Current efficiency measurements of variable hydraulic axial piston pumps are performed with the displacement system locked at maximum volume, thus without the controller. Therefore, the controller’s effect on the efficiency is not quantified at state of the art measurements. Former research on control systems mainly focused on the dynamic behaviour. This paper aims to quantify the losses in the displacement and control system and to research the dependencies of those. Therefore, a test rig is built up at IFAS to measure the control power of displacement controlled pumps. Furthermore, a simulation tool is developed to increase the understanding of the loss mechanisms of the investigated control systems. In conclusion, the paper shows the potential of efficiency improvements for displacement controlled pumps.

In all common hydrostatic pumps, compressibility affects the commutation phases of the displacing chambers, as they switch their connection from/to the inlet to/from the outlet port, leading to pressure peaks, localized cavitation, additional port flow fluctuations and volumetric efficiency reduction. In common pumps, these effects are reduced by proper grooves that realizes gradual port area variation in proximity of these transition regions. This paper presents a method to automatically find the optimal designs of these grooves, taking as reference the case of external gear pumps. The proposed procedure does not assume a specific geometric morphology for the grooves, and it determines the best feasible designs through a multi-objective optimization procedure. A commercial gear pump is used to experimentally demonstrate the potentials of the proposed method, for a particular case aimed at reducing delivery flow oscillations.

This paper describes a high fidelity simulation model for GEROTOR pumps. The simulation approach is based on the coupling of different models: a geometric model used to evaluate the instantaneous volumes and flow areas inside the unit, a lumped parameter fluid dynamic model for the evaluation of the displacing action inside the unit and mechanical models for the evaluation of the internal micro-motions of the rotors axes. This paper particularly details the geometrical approach, which takes into account the actual geometry of the rotors, given as input as CAD files. This model can take into account the actual location of the points of contact between the rotors as well for the actual clearances between the rotors. The potentials of the model are shown by considering a particular GEROTOR design. A specific test set-up was developed within this research for the model validation, and comparisons in terms of steady-state pressure versus flow curves and instantaneous pressure ripples are shown for the reference pump.

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.

Friction force oscillations caused by changing properties of the contact zone between brake disc and pad are well known from various applications. Resulting effects like brake judder are known phenomena in brake technologies and in the scope of various scientific work. A new measure to potentially reduce brake torque oscillations is the active compensation with the use of the control system of a self-energizing hydraulic brake (SEHB). New in comparison to traditional disc brakes is the fact that the brake torque is measured by the pressure in an additional supporting cylinder. Thus, the brake system is able to work in brake torque control mode. Within this paper a dynamic simulation model of the SEHB is shown and evaluated with measurement data achieved from a full scale test rig for railway applications. Based on the simulation model a pressure control strategy is developed to minimize brake torque oscillations of lower frequencies. The control parameters of the simulation are transferred to the experimental setup. Finally, simulation and experimental results are compared. Future work will deal with the development of control strategies to additionally minimize brake torque oscillations of the higher dynamics.

The implementation of an energy recovery system for retreiving otherways wasted energy is an effective method for reducing the overall energy consumption of a mobile machine. In a fork lift, there are two subsystems that can be effectively modified for recovering energy. These are the driveline and the lift/lower function of the mast. This study focuses on the latter by studying a recovery system whose main component is a hydraulic transformer consisting of a hydraulic motor, a variable displacement pump and an induction motor. Since the flow rate/pressure - ratio can be modified, the utilization of the hydraulic transformer enables downsizing of the accumulator volume. However, the decrease of the gas volume leads to an increase in the compression ratio of the accumulator, which in terms leads to higher gas temperatures after charging and consequently to higher thermal losses during holding phase. In order to reduce these losses, a thermally regenerative unit was implemented to the gas volume of an accumulator to reduce the temperature build up during charging. In this study, the effect of improving the thermal characteristics of the accumulator to the efficiency of the whole energy recovery system is investigated by means of measurements.

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.

Dirt ingress in hydraulic cylinders is one of the sources that leads to pollution of hydraulic systems. There are already several test rigs to investigate external contamination mechanisms. However, until now only the behavior of the whole sealing system was analyzed. A new testing method to understand the dirt particle transport between a reciprocating motioned rod and a wiper is presented. The new approach aims to avoid known issues such as limited reproducibility and long duration. The paper describes the test rig design and operating principle. First measurement results are shown.

Air contamination strongly decreases the efficiency of fluid power systems and when the allowable limits are exceeded, the performance of the system deteriorates. The hydraulic reservoir performs the function of releasing the entrained air of the hydraulic system to the surroundings. In recent years, the reservoir design has become an important task in the design of the hydraulic system due to space restrictions forcing the use of small sized reservoirs. Despite this fact, experimental results on an air release are not available. In this paper, an experimental investigation of the air release in hydraulic reservoirs is presented. A test apparatus using an optical method as well as the post-processing of the results is described. These are given in terms of an air release rate for different reservoir designs over a wide range of oil flow rates and air loads. The current study is a significant step forward in the design of fluid power systems, as it provides an experimental procedure to measure the air release in the hydraulic reservoir as well as its quantitative analysis.

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.