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Barbara ZARDIN

Professore Associato presso: Dipartimento di Ingegneria "Enzo Ferrari"


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Pubblicazioni

2020 - A study on PVD coatings for reduction of friction and wear of swashplate axial piston pumps and motors [Relazione in Atti di Convegno]
Sola, R; Veronesi, P; Zardin, B; Borghi, M
abstract

Swashplate axial piston pumps and motors are widely used under severe conditions because of their capability to operate at high pressure values and various ranges of speeds, maintaining a good efficiency. In some operating conditions however, the machine efficiency may be relatively low because of insufficient lubrication and this causes rapid wear and high friction losses. PVD coatings may help in reducing the friction thus having a positive impact on the machine efficiency. For this reason, pin on disk testing were conducted to investigate the friction and wear behavior of different PVD coatings on various metallic substrates. A copper and tin alloy coated with PA-CVD DLC, a carburized 17NiCrMo7 with a PVD DLC coating and a nitrided 41CrAlMo7 PVD coated with TiCN were studied. Results of tribological testing, carried out at 0.2 and 0.5 m/s as sliding speed and 5000, 10000 and 20000 rounds as ending conditions, showed that wear and friction had been reduced; moreover, microstructure features were analyzed for understanding underlying mechanism and to allow selecting the most suitable coating for the application on the swashplate axial piston machine.


2020 - Analysis of the flow force compensation in relief valves with conical poppet [Relazione in Atti di Convegno]
Fornaciari, A.; Zardin, B.; Borghi, M.; Ceriola, M.
abstract

The paper deals with experimental tests and numerical simulations (3D and 0D fluid-dynamic modelling) of a conical poppet pressure relief valve with flow force compensation. The aim of the study was to realize a dynamic model of the valve, able to consider the effect of the pressure force, which arises downstream the metering edge and is determined by both the flow forces and the pressure recovery on the flow deflector. Starting from a 3D-CFD model, it was possible to study the interaction between the poppet opening and the pressure field, in order to evaluate the total pressure force as a function of the poppet displacement. The contribution of the pressure recovered on the deflector was separated from the traditional flow force and then parametrized as a function of some geometric features. It was then possible to develop a 0D fluid-dynamic model that is suitable not only for the considered valve but also for valves with similar geometries. Lastly, the model was validated using experimental data acquired on test bench for three different valves. The comparison of the predicted flow-pressure characteristics with the experimental ones indeed showed a good result matching. This model can also lead towards design considerations to study the behaviour of a larger number of valve geometries.


2020 - Modelling of hydraulic locking balancing circumferential grooves for servo-cylinders' piston [Relazione in Atti di Convegno]
Natali, E.; Zardin, B.; Cillo, G.; Borghi, M.
abstract

In the hydraulic servo-cylinders design, the circumferential grooves are used in order to reduce the effect of the locking force. This force arises as a consequence to the distribution of pressure around the piston, when both an eccentric position, caused by the load on the piston, and the manufacturing defects on the piston and cylinder surfaces are present. In this work an approach is presented for the calculation of the contribution of the grooves in the definition of the locking force and of the leakage flow rate. The mathematical model proposed is based on the Reynolds equation, properly combined with the continuity equation applied within the grooves. The results of the analysis are combined together with the ones coming from the analysis at the hydrostatic bearings at the rod ends, which have been analyzed on a previous step of the research. A numerical procedure is then created that, with the appropriate input, allows to study the different design configurations of the servo-cylinder. Results here shown are focused on exploring the effect of number, position, size of the grooves and manufacturing tolerances on the piston and cylinder. Simulations are also run under different operating conditions. For the real servo-cylinder configurations tested here, it is shown that five equally spaced grooves may be sufficient to decrease consistently the locking force while containing the flow losses. The procedure is also functional to investigate the bending and seizing of the piston during the different operating conditions, both in steady state and dynamic conditions.


2020 - The Hydraulic Power Generation and Transmission on Agricultural Tractors: Feasible architectures to reduce dissipation and fuel consumption-Part 2 [Relazione in Atti di Convegno]
Casoli, P.; Zardin, B.; Ardizio, S.; Borghi, M.; Pintore, F.; Mesturini, D.
abstract

Increasing interest in reducing pollutant emissions and fuel consumption of off-road vehicles has led to research alternative systems that aim to reduce the power dissipations of the hydraulic circuits. This work presents the advantages of few alternative solutions for a hydraulic high-pressure circuit of a medium-size tractor. The standard high-pressure circuit is a typical multiusers load sensing system that uses a single variable displacement pump to feed: steering, trailer brake, rear remotes, hitch and suspension. The alternative architectures have been simulated and compared in terms of mechanical energy consumption. In particular, the steering has been separated from the circuit, it has been actuated by means of a dedicated pump moved by an electric motor, in this way the priority valve could be removed and losses due the pressure compensators are reduced. A further architecture based on the insertion of the LS signal conditioner was studied. The results show that relevant energy saving can be achieved with the new alternative architectures; the physical prototyping of the most promising solutions will be realized as the next step of the project.


2020 - The Hydraulic Power Generation and Transmission on Agricultural Tractors: Feasible architectures to reduce dissipation and fuel consumption-Part i [Relazione in Atti di Convegno]
Gaiola, A.; Zardin, B.; Casoli, P.; Borghi, M.; Mazzali, F.; Pintore, F.; Fiorati, S.
abstract

This paper is aimed at investigating the benefits in terms of energy efficiency of new electro-hydraulic architectures for power distribution systems of a medium-size agricultural tractor, with a focus on the hydraulic high-pressure circuit. The work is part of a wider industrial research project called TASC (Smart and Clean Agricultural Tractors [1]). Traditional and alternative architectures have been modelled and energetically compared through simulation, using a lumped parameter approach. Experimental data previously acquired have been used to validate the models and to replicate real working conditions of the machine in the simulation environment. A typical on-field manoeuvre has been used as duty cycle, to perform an effective energetic analysis. The standard hydraulic circuit is a multi-users load sensing system that uses a single variable displacement pump to feed steering, trailer brake and auxiliary utilities in that order. The key idea of the proposed solutions is the separation of steering from the other implements, to optimize the entire energy management. In particular, the paper investigates new and flexible solutions for the auxiliary utilities, including an electro-hydraulic load sensing architecture with variable pump margin, an electronic flow matching and flow sharing architecture, and an electronic strategy for automatic pressure compensation. The simulation results show that good energy saving can be achieved with the alternative architectures, so that physical prototyping of the most promising solutions will be realized as next step of the project.


2019 - DESIGN AND MODELLING OF A CARTRIDGE PRESSURE AMPLIFIER [Relazione in Atti di Convegno]
Zardin, Barbara; Cillo, Giovanni; Zavadinka, Peter; Hanusovsky, Juraj; Borghi, Massimo
abstract

This works describes the modelling and simulation of a compact cartridge pressure amplifier for linear actuators, especially designed to fit within the rod of the piston. Hydraulic pressure amplifiers of the cylinder type are appreciated in hydraulic systems where high pressure work is needed, especially for a small part of the overall duty cycle. The use of these boosters allows the designer not to oversize the system, which will perform confining the high pressure operation only on the side of the hydraulic actuator. Starting from a previous research work on the same topic, this work proposes new designs for the cartridge amplifier to explore the influence of the control valve, which is the responsible for the delivering of the fluid to the amplifier. The new designs are discussed and then the results coming from the simulation performed with a lumped parameter model in a virtual test rig are shown. The operation of the amplifier is then applied to a more realistic duty cycle to illustrate and validate its operation.


2019 - Evaluation of the hydro - Mechanical efficiency of external gear pumps [Articolo su rivista]
Zardin, B.; Natali, Emiliano; Borghi, M.
abstract

This paper proposes and describes a model for evaluating the hydro-mechanical efficiency of external gear machines. The model is built considering and evaluating the main friction losses in the machines, including the viscous friction losses at the tooth tip gap, at the bearing blocks-gears gaps, at the journal bearings, and the meshing loss. To calculate the shear stress at each gap interface, the geometry of the gap has to be known. For this reason, the actual position of the gears inside the pump casing and consequent radial pressure distribution are numerically calculated to evaluate the gap height at the tooth tips. Moreover, the variation of the tilt and reference height of the lateral gaps between the gears and the pump bushings are considered. The shear stresses within the lateral gaps are estimated, for different lateral heights and tilt values. At the journal bearings gaps, the half Sommerfeld solution has been applied. The meshing loss has been calculated according to the suggestion of the International Standards. The hydro-mechanical efficiency results are then discussed with reference to commercial pumps experimentally characterized by the authors in a previous work. The average percentage deviation from experimental data was around 2%, without considering the most critical operating conditions (high delivery pressure, low rotational speed). The limits of this approach are also explained. Finally, the role of each source of loss is discussed, considering different operating conditions and two values of fluid viscosity. Lateral gap losses and meshing loss are much more relevant in determining the hydro-mechanical efficiency variation in the pump's operating range, especially at a low delivery pressure. Moreover, while lateral gap losses increase with the rotational speed, the meshing loss shows the opposite behavior. The tooth tip gap losses are never as relevant, but they increase at high pressure. The journal bearings losses become comparable with the lateral and meshing ones at high delivery pressure values. Considering the pumps analyzed and the operating range of delivery pressure values and rotational speed values, the meshing loss made the mechanical efficiency vary in a percentage range of ±7%, with lateral losses in the range of about the ±15%, when also considering the extreme operating points (low speed, high pressure; high speed, low pressure). The weight of the lateral losses slightly reduced when we analyzed the higher temperature results, while the meshing losses slightly increased.


2019 - Modelling of hydrostatic bearings for servo-cylinders [Relazione in Atti di Convegno]
Zardin, B.; Natali, E.; Cillo, G.; Borghi, M.
abstract

Hydraulic servo cylinders are widely used in versatile industrial applications such as machine tools, industrial robots, autonomous manufacturing systems and special applications in laboratories. To reduce friction and allow smooth and controllable displacement of the actuator, hydrostatic journal bearings are used at the ends of the rod. The design and manufacturing of this elements is challenging since the good operation relays on the very small tolerances required to bear the load on the cylinder and to reduce leakages. In this work, a virtual design and test tool for hydrostatic journal bearing with pockets, developed in OpenModelica environment, is presented. The influence of eccentricity and manufacturing tolerances is then studied and discussed. The model proposed has the aim to explore the extreme and critical operating conditions of the servo-cylinder and to help and/or improve the design phase.


2018 - Fluid-dynamic analysis of an in-line water piston pump [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Materi, Sergio; Argentino, Pierluigi
abstract

The paper focuses on the analysis of inline water piston pumps, by means of simulation of the fluid-dynamic behaviour and experimental characterization. These pumps are commonly used on the car wash systems, industrial washes systems and fire protection systems. They possess a robust architecture, made of a typical rod-crankshaft mechanism, which transforms the circular motion of the pump shaft in the reciprocating displacement of the piston. The pump analyzed in the paper, in particular, moves three pistons, shifted one another of 120°; each piston sucks from a tank and delivers water to a hydraulic line via automatic, spring loaded, poppet valves. The shaft, rod and other movable components are lubricated with mineral oil; the three ceramic pistons are isolated from this environment using opportune seals and work with water. This pump is robust and durable but suffers of some problems: the instantaneous pressure trend within each piston is ideally a square wave: the pressure is equal to the tank pressure during suction, while it is equal to the delivery pressure during the delivery phase. Instead, non –ideal behaviour of the poppet valves, leakages, fluid properties make the pressure trend more critical: during the pressure transient between the two high and low levels, pressure peaks and de-pressurization till aeration and cavitation occurrence may happen. These phenomena generate vibrations and noise and can damage the pump components. In order to study this, a lumped parameter fluid dynamic model of the pump has been realized, later compared with experimental results coming from the test rig to validate it. The model has been used to explore the dynamic pump behaviour in several operating conditions (various speed values and delivery pressure levels), calculating the flow irregularity, the pressure and forces instantaneous trends. The design characteristics of the poppet valves have been explored, in particular the spring characteristics, to discuss the trend of the previous variables.


2018 - Modelling and Simulation of a Cartridge Pressure Amplifier [Relazione in Atti di Convegno]
Zardin, Barbara; Cillo, Giovanni; Borghi, Massimo; Zavadinka, Peter; Hanusovsky, Juraj
abstract

Hydraulic pressure amplifiers of the cylinder type are much appreciated in hydraulic systems where high pressure work is needed only for a limited period of time, while during the remaining duty cycle the system operates at a standard level of pressure. The use of these elements allows the designer not to oversize the system, which will perform the work with a considerable power saving, confining the high pressure operation only on the side of the hydraulic cylinder. This works describes the modelling and simulation of a compact cartridge pressure amplifier for linear actuators. The cartridge amplifier is able to double or more the pressure in the system when needed and to not interfere during normal operation of the system. It has been designed to fit in the narrow space of the rod of normal hydraulic cylinder, being extremely compact and efficient. Designing such a component and the study of the main design parameters influence have required a strong work of modelling and simulation, performed with a lumped parameters approach to depict the dynamic behaviour of the amplifier. This work illustrates the building of the model and a first comparison between simulated and experimental data. Moreover, the simulation activity is enlarged to analysis of the influence of some operating and design parameters on the amplifier dynamic behavior


2018 - Modelling and Simulation of a Hydrostatic Steering System for Agricultural Tractors [Articolo su rivista]
Zardin, Barbara; Borghi, Massimo; Gherardini, Francesco; Zanasi, Nicholas
abstract

The steering system of a vehicle impacts on the vehicle performance, safety and on the driver’s comfort. Moreover, in off-road vehicles using hydrostatic steering systems, the energy dissipation also becomes a critical issue. These aspects push and motivate innovation, research and analysis in the field of agricultural tractors. This paper proposes the modelling and analysis of a hydrostatic steering system for an agricultural tractor to calculate the performance of the system and determine the influence of its main design parameters. The focus here is on the driver’s steering feel, which can improve the driver’s behavior reducing unnecessary steering corrections during the working conditions. The hydrostatic steering system is quite complex and involves a hydraulic circuit and a mechanical mechanism to transmit the steering to the vehicle tires. The detailed lumped parameters model here proposed allows to simulate the dynamic behavior of the steering system and to both enhance the understanding of the system and to improve the design through parameters sensitivity analysis.


