A Design Strategy Based on Topology Optimization Techniques for an Additive Manufactured High Performance Engine Piston

In this paper, a methodology for the design of a motorcycle piston is presented, based on topology optimization techniques. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminum piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. In this methodology, the minimum mass of the component is considered as the objective function and a target stiffness of important parts of the piston is employed as a design constraint. The results demonstrate the general applicability of the methodology presented for obtaining the geometrical layout and thickness distribution of the structure

Development of an Experimental/Numerical Validation Methodology for the Design of Exhaust Manifolds of High Performance Internal Combustion Engines

Several typical failure modes in the exhaust manifold of an internal combustion engine are commented on. In particular, thermal loading and the related thermal fatigue damage mechanism are addressed. The component under investigation is a cast exhaust manifold including the turbine involute. Finite Element simulations are performed, and a numerical methodology is presented to interpret and understand the observed failures, with the aim of developing a useful tool to virtually validate the component, before the manufacturing phase. The Finite Element analysis closely mimics the experimental validation procedure that considers several heating and rapid cooling cycles to simulate typical engine operating conditions. A static mechanical characterization at high temperatures of the materials involved is carried out, aimed at identifying a suitable alloy and its mechanical characteristics useful for feeding the numerical models. The developed design methodology proposes a damage criterion for thermal fatigue investigation, considering the elastoplastic behaviour of the material when subjected to high temperature cycles. In particular, the accumulated equivalent plastic strain range for a single thermal cycle (ΔPEEQ) is used, following the Ferrari expertise. The methodology appears to be well correlated with the experimental evidence, thus limiting the number of tests necessary for the approval of the component

Finite Element Analysis of the Influence of the Assembly Parameters on the Fretting Phenomena at the Bearing/Big End Interface in High-Performance Connecting Rods

Fretting fatigue is a well-known and dangerous damage mode that occurs on the mating surfaces of mechanical components, mainly promoted by a combination of stress distribution, contact pressure distribution, and relative sliding (micro)motion between the surfaces. However, predicting this mechanism is challenging, necessitating specific studies for each assembly due to variable influences. This article presents a methodology for evaluating fretting fatigue damage at the contact between a titanium connecting rod big end and the bearing, adopting the Ruiz parameter as a quantifying damage index. For this purpose, a thermal-structural finite element model is prepared. In particular, the machining and assembly of the split conrod big end are simulated, considering thermal effects. A full engine cycle is first simulated, and results are used for identifying critical instants to be considered for accurate yet computationally efficient calculations. The dependence of fretting fatigue on three factors is studied: bearing crush, bolts tightening torque, and friction coefficient between the big end and the bearing. In summary, the damage increases with a higher crush and friction, while tightening torque has marginal effects. Following a 20% increase in crush height, a corresponding 10% rise in the Ruiz parameter is observed. Conversely, reducing the crush height by 20% leads to an approximately 8% decrease in the Ruiz parameter. When the influence of the bolt preload is taken into account, only a marginal 1% increase of the Ruiz parameter is recorded despite a 30% rise in preload. Evaluating the impact of the friction coefficient on the Ruiz parameter reveals an almost linear relationship. These findings suggest that adjusting the screw preload can enhance the hydrodynamic behavior of the bearing without exacerbating fretting. Furthermore, exploiting the linear correlation between Ruiz and the friction coefficient allows for the generalization of results obtained with specific coefficient values. This methodology can, therefore, serve as a valuable reference for adjusting different variables during the initial design phases of a four-stroke internal combustion engine’s dismountable connecting rod

Investigation on the Low Cycle Thermal Fatigue of a Hybrid Power Unit Transmission Clutch

A numerical methodology for the thermal-structural assessment of a clutch for a high-performance hybrid power unit is proposed. Clutches are commonly adopted in internal combustion engines to connect the crankshaft to the gearbox. However, the specific clutch under investigation is employed for the coupling between the electric motor and the engine transmission primary shaft in a P2 hybrid architecture. In this specific configuration, the clutch may be activated and deactivated frequently to maximise the efficiency of the power unit depending on the required output torque and on the particular control strategy developed. As a consequence, the thermal loads insisting on the clutch may differ with respect to the ones encountered in a typical full combustion architecture. The results of the presented research show the great influence of the thermal deformation on the stress state of this component, and the onset of possible failure due to low cycle fatigue phenomena is detected. In addition, the influence of different modelling strategies is considered

Investigation on the Torsional–Flexural Instability Phenomena during the Bending Process of Hairpin Windings: Experimental Tests and FE Model Validation

Modern electric motors developed for the automotive industry have an ever higher power density with a relatively compact size. Among the various existing solutions to improve torque and power density, a reduction in the dimensions of the end-windings has been explored, aiming to decrease volume, weight, and losses. However, more compact end-windings often lead to complex shapes of the conductors, especially when preformed hairpin windings are considered. The rectangular cross-section of hairpin conductors makes them prone to deviating out of the bending plane during the forming process. This phenomenon, known as torsional–flexural instability, is influenced by the specific aspect ratio of the cross-section dimensions and the bending direction. This study focuses on understanding this instability phenomenon, aiming to identify a potential threshold of the cross-section aspect ratio. The instability makes it difficult to predict the final geometry, potentially compromising the compliance with the geometric tolerances. A finite element model is developed to analyse a single planar bend in a hairpin conductor. Various cross-section dimensions with different aspect ratios are simulated identifying those that experience instability. Moreover, an experimental campaign is conducted to confirm the occurrence of instability by testing the same single planar bending. The experimental data obtained are used to validate the finite element model for the tested dimensions. The aim is to provide designers with a useful tool to select hairpin geometries that are more suitable for the folding process, contributing to successful assembly and improving the overall design process of preformed hairpin conductors

Analysis of the Tribological Behaviour of the Lubricated Contacts of a Connecting Rod Equipped with a Direct Pin Oiling Gallery

This paper describes a methodology for identifying a suitable design of a Direct-Pin-Oiling (DPO) gallery, drilled through the conrod shank of a high-performance internal combustion engine, to directly supply pressurized lubricant to the piston pin/small-end interface. Initially, a multibody elastohydrodynamic model is set up to analyse the tribological behaviour of conrod bearings, when considering a standard configuration employing a passive lubricating hole drilled on the top of the small-end. Then, a preliminary DPO gallery is introduced to examine how it affects the oil flows at lubricated interfaces and their tribological behaviour. The numerical results and parallel experimental evidence underline the need to modify the initial configuration of the DPO gallery and a more performing gallery design is proposed

Un’architettura innovativa per Power Unit ibride per veicoli di piccole dimensioni: progettazione, analisi, produzione e sperimentazione

