International Journal of Fluid Power

Editorial

Jürgen Weber — 2024-12-19

It is a great pleasure for me to introduce this special issue “14th International Fluid Power Conference”. This special issue presents six fascinating con- tributions, which were originally presented at the International Fluid Power Conference (IFK) in March 2024 in Dresden and have been revised and expanded by their authors with their newest research results.

The IFK is one of the world’s most significant scientific conferences on Fluid-Mechatronic Systems, which offers a common platform for the presen- tation and discussion of trends and innovations to manufacturers, users and scientists. The Chair of Fluid-Mechatronic Systems (LFD) at the TU Dresden was organising and hosting the IFK for the seventh time. The organization and the conference location alternates every two years between Dresden at the LFD and Aachen at the Institute for Fluid Power Drives and Systems (ifas). The 14th IFK covered under the motto “Fluid Power: Sustainable Productivity” a wide range of topics from component developments like pumps or valves towards system applications for mobile, industrial or pneu- matic applications in 91 peer-reviewed and non-peer-reviewed presentations, respectively papers. Due to this almost unmanageable number of exciting contributions, it is a great pleasure for me to present this special issue, which represents a small and finely sorted selection of particularly promising and high rated contributions of the IFK.

Energy Efficient Excavator Implement by Electro-Hydraulic/Mechanical Drive Network

Lasse Schmidt — 2024-12-19

The focus on electrification of mobile working machines is increasing in industry as well as in the academic community, and ways to realize both technically and commercially feasible solutions are continuously being pursued. At this point, solutions presented by industry has mainly focused on avoiding internal combustion engines by installing cable or battery fed electric motors powering the main pump(s) which supplies the working hydraulics. However, rotary functions are sought powered directly by electro-mechanical drives, not including hydraulics. In this endeavor a main challenge is the operation of linear actuators that remain controlled by hydraulic control valves. The associated throttle losses necessitates large batteries to be compensated or alternatively results in low machine uptimes, potentially rendering electrified machines commercially infeasible. An obvious approach to avoid throttle losses may be the replacement of valve-controlled linear actuators by electro-mechanical solutions in low to medium force applications, whereas heavy duty working machines subject to large forces such as medium/large excavators may benefit from standalone electro-hydraulic primary controlled/variable-speed drives. Utilization of such solutions will substantially increase the energy efficiency due to absent or at least limited throttle losses, and the electric power sharing and electric energy recuperation capabilities offered by common DC-bus’ and batteries. However, such standalone solutions/drives must be able to meet both the required maximum force and maximum speed, and even thought these maximum quantities seldom are required concurrently, these requirements may render the associated motors and inverters somewhat large. Hence, applying such solutions may lower the battery requirements, but require substantial levels of motor and inverter power to be installed, which again may compromise the commercial feasibility. This paper presents a potentially feasible alternative to these solutions for an excavator implement, in the form of an electro-hydraulic/mechanical drive network. This is applied for actuation of three linear implement functions as well as the rotary swing function. The realization of the electro-hydraulic/mechanical drive network involves chamber short-circuiting and electro-hydraulic variable-speed displacement machines enabling electro-hydraulic power sharing. The proposed drive network is compared to a highly efficient standalone dual motor electro-hydraulic drive solution as well as a separate metering valve drive supplied by a battery fed electro-hydraulic pump. Results demonstrate that, compared to the standalone dual motor electro-hydraulic drive solution, the proposed drive network is realizable with similar energy efficiency and hydraulic displacement but less installed motor power and likely less integration effort, rendering this a more sustainable and cost-efficient solution. Finally, besides being realizable with less installed motor power and hydraulic displacement, the proposed drive network shows substantially improved energy efficiency compared to the separate metering valve drive solution.

Fast Computation of Hydrodynamic Pressure in Lubricated Contacts: Which Lp Loss is Most Suitable for Physics-Informed Neural Networks Solving the Reynolds Equation?

