Along with the general requirement of continuously increasing efficiency of hydrostatic drivetrains, variable displacement machines are of major concern in research and development. To this effect, the whole machine performance is mainly dependent of the displacement variation system (DVS) performance. A lot of work to this topic focusses on the controller and actuator level. The aim of this paper is to offer a more fundamental view on DVS by giving a focus to the basic hydro-mechanical principles.

Nowadays sealing systems are commonly designed by means of hydrodynamic and elastohydrodynamic theories. Although the analytical as well as the computational approaches have improved in meaning full manner since the last decades: For small sealing gaps, in the order of micrometers and below, a discrepancy between experimental investigated and theoretically predicted leakage flows occur. As a cause for the discrepancy a breakdown of the no slip boundary condition is suspected. Since in small sealing gaps the continuum hypothesis is violated and molecular effects have to be considered. One fundamental quantity to take molecular affects into account is the slip length. Within this paper a new measurement apparatus to evaluate the slip length for hydraulic applications is presented. The adjustable gaps between two planar surfaces are in the order of magnitude of 1 μm. In a first step the slip length for the system steel-oil –steel is investigated at three different temperatures: 18°C, 22°C and 25°C. The measured slip lengths are in the order of magnitude of ~100 nm.

Suspension systems are used to diminish the vibration of vehicles. The hydraulic dampers in conventional suspension systems are mainly designed with the orifices of the piston; however, the vibration energy will be transferred into waste heat. In recent years, conventional vehicles with internal combustion engines and hybrid vehicles are used commonly. However, with the gradual depletion of fossil fuels, electric vehicles are developing. For this reason, the research focuses on recycling energy from the suspension of vehicles to improve the vehicle’s endurance. The purpose of this study is to develop a semi-active suspension control system with an energy harvesting system. Instead of the fixed orifices in conventional vehicles, an adjusting damping force method with variable resistance circuits system is studied for the semi-active suspension control system. Thus, we are able to develop semi-active control to improve the riding comfort. The energy harvesting system contains a hydraulic gear motor and a DC generator. When vehicles vibrate, the hydraulic damper serves as a hydraulic pump to compress the oil and drive the hydraulic motor. At the same time, the hydraulic motor drives the generator to generate electricity which will be stored in a battery. In this study, the test rig is the quarter-car system. We first design the novel hydraulic suspension system combining with the energy harvesting system. The simulation of dynamic mathematical model will be performed and analyzed by MATLAB/Simulink. Besides that, the semiactive control by the fuzzy sliding mode controller will be realized in the hydraulic suspension system with energy harvesting system. Finally, a test rig is set up for practical experimental implementation and verification.

Measures of individualization and integration offer a great potential for further development and optimization in hydraulic drive technology. Advantages are seen especially for energy efficiency and functionality. These potentials motivate current research activities for displacement controlled systems and for valve controlled structures. For the latter, the focus lies on strategies of independent metering. Furthermore, expected challenges for the future are discussed.

The floating cup principle is a general hydrostatic principle for both constant and variable displacement pumps and motors, as well as for hydraulic transformers. In this paper, the focus will be entirely on the control of the displacement of the variable 28 cc Floating Cup pump (FCVP28). The floating cup principle features two opposed swash plates, for which both angular positions need to be controlled in order to cover the entire range from zero to full displacement. The results of both extended numerical analysis as well as simplified linearized models will be compared to test results on a 28 cc FCVP. Special emphasis will be on the dynamic behaviour of the displacement control.

For delivery, dosing and pressure control of fluids in mobile and stationary applications electromagnetically operated piston pumps are an established solution. The volume per stroke is exactly defined by the geometry. Nevertheless cavitation, more likely with the new fuel blends containing a high proportion of ethanol /1/, deteriorates the dosing precision of the liquid portion. One important criterion of precise metering is the transport of the liquids through the reciprocating piston pump without transferring bubbles. Especially, pumping in the range of vapour pressure of gasoline fuels implies challenges for precision. The objective of this work is revealing potential sources of reduced cavitation by optimising the design. For doing so, optical investigations have been applied. In addition to this, cavitation can be diminished controlling the piston’s travel externally. The second important item covers pumping of degenerated fluids even without negative effects on the pump’s performance. Up to now, wide, inefficient gaps or high force surplus are necessary. A new helix-design /2/ has been investigated and built up in order to reduce the described effort. The effects coming with the helix allow a permanent rinsing of the stressed surfaces, leading to lubrication and lower temperature loads. The results are shown in simulation, fundamental tests and is validated in practical pump operation.

Axial piston pumps and motors are widely used in heavy-duty applications and play a fundamental role in hydrostatic and power split drives. The mechanical power losses in hydraulic piston pumps come from the friction between parts in relative motion. The improvement, albeit marginal, in overall efficiency of these components may significantly impact the global efficiency of the machine. The friction between slipper and swash plate is a functional key in an axial piston pump, especially when the pump (at low rotational speed or at partial displacement) works in the critical areas where the efficiency is low. 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. The potential of structured coatings at nanoscale, with superhydrophobic and oleophobic characteristics, has never been exploited. Due to the difficulty to reproduce the real working conditions of axial piston pump slippers, it has been made a hydraulic test bench properly designed in order to compare the performance of nano-coated slippers with respect to standard ones. The nano-coated and standard slippers have been subjected to the following working conditions: a test at variable pressure and constant rotational speed, a test at constant pressure and variable rotational speed. The comparison between standard and nanocoated slippers, for both working conditions, shows clearly that more than 20% of friction reduction can be achieved using the proposed nano-coating methodology.

Retrofits of hydraulic and mechanical deep drawing presses often stop with the exchange of the electrical and the hydraulic parts. But that is only half the job. The use of high definition control electronics, faster CPUs and more dynamic hydraulic actuators, offers the opportunity of redesigning the already existing control concepts of the press. In this paper we present how the performance of the press, i.e. the control quality, can be increased for hydraulic ram and cushion axes. The improvement in control quality is achieved through the use of intelligent closed-loop and open-loopcontrol algorithms. Therefore, creasing and crack formation can be reduced, since enhancements in control quality have direct influence on the quality of the forming process. Results will be shown for hydraulic drawing cushion control, i.e. pressure control, as well as for hydraulic ram control, i.e. position, velocity and parallelism control. We present findings for hydraulic cushion control of a mechanical press type Arisa S-4-1600-470-230-LDE (link-drive press with 10 hydraulic cushions) and for ram- / cushion-control of hydraulic press type Müller-Weingarten ZE2100 (multi-curve press with 8-point cushion).

Digitalization is finding it’s way into production and machine-building. Autonomous, sefoptimizing and highly interconnected units will determine the functionality of machines and production facilities. Communication and automation layout will fundamentally change, data will be more and more the base for new business modells. Innovation is determining pneumatics and handling technology. The innovation topics performance improvement, modular and mechatronic design of systems, sustainability and efficiency are keeping pneumatics and vacuum technology on the pathway of success. But is the technology field also prepared for the tremendous challenges caused by the digitalization? This paper is focusing on the significance of digitalization for fluid technology, especially for pneumatics and vacuum technology. The new concepts of digitalization and autonomization are based on the Internet of Things with open Communication of cyber-physical systems. These cyber-physical systems are able to react autonoumously. Cyber-physical systems can collect, interpret and analys data and transfer it into valuable information. Based on these data, cyberphysical systems will provide services to all participants of the smart factory. There will be a digital image inside the factory cloud, which is the base of new business models. Systems of pneumatics, vacuum technology and hydraulics will play a core role in this world. They are placed directly at the interface to the real technical process, they have direct contact with the workpieces, they are collecting multitude of sensor data and are evaulating it, they have functionality like Condition Monitoring and Energy Efficiency optimization on board and are able to communicate with the world of automation. This paper will show, that the innovation trends of the last years are supporting the way towards digitalization and Industrial Internet of Things. There are already a lot of different approaches to establish vacuum and pneumatic systems as adequate elements of the digitalized world. It will also be shown, that fluid technology still is facing tremendous challenges It will be not sufficient to equip the systems with more functionality and better communication. It will be essential, that from the interpretation and correlation of data will be derived valuable services with real customer benefit. This should happen under control of the vendors of smart field devices in fluid technology. Then it will be possible to turn this new kind of value generation also into new business models.

Pneumatic linear drives are widely used in manufacturing, mainly for handling tasks. Due to rising interest in environmental matters and increasing energy costs, energy efficiency has become a major issue in industrial applications. There is a growing competition between pneumatic and electromechanical drives. Pneumatic drives are said to have a lower efficiency while the initial costs of electromechanical drives are higher. The operating costs of electromechanical as well as pneumatic drives are induced by their exergy efficiency. The efficiency of the drives depends on parameters like cycle time, load applied to the cylinder and its acceleration and velocity. Former research did only provide limited data on the influence of these parameters. The paper provides an overview on the exergy efficiency of pneumatic and electromechanical drives and its dependency on the mentioned parameters. Since electromechanical drives are often used to replace pneumatic drives both technologies are examined in typical applications for pneumatic drives, including horizontal and vertical movement and sustaining a load for different periods in vertical usage.