2017 - Design Of Two-Stage On/Off Cartridge Valves For Mobile Applications [Relazione in Atti di Convegno]
Zardin, Barbara; Borghi, Massimo; Cillo, Giovanni; Rinaldini, Carlo Alberto; Mattarelli, Enrico
abstract

Cartridge valves are widely used in mobile applications, where they are screwed in manifolds, to realize opportune circuit layouts. These valves are quite simple in operation but require a sophisticated design in order to meet all the requirements needed in the mobile machines. Typically, the design process is developed realizing a first design concept and some prototypes and experimentally testing them; after this, the designer chases the optimal performances requested to the valve with a trial and error approach on the prototypes, involving high time and cost resources. In this paper an alternative design procedure is proposed, which involves dedicated simulations to analyze the main critical issues regarding the cartridge valve object of the study. Modelling and simulations here have been considered as steps into the design process of a new valve, which satisfies the requirements and well adapt to the necessities to operate at higher flow and pressure levels without compromising its performances. In that way, the number of prototypes, realized to validate the numerical results and verify the design process, has been considerably reduced, together with related time and costs.


2017 - Design and experimental development of a compact and efficient range extender engine [Articolo su rivista]
Borghi, Massimo; Mattarelli, Enrico; Muscoloni, Jarin; Rinaldini, Carlo Alberto; Savioli, Tommaso; Zardin, Barbara
abstract

The paper reviews the design and experimental development of an original range-extender single-cylinder two-stroke gasoline engine, rated at 30 kW (maximum engine speed: 4500 rpm). The goal of the project is to get most of the benefits of the two-stroke cycle (compactness, high power density, low cost), while addressing the typical issues affecting the conventional engines of this type. Among many recent similar propositions, the peculiarities of this engine, besides the cycle, are: external scavenging by means of an electric supercharger, piston controlled scavenge and exhaust ports (no poppet valves), gasoline direct injection (GDI), and a patented rotary valve for the optimization of the scavenging process, of the loop type. Lubrication is identical to a conventional four-stroke engine, and the rotary valve, connected to the crankshaft, helps to improve the balance of the piston reciprocating forces, yielding an excellent NVH behavior. It should be noted that, except the patented rotary valve, all the engine parts are standard automotive commercial components, that don’t require any specific expensive technology. In fact, the originality of the engine consists in the optimum combination of existing well assessed concepts. The scavenging and combustion systems of the engine are developed in the first phase of the project, including the construction and the experimental testing of a prototype. In the second phase, the air metering system of the prototype is completely modified: the piston pump is replaced by an electric supercharger, and engine load is now controlled by the supercharger speed, without throttle valve. The new engine is compared to a standard 4-stroke engine, developed in a previous project for the same application. The main advantages of the two-stroke engine may be summarized as follows: lower weight (−35%), higher brake efficiency (+6%, on average), less heat rejected (−18%), lower thermal and mechanical loads within the cylinder (−40%). The only concern, that will be addressed in a future phase of the study, is the compliance with very low NOx limits: in the worst scenario, the 2-stroke engine could be forced to adopt a well assessed but expensive after-treatment device.


2017 - Development of a 2-Stroke GDI Engine [Relazione in Atti di Convegno]
Savioli, Tommaso; Zardin, Barbara; Borghi, Massimo
abstract

Nowadays, high-pressure gasoline direct injection (GDI) can be considered a standard technology, due to the wide application on 4-stroke turbocharged engines. This technology - in combination with other specific solutions - has been successfully applied to a 500 cc, 30 kW 2-stroke engine, initially developed as a range extender. The engine is valve-less and cam-less, being the scavenge and exhaust ports controlled by the piston. An electric supercharger delivers the required airflow rate, without need of a throttle valve; the lubrication is identical to a 4-stroke. The current study reviews the development process, assisted by CFD simulation, that has brought to the construction of a prototype, tested at the dynamometer bed of the University of Modena and Reggio Emilia (Engineering Department "Enzo Ferrari"). An experimentally calibrated CFD-1d model is applied to predict full load engine performance. The results show an excellent fuel efficiency and a very low level of thermal and mechanical stress despite the high power density.


2017 - Development of a RANS-Based Knock Model to Infer the Knock Probability in a Research Spark-Ignition Engine [Articolo su rivista]
D'Adamo, Alessandro; Breda, Sebastiano; Iaccarino, Salvatore; Berni, Fabio; Fontanesi, Stefano; Zardin, Barbara; Borghi, Massimo; Irimescu, Adrian; Merola, Simona
abstract

Engine knock is one of the most limiting factors for modern Spark-Ignition (SI) engines to achieve high efficiency targets. The stochastic nature of knock in SI units hinders the predictive capability of RANS knock models, which are based on ensemble averaged quantities. To this aim, a knock model grounded in statistics was recently developed in the RANS formalism. The model is able to infer a presumed log-normal distribution of knocking cycles from a single RANS simulation by means of transport equations for variances and turbulence-derived probability density functions (PDFs) for physical quantities. As a main advantage, the model is able to estimate the earliest knock severity experienced when moving the operating condition into the knocking regime. In this paper, improvements are introduced in the model, which is then applied to simulate the knock signature of a single-cylinder 400cm3 direct-injection SI unit with optical access; the engine is operated with two spark timings, under knock-safe and knocking conditions respectively. The statistical prediction of knock resulting from the presented knock model is compared to the experimental evidence for both investigated conditions. The agreement between the predicted and the measured knock distributions validates the proposed knock model. Finally, limitations and some unprecedented possibilities given by the model are critically discussed, with particular emphasis on the meaning of RANS knock prediction.


2017 - Pressure Losses in Multiple-Elbow Paths and in V-Bends of Hydraulic Manifolds [Articolo su rivista]
Zardin, Barbara; Cillo, Giovanni; Borghi, Massimo; D'Adamo, Alessandro; Fontanesi, Stefano
abstract

Hydraulic manifolds are used to realize compact circuit layouts, but may introduce high pressure losses in the system because their design is usually oriented to achieving minimum size and weight more than reducing the pressure losses. The purpose of this work is to obtain the pressure losses when the internal connections within the manifold are creating complex paths for the fluid and the total loss cannot be calculated simply as the sum of the single losses. To perform the analysis both Computational Fluid Dynamic (CFD) analysis and experimental tests have been executed. After the comparison between numerical and experimental results, it was possible to assess that the numerical analysis developed in this work is able to depict the correct trends of the pressure losses also when complex fluid path are realized in the manifold. Successively, the numerical analysis was used to calculate the pressure loss for inclined connections of channels (or V-bends), a solution that is sometimes adopted in manifolds to meet the design requirements aimed towards the minimum room-minimum weight objective.


2017 - Pressure losses in hydraulic manifolds [Articolo su rivista]
Zardin, Barbara; Cillo, Giovanni; Rinaldini, Carlo Alberto; Mattarelli, Enrico; Borghi, Massimo
abstract

Hydraulic manifolds are used to realize compact circuit layout, but may introduce a high pressure drop in the system. Their design is in fact oriented more toward achieving minimum size and weight than to reducing pressure losses. This work studies the pressure losses in hydraulic manifolds using different methods: Computational Fluid Dynamic (CFD) analysis; semi-empirical formulation derived from the scientific literature, when available; and experimental characterization. The purpose is to obtain the pressure losses when the channels' connections within the manifold are not ascribable to the few classic cases studied in the literature, in particular for 90° bends (elbows) with expansion/contraction and offset intersection of channels. Moreover, since CFD analysis is used to predict pressure losses, general considerations of the manifold design may be outlined and this will help the design process in the optimization of flow passages. The main results obtained show how CFD analysis overestimates the experimental results; nevertheless, the numerical analysis represents the correct trends of the pressure losses.


