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Research Progress on Hydraulic Fluid and Hydraulic Systems
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Research Progress on Hydraulic Fluid and Hydraulic Systems

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Mechanical Engineering".

Deadline for manuscript submissions: closed (20 February 2025) | Viewed by 13583

Special Issue Editors

Prof. Dr. Vito Tič

E-Mail Website
Guest Editor
Faculty of Mechanical Engineering, University of Maribor, SI-2000 Maribor, Slovenia
Interests: hydraulics; pneumatics; automation; Industry 4.0; maintenance; condition monitoring; testing device
Prof. Dr. Darko Lovrec

E-Mail Website
Guest Editor
Faculty of Mechanical Engineering, University of Maribor, SI-2000 Maribor, Slovenia
Interests: hydraulics and pneumatics; automation; maintenance; development; testing

Special Issue Information

Dear Colleagues,

Progress in the field of hydraulic drive and control technology is seen not only in the field of components and systems, but also in hydraulic fluids. At the forefront of the development of hydraulic components and systems are ever-higher operating pressures, tighter tolerances in components, demands for greater efficiency, new materials and higher energy density of components and systems. Hydraulic fluids with their material properties must also adapt to these trends and follow them. Hydraulic systems are smaller, and so residence times are shorter and circulation numbers are higher; the desired temperature operating range should be as wide as possible, and both the energy efficiency and environmental friendliness are improved. There is also a demand for the universal use of the liquid, or for the fulfillment of special operating conditions and requirements, such as those arising from difficult, harsh operating conditions or special use cases.

The subject matter of this Special Issue relates to the latest developments in the field of hydraulic fluids and corresponding hydraulic systems. It covers a very wide area, from innovations and findings related to different types of liquids to their individual material properties and to testing and areas of application, and on the other hand, to the systems, which also have to be adopted for the new fluid types. It also addresses the field concerned with the energy suitability of the used liquid as well as issues of its environmental suitability.

Prof. Dr. Vito Tič
Prof. Dr. Darko Lovrec
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • hydraulic fluids
  • hydraulic systems
  • conventional
  • alternative and new fluids
  • energy saving fluids
  • high-performance fluids
  • material properties
  • additives
  • operational conditions
  • testing
  • material compatibility
  • standards
  • applications

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Published Papers (7 papers)

