Validation of a soft sensor network for condition monitoring in hydraulic systems

With increasing digitization, models are more important than ever. Especially their use as soft sensors during operation offers opportunities in cost saving, easy data acquisition and therefore additional functionality of systems. In soft sensor networks there is redundant data acquisition and consequently the occurrence of inconsistent values from different soft sensors is encouraged. The resolution of these data-induced conflicts allows for the detection of changing components characteristics. Hence soft sensor networks can be used to detect wear in system components. In this paper this approach is validated on a test rig. It is found, that the soft sensor network is capable to determine wear and its extent in eccentric screw pumps and valves via data induced conflicts with relatively simple models

Ähnlichkeitsbeziehungen bei Verdrängermaschinen - eine einheitliche Wirkungsgradmodellierung

Verdrängermaschinen zeichnen sich durch ihr breites Einsatzspektrum aus. Dies zeigt sich in der Vielzahl zum Einsatz kommender Medien und in der Vielfalt konstruktiver Ausführungen. Aufgrund dieser Vielfalt ist eine einheitliche Wirkungsgradmodellierung, die für eine konsistente energetische Bewertung von Maschinen notwendige Voraussetzung ist, bisher nur in Ansätzen gelungen. Die hier vorgestellte dimensionsanalytische Modellierung ermöglicht nunmehr eine kompakte und typenunabhängige Beschreibung des Wirkungsgrads anhand lediglich folgender vier dimensionslosen Kenngrößen: (i) Spezifischer Druck, (ii) Reynoldszahl, (iii) spezifische Nachgiebigkeit und (iv) relativer Spalt. Im Modell unterscheiden sich die Maschinentypen allein durch den relativen Spalt. Maschinen gleichen Typs ordnen sich zu einer Spaltklasse. Dies ist das Ergebnis der Modellanwendung auf vier verschiedene Maschinentypen mit 155 unterschiedlichen Größen und über 2680 Betriebspunkten. 1.Kernaussage: Die energetische Effizienz von Verdrängermaschinen lässt sich typunabhängigvon nur vier dimensionslosen Größen darstellen. 2.Kernaussage: Unterschiedliche Maschinentypen unterscheiden sich im Rahmen des Modellsallein im relativen Spalt. Die Spaltklasse ψ/ψref wird als neue charakteristische Größe für dieverschiedenen Maschinentypen eingeführt

A Similarity based Efficiency Model of Spindle Screw Pumps

Spindle screw pumps are used in numerous different applications and industrial sectors. When selecting a suitable spindle screw pump for a specified application, manufacturers are often confronted with a lack of comparable measurement data for the desired combination of operating conditions and pumping fluid. Consequently, the volumetric and mechanical-hydraulic efficiency of a pump under the operating conditions of the application need to be estimated. In this context, this paper discusses the application of similarity for three-spindle screw pumps and introduces a similarity based efficiency model. The model is validated by means of a measured pump characteristic at different operating conditions varying pressure, rotational speed and the viscosity of the pumping fluid. The validation results prove that a pump characteristic can be represented over a wide operating range based on similarity. An estimation of the volumetric and the mechanical-hydraulic efficiency at a changed viscosity is achieved with high accuracy. Furthermore, a new approach to monitor and to evaluate manufacturing uncertainty based on the model parameter relative gap is presented. Finally, the paper gives an outlook on future experimental investigations at TU Darmstadt on model series of three-spindle screw pumps containing pumps of different displacement volume

ERP Positive Displacement Pumps – Physically Based Approach Towards an Application-Related Efficiency Guideline

There is a high probability that the Ecodesign Directive of the European Union will include positive displacement pumps in the near future. The Ecodesign Directive sets the framework of a legislative efficiency guidelines of energy-related products (ERP) to reduce their energy consumption. However, positive displacement pumps are used in various applications that affect the attainable efficiencies. Consequently, a regulation for all positive displacement pumps on the pure basis of the efficiency is not sufficient. This paper illustrates the necessity of an application-related consideration of positive displacement pumps and provides two major steps towards an application-related efficiency guideline: firstly, a concept of data acquisition and analysis is presented and discussed. The concept aims to identify the energetically relevant applications of positive displacement pumps and to determine a relationship between the various pump types, their applications and energy consumption. Secondly, a physically based, type independent and easy to apply model of the efficiency of positive displacement pumps is presented and its suitability in the context of an efficiency guideline is discussed. The model has been introduced by the authors recently and describes the efficiency as a function of four dimensionless variables. A parameter identification and model application on four different pump types and 155 different pump sizes including 2680 operating points proves its practicability to compare different pump types