2016 - A parametric CAD-based method for modelling and simulation of positive displacement machines [Articolo su rivista]
Gherardini, Francesco; Zardin, Barbara; Leali, Francesco
abstract

We present an efficient and user-friendly parametric CAD-based design method for the graphical description of positive displacement machines, exploiting commercial parametric CAD software and a tailored interface. An executable module simulates the motion of the machine components, analyzes the machine geometry, and automatically extrapolates the geometrical data from the 3D CAD model, generating data files that can be directly used for following fluid dynamic analyses. The graphical approach supports investigation of the machine performance and exploring optimized design variants. The method has been applied to three industrial test cases: An external gear pump, an axial piston pump, and a gerotor pump. A complete case study focused on the external gear pump is proposed, as well as the results from the other two types are summarized. We validate the CAD-based method by comparing the obtained data with the data coming from the application of state-of-the-art analytical methods.


2015 - Axial Balance of External Gear Pumps and Motors: Modelling and Discussing the Influence of Elastohydrodynamic Lubrication in the Axial Gap [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara
abstract

This paper focuses on the analysis of hydraulically balanced external gear pumps, in particular on the lubricating gap between the bushes and the gears. This topic is of key importance for the optimization of the machine efficiency because it both influences the mechanical-viscous friction and the volumetric losses. In this paper the intent is to investigate the role of the elastic deformation of the bushes surfaces, to compare the analysis done with rigid and elastic surfaces and finally to correlate the results with the design of the bushes balancing surfaces. A numerical procedure for the determination of the pressure distribution inside the gap bounded by gears sides and the bushes internal surfaces is presented and applied. With respect to past works of the authors, the procedure has been integrated taking into account the elastic deformation of the internal surfaces of the bushes and the variation of the dynamic viscosity of fluid, two well recognized phenomena that can play a key role on the determination of the bushes behaviour and lubricating gap pressure distribution. It is shown that, when the design of the bushes rear surfaces determines a strong balancing thrust, the bushes themselves need to tilt strongly with respect to the gears to generate an opportune widening thrust to avoiding contact with the gears. Useful suggestions for the bushes balancing surface design may be drawn from the analysis of the balancing maps reported in the paper, which illustrate the widening thrust magnitude and position in both the pure hydrodynamic and elasto-hydrodynamic cases, for different tilted positions and operating conditions.


2015 - Dynamic Modelling of an Off-Road Vehicle for the Design of a Semiactive, Hydropneumatic Spring-Damper System [Relazione in Atti di Convegno]
Panetta, Giuseppe; Mancarella, Francesco; Borghi, Massimo; Zardin, Barbara; Pintore, Francesco
abstract

In this paper a tool integrating a multibody full car model of a tractor and the hydraulic model of the suspension system is presented as a virtual tool able to help the designer and also the control tuning of the system. The full car approach is chosen in order to be able to describe all the vehicles movements (roll, yaw, pitch) while the detailed lumped parameters model of the hydraulic suspensions allows to consider the role of the electrohydraulic valves, accumulator, hydraulic actuator on the vehicle dynamic behaviour. The hydraulic model and the multibody model exchange forces and displacements at the joint points: one between actuator and sprung mass (chassis) and the other one between actuator and unsprung mass (front axle and wheels). Experimental test have been performed (suspension leveling maneuvers, tests on ISO 50008 track, bump tests) and the results of the numerical model have been compared with the experimental data, allowing the understanding of the influence of the numerous design and control parameters involved in the determination of the vehicle dynamic behaviour. The influence of mechanical and geometrical parameters on the damping force hysteresis measured during levelling test are shown and described. Finally, the dynamic behavior of the suspension is analyzed making reference to a dynamic test over a bump.


2015 - Energy Saving in the Hydraulic Circuit for Agricultural Tractors: Focus on the Power Supply Group [Articolo su rivista]
Borghi, Massimo; Zardin, Barbara; Pintore, Francesco
abstract

This work aims to analyze a complete hydraulic system of a medium size agricultural tractor, in order to perform an energy dissipation analysis and to suggest possibly alternative configurations and solutions. The fuel consumption and energy dissipation in off road vehicles have in fact become a key feature, given the great attention devoted to the need of reducing pollutant emissions, in order to satisfy the future emission limits. In this work the focus is on the fluid power supply group and the standard architecture of this unit has been compared with an alternative solution, called variable pump margin strategy and compared on the basis of the power consumption to perform the same duty cycle, showing that a relevant percentage of energy may be saved with simple modifications in the hydraulic power generator group.


2014 - Energy Savings in the Hydraulic Circuit of Agricultural Tractors [Relazione in Atti di Convegno]
BORGHI, Massimo; ZARDIN, Barbara; PINTORE, FRANCESCO; BELLUZZI, FRANCESCO
abstract

Increasing interest in reducing pollutant emissions and fuel consumption of off-road vehicles has led to research into alternative systems that aim to reduce the power dissipation of the hydraulic circuits equipping such vehicles. This work proposes alternative hydraulic architectures for agricultural tractors in comparison with traditional systems. The alternative circuit architecture uses independent metering valves and electronically controlled variable pump and involves different control strategies. The analysis is performed with reference to the hydraulic circuit and operating conditions of the remote utilities of a medium-sized tractor. A duty cycle for remote utilities is used for the analysis, obtained from experimental measurements on a tractor equipped with a front loader. Traditional and alternative architectures are modelled using a lumped parameter approach. In this way it is demonstrated that considerable energy savings can be achieved using the alternative architectures.


2014 - MODELLING AND SIMULATION OF THE HYDRAULIC CIRCUIT OF AN AGRICULTURAL TRACTOR [Relazione in Atti di Convegno]
Pintore, Francesco; Borghi, Massimo; Morselli, Riccardo; Benevelli, Alessandro; Zardin, Barbara; Belluzzi, Francesco
abstract

This work aims to analyse a complete hydraulic system of a medium size agricultural tractor, in order to perform an energy dissipation analysis and to test possible alternative configurations and solutions. The fuel consumption and energy dissipation in off-road vehicles have infact become a key feature, given the great attention devoted to the need of reducing pollutant emissions, in order to satisfy the future emission limits. Standard and alternative architecture configurations are modelled and compared on the basis of the power consumption to perform the same duty cycle. Among the results, it is worth highlighting that a relevant percentage of energy may be saved with simple modifications in the hydraulic power generation group.


2014 - Sperimentazione e simulazione nell'analisi del circuito idraulico di una trattrice agricola [Articolo su rivista]
Borghi, M.; Zardin, B.; Zanasi, N.; Pintore, F.; Belluzzi, F.
abstract

In questo lavoro si descrive la metodologia utilizzata per caratterizzare una parte del circuito idraulico di una trattrice agricola. Lo scopo dell’attività è stato quello di ricavare informazioni necessarie alla definizione delle caratteristiche di regolazione della parte di circuito analizzata da utilizzare successivamente in un modello di simulazione del circuito stesso con il quale replicare poi in un ambiente virtuale le effettive condizioni di lavoro incontrate dal veicolo durante le lavorazioni.


