent Light Source II, LCLS-II) was used. Furthermore, the results of the MB model were used to perform the structural verification of some critical components of the CM

Fatigue assessment of a FSAE car rear upright by a closed form solution of the critical plane method

Material fatigue is extensively discussed and researched within scientific and industrial communities. Fatigue damage poses a significant challenge for both metallic and non-metallic components, often resulting in unexpected failures of in-service parts. Within multiaxial fatigue assessment, critical plane methods have gained importance due to their ability to characterize a component's critical location and detect early crack propagation. However, the conventional approach to calculate critical plane factors is time-consuming, making it primarily suitable for research purposes or when critical regions are already known. In many real-world scenarios, identifying the critical area of a component is difficult due to complex geometries, varying loads, or time limitations. This challenge becomes particularly crucial after topological optimization of components and in the context of lightweight design. Recently, the authors proposed an efficient method for evaluating critical plane factors in closed form, applicable to all cases that necessitate the maximization of specific parameters based on stress and strain components or their combination. This paper presents and validates the proposed methodology, with reference to a rear upright of a FSAE car, which is characterized by a complex geometry and is subjected to non-proportional loading conditions. The efficient algorithm demonstrated a substantial reduction in computation time compared to the standard plane scanning method, while maintaining solution accuracy

A multi-gap magnetorheological clutch with permanent magnet

This paper describes the design and testing of a novel permanent magnet clutch based on a magnetorheological fluid. It was inspired by a prototype previously developed by the authors and contains a novel gap shape conceived to reduce torque loss in the disengaged operating mode. Several geometries and material arrangements were investigated and the performance in terms of transmissible torque in different operating conditions was assessed using finite element numerical models. The prototype was manufactured and some experimental tests were performed. The new prototype was rated on the basis of performance indices and the design effectiveness was proven by a higher value of efficiency in the disengaged operating mode

Design of novel tilting electric four-wheelers

EU cities are increasingly congested due to the demand and usage of motor vehicles. Future scenarios for EU urban centers see a modal shift in personal mobility from cars to lighter, smaller, more specialized and environmental-friendly alternatives. Electric L-category Vehicles (ELVs) are viable alternatives that can fulfill the commuter needs due to their small size and light-weight: by consequence the energy requirement, battery size and related costs can be strongly reduced respect to conventional electric cars. However, this modal shift must overcome one main challenge: most car drivers do not consider Lcategory vehicles as a suitable option mainly due to L-vehicle dynamic limitations. To achieve that, the RESOLVE (Range of Electric SOlutions for L-category VEhicles) project, funded in the Horizon 2020 framework - Green Vehicles GV5-2014 call, will develop components and systems aimed to meet the low cost target required for this segment. At the same time, the project will deliver an exciting and attractive ELV driving experience by proposing new concepts (tilting and narrow track), while containing as much as possible the vehicle energy consumption. In this paper, the dynamics analyses carried out to develop the architecture of ELV vehicles are presented. A stability analysis of the vehicles in straight line was firstly carried out and the results were compared to tilting two and three-wheelers for a wide range of speed. A detailed multibody model was developed to simulate the steady-state behavior of the 4-wheelers during turning and to perform further dynamic analyses. In addition, an entire vehicle model including electrical and mechanical components (battery, power electronics, e-motor, driveline, etc.) was developed to assess the ELVs energy needs during reference and real-world driving maneuver. The results demonstrated the feasibility of this novel kind of vehicles, confirming the exciting driving experience typical of tilting vehicles, combined with comfort, low environmental impact and limited energy requirements

The effect of the front-to-rear wheel torque distribution on vehicle handling: an experimental assessment

The front-to-rear wheel torque distribution influences vehicle handling and, ulti-mately, it affects key factors such as vehicle safety and performance. At a glance, due to part of the available tire-road friction being used for traction at the driven axle, a Front-Wheel-Drive (FWD) vehicle would be expected to be more understeering than a Rear-Wheel-Drive (RWD) vehicle. However, such effect may be counterbalanced, or even reversed, mainly due to the yaw moment caused by the lateral contribution of the traction forces at the front wheels. This paper proposes an experimental assessment, carried out on a fully electric vehicle with multiple mo-tors, allowing different front-to-rear wheel torque distributions. The results confirm that the yaw moment effect discussed is considerable, especially at low vehicle speeds and high steering an-gles. In particular, the RWD vehicle resulted more understeering than the FWD one at 30 km/h