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Research

24 pages, 14227 KiB  
Article
Polynomial Regression-Based Predictive Expert System for Enhancing Hydraulic Press Performance over a 5G Network
by Denis Jankovič, Miha Pipan, Marko Šimic and Niko Herakovič
Appl. Sci. 2024, 14(24), 12016; https://doi.org/10.3390/app142412016 - 22 Dec 2024
Viewed by 1160
Abstract
In industrial applications, hydraulic presses maintain workloads by controlling the hydraulic cylinder to extend and retract, ensuring optimum tracking performance in terms of position and force. Dealing with nonlinear and multinode systems, such as hydraulic systems, often requires an advanced approach that frequently [...] Read more.
In industrial applications, hydraulic presses maintain workloads by controlling the hydraulic cylinder to extend and retract, ensuring optimum tracking performance in terms of position and force. Dealing with nonlinear and multinode systems, such as hydraulic systems, often requires an advanced approach that frequently includes machine learning and artificial intelligence methods. Introducing an adaptive control system to significantly improve the response of hydraulic presses is a challenge. Therefore, a polynomial regression model predictive control (PR-MPC) mechanism is proposed in this paper to compensate for external disturbances such as the forming processes and friction dynamics. Using polynomial regression modeling and least squares optimization, the approach produces highly accurate data-driven models with an R2 value of 0.948 to 0.999. The simplicity of polynomial regression facilitates the integration of smart algorithms into an expert system with additional decision-making rules. Remote adaptive control integrated within a 5G network is based on I 4.0 distributed system guidelines that provide insights into the behavior of the hydraulic press. The results of real-time experiments have shown that the PR-MPC mechanism integrated into the expert system reduces the absolute response error of the hydraulic press by up to 98.7% compared to the initial control system with a PID regulation. Full article
(This article belongs to the Special Issue Research Progress on Hydraulic Fluid and Hydraulic Systems)
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13 pages, 3211 KiB  
Article
Dependence of the Preload on the Tightening Torque for Hydraulic Plugs
by Jurij Hladnik, Franc Majdič, Anže Čelik and Boris Jerman
Appl. Sci. 2024, 14(24), 11920; https://doi.org/10.3390/app142411920 - 19 Dec 2024
Viewed by 817
Abstract
In hydraulics, threaded plugs are used to close various manufacturing holes and other fluid channels. They are preloaded to ensure sufficient sealing force. Since the range of recommended thread and underhead friction coefficients for preloaded threaded connections in the literature is very wide, [...] Read more.
In hydraulics, threaded plugs are used to close various manufacturing holes and other fluid channels. They are preloaded to ensure sufficient sealing force. Since the range of recommended thread and underhead friction coefficients for preloaded threaded connections in the literature is very wide, they are not suitable for accurate determination of the preload–torque relationships of plug–valve connections. In the study, two non-standard plugs with metric threads were equipped with strain gauges and repeatedly tightened three times in valve housings under lubricated and unlubricated conditions. The preload and tightening torque were measured. (1) Although the plug–valve connections had a similar geometry with the same surface roughness of the contacting surfaces, the average overall friction coefficient (uniform thread and underhead friction coefficient) and torque coefficient differed between the two connections in the unlubricated and lubricated conditions by 16% and 18%, respectively. This indicates that even small geometrical differences can have a considerable influence on these coefficients. The overall friction and torque coefficients were between 8% and 17% higher in the unlubricated condition than in the lubricated condition (not statistically proven). (2) The overall friction and torque coefficients decreased with repeated tightening under lubricated conditions. This influence decreased with the number of tightening repetitions. (3) Consideration of the minimum and maximum thread and underhead friction coefficients given in VDI 2230 would lead to an error in the estimated preload of −15% to +86%. In conclusion, for accurate determination of the preload–torque relationship of the plug–valve connections, measurements considering repeated tightening are crucial. These should be performed for each type and size of plug–valve connection separately. To minimize the repeated tightening influence, it is recommended to re-tighten the connections several times before leaving production. Full article
(This article belongs to the Special Issue Research Progress on Hydraulic Fluid and Hydraulic Systems)
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17 pages, 6478 KiB  
Article
Investigation of Innovative High-Response Piezoelectric Actuator Used as Smart Actuator–Sensor System
by Marko Šimic and Niko Herakovič
Appl. Sci. 2024, 14(18), 8523; https://doi.org/10.3390/app14188523 - 22 Sep 2024
Viewed by 2108
Abstract
This paper presents an experimental analysis of a high-response piezoelectric actuator system for the modular design of hydraulic digital fluid control units. It focuses on determining static and dynamic characteristics, forming the basis for developing a smart Industry 4.0 component that incorporates both [...] Read more.
This paper presents an experimental analysis of a high-response piezoelectric actuator system for the modular design of hydraulic digital fluid control units. It focuses on determining static and dynamic characteristics, forming the basis for developing a smart Industry 4.0 component that incorporates both actuator and sensor function. The design process examines the main challenges, advantages, disadvantages, and working principles to define parameters that impact the actuator’s behaviour and performance. The new piezoelectric actuator system features three piezoelectric stack actuators in series, enabling simultaneous actuation and sensing by applying and measuring the electrical voltage at each piezo element. The experimental setup and test methodology are explained in detail, revealing that the new design, combined with an appropriate open-loop or closed-loop control method, offers superior actuator stroke control, high stroke resolution, and a high-dynamic step response. This paper proposes a concept of a smart piezo actuator system focused on I4.0 and an actuator administration shell, integrated with 5G and RFID technology, which will allow automatic plug-and-play functionality and efficient interconnection, communication, and data transfer between the hydraulic valve and the piezoelectric actuator system. Full article
(This article belongs to the Special Issue Research Progress on Hydraulic Fluid and Hydraulic Systems)
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16 pages, 4442 KiB  
Article
Analysis of Underlapped Symmetrically Ported Valve-Controlled Asymmetric Cylinder Drive
by Huankun Wang, Man Xu and Zijian Cao
Appl. Sci. 2024, 14(7), 2870; https://doi.org/10.3390/app14072870 - 28 Mar 2024
Viewed by 909
Abstract
The valve-controlled cylinder drive system is the most common type among hydraulic applications. Nonlinear behaviour in such systems is inevitable when the valve spool is around its null position. We utilised the component linking method to investigate the nonlinearities in a Moog valve-controlled [...] Read more.
The valve-controlled cylinder drive system is the most common type among hydraulic applications. Nonlinear behaviour in such systems is inevitable when the valve spool is around its null position. We utilised the component linking method to investigate the nonlinearities in a Moog valve-controlled asymmetric cylinder drive system by simulation in Fortran, in which a generalised concept is introduced and validated by comparing to the experimental results. An X factor is proposed in the generalised concept to describe the asymmetric cylinder state, which is a constant when the cylinder is extending or retracting, but numerically calculated when the valve spool is in the underlap region. This analytical solution is approximately 200 times more computationally efficient than the numerical solution method. This paper utilises the component linking method to simulate the Moog valve-controlled asymmetric cylinder drive system in Matlab Simulink, and proposes an analytical solution for the X factor when the valve spool is in the underlap region. This analytical solution is approximately 200 times more computationally efficient than the numerical solution method. Full article
(This article belongs to the Special Issue Research Progress on Hydraulic Fluid and Hydraulic Systems)
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14 pages, 966 KiB  
Article
Ionic Hydraulic Fluids and Seal-Material Compatibility
by Darko Lovrec, Roland Kalb and Vito Tič
Appl. Sci. 2024, 14(5), 2187; https://doi.org/10.3390/app14052187 - 5 Mar 2024
Cited by 2 | Viewed by 1968
Abstract
Manufacturers of hydraulic fluids invest a lot of effort and resources in improving their physico-chemical properties, with the goal of getting as close as possible to the properties of an ideal hydraulic fluid. It should be non- flammable, environmentally friendly, sustainable and should [...] Read more.
Manufacturers of hydraulic fluids invest a lot of effort and resources in improving their physico-chemical properties, with the goal of getting as close as possible to the properties of an ideal hydraulic fluid. It should be non- flammable, environmentally friendly, sustainable and should have excellent physical and chemical properties. After decades of development in the field of ionic liquids and the search for an ionic liquid suitable for use in hydraulic systems, ionic hydraulic liquids are now already in industrial use, especially on devices that operate in harsh and risky operating conditions. Since ionic hydraulic fluids are a completely new type of hydraulic fluid, one of the issues is their compatibility with the materials present in the hydraulic components, including all the seals. This paper refers to the process of testing the compatibility of hydraulic seal materials with different types of ionic hydraulic fluids according to the standardized percentages and recommendations, with emphasis on changes in the swell, shrinkage and hardness of the seals. The presented results are a useful guide for selecting suitable seal materials in case of using high-tech ionic hydraulic fluids. Full article
(This article belongs to the Special Issue Research Progress on Hydraulic Fluid and Hydraulic Systems)
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20 pages, 8807 KiB  
Article
Degradation of Hydraulic System due to Wear Particles or Medium Test Dust
by Nejc Novak, Ana Trajkovski, Mitjan Kalin and Franc Majdič
Appl. Sci. 2023, 13(13), 7777; https://doi.org/10.3390/app13137777 - 30 Jun 2023
Cited by 8 | Viewed by 3502
Abstract
Contamination in hydraulic systems is the cause of 70% of failures. This study highlights the performance degradation caused by solid particle contamination of hydraulic components: hydraulic gear pump, 4/3 valve, and orbital motor. Experimental durability tests of components with wear particles and test [...] Read more.
Contamination in hydraulic systems is the cause of 70% of failures. This study highlights the performance degradation caused by solid particle contamination of hydraulic components: hydraulic gear pump, 4/3 valve, and orbital motor. Experimental durability tests of components with wear particles and test dust are used to investigate the effects of accelerated wear caused by these two types of contaminants. Results show that oil contaminated with wear particles reduces the volumetric efficiency of the gear pump by 18% and the hydraulic valve by only 0.8%, while oil contaminated with test dust reduces the efficiency of the pump by 76% and the hydraulic valve by 0.9%. This research provides insights for accelerating hydraulic component testing to improve system reliability and longevity. Full article
(This article belongs to the Special Issue Research Progress on Hydraulic Fluid and Hydraulic Systems)
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14 pages, 5522 KiB  
Article
Performance of Polymer Composites Lubricated with Glycerol and Water as Green Lubricants
by Ana Trajkovski, Nejc Novak, Jan Pustavrh, Mitjan Kalin and Franc Majdič
Appl. Sci. 2023, 13(13), 7413; https://doi.org/10.3390/app13137413 - 22 Jun 2023
Cited by 6 | Viewed by 2082
Abstract
The study analysed the tribological performance of five different polymer composites: polyetheretherketone reinforced with 30% carbon fibres—PEEK CF30, polyetheretherketone reinforced with 10% carbon fibres, 10% graphite and 10% polytetrafluoroethylene—PEEK MOD, polytetrafluoroethylene reinforced with 25% carbon fibres—PTFE CF25, polyoxymethylene with 30% carbon fibres—POM CF30 [...] Read more.
The study analysed the tribological performance of five different polymer composites: polyetheretherketone reinforced with 30% carbon fibres—PEEK CF30, polyetheretherketone reinforced with 10% carbon fibres, 10% graphite and 10% polytetrafluoroethylene—PEEK MOD, polytetrafluoroethylene reinforced with 25% carbon fibres—PTFE CF25, polyoxymethylene with 30% carbon fibres—POM CF30 and ultra-high molecular weight polyethylene—UHMW PE. The polymers were tested under the sliding regime of a reciprocating stainless-steel ball on a polymer disc, with test parameters expected for hydraulic valves. Two environmentally safe lubricants were used: glycerol and water. The selected polymer materials and their tribological properties were compared based on the coefficient of friction and the specific wear rate. The worn surfaces were examined using scanning electron microscopy, and the transfer film was analysed using the energy dispersive spectroscopy technique. When tested in glycerol, a comparable and low coefficient of friction was measured for all polymers (~0.02). At the same time, a significantly lower coefficient was measured for all polymers in glycerol compared to water-lubricated conditions (~0.06–0.22). The polymers differed in the measured specific wear rate, which increases significantly in water for all polymers. A lower specific wear rate was measured for three polymers with higher microhardness: PEEK CF30, PEEK MOD and POM CF30. In water, PEEK CF30 showed superior tribological properties under harsh conditions but was well followed by POM CF30, which showed the most intense transfer film. Full article
(This article belongs to the Special Issue Research Progress on Hydraulic Fluid and Hydraulic Systems)
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