Lukas Merkle

Abstract

Gearbox failure in offshore wind turbines can be caused by fatigue damages like tooth fank fracture (TFF) or pitting damage. For damage detection in current applications, simple threshold values for vibration amplitudes are used to initiate a shutdown of the wind turbine. At this time significant damage to the gear is already present and an external maintenance is inevitable. The objective of this experimental study is to determine a better sensor concept for detection of gear damage in wind power drives during operation. The damage needs to be detected at a very early stage before the health condition of the gears becomes critical. Evaluation criteria for comparison of sensor concepts include the earliest possible detection of damage, robust and reliable detection under varying operating conditions, as well as practicality and cost-effectiveness. The test results show, vibration measurement in radial direction and in high frequency ranges is most suitable and most robust for pitting detection during operation. With the best sensor concept in place, it is possible to detect gear damage like pitting at a very early stage of 0.3 % pitting size.

Abstract

Condition monitoring with very early gear damage detection enables remaining useful life prediction and health management of drive units. For a reliable detection of tooth flank damage during operation, a holistic approach combines experimental investigations, physical and AI-based data evaluation and is supplemented by FE and multi-body simulation.

Abstract

Early damage detection in gearbox applications enables the implementation of Prognostics and Health Management (PHM). On the one hand, the earliest possible damage detection provides a precise in-sight into the state of health of a gearbox. In addition, early damage detection offers the possibility to slow down the damage progress and extend the remaining useful life (RUL) by intervening in the operating state at an early damage stage. The main contribution of this work is that existing Machine Learning tools are applied to the challenge of very early damage detection in gearboxes. Thus, the need for complex physically based data evaluation is avoided. The aim of this investigation is a comparison of two different machine learning approaches. To investigate the detection possibilities test bench experiments were conducted with a single stage spur gearbox. For a comprehensive investigation, i.e. to detect damage under different operating conditions, the test runs are carried out at different damage sizes, speeds and torques. Based on the recorded vibration data, the damage detection is examined. Two machine learning approaches of anomaly detection are considered: An encoding approach and a loss approach. The same sparse autoencoder is developed for both approaches Both machine learning approaches are able to detect even the smallest damage of about 0.5 % in most operating states. The loss approach allows the different damage stages to be recognized much more clearly than the encoding approach. The comparison of the different approaches provides valuable insights for the further development of robust damage detection algorithms.

Abstract

The economic efficiency of machinery operation is significantly impacted by maintenance strategies. In the realm of condition-based or predictive maintenance strategies, the early detection of fatigue-induced damages is crucial. Therefore, this study focuses on the early detection of pitting damages during operation. Experimental investigations are conducted on a test gearbox acquiring acceleration data for different sizes of pitting damages under diverse operating conditions. A successful detection of the pitting damages during operation is achieved at a very early stage of progression, with a minimum size of 0.41% of an active tooth flank area. The utilization of design of experiments techniques facilitates the identification of factors influencing the detectability of pitting damages. The obtained results are analysed to elucidate the physical basis for the reliable detection of pitting damages across diverse operating conditions.

Abstract

In critical industrial applications, gearboxes are already equipped with Condition Monitoring Systems (CMS) based on vibration sensors. However, these systems are only developing their full potential if damages can be detected early and if the accumulated sensor data can be assigned to a type of damage and a damage size. The aim of this investigation is a systematic evaluation of gear damages at different stages to use the CMS sensor data for Prognostics and Health Management (PHM). It is also the objective to evaluate different sensor concepts for data acquisition regarding damage detection in gearbox applications. To investigate the detection possibilities on the test bench, a single stage spur gearbox is developed. The test gearbox is used on a test bench, which is designed as electrical load unit consisting of two electric motors. The tooth flanks of the test gears are manufactured with artificial pitting dam-age with different sizes. The test gearbox is equipped with torque, speed and vibration sen-sors. The experiments are statistically designed by means of Design of Experiments (DOE). The factors pitting damage size, rotational speed, torque and viscosity are varied. This offers a valid basis for developing an empiric model that relates the damage size to the observed sen-sor data. Using machine learning approaches, the vibration signal data are analyzed. By means of anomaly detection, early damage stages can be identified during operation. A con-clusion from the acquired sensor data on the extent of damage is possible through the sys-tematic DOE. This enables PHM which allows a more reliable and sustainable operation of drivetrains in industrial plants and systems.