Faras Brumand-Poor — 2024-12-19

The frictional behavior of pneumatic seals significantly impacts the functionality of fluid power systems, particularly in fast-switching applications where precision and responsiveness are critical. However, the complex relationship between component properties and friction often makes experimental characterization infeasible or prohibitively expensive. To address this challenge, the Institute for Fluid Power Drives and Systems (ifas) developed the ifas Dynamic Seal Simulation (DDS), an iterative elastohydrodynamic lubrication (EHL) simulation capable of accurately solving the relevant partial differential equations (PDEs) [3]. Since iterative solvers are computationally intensive, neural networks have been explored as a more efficient alternative. While traditional neural networks offer computational advantages, they often lack the ability to understand the physical context of the systems they model, potentially limiting their accuracy and reliability. Physics-Informed Neural Networks (PINNs) have been introduced to overcome these limitations. PINNs integrate the governing physical laws directly into the training process, allowing them to grasp the system’s physical context. This approach opens up new possibilities, including more robust training and the ability to extrapolate beyond the training domain, thereby providing a more reliable and efficient tool for modeling the friction of seals in fluid power systems. In this paper, a previously validated hydrodynamic PINN framework [8, 9] is utilized to solve a variant of the averaged Reynolds equation across three scenarios: divergent, convergent, and curved gaps. The investigation focuses on four p-norm training metrics: L1, L2, L²₂, and L∞. The results indicate that the commonly used L²₂ metric is the most suitable for the scenarios examined.

Comparative Analysis of External Gear Machine Performance Considering Deformation and Thermal Effects

Ajinkya Pawar — 2024-12-19

The energy efficiency of external gear pumps (EGPs), as in other positive displacement machines for high-pressure applications, is significantly influenced by the power losses occurring in the lubricating interfaces that seal the internal displacement chambers. Therefore, it is crucial to account for these interfaces accurately when developing predictive simulation tools. However, in literature various modeling approaches can be found that consider different assumptions regarding the analysis of these interfaces. This makes it challenging for a designer to determine which physical domains needed to be modelled accurately in order to assess the EGP performance.

This paper addresses the above research question by leveraging a comprehensive simulation tool (Multics-HYGESim) developed at the authors’ research team which includes thermal-tribological considerations pertaining to the meshing of the gears, the lubricating films at the tooth tip interfaces, at the journal bearings, and at the lateral interfaces. The tool considers realistic fluid properties, including the effects of cavitation and aeration, mixed lubrication effects, as well as material deformation effects for the gears, lateral bushings and the EGP housing. Additionally, recent advancements to the model, presented for the first time in this work, include coupled thermal analysis of the EGP, including fluid domain, lubricating interface domain and solid domain. The heat transfer evaluation in the solid domain allows predicting the body temperatures along with their thermal deformation. Material deformation effects strongly affect the internal balancing features of an EGP as well as its internal pressurization. All the mutual interaction between the geometrical domain, the body motions and their deformation, the fluid dynamic and the thermal domains make a realistic quantification of these effects difficult in simulation.

Using a commercial EGP as a reference, for which experimental results are available concerning volumetric and hydromechanical efficiency, this paper demonstrates how predictions can vary based on different simulation assumptions regarding body and lubricating film behavior. The paper will present simulated predictions starting from a basic rigid body assumption that considers only body motion and analytical formulations of lubricating interfaces, to simulation model cases of progressively increasing in complexity to account for deformations different bodies i.e. the gears, bushings and the housing. The most complex case would include evaluation of thermal behavior along with deformation effects. A detailed distribution of power loss and leakages arising from different sources of hydromechanical and volumetric losses is presented for all cases under consideration. The results will offer valuable insights to EGP designers, enabling them to understand the strengths and limitations of different modeling assumptions on the prediction of EGP behavior, especially regarding the effects of body deformation.

Determination of the Flow Angle in Hydraulic Components

Lennard Günther — 2024-12-19

The paper presents a general analytical equation for the determination of the flow angel in hydraulic components like valves and pumps. Exemplary, the method is applied to two different valve concepts – a cartridge valve and a rotary slide valve.
cos(ε_avg)=1/2(cos(α_l)−cos(α_r))

The huge advantage of this equation is the simple expression with no dependencies on operation conditions. Only the geometry is important. The underlying phenomenon is valid for turbulent flows. Thus it is useable for almost all hydraulic applications. It makes it possible to predict the flow force as well as to optimize the flow geometry. It describes the flow angle of the free jet behind a narrow section (e.g. a control edge of a valve). By a suitable choice of the angle of the free jet, the flow force can be reduced by changing the direction of the outgoing impulse. With regard to cavitation, the impact of the free jet can be shifted and thus the cavitation erosion can be shifted or weakened.