2013 - Banco prova per analisi e test di componenti oleodinamici [Articolo su rivista]
Borghi, Massimo; Zardin, Barbara; Pintore, Francesco; Benevelli, Alessandro
abstract

Presso il Dipartimento di Ingegneria “Enzo Ferrari” di Modena è installato un banco prova attrezzato sia per il test di componenti oleodinamici di piccole e medie dimensioni, sia per l’esecuzione di esercitazioni a scopo didattico. L’attrezzatura è stata sviluppata e messa insieme negli anni dal gruppo di ricerca che si occupa in particolare di sistemi e applicazioni oleodinamiche. In questi ultimi anni il gruppo ha concentrato i propri sforzi avendo come obiettivo principale l’ottimizzazione energetica di componenti e sistemi oleodinamici, in particolare relativamente al caso delle applicazioni mobili. Il Prof. M. Borghi ha coordinato come responsabile scientifico un progetto di ricerca di rilevante interesse nazionale PRIN07 [3] la cui tematica era volta all’analisi e ottimizzazione energetica del circuito idraulico di una trattrice agricola e le varie attività di ricerca che si sono sviluppate a partire dal progetto stanno tuttora progredendo anche verso una generalizzazione dei risultati verso altre tipologie di veicoli off-road. L’attrezzatura presente presso il Dipartimento di Ingegneria è stata potenziata proprio nell’ottica di fornire essa stessa un ausilio nella ricerca, oltre che nell’ambito dimostrativo puramente didattico; corredando l’unità di generazione della potenza idraulica con elementi esterni, si prevede di poter realizzare in futuro caratterizzazioni sperimentali mirate di componenti oleodinamici, avendo come obiettivo principale la valutazione delle caratteristiche dinamiche e delle prestazioni energetiche.


2012 - Fluid power supply unit for agricultural tractors: towards energy saving through simulation [Relazione in Atti di Convegno]
Pintore, Francesco; Zardin, Barbara; Borghi, Massimo
abstract

The final aim of the research is to test and verify the effectiveness of high efficiency hydraulic architectures in agriculture tractors. In this paper the attention has been focused on the fluid power delivery group of the vehicle in order to generate a model of the fluid power supply unit used to supply the high pressure circuit of an agricultural tractor able to replicate the performances and the dynamic behaviour of the actual system. The group is composed of a variable displacement axial piston pump equipped with pressure and flow compensators. Despite the evident advantages of the use of this system in the hydraulic applications for off-road vehicles, there are still some critical issues mainly due to instability in some operating onditions and to energy dissipation, that is a direct consequence of the use of dissipative elements to maintain control and avoid interference of loads. In this work an axial piston pump is modelled in detail and analysed in terms of dynamic behaviour of the swashplate, in particular two different versions of the displacement actuations are considered, the first realized using a single actuator that works against the pistons momentum and against a spring, the second that uses a bias and a control actuator to manage the displacement variation. A simple duty cycle is used to study the performance of the pressure and flow compensators. The dynamic behaviour of the two pumps isanalysed and compared allowing to evidence the main design parameters that play a relevant role in the pump performances; this is a key step for the future work, which aims at introducing electronic control for the pump displacement.


2012 - Hydraulic Circuit in Agricultural Tractors, a Step Forward for Energy Saving [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Pintore, Francesco; Belluzzi, Francesco
abstract

The increasing interest to reduce the pollutant emissions in off road vehicles drives the research to alternative solutions aimed to decrease power dissipation for the hydraulic circuit that equips these vehicles. In this work higher efficiency hydraulic architectures in agriculture tractors are proposed and compared with the traditional layout. The alternative circuit architecture uses independent metering valves and electronically controlled variable pump. The analysis is performed with reference to the hydraulic circuit and operating conditions typical of the remote utilities has been used, obtained through experimental measurement on a tractor equipped with a front loader. The traditional and alternative architectures have been modelled using a lumped parameter approach. In that way it has been possible to show that a considerable quantity of energy can be saved using the alternative architectures.


2012 - Independent metering architectures for agricultural tractors auxiliary utilities. [Relazione in Atti di Convegno]
Benevelli, Alessandro; Zardin, Barbara; Borghi, Massimo
abstract

The aim of this paper is to investigate the behaviour of an independent metering circuit architectures equipped with electro-hydraulic controlled multi-spools valves. The analysis is performed with reference to the hydraulic circuit and operating conditions usual of the auxiliary utilities of a mid-size power tractors. The increasing interest to reduce pollutant emissions drives the research to alternative solutions for the hydraulic circuit aimed to decrease power dissipation. From this point of view the independent metering architecture is a potentially energy saving system if compared with the traditional single spool valve architecture. This general feeling has however to be proved in the single application field because the amount of energy saved strongly depends on the kind of duty cycle involved in the analysis. For this work, a typical duty cycle for auxiliary utilities has been used, previously obtained through experimental measurement on a tractor equipped with a front loader. The duty cycle adopted involves two linear actuators, working togetherwith different loads and requiring different flows; this general condition cannot be considered favourable from the point of view of the energy saving potential of the new system but it highlights the fact that if there is an amount of energy saved in this condition, the investment need in time and costs is worth. The modelling is based on a lumped parameter approach and the independent metering valves are created developing a distributor block where any single metering element is modelled on the basis of the commercial EHPV Husco. Different control algorithms have been developed in C++ language to test different control strategy,evidencing the amount of energy saved with respect to the traditional architecture.


2012 - MISSION PROFILE FOR AGRICULTURAL TRACTORS: A FOCUS ON HYDRAULIC CIRCUIT [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Belluzzi, Francesco; Lanzoni, Luca
abstract

Mission profile for agricultural vehicles aims to define a picture of a typical working condition of the vehicle. The collection of these pictures gives information about the performance, the efficiency, and the eventual critical conditions with reference to the kind of operation and terrain. Unfortunately, to be at the same time quick, easy to be interpreted and effective, this analysis has to neglect the details and to take into consideration the whole situation. However, detailed considerations about the efficiency of the vehicle subsystems and of their components may derive only from a deeper analysis and it is from these information that designers and technicians can derive improvements of the system. A promising way to solve this discrepancy is to integrate experimental analysis with simulation: from experimental test on field is possible to define several duty cycles representing different working conditions on the vehicle. These data can then be used as input in a simulation model representing the system, able to replicate its dynamic behaviour. Finally, possible modifications of the system architecture or components, aimed at the improvement of the performance or efficiency, may be more easily tested on the virtual model. In this paper this methodology is presented with reference to the hydraulic circuit of an agricultural tractor, in particular the portion related to the managing of the auxiliary utilities, showing the capability to represent in detail the behaviour of the system and to explore the critical performances.


2011 - Analisi di macchine oleodinamiche a pistoni assiali a piatto inclinato [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Specchia, Emiliano; Pintore, Francesco
abstract

Questo articolo vuole presentare il compendio di diverse attività di analisi e modellazione sulle macchine oleodinamiche apistoni assiali a piatto inclinato, in corso di svolgimento presso il Dipartimento di Ingegneria Meccanica e Civile di Modena. Inparticolare si riferisce di un modello a parametri concentrati che è in grado di descrivere il comportamento in termini digrandezze istantanee (pressione nelle camere pompanti, portate, contributi di coppia all’albero e al piatto). Il modello integradiversi aspetti di interesse e rappresenta uno strumento particolarmente utile nella fase di progetto della macchina perché ingrado di mettere in luce, in modo qualitativo ma significativo, l’influenza dei principali parametri geometrici caratteristici,anche al variare delle condizioni di funzionamento; inoltre, il modello si presta allo studio dell’interazione tra la macchina ed ilcircuito in cui essa si trova inserita, indicando quindi strade per possibili ottimizzazioni dedicate all’applicazione specifica. Ilmodello integra anche lo studio del meccanismo di variazione della cilindrata, sottolineando i parametri di maggior influenzasul comportamento dinamico dello stesso. Dove è stato finora possibile, i risultati numerici ottenuti sono confrontati con quelliprovenienti dalla caratterizzazione sperimentale.


