Condition monitoring of epicyclic gearboxes through vibration signature analysis, with particular focus on time domain methods and the use of adaptive filtering techniques for the purpose of signal enhancement, is the central theme of this work. Time domain filtering methods for the purpose of removal of random noise components from periodic, but not necessarily stationary or cyclostationary, signals are developed. Damage identification is accomplished through vibration signature analysis by nonstationary timefrequency methods, belonging to Cohen’s general class of time-frequency distributions, strictly based in the time domain. Although a powerful and commonly used noise reduction technique, synchronous averaging requires alternate sensors in addition to the vibration pickup. For this reason the use of time domain techniques that employ only the vibration data is investigated. Adaptive filters may be used to remove random noise from the nonstationary signals considered. The well-known Least Mean Squares algorithm is employed in an adaptive line enhancer configuration. To counter the much discussed convergence difficulties that are often experienced when the least mean squares algorithm is applied, a new unconditionally convergent algorithm based on the spherical quadratic steepest descent method is presented. The spherical quadratic steepest descent method has been shown to be unconditionally convergent when applied to a quadratic objective function. Time-frequency methods are succinctly employed to analyse the vibration signals simultaneously in the time and frequency domains. Transients covering a wide frequency range are a clear and definite indication of impacting events as gear teeth mate, and observation of such events on a timefrequency distribution are used to indicate damage to the transmission. The pseudo Wigner-Ville distribution and the Spectrogram, both belonging to Cohen’s general class of time-frequency distributions are comparatively used to the end of damage identification. It is shown that an unconditionally convergent adaptive filtering technique used in conjunction with time-frequency methods can indicate a damaged condition in an epicyclic gearbox, where the non-adaptively filtered data did not present clear indications of damage. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2007. / Mechanical and Aeronautical Engineering / MEng / MEng / unrestricted

Vibration monitoring is widely used to determine the condition of various mechanical systems. Traditionally a transducer is attached to the structure under investigation and the vibration signal recorded. This signal is then processed and the required information extracted from the signal. With epicyclic gearboxes this traditional approach is not advisable. This is in part due to the fact that the planet gears rotate internally on a planet carrier. Special techniques are therefore required to extract a viable data signal from the measured vibration signal. These techniques require an additional post-processing step in which a compiled data signal is extracted from the measured data signal. This work investigates the possibility of mounting transducers internally on the rotating planet carrier. Mounting transducers at this location removes the relative motion seen in traditional measurement techniques. An epicyclic gearbox is modified to facilitate the internal mounting of the accelerometers. A number of implementation problems are highlighted and solutions to these problems are discussed. A large portion of the work is dedicated to implementing and qualifying the epicyclic time synchronous averaging technique which is traditionally used to evaluate epicyclic gearboxes. As this technique forms the basis to evaluate the data obtained from internal measurements, it is of fundamental importance that the technique is implemented correctly. It is shown that vibration data can be reliably measured internally, by means of accelerometers mounted on the planet carrier. The internally measured data is compared to data obtained by traditional techniques and shown to be equally adept in detecting deterioration of a planet gear tooth. Simple condition indicators were used to compare the vibration data of the two techniques. It was seen that the data obtained from the internally mounted accelerometers was equally, and in certain cases, slightly more sensitive to planet gear damage. This implies that the technique can be used successfully to evaluate epicyclic gearbox damage. There are a number of practical implementation problems that will limit the use of this technique. As the technology becomes available to transmit measured vibration signals wirelessly, the application of the internal measurement technique will become more viable. A preliminary investigation was also launched into the relationship between a planetary gearbox with a single planet gear and one with multiple planet gears. It is illustrated that vibration data, measured from a gearbox containing a single planet gear, shows an increased sensitivity to planet gear damage. Although a special test rig might be required, the increased sensitivity to damage can provide a method to test planet gears in critical applications such as aircraft gearboxes. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Mechanical and Aeronautical Engineering / unrestricted

De nombreux projets visant à réduire l’impact environnemental global des avions sont lancés au niveau européen. L’un des moteurs étudié pour les avions moyens et longs courriers est le moteur Ultra High Bypass Ratio (UHBR) : un moteur simple corps, double flux, à flux externe fortement augmenté. Le moteur UHBR doit être équipé d’un réducteur épicycloïdal, qui est un composant jamais utilisé dans un turboréacteur jusqu’à présent. L’optimisation d’un réducteur épicycloïdal a conduit à l’utilisation de paliers hydrodynamiques pour supporter les pignons satellites du porte-satellites.Pour une telle application, le palier hydrodynamique subit une déformation très élevée due aux charges de l’engrènement sur le pignon satellite et à l’effet centrifuge engendré par la rotation du porte-satellites. La géométrie optimisée des composants du palier varie avec le comportement thermique et mécanique des pièces, nécessitant la prise en compte d’une modélisation thermoélastohydrodynamique (TEHD).Afin de modéliser précisément ces phénomènes, un modèle conservatif dans la zone inactive en régime TEHD a été développé et validé à l’aide des résultats d’essais de la littérature et des bancs d’essais de Safran Transmission Systems. Les résultats obtenus montrent un double champ de pression dans le palier hydrodynamique du réducteur épicycloïdal, engendré par la forte déformation élastique du pignon agissant ainsi de façon significative sur le comportement dynamique du palier. De plus, l’influence de l’effet centrifuge sur l’huile dans le palier a été également examinée. / Several projects aimed at reducing the overall environmental impact of aircrafts are launched at European level. One of the engines studied for medium and long-haul aircraft is the Ultra High Bypass Ratio (UHBR) engine: a single-body, dual-flow gas turbine, with a greatly increased external flow rate. The UHBR engine must be equipped with an epicyclic reduction gearbox, which is a component never used before in a turbofan engine. The optimization of an epicyclic gearbox has resulted to the use of hydrodynamic bearings for supporting the satellite gears on the planet carrier.The hydrodynamic bearing of such application undergoes high deformations due to the gear contact loads on the satellite gear and to the centrifugal effect generated by the rotation of the planet carrier. The optimized geometry of the bearing components is influenced by the thermal and mechanical behavior of the bearing components, which requires a thermoelastohydrodynamic (TEHD) modeling taking into account the real film thickness under operation.In order to precisely simulate these phenomena, a conservative modeