Evaluation of the hydro - Mechanical efficiency of external gear pumps

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

Anatomie du sacré: la certification des reliques après le concile de Trente, entre procès et prière

Après que le concile de Trente a intimé aux évêques de vérifier l\u27authenticité des reliques de leur diocèse, comment cette injonction est-elle mise en oeuvre ? L\u27article y répond par l\u27exemple de la chancellerie de Milan, modèle à l\u27échelle de la catholicité. Un corpus composé de sources judiciaires et de gravures de dévotion permet de comprendre l\u27ambiguïté de cette procédure de vérification, entre examen critique et prière

Development of a 2-Stroke GDI Engine

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

Modelling of hydrostatic bearings for servo-cylinders

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

Caracterização de ligantes e misturas asfálticas modificados com a adição de Trinidad Lake Asphalt

The use of modifiers to improve the performance of asphalt materials when subjected to loading and climate effects has become an increasingly common practice in Brazil. Among the modifiers, the natural asphalt Trinidad Lake Asphalt (TLA) has characteristics that compensate some deficiencies of conventional petroleum-based asphalt binders, increasing the service life and improving the pavement performance. This study evaluated the influence of the addition of different TLA contents (15%, 25% and 50%) on the properties of two Brazilian petroleum-based asphalt binders of conventional use (AC 30/45 and AC 50/70) and the performance of asphalt mixtures. The properties of the asphalt binders were obtained through tests that are included in the Brazilian specification and a Dynamic Shear Rheometer was used to determine their rheological characteristics. Mechanical tests were performed to characterize the stiffness, resistance to permanent deformation and fatigue damage, and susceptibility to induced moisture damage of asphalt mixtures. The results obtained in this research indicate that the addition of TLA stiffens the asphalt binders (and consequently the asphalt mixture) and improves its rutting resistance. The fatigue damage resistance of the materials was not necessarily affected by the stiffening effect provided by the TLA, especially if a proper amount is added to the conventional petroleum-based binder.O uso de modificadores para melhorar o desempenho de materiais asfálticos quando sujeitos ao carregamento e aos efeitos do clima tem se tornado uma prática cada vez mais comum no Brasil. Entre os modificadores, o ligante asfáltico natural Trinidad Lake Asphalt (TLA) apresenta características que compensam algumas deficiências de ligantes asfálticos convencionais, aumentando a vida útil e melhorando o desempenho do pavimento. Este trabalho avaliou a influência da adição de diferentes teores de TLA (15%, 25% e 50%) nas propriedades de dois ligantes asfálticos brasileiros de uso convencional (CAP 30/45 e CAP 50/70) e no desempenho de misturas asfálticas. As propriedades dos ligantes asfálticos foram obtidas por meio de testes que constam na especificação brasileira e um Reômetro de Cisalhamento Dinâmico foi utilizado para determinar suas características reológicas. Ensaios mecânicos foram realizados para caracterizar a rigidez, a resistência à deformação permanente e ao dano por fadiga, e a susceptibilidade ao dano por umidade induzida das misturas asfálticas. Os resultados obtidos nesta pesquisa indicam que a adição de TLA conferiu aos ligantes asfálticos (e consequentemente às misturas asfálticas) um aumento de rigidez e elevou suas resistências à deformação permanente. A resistência ao dano por fadiga dos materiais não foi afetada, necessariamente, pelo efeito de rigidez fornecido pelo TLA, especialmente se uma quantidade adequada for adicionada ao ligante convencional

Energy Savings in the Hydraulic Circuit of Agricultural Tractors

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

Pressure Losses in Multiple-Elbow Paths and in V-Bends of Hydraulic Manifolds

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

Design Of Two-Stage On/Off Cartridge Valves For Mobile Applications

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