2011 - Displacement Control in Variable Displacement Axial Piston Swashplate Type Pumps [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Specchia, Emiliano; Pintore, Francesco; E., Corradini
abstract

This work deals in particular with variable displacement swashplate axial piston pumps which play a relevant role in feeding adjustable power for hydraulic mobile systems. In these machines the displacement changes with the inclination of the swashplate and to ensure a stable displacement setting is necessary to analyze the moments acting on the swashplate: the relevant contributions to this moment are due to the forces exerted by the pistons on the swashplate through the slipper bearings, which mainly depend on operating conditions, valve plate geometry, pistons angular positions, piston-slipper assembly inertia, viscous friction and on the force of the variable displacement actuator. The resistant moment is never equal to zero when speaking of actual machine and rises with delivery pressure up to consistent values which compromise the operation of the variable displacement mechanism. In the case of the machine studied the variable displacement mechanism is manually operated by the user, who has found significant difficulties in the displacement setting in some operating conditions.A lumped parameter model of the machine has been created which allows to determine the pressure transients within the pistons, taking into account the actual geometry of the valve plate and allowing to compute instantaneous and average moments acting on the swashplate. Comparison between the numerical average moment acting on the swashplate and experimental measurements on the machine has been done. At this point the influence of operating and design parameters has been analyzed and in particular it was found that the valve plate design together with the timing of the high and low pressure flow passages strongly influence the resistant moment arising on the swashplate. In particular, few modifications on the flow areas can lead to significant reduction of the resistant moment without compromising the machine operation.


2011 - Modellazione di una pompa duocentric e riduzione delle emissioni sonore [Articolo su rivista]
Pintore, Francesco; Lorenzelli, Marco; Zardin, Barbara; Specchia, Emiliano
abstract

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2011 - Simulazione integrata per macchine a pistoni assiali [Articolo su rivista]
Zardin, Barbara; Specchia, Emiliano; Pintore, Francesco
abstract

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2011 - Soluzioni innovative per la riduzione del consumo energetico di circuiti idraulici per trattrici agricole [Curatela]
Borghi, Massimo; Zardin, Barbara
abstract

I lavori raccolti in questa pubblicazione presentano i principali risultati ottenuti nell’ambito del Progetto di Rilevante Interesse Nazionale “Soluzioni innovative per la riduzione del consumo energetico di circuiti idraulici per trattrici agricole” (PRIN07 cod.2007Y3N8B7, coordinatore Prof. Massimo Borghi, Università di Modena e Reggio Emilia ), parzialmente finanziato dal MIUR, Ministero dell’Università e della Ricerca Scientifica, nell’arco del biennio 2008-2010.Il programma di ricerca ha perseguito l’obiettivo di investigare possibili strade per ottenere un incremento delle prestazioni energetiche dei sistemi idraulici presenti a bordo delle trattrici agricole di media potenza (90-150kW).Alcuni principali sottosistemi che costituiscono l’impianto idraulico di una trattrice agricola sono stati analizzati e modellati nell'intento di determinare un incremento dell'efficienza complessiva del sistema attraverso la riduzione della potenza e l'ottimizzazione del rendimento totale di conversione dell'energia.Particolarmente rilevante è l'approccio di ottimizzazione multi-obiettivo vincolata dato alla generazione dei sottosistemi parziali in vista della loro integrazione nel veicolo, dove la gestione ottimale delle caratteristiche di interfaccia con la sorgente di potenza vengano valutate alla luce della risposta all'interno di un modello virtuale della dinamica del veicolo.


2010 - Energy Comsumption of the Hydraulic Circuit of a Mid-Size Power Tractor [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Mancarella, Francesco; Specchia, Emiliano
abstract

This work focuses on the hydraulic circuit that feeds the remote actuators of a mid-size power agricultural tractor. First of all, the energy consumption of a traditional load sensing architecture, which uses a single electronically controlled spool valve, is analyzed. For this kind of circuit, the position of the spool generally determines, at the same time, pressure drops both at the inlet and at the outlet section. The consequence is that in the majority of the situations both the meter-in and the meter-out configuration is not optimized in terms of energy consumption.An alternative architecture, with an independent metering configuration, based on a pressure based control strategy is analyzed and modelled. Energy consumption comparisons of the two systems are made, using different duty cycles, involving resistant and overrunning loads.


2010 - Energy dissipation of the hydraulic circuit of remote auxiliary utilities of an agricultural tractor [Relazione in Atti di Convegno]
Borghi, Massimo; Mancarella, Francesco; Zardin, Barbara
abstract

The aim of this work is to analyze the energy dissipation related to the hydraulic circuit which controls the remote auxiliary utilities of an agricultural tractor. This circuit is a typical hydraulic load sensing multi actuators system. This kind of system provides a good control strategy but it is characterized by quite high energy dissipation, especially when several actuators are working together under different variable loads. In this paper, the traditional load sensing system is modelled using a lumped parameter approach, and theenergy dissipations are evaluated with reference to an actual duty measured on an agricultural tractor. Then, an alternative and more energy saving circuit architecture is introduced, based on an independent metering concept: in this architecture the single spool auxiliary valve is substituted with two electronically controlled proportional valves. The system has been also equipped with an electronically controlled variable pump; twostrategies to control both the pump and the proportional valves are introduced. The energetic analysis is performed also for the alternative architecture using the same duty cycle, with the aim to identify the advantages, disadvantages and the critical features of this system with respect to the original one. Significant energy saving percentage characterizes the independent metering architecture, which seems to be a promising alternative to the standard hydraulic load sensing system.


2010 - Numerical Analysis Of The Dynamic Behaviour Of Piston Journal Bearing In Axial Piston Pumps And Motors [Relazione in Atti di Convegno]
Specchia, Emiliano; Zardin, Barbara; Borghi, Massimo
abstract

This work presents a numerical analysis of the piston dynamic behaviour in axial piston swash plate type pumps and motors. The numerical method adopted is based on the solution of the piston motion equations which depend on the pressure distribution within the cylinder-piston gap. In order to determine this contribution, the Reynolds equation is applied in the lubricating fluid film between the piston and the cylinder. Besides the piston dynamic behaviour, the model permits to calculate the leakage flow through the gap and the friction forces acting on the piston and cylinder surface.After the presentation of the numerical procedure, the dynamic behaviour of the piston is firstly discussed, highlightingthe stability of the bearing. This work is part of a wider research activity focused on the study of positive displacement machines, with the aim to determine and maximize their global efficiency.


2010 - Remote actuation hydraulic circuit of agricultural tractors: alternative architectures for reducing energy consumption. [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Mancarella, Francesco
abstract

Nell’ambito di questo lavoro si analizza dal punto di vista energetico il circuito idraulico che alimenta le attrezzature ausiliarie di una trattrice agricola di media potenza. A tale scopo la tipica architettura circuitale del sistema, load sensing multi-attuatore, viene modellata in ambiente AMESim® al fine di individuare le criticità del sistema. Successivamente, viene analizzata un’architettura circuitale alternativa, basata sul concetto di metering indipendente e sull’utilizzo di una pompa a cilindrata variabile controllata elettronicamente, che mantiene le funzionalità del sistema standard e riduce allo stesso tempo il dispendio energetico. Il terreno comune per effettuare un confronto energetico fra le architetture è rappresentato da un ciclo di lavoro definito sperimentalmente utilizzando un caricatore frontale connesso ai distributori ausiliari di una trattrice agricola.Tale scelta è dovuta all’esigenza di utilizzare un termine di paragone per le diverse strategie che fosse verosimile e somigliante alle condizioni di lavoro tipiche della trattrice. I risultati raggiunti evidenziano un ampio margine di risparmio energetico caratterizzante l’architettura alternativa che dimostra così di essere promettente; nel seguito dell’attività di ricerca, un’analisi dettagliata del comportamento dinamico della pompa di alimentazione e delle valvole proporzionali che sostituiscono i distributori ausiliari permetterà di verificare la stabilità del sistema e valutare con maggior precisione il risparmio energetico.