This paper deals with the investigation of the flow angle of free jets as well as the prediction of the flow force in valves without CFD. For the illustration a cartridge and a rotary slide valve are used as technical applications. In the first section, geometric factors influencing the flow angle are discussed, as well as the transferability of the results under varying operating conditions (laminar and turbulent). Using a generic minimal model, the behaviour of the flow angle with respect to geometric influence factors and operating conditions is investigated by means of CFD. The results are adapted to real applications in the second section. The direct adjustment of the flow angle results in a significant improvement in the characteristic behaviour of the presented valves (such as flow force and resistance torque). It becomes clear how efficient the adjustment of the flow angle can be if the basis of the formation of the free jet is known. Due to the derivation of the relationship with the help of an abstracted minimal model, the knowledge gained can be used in many ways and can also be transferred to other applications in the field of fluid technology. Optimization processes are more efficiently without using elaborated simulation models e.g. driven by CFD.

Adaptive Meter-out Control of Pneumatic Drives by Using Novel Multi-stable Solenoids

Thomas Kramer — 2024-12-19

Multi-stable solenoids are novel energy-efficient actuators, which combine the continuous adjustability of proportional solenoids with the energy efficiency of polarised magnetic circuits. They can hold any armature position without power supply. Thus, they are well suited for an automation of pneumatic throttle check valves, in order to set the throttle cross-section and thus the cylinder piston velocity to a specific value and hold it for a certain time. This is useful in the context of industry 4.0 to produce on demand with customised piston velocities or to gradually compensate for the increasing frictional forces during cylinder lifetime.

This paper deals with the application of novel multi-stable solenoids to actuate a throttle check valve for an adaptive meter-out control of pneumatic cylinder drives. Therefore, the design of a multi-stable solenoid for a given throttle valve is presented. The functionality of the combination is verified by measurements. The automated throttle is integrated in a simple pneumatic cylinder drive to investigate the adjustability of and disturbance influences to the piston velocity. On that basis, a feed forward and a closed loop control are presented for setting of specific piston velocities.

Advancing Thermal Monitoring in Axial Piston Pumps: Simulation, Measurement, and Boundary Condition Analysis for Efficiency Enhancement

Roman Ivantysyn — 2024-12-19

To prepare today’s fluid power systems for the future digitalization of the industry, it is necessary to improve the information available regarding the current condition of crucial components of the system. Positive displacement machines, which constitute the core of any hydraulic system, play a vital role in this process. Future smart systems will require more information about the current state of the pump such as power usage and efficiency. Current condition monitoring approaches utilize an array of sensors that need to be sampled at high frequency. The transmission, storage, and post processing of this vast amount of data requires an enormous number of resources, especially if exercised at scale. Previous work conducted at the Institute of Mechatronics Engineering at TU Dresden has demonstrated that measuring the temperature in the lubricating gaps can allow for a deeper insight into the tribological mechanisms in these interfaces. Not only can the gap height, viscous friction and leakage be determined from this information, but also crucial information such as wear level and expected component lifespan can be derived from temperature levels with adequate reference models [1–4].

This paper demonstrates that monitoring the thermal condition of the cylinder block is an effective approach to estimate the pump’s efficiency. This will be illustrated through both simulation and measurement, in addition to the pioneering measurement of the heat convection coefficient on the cylinder block surface, a critical boundary condition for the simulation.

To measure the temperature of a moving cylinder block, a 160cc axial piston pump was equipped with a telemetric system, which was specially designed and built for this task. In addition to 20 temperature sensors, four heat convection coefficient sensors were carefully placed inside the cylinder block. High-speed pressure and temperature measurements within the displacement chamber provided further insight into the dynamic thermal behavior, capturing both fluid and wall temperatures in real-time. These measurements not only validated the simulation but also offered a unique perspective on the internal mechanics of an axial piston pump.