Abstract

Gear failure caused by pitting is one of the leading reasons of downtime in wind turbines. An adaptive operating strategy applies a load reduction of a damaged tooth by the means of torque variation to increase the remaining useful life. For the highest possible increase of service life, a detection of pitting damage at an early stage during operation is necessary. To investigate the detection possibilities on the test rig, a test gearbox is developed. The tooth flanks of test gears are manufactured with artificial pitting damage at different stages. The test gearbox is equipped with various load and vibration sensors mounted at different positions of the housing. The sensors acquire a large amount of data, depending on the size of the damage. The test results are used to train deep neural networks for AI based plant operation. The experiments not only show at which stage pitting damage is detectable, but also form the data basis for AI based condition monitoring of wind power drives.

Abstract

Many failures of wind turbines are due to drive failures caused by pitting. Each failure can be associated with high repair costs and time-consuming repair work. This particularly applies to offshore facilities. For these reasons, increasing the remaining useful life of wind power drives is essential to leave a minimal ecological footprint by simultaneously increasing power output. Pitting damage occurs first on the weakest tooth. Artificial Intelligence is used to apply a local load reduction to a pre-damaged tooth and delay degradation. The other intact teeth compensate for the load reduction in order to achieve a constant average power. To increase the service life of wind power drives and to avoid unexpected failures an adaptive operating strategy can be implemented. With a test gearbox the adaptive operating strategy is examined on a test bench. The test gearbox is equipped with test gears with varying degrees of pre-damage. The objective of the examinations on the test gearbox is to detect pitting damage at the earliest possible stage. The earlier damage is detected, the greater the potential for increasing useful life. For detection, multiple high frequency acceleration sensors are integrated in the gearbox. Using machine learning approaches, the vibration data are analyzed. By means of anomaly detection damage can be identified during operation. Using torque control on the test bench, the load on pre-damaged teeth is minimized depending on the detected damage. In summary, the findings on the test gearbox will provide fundamental knowledge that will enable the implementation of the adaptive operating strategy inwind power drives.

Abstract

Various operating conditions can cause sealing systems to be insufficiently supplied with oil, resulting in starved lubrication. This paper deals with the experimental investigation of starved lubrication operating conditions. For this purpose, the test rig configuration used is introduced. The influence of starved lubrication on 3 different sealing systems was investigated. In addition to a standard elastomeric rotary shaft seal, a multi-lip initially grease-filled elastomeric rotary shaft seal and a PTFE sleeve with circumferential grooves were employed. The results show that the standard rotary shaft seal is unsuitable for the investigated starved lubrication conditions. The other two sealing systems performed better in comparison and are suitable for operation with a starved oil supply, at least for short durations.

Abstract

Elastomeric rotary shaft seals are a common seal type for various industrial applications. They are comparably cheap and easy to use and offer an overall good performance. But the wear behavior of these sealing systems is not fully understood and not predictable so far. If a lip seal fails, it causes high maintenance costs and environmental damage. In this article, various tribological conditions are considered. For this purpose, the sealing systems are tested with multiple operating conditions relevant to practice. Three test series are conducted with rotary shaft seals BAUM5X7 75FKM585 on plunge ground shafts. The tests are carried out with two different circumferential velocities of the shaft (4.2 and 10 m/s), three different oil sump temperatures (40, 80, and 120 °C), two different lubricant types (FVA 3 and PG 3), and five different test durations (between 100 and 625 h). For a complete acquisition of the system condition, all shaft surfaces are measured in 2D and 3D before and after the test runs and the wear of the sealing edges is evaluated with a recently developed laser line triangulation method on the complete circumference of the sealing rings. Results show large amounts of wear, depending significantly on the operating conditions. A strong correlation of the wear effects in the tribocontact area of the sealing system becomes evident. This article helps to understand and avoid critical operating conditions concerning abrasive wear.