2009 - External Gear Pump Volumetric Efficiency: Numerical and Experimental Analysis [Relazione in Atti di Convegno]
Borghi, Massimo; Zardin, Barbara; Specchia, Emiliano
abstract

External gear pumps and motors are robust and low cost components and are widely used in industrial and mobile applications; nowadays however, optimal global efficiency represents a more crucial aspect to be considered when designing a hydraulic machine. For this reason, it becomes a primary necessity to investigate the phenomena which determine and affect the hydraulic machine total efficiency.In this work, the volumetric efficiency of external gear pumps is investigated by means of a mathematical model already presented in a previous paper and the results obtained are compared with experimental data.First of all, the mathematical model is briefly presented; then the predicted results are discussed considering the influence of the pump operating conditions. Moreover, the influence on the volumetric efficiency of the behaviour of the hydraulically balanced bearing blocks, and hence of the pump axial balance, is exposed. In particular, it is shown that the tilted position of the bearing blocks and the height of the lateral clearance can greatly affect the volumetric efficiency.The data coming from an experimental investigation carried out on commercial external gear pump units are then presented; both the volumetric and the mechanical efficiency have been measured.The comparison between the experimental data and the numerical results allows discussing the bearing blocks balancing behaviour during pump operation.


2009 - Numerical Analysis of the Dynamic Behaviour of Axial Piston Pumps and Motors Slipper Bearings [Articolo su rivista]
Borghi, Massimo; Specchia, Emiliano; Zardin, Barbara
abstract

This paper reports an analysis of the lubricationmechanism and the dynamic behaviour of axial pistonpumps and motors slipper bearings. A numericalprocedure is used to solve the Reynolds equation,written here with respect to the slipper-swash plate gap,whose height is considered variable in a twodimensional field and with time.The contributions of forces and moments acting on theslipper are illustrated and discussed, then the numericalmethod is presented to solve the Reynolds equation.Taking into consideration the slipper surface that isfacing the swash plate, different geometry profiles areconsidered and the subsequent dynamic behaviour ofthe slipper is investigated; in particular, it is shown that aflat profile cannot always guarantee the bearingcapability of the slipper and the lubrication in the gap iscompromised for some critical operating conditions.Successively, different non-flat profiles of the surface areconsidered and their impact on the slipper bearingdynamic behaviour is investigated in terms of tilt of theslipper α and central clearance height h0. Then, focusingon one of these non-flat profiles, the results arediscussed highlighting the influence of machineoperating conditions. These include rotational speed anda high pressure level and involve introducing a frictioncoefficient in order to evaluate the magnitude of frictionlosses determined by the slipper behaviour. Finally,some considerations are expressed about differencesbetween mode of operation of the pump and the motorrelated to slipper behaviour.


2009 - Numerical analysis of the dynamic behaviour of axial piston pumps and motors slipper bearings [Relazione in Atti di Convegno]
Borghi, M.; Specchia, E.; Zardin, B.
abstract

This paper reports an analysis of the lubrication mechanism and the dynamic behaviour of axial piston pumps and motors slipper bearings. A numerical procedure is used to solve the Reynolds equation, written here with respect to the slipper-swash plate gap, whose height is considered variable in a two dimensional field and with time. The contributions of forces and moments acting on the slipper are illustrated and discussed, then the numerical method is presented to solve the Reynolds equation. Taking into consideration the slipper surface that is facing the swash plate, different geometry profiles are considered and the subsequent dynamic behaviour of the slipper is investigated; in particular, it is shown that a flat profile cannot always guarantee the bearing capability of the slipper and the lubrication in the gap is compromised for some critical operating conditions. Successively, different non-flat profiles of the surface are considered and their impact on the slipper bearing dynamic behaviour is investigated in terms of tilt of the slipper α and central clearance height h0. Then, focusing on one of these non-flat profiles, the results are discussed highlighting the influence of machine operating conditions. These include rotational speed and a high pressure level and involve introducing a friction coefficient in order to evaluate the magnitude of friction losses determined by the slipper behaviour. Finally, some considerations are expressed about differences between mode of operation of the pump and the motor related to slipper behaviour. Copyright © 2009 SAE International.


2009 - Sviluppi nello studio di pompe e macchine volumetriche ad ingranaggi esterni [Articolo su rivista]
Borghi, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

L'articolo presenta un resoconto delle attività di ricerca, modellazione e simulazione relative alle macchine ad ingranaggi esterni, portate avanti dal gruppo di ricerca di Macchine e Sistemi Energetici presso il Dipartimento di Ingegneria Meccanica dell'Università di Modena e Reggio Emilia


2009 - The Critical Speed of Slipper Bearings in Axial Piston Swash Plate Type Pumps and Motors [Relazione in Atti di Convegno]
Borghi, Massimo; Specchia, Emiliano; Zardin, Barbara; E., Corradini
abstract

A stationary model is adopted to determine the criticalcondition for which the slipper moves away from the swashplatein an axial piston machine. The aim of the analysis is to find thecritical speed, i.e. the value of the machine speed for which theslipper moves away from the swashplate; usually this conditionmay determine bad operating behaviour of the machine, althougha retainer plate is used to maintain the slipper sufficiently near tothe swashplate.The influences of the pressure transition in the cylinder, theswashplate angle and the radial clearance between piston andcylinder on the critical speed are depicted. Successively, the roleof the position of the point of application of the resultant forcedue to the slipper-retaining plate contact is analyzed.


2008 - External Gear Pumps and Motors Bearing Blocks Design: Influence on the Volumetric Efficiency [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

External gear pumps and motors, in their typical commercial design, are equipped with hydraulically balanced bearing blocks, which allow to maintain good volumetric efficiencies also when the pressure drop between the ports is high. The aim of this work is to analyze some geometrical aspects characterizing the bearing blocks design, evaluating their influence on the volumetric efficiency of the machine with the aid of a numerical model properly created. External gear pumps and motors operation behavior is strongly influenced by the volumetric efficiency; this parameter takes into account the leakages of fluid which typically affect the hydraulic machine operation and, together with the mechanical efficiency, determines its total efficiency and, consequently, has a great influence on power loss.


2008 - Modelling and Simulation of External Gear Pumps and Motors [Relazione in Atti di Convegno]
Zardin, Barbara; Borghi, Massimo
abstract

In this paper a lumped parameter model for the numerical simulation of the dynamic behaviour of external gear pumps and motors is presented. The model is developed in AMESim® environment, combining the use of AMESim® libraries of components and a self-made library developed in C++ code. The choice of a single modelling environment allows both the simulation of the machine dynamic behaviour and the analysis of the interaction between the external gear unit itself and the hydraulic circuit in which it is working. Particular attention is devoted in the model in order to consider the eccentric position of the gears inside the casing. Moreover, the relevance of an accurate definitions of the flow leakages involving the inter-teeth volumes, considering also the Couette flow contribution, is highlighted. Finally, a numerical analysis has been carried out by means of the model in order to determine the influence of load and rotational speed on the dynamic behaviour of the machine; results about the pressure ripple, flow rate at the outlet port, pressure transients on the inter-teeth volumes and gears position inside the casing are exposed and commented.


