This paper shows the experimental results obtained using a nanocoating (developed by ISTEC-C.N.R.) applied to the slippers of an axial piston pump to reduce the friction losses in order to improve the pump overall efficiency map. It is well known that the mechanical power losses in a hydraulic pump come from the friction between parts in relative motion. The need to provide, especially at low rotational speed, hydrodynamic lift causes power losses in terms of volumetric and mechanical efficiency, due to the contrasting need to increase leakage to provide lubrication and to keep a minimum clearance in meatus to limit the volumetric losses. The application of special surface treatments have been exploited in pioneering works in the past, trying different surface finishing or adding ceramic or heterogeneous metallic layers, but the potential of structured coatings at nanoscale, with superhydrophobic and oleophobic characteristics, has never been exploited. Using a dedicated test rig developed at IMAMOTER-C.N.R., able to ensure hydrostatic working condition during the mutual rotation between the slippers and the swash plate, the functional performance of the nanocoated slippers' surface have been studied. In the first part of the paper, the functionalization method is presented; in the second part, a comparison between the experimental performances of coated and uncoated surfaces is showed.

The proper operation of a fluid power system in terms of efficiency and reliability is directly related to the fluid state; therefore, the monitoring of fluid ageing in real time is fundamental to prevent machine failures. For this aim, an innovative methodology based on fluid vapor analysis through metal oxide (shortened: MOX) gas sensors has been developed. Two apparatuses were designed and realized: (i) a dedicated test bench to fast-age the fluid under controlled conditions; (ii) a laboratory MOX sensor system to test the headspace of the aged fluid samples. To prepare the set of MOX gas sensors suitable to detect the analytes’ concentrations in the fluid headspace, different functional materials were synthesized in the form of nanopowders, characterizing them by electron microscopy and X-ray diffraction. The powders were deposited through screen-printing technology, realizing thick-film gas sensors on which dynamical responses in the presence of the fluid headspace were obtained. It resulted that gas sensors based on solid solution TixSn1–xO2 with x = 0.9 and 0.5 offered the best responses toward the fluid headspace with lower response and recovery times. Furthermore, a decrease in the responses (for all sensors) with fluid ageing was observed.

A key component of hydraulic fluid power systems — the standard orifice and, consequently, all equivalent components — apparently has, to this day, some mysteries yet to be unveiled. Knowledge on cavitation-induced liquid flow choking or saturation, which is a well founded topic in some areas of the wide field of hydraulics, e.g. water distribution piping systems, is practically neglected when assessing the design of typical mineral-oil-based power generation and control systems, for both mobile and industrial applications. This conclusion holds true at every level of study, from the technical reference literature adopted by designers to the more popular textbooks and journal papers. Moreover, the rare works addressing the phenomenon are focused on the underlying physical mechanics, completely missing any kind of evaluation of the functional consequences, especially the need to “revise” the standard quadratic law of turbulent flow. Prompted by one of these works, a preliminary experimental activity has been carried out, aimed at determining the actual flow characteristic of standard screw-in orifices used in fluid power pilot circuits. The results confirmed the undoubted presence of flow saturation; based on that, a suitable theoretical description was developed, and some practical applications are outlined in the paper. Finally, few open questions are listed, which need to be answered.

In recent years many studies were performed with the aim of reducing losses and to optimize the oil flow management in complex machines like excavators. One of the most promising ideas is to implement multiple hydraulic power sources but this requires a flexible pump switch system, in fact depending on flow request and machine mode one or more pumps can be switched to serve each actuator. To put into practice these studies it is necessary to in-depth design the distribution system, through which hydrostatic transmissions are applied to the different loads. The system presented couples more actuators to every single pumps and offers also cross connections, in order to increase systems flexibility in flow management. The paper presents a new component to realize the pump switch management, applying the matrix concept to the hydraulic flow connections. The matrix for oil flow management is a new hydraulic component, flexible, safe and scalable, that can be coupled to other similar, offering a real matrix of lines and columns. From the working principle point of view, each line is connected to a pump and each column is connected to a load, only a section can be opened for each pump, but more connections can be opened for an actuator, offering a flexible flow management. The component is a rotating distributor with a safety spool, that can connect P and T port of one pump to the A and B port of each actuator, moving the safety spool only when the rotary distributor is coupled with the desired actuator. Both closed center and open center configurations are possible, as well as regenerative systems can be implemented. The solution is presented with focus on the mechanical design and on the working principle, offering an optimal solution to the switching system, that free the distribution system design from the constraint of a predefined coupling of pumps with actuators. Since the component is in its early stage of development, the paper will focus mainly on design concept and architectural alternatives and potential benefits of the implementation of the concept on state of art architectures from the functional capability point of view. Some argument will be given then on the topic of Functional Safety disclosing some of the operability and safety potentials of the system. Further important design aspects such as Internal Leakage, Axial and Radial Forces on Spools, Dynamic Response will be addressed in later publications, as well as system simulation of working cycles and Testing of Prototype has to be obviously undertaken in the future.

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