Concept validation of a soft sensor network for wear detection in positive displacement pumps

With increasing digitization, models are not only used during the design phase but throughout the life cycle of systems. Especially the use of models as soft sensors during operation offers opportunities in cost saving, easy data acquisition and therefore additional functionality of systems. Soft sensors are models of components that use easily accessible auxiliary quantities to estimate target quantities that are difficult to measure. Networks of soft sensors are the prerequisite for redundant data acquisition in a system and thus encourage the occurrence of data-induced conflicts, i.e., inconsistent values from different soft sensors, which may result from: (i) the breakdown or defect of a measuring sensor, (ii) model uncertainties of the soft sensors, (iii) change of component characteristics, e.g. due to wear. The resolution of these conflicts either leads to greater confidence in the model-based system quantities or allows the detection of changing components characteristics. Hence soft sensor networks can be used to detect wear in system components. Wear in pumps and valves leads to a change in the flow rate and the inner leakage. Therefore, the detection of wear with soft sensors requires the detection of small changes in the system flow rates. In the full paper an analysis of the influence of small flow rate variations on redundant soft sensor outputs is carried out. For this, small flow rate variations are implemented on a test bench for positive displacement pumps. Furthermore, a systematic analysis of parameter and data uncertainties and their propagation in models for positive displacement pumps is carried out. The resulting flow rates and the measurement uncertainties from the models of the pump and the throttle valve of the test bench are compared and discussed with respect to data induced conflicts and the detection of wear

Modeling the Efficiency of External Gear Pumps Based on Similarity Considerations

Gear pumps are used in numerous different applications and industrial sectors. However, when selecting a suitable gear pump for a specified application, manufacturers are often confronted with a lack of comparable measurement data for the desired combination of operating conditions and pumping fluid. Consequently, an estimation of the volume flow rate and the power consumption of a pump under the operating conditions of the application is necessary. In this context, this paper discusses the application of similarity on external gear pumps and presents its validation by means of measured pump characteristics. Seven gear pumps of different displacement volume are measured at different operating conditions varying pressure, rotational speed and the viscosity of the pumping fluid. The validation results prove that similarity is useful to represent a pump’s characteristic over a wide operating range. The prediction of the volume flow rate and the power consumption at a changed viscosity show good accuracy. However, the scaling of the pump characteristic based on the displacement volume show contradictory results

Hydrospeicher mit Sorbentien - Verhalten, Modellierung und Diskussion

Werden Hydrospeicher in Hydrauliksystemen zur Speicherung von Energie eingesetzt, müssen bei der Auslegung und zukünftig auch im Betrieb Zeitbetrachtungen der Zustandsänderungen des Speichermediums durchgeführt werden. Neben einem hohen Wirkungsgrad sind bei mobilen Anwendungen insbesondere die Reduktion von Gewicht und Bauraum von hohem Interesse. Unter dieser Zielsetzung stellen Speicher mit Sorbentien eine innovative und vielversprechende Entwicklung dar. Das hier vorgestellte allgemeine physikalische Modell ermöglicht nunmehr die Beschreibung solcher Hydrospeicher unter Berücksichtigung der Sorptionsvorgänge. Die Ergebnisse werden anhand einer Analyse des Zeitverhaltens diskutiert und konventionellen Speichern gegenübergestellt

Towards digitalization of hydraulic systems using soft sensor networks

Today buzzwords like “smart machine” and “intelligent component” dominate the discussion about digitalization in the fluid power domain. However, the engineering fundamentals behind the words “smart” and “intelligent” often remain unclear. A common and target-oriented discussion needs transparent approaches including the applied technical system understanding. Therefore, t his paper presents new concepts of soft sensor networks which allow the aggregation of information about fluid systems from heterogeneous sources. Soft sensors presented in this paper are physical models of system components that ensure transparency. Soft sensors and soft sensor networks are applied on exemplary hydraulic systems on three different levels: (i) the sensor level, (ii) the component level and (iii) the system level