Questa tesi presenta lo sviluppo di una power-unit ibrida partendo da un motore di derivazione motociclistica. Il sistema è costituito da un motore monocilindrico di 480 cc di cilindrata sviluppato sulla base del bicilindrico a V di 90 gradi della Ducati "959 Superquadro". Il motore termico è assistito da un motore elettrico realizzato per questa specifica applicazione (30 kW), alimentato da un pacco batterie agli ioni di litio. Il motore Ducati è stato scelto per l’elevato rapporto peso-potenza e per sfruttare il layout dell’architettura a V. Infatti, la testata verticale è stata rimossa e sostituita dal motore elettrico, direttamente collegato all'albero motore tramite la catena di distribuzione originale, ottenendo così un sistema molto compatto. Questa soluzione è adatta per molti motori a V e mira a ottenere un propulsore ibrido di piccola taglia, lasciando la porta aperta per possibili applicazioni motociclistiche. Il motore a combustione interna di questo progetto è quindi un motore monocilindrico che risulterebbe sbilanciato rispetto alla configurazione originale (V90). Per questo motivo, sono stati analizzati diversi sistemi di equilibratura non convenzionali. In particolare, una delle soluzioni consiste nel sostituire il pistone inutilizzato con un bilanciere, ottenendo un meccanismo a quadrilatero articolato. Questa soluzione consente di ridurre le perdite per attrito e di eliminare le perdite di pompaggio. Tuttavia, è stata considerata la possibilità di mantenere il pistone originale che determina una perdita di potenza dovuta sia all'attrito che al pompaggio, ma che rappresenta però una soluzione meno invasiva. Il comportamento meccanico della catena originale è stato valutato eseguendo un'analisi dinamica dell'intero manovellismo. In particolare, è stato fatto un confronto tra il modello del motore bicilindrico, che considera il sistema di distribuzione originale, e il modello del monocilindrico collegato al motore elettrico, al fine di valutare la possibilità di utilizzare la catena per questo scopo specifico. Un altro aspetto importante riguarda la definizione della particolare geometria del case del motore elettrico, realizzato in Additive Manufacturing, al fine di includere l'alloggiamento della catena, il sistema di raffreddamento del motore elettrico e il sistema di lubrificazione. In particolare, la flangia di collegamento è progettata per adattarsi perfettamente al motore originale al fine di consentire al circuito di raffreddamento di combaciare con quello del motore elettrico. Inoltre, è stata eseguita un'analisi termo-strutturale al fine di valutare la resistenza meccanica del case. Il dimensionamento del motore elettrico e del pacco batterie sono stati stimati sviluppando un foglio di calcolo che considera la potenza dissipata dal veicolo tenendo conto della massa della vettura, della resistenza al rotolamento e delle forze aerodinamiche. In particolare, il modello consente di identificare il miglior punto di funzionamento sia per il motore elettrico che per il motore a combustione interna. Sono state sviluppate diverse strategie relative alla suddivisione della potenza durante diversi cicli operativi tenendo conto delle prestazioni del veicolo, del consumo di carburante e del consumo di energia elettrica. Infine, un primo prototipo della power-unit sviluppata è stato realizzato e testato al banco prova motore, fornendo così dati sperimentali utili per la validazione dei diversi modelli numerici impiegati.This thesis presents the development of a hybrid power-unit starting from a small engine derived from a motorcycle application. In particular, the system is made up of a brand new, single-cylinder 480 cc internal combustion engine developed on the basis of the Ducati “959 Superquadro” V90 2-cylinders engine. The thermal engine is assisted by a custom electric motor (30 kW), powered by a Li-Ion battery pack. The Ducati “959 Superquadro” engine is chosen because of its high power-to-weight ratio, and for taking advantage of its V90 2-cylinder layout. In fact, the vertical engine head is removed and it is replaced by the electric motor directly engaged to the crankshaft using the original valvetrain transmission chain, thus achieving a very compact package. This solution is suitable for many V-type engines and aims to obtain a small hybrid power unit, leaving the way open for possible motorcycle/small vehicle applications. The resulting internal combustion engine of this project is a single cylinder engine which would result to be unbalanced if compared to the original V90 configuration. For this reason, several unconventional balancing systems are investigated. In particular, one of the solutions consists in replacing the unused piston with a balancer rod obtaining an articulated quadrilateral mechanism. This solution allows to reduce the friction losses and to specially drop off the pumping losses. Parallelly, the possibility of keeping the original piston is considered which definitely represents a less invasive solution but determines a certain power loss due to both friction and pumping. The mechanical behaviour of the original chain is investigated performing a dynamic analysis of the whole crank mechanism. In particular, the twin cylinder model considering the original valvetrain system is compared with the single cylinder model engaged with the electric motor, in order to assess the possibility to use the chain for this specific purpose. A specific electric motor case is designed and manufactured via Additive Manufacturing technology, in order to include the chain housing, the electric motor cooling system and the lubricating system. Furthermore, the case flange is designed to perfectly fit with the original engine deck in order to allow the engine cooling circuit to match with the electric motor one. Specifically, a thermo-structural analysis is performed in order to assess the mechanical strength of the electric motor case. The output power and size of the electric motor are estimated developing a spreadsheet which considers the power dissipated by the vehicle taking into account the mass of the car, the rolling resistance, the drag force and the lift force. Moreover, the maximum amount of energy needed is calculated thus allowing the capacity of the battery to be determined. In particular, the model allows the best operating point for both the electric motor and the internal combustion engine to be identified. Several strategies are developed concerning the power split during different operating cycles and taking into account the vehicle performance, the fuel consumption and the electric energy consumption. Finally, a first prototype of the developed power-unit is manufactured and tested at the bench test thus providing useful experimental data for the validation of the different numerical models employed

