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

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

The Hydraulic Power Generation and Transmission on Agricultural Tractors: Feasible architectures to reduce dissipation and fuel consumption-Part i

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

La vérité des reliques selon Charles Borromée : réforme interne ou aiguillon protestant ?

Sous le feu des critiques protestantes, le Concile de Trente, au cours de la XXVe et dernière session (3-4 décembre 1563), proclame solennellement la légitimité de la vénération due aux reliques : condamnant toute forme de critique à l’égard du culte des saints et des pèlerinages auprès de leurs corps, il enjoint aux évêques d’enseigner à leurs fidèles « les honneurs dus aux reliques », de réprimer toute forme d’« abus » et de « superstition » et de s’assurer de leur authenticité. Toutefois, dans la mise en œuvre concrète du décret, le contrôle épiscopal des reliques relève plus de l’exigence de réforme interne de l’Église que du combat anti-protestant. Cette contribution met en lumière la place de la réforme interne et de la polémique anti-protestante dans l’interprétation du décret tridentin donnée dans l’archevêché de Milan, pendant l’épiscopat de Charles Borromée (1564- 1584), en prenant en considération la méthode prescrite et quelques exemples de sa pratique de la reconnaissance.

Studi confraternali: orientamenti, problemi, testimonianze

Il volume raccoglie interventi di studiosi italiani e stranieri miranti a offrire una panoramica di percorsi storiografici e di problematiche relativi alla storia del movimento confraternale, così come sono emersi nell'ambito di discipline storiche, sociali, giuridiche, letterarie e artistiche sviluppatesi nel corso del Novecento. I contributi si riferiscono al contesto storico dell'Europa occidentale, con più specifico riguardo per l'Italia, nel periodo compreso fra medioevo e prima età moderna. La raccolta si articola in quattro sezioni: Individui e gruppi, che sonda l'emergere di un interesse verso le comunità confraternali all'interno di ambiti di studio come la storia dei gruppi sociali, del mondo rurale, delle donne, dei giovani; L'inquadramento giuridico e istituzionale, che affronta problemi di legittimità e di assetto istituzionale; L'economia della carità, che analizza il rapporto delle confraternite con gli enti ospedalieri, le modalità amministrative dei patrimoni confraternali, le culture di governo che sottostanno a politiche assistenziali di cui le confraternite sono tramite principale; Testimonianze teatrali, musicali, artistiche, documentarie dedicata alle fonti che le confraternite hanno saputo trasmettere