Abstract

Elastomeric rotary shaft seals are a common seal type for automotive and industrial applications. The wear mechanism of these sealing systems is not fully understood and not predictable so far. If a lip seal fails, it causes high maintenance costs and environmental damage. In order to investigate the wear mechanism, an empirical test series is conducted with shaft seals on plunge ground shafts. Various tribological conditions are considered, including operating conditions relevant to practice. For a complete acquisition of the system condition, all shaft surfaces are measured 2- and 3-dimensional before and after the test runs. The wear of the sealing edges is evaluated with a recently developed laser line triangulation method on the complete circumference of the sealing rings. Results show large amounts of wear, depending significantly on the operating conditions. We discuss the wear mechanisms and the correlations of wear effects in the tribo contact area of the sealing system.

Abstract

Elastomere Radial-Wellendichtungen werden in fast jedem antriebstechnischen Aggregat eingesetzt. Ohne Abdichtung der Wellendurchtrittstelle ist ein Betrieb unmöglich. Obwohl die Dichtringe millionenfach eingesetzt werden, kommt es immer wieder zum Systemschaden „Leckage“. Die Dichtringe zeigen als tribologischen Primärschaden beispielsweise Verhärtung, Risse oder exzessiven Verschleiß. Eine Berechnung der Lebensdauer ist für RWDR nach wie vor nicht möglich, daher sind Prüfläufe das einzige Werkzeug zur sicheren Auslegung von Dichtsystemen. Die Forschungsvorhaben der Projektreihe 696 haben zum Ziel, KmU und anderen Unternehmen einen Leitfaden zur systematischen Prüfung von Dichtsystemen zur Verfügung zu stellen. Wichtigstes Werkzeug dafür ist der vollständige Gesamtschadenskatalog. Das Wissen aus 696 I bis IV zum Thema Schadenanalyse, einstufigen und wechselnden Belastungen sowie zur Validierung der Ergebnisse unter industriellen Einsatzbedingungen wird in diesem Gesamtbericht zusammengeführt. Die Unternehmen können mit dem Leitfaden Schadensfälle analysieren und angepasste Kollektive für tribometrische Versuche erstellen. Damit können Dichtsysteme untersucht und optimiert werden. Leckage und Imageverlust können sicher vermieden werden. Die Erkenntnisse sind digitalisiert und stehen für den Wissenstransfer zur Verfügung. In der Projektreihe 696 wurden 278 Prüfläufe mit einer kumulierte Versuchslaufzeit von 108.117,4 h (= 12,3 Jahre) und einem kumulierten Laufweg von fast 2 Millionen km individuell ausgewertet. Das Ziel des Forschungsvorhabens wurde erreicht.

Abstract

Radial lip seals are used in various sizes and designs to seal shaft interfaces. In contrast to other sealing systems, elastomeric radial lip seals have a back-pumping capability. Fluid is pumped under the sealing edge from the air side to the fluid side. The simplest method for measuring the back-pumping rate is the converse installation of the radial lip seal. This paper describes the current state of the art in back-pumping rate measurement. It shows the advantages over other methods and the limitations of the method. For the converse installation, there was always the assumption of hydrodynamic lubrication. This means there would be only minimal initial run in effects and no further wear. Current research work however, question this assumption. To analyze the wear formation during back-pumping rate measurements, various long-term tests were carried out. The resulting wear is compared with identical tests in normal installation.

Abstract

In the event of damage to sealing systems, expert knowledge in dealing with these problems is often not available to many industrial users. The development engineer is faced with the question of improving the product to meet the new requirements. The aim of this publication is to provide a proven guide for dealing with problematic sealing systems.

Abstract

Radial lip seals are a common seal type for drive units in various industrial applications. Environmentally friendly operation strategies require these drive units to be driven on demand in short time duty. The sealing systems have to deal with fast changing oil sump temperatures. This cannot be reproduced on usual test rigs. Firstly, a test rig with advanced heating and cooling capacities was developed. Then, comprehensive test series were carried out. As expected, test results show, different constant temperature levels lead to a significant change of wear. Furthermore, fast changing temperatures are adding additional tribological stress to the sealing system.