The Effects of the Specific Material Selection on the Structural Behaviour of the Piston-Liner Coupling of a High Performance Engine

The materials commonly employed in the automotive industry are various and depend on the specific application field. For what concern the internal combustion engines the choice is guided by the thermomechanical performance required, technological constraints and production costs. Actually, for high-performance engines, steel and aluminium are the most common materials selected for the piston and the cylinder liner manufacturing. This study analyses the effect of possible material choice on the interaction between piston and cylinder liner, via Finite Element analyses. A motorcycle engine is investigated considering two possible pistons: one (standard) made of aluminium and one made of steel. Similarly, two possible cylinder liners are considered, the original one made of aluminium and a different version made of steel obtained by simply thinning the aluminium component in order to obtain two structurally equivalent components. In particular, four possible combinations of coupling between piston and cylinder liner are identified, derived from the two variants of applied materials. The components theoretically necessary for the Finite Element model are the engine head, the engine block, the bolts, the gasket, the upper part of the crank mechanism and the cylinder liner. Nevertheless, a simplified methodology is employed to reduce the computational effort. This analysis makes it possible to evaluate gap and interference with respect to the material choice. A first proposal of the barrel shape and ovality of the steel piston is obtained starting from the original aluminium piston and the thermal field involved in the analysis. Besides, the presented methodology consists of a useful tool to estimate the stress field and the fatigue safety factor of the components involved. The results obtained with this methodology can guide the definition of the correct piston profile, temperature field and stress distribution estimation, as a function of the specific materials employed for piston-liner coupling

Design of an Additive Manufactured Steel Piston for a High Performance Engine: Developing of a Numerical Methodology Based on Topology Optimization Techniques

Modern high performance engines are usually characterized by high power densities, which lead to high mechanical and thermal loadings acting on engine components. In this scenario, aluminum may not represent the best choice for piston manufacturing and steel may be considered as a valid alternative. In this article, a methodology involving optimization techniques is presented for the design of an internal combustion engine piston. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminum piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. Three different loading conditions are employed for the topology optimizations setup. Optimization results are then interpreted and the various structural features of the steel piston are designed starting from the density distribution contour plots. Different Finite Element thermomechanical models are finally prepared in order to correct and validate the designed geometry

Oil jets piston cooling: A numerical methodology for the estimation of heat transfer coefficients and optimization of the piston temperature field through a genetic algorithm

High-efficiency internal combustion engines need specific methodologies to be developed for the design improvement of the components. Predicting and reducing the thermal loadings on the parts are critical tasks to be addressed. This contribution focuses on the thermal management of the piston through oil jets. The operating temperature of the piston deeply affects its thermo-mechanical behavior, thus possibly jeopardizing the structural integrity of the component. The design of piston cooling jets is usually addressed through Computational Fluid Dynamics, which can guarantee accurate results, usually at a high computational cost. In this contribution, a faster tool is derived to grasp the effect of the cooling jets on the temperature of the piston. Empirical correlations are applied to predict the instantaneous heat transfer coefficients on the piston. The reciprocating motion of the piston is considered since it affects the interaction between the surface and the oil jets. Instantaneous coefficients are cycle-averaged and used to estimate the temperature of the piston through a Finite Element thermal analysis. Finally, an optimization code is developed to find the best jet configuration capable to minimize the temperature of the piston. This methodology is a powerful tool to select the optimal oil jet nozzles for piston cooling