2006 - Numerical Characterization of Pipes And Hoses Dynamic Response [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

This paper deals with the study of pipes and hoses dynamic characteristics variation with the fluid-wall equivalent bulkmodulus description, with particular attention devoted to the analysis of the wall thickness, of the mechanical constraintsand of the internal pressure both on the fluid celerity, and on the pipe frequency response. In particular, consideringboth the case of plain stress and of plain strain, the pipe wall compliance and bulk modulus are firstly derived as afunction of the internal pressure and of the wall elastic and geometrical characteristics. Then, the influence of the pipegeometry and of the wall thickness on the pipe wall compliance and bulk modulus are highlighted for some materials ofinterest for industrial, automotive and aerospace applications (steel, aluminium, titanium and wired rubber), and thedependency of the equivalent bulk modulus on these parameters and on fluid physical characteristics is highlighted.Finally, the influence of mechanical constraints, of pipe geometry, of fluid physical properties, of wall material and offluid pressure on the global pipe dynamic response characteristics, and in particular on the fluid celerity, on the Machnumber and on the natural frequency, is evidenced.


2006 - The influence of aeration and cavitation on gear pumps and motors meshing volumes pressures [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

The paper describes the influence of the fluid modeling on cavitation and aeration detection in external gear pumps and motors inter-teeth volumes during the gears meshing process, in order to compare the results coming from the use of different physical models of air release/adsorption and cavitation. A simplified cavitation model is firstly involved, and pressure transients are calculated imposing a pressure cut when the fluid vapor pressure (or the dissolved air partial pressure) is reached. After, assuming an equivalent approach able to involve the vapor phase generation, the cavitation phenomena in the meshing volumes are deepened, and the influence of the fluid modeling enhancement on the cavitating machine behavior is highlighted. Then, the equivalent fluid approach is enhanced introducing the air release, and properly coupling the gaseous phases release/adsorption to the Henry's Law for not instantaneous processes. Finally, the influence of the air release/adsorption time constant on meshing volumes pressure transients are detailed, with particular attention devoted to the modification introduced by the cavitation detailing on the gaseous phase void fraction determination and on the angular extension of the cavitation phenomena detection.


2005 - Pressure Transients in External Gear Pumps and Motors Meshing Volumes [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

In this paper a lumped parameters numerical model isreviewed to study the meshing process of external gearpumps and motors, with the aim of highlighting theinfluence of some geometrical design parameters andoperating conditions on inter-teeth volumes pressures.The inter-teeth space is modeled adopting a two-volumeapproach, properly tailored both for the pump and for themotor units behavior description. In both cases, thecommunications between the interconnected inter-teethvolumes and the high and low pressure ports aresketched as variable equivalent turbulent restrictors; flowareas have been determined as functions of the gearsand of the meshing grooves main design parameters.The inter-teeth pressures, and the leakage flows, arecalculated solving the incompressible and isothermalcontinuity equation, contemporarily applied to bothvolumes and properly combined with the classicalturbulent orifice equation. Successively, for a referenceoperating condition, properly chosen for underlining theinter-teeth meshing cycle and corresponding to a verylow pressure load, the meshing processes of an externalgear pump and of an external gear motor are compared.Among others, the attention is focused on the behaviorof those hydraulic variables more conditioning themeshing cycle, and the differences rising up in interteethpressure peaks and in cavitation interval amplitudeand angular positioning are evidenced. Then, themeshing process analysis is expanded to cover theexternal gear units common operating field, both interms of rotational speed (from 500 to 3000 rpm) and interms of the high pressure port value (from 10 to 250bar). In all cases, the general trend shows that cavitationhas a deeper influence on external gear pumpsoperation, while external gear motors are subjected tomore significant pressure peaks, particularly markedduring the low pressure part of the meshing cycle.Attention is also focused on the influence of gears interaxialdistance and axial width on the meshing processcharacteristics, in order to assess how the volumedimensions could differently affect pressure peaks andcavitation phenomena in pumps and motors.Finally, the role of the balancing plates grooves inconditioning pressure peaks and cavitation is highlightedand, with particular care devoted to external gearmotors, some useful guidelines for their design areoutlined.


2005 - Studying the Axial Balance of External Gear Pumps [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

In this paper some design aspects related to externalgear pumps balancing surfaces are studied, and someuseful guidelines for designing bearing blocksbalancing surfaces are suggested. In order to studybearing blocks axial balance, a numerical procedurefor the determination of the pressure distribution insidethe clearance bounded by gears sides and bearingblocks internal surfaces is firstly presented andapplied. After, the influence of bearing blocksgeometry and pump operating conditions on thewidening thrust is highlighted, considering bothconstant and variable lateral clearance heights. Then,the computations are performed to evaluate thewidening thrust variation as a function of bearingblocks relative tilt with respect to gears lateral sides,and both positive and negative bearing blocks tilts areevidenced and discussed. Finally, the numericalprocedure is validated through a comprehensivecomparison of its results with experimental data(coming from some bibliographic sources), and someuseful guidelines in designing external gear pumpsbalancing surfaces are defined.


2005 - Studying the Efficiency of a Compact Excavator Primary Workgroup Hydraulic Control System [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

This paper studies the proportional directional controlvalves design influence on the energetic behavior of amid-power compact excavator.In particular, with reference to the hydraulic circuitactuating the primary workgroup, in the paper thehydraulic power metering performed with the boomcylinder proportional control valve is studied, and somedesign solution useful in reducing both the hydraulicpower dissipation, and the power absorption from themachinery prime mover are highlighted.The analysis, experimentally performed for differentoperating conditions, is carried out highlighting theinfluence of a metering configuration both on the supplypressure modulation and on the flow-rate supplied tothe actuator.The hydraulic power metering and the boom actuationhydraulic efficiency are defined for two alternativeproportional control valve metering configurations and,within the limits implicitly implied on the actuation circuitarchitecture, a possible design solution in determiningthe improvement of the boom actuation systemperformances is investigated.


2004 - About the Prediction of Pressure Variation in the Inter-Teeth Volumes of External Gear Pumps [Relazione in Atti di Convegno]
Borghi, Massimo; Milani, Massimo; Paltrinieri, Fabrizio; Zardin, Barbara
abstract

The paper deals with the analysis of the inter-teeth pressure transients during gears meshing cycle of external gear pumps. A lumped parameter model, tailored for the prediction of pressures in the meshing zone, is firstly presented. The numerical model, based on the integration of the continuity equation, is applied to the inter-teeth volumes, communicating with the neighbouring ambient through geometry dependent orifices. A comparison between numerical results, obtained considering both constant and variable discharge coefficients, is illustrated. Successively, the dependency of pressure transients on gear pump operating conditions, mainly in terms of delivery pressure and rotational speed, is investigated. The effect of some geometric parameters is also discussed, mainly considering different gears widths and interaxial distances, and high-pressure recess positioning. Finally, in order to highlight the influence of the cavitation modelling on low pressure transition, the results coming from the application of two simplified approaches are shown and compared.