ERP Positive Displacement Pumps - Experimental Validation of a Type-Independent Efficiency Model

The European Union pursues ambitious objectives reducing greenhouse gas emissions. Thus, energy related products (ERP) are regulated by the European Union's Ecodesign Directive in terms of energy efficiency. Until now positive displacement pumps are not involved. However, considering the EU strategy in similar domains, the probability is high that the Ecodesign Directive will focus on positive displacement pumps in the future due to the large quantity of sold pumps and the collective energy consumption. Positive displacement pumps are characterized by their wide range of applications, e.g. mobile hydraulics, chemical, or food industry, with very different application-relevant requirements (low pulsation, high precision etc.). For this reason, a variety of pump designs exist, e.g. piston pumps, gear pump or screw pumps. From a scientific and technical point of view, legal requirements are considered adequate if they take into account the physical behavior of the machines as well as the application-relevant requirements. Against this background, the authors presented a physically based approach towards an application-related efficiency guideline at IREC 2016 considering a methodology to identify the energetically relevant applications of positive displacement pumps and introducing a physically based, type independent and easy to apply efficiency model. Since 2017, within the framework of an AiF project, the authors collaborate with the VDMA to validate the above mentioned efficiency model by means of precise experimental measurements. Until the submission of this paper, efficiency measurements are conducted on gear pumps, screw pumps and rotary piston pumps. The full paper presents the validation results and discusses the conclusions in the context of a future energy efficiency guideline of positive displacement pumps

Wirkungsgradmodell rotierender Verdrängerpumpen auf Grundlage von Ähnlichkeitsbeziehungen

Der Wirkungsgrad von rotierenden Verdrängerpumpen wird im Rahmen der allgemeinen Bemühungen um Energieeffizienz zukünftig an Bedeutung gewinnen. Eine zentrale Bedeutung kommt in diesem Zusammenhang der Berechnung des Wirkungsgradverhaltens von rotierenden Verdrängerpumpen zu, sowohl hinsichtlich möglicher legislativer Anforderungen als auch durch Bestrebungen auf Anwenderseite, den Energieverbrauch von Verdrängerpumpen bei der Anlagenplanung zu berücksichtigen und zu optimieren. Dazu bedarf es physikalisch basierter und einfach anwendbarer Modelle. Darunter werden stationäre 0D-Modelle verstanden, die das Wirkungsgradverhalten mit algebraischen Gleichungen in Abhängigkeit der relevanten Einflussgrößen beschreiben. In diesem Kontext wird in dieser Arbeit die Frage nach Ähnlichkeitsbeziehungen gestellt, die sich für die Wirkungsgradmodellierung rotierender Verdrängerpumpen sinnvoll anwenden lassen. Zur Beantwortung werden sowohl theoretische als auch experimentelle Untersuchungen an den drei Pumpentypen dreispindlige Schraubenpumpe, Außenzahnradpumpe und zweiflügelige Drehkolbenpumpe durchgeführt. Der Schwerpunkt der theoretischen Untersuchungen ist die Herleitung problemspezifischer dimensionsloser Größen mittels Dimensionsanalyse, anhand derer der Wirkungsgrad für die verschiedenen Pumpentypen einheitlich dargestellt werden kann. Ferner werden zwei semi-axiomatische Modelle für die volumetrischen und mechanisch-hydraulischen Verluste aufgestellt, auf deren Grundlage das Wirkungsgradverhalten bei quantifizierter Modellunsicherheit vorhergesagt werden kann. Die Messung von stationären Kennfeldern an Baureihen von Schrauben- und Zahnradpumpen sowie an einer einzelnen Drehkolbenpumpe mit insgesamt vier unterschiedlichen Hydraulikölen stellen die experimentellen Untersuchungen dar. Im Rahmen der Modellvalidierung werden die Abweichungen der Modellvorhersagen anhand der experimentellen Vergleichsdaten sowie die Unsicherheit der Modellvorhersagen über ein Vertrauensintervall dargestellt, diskutiert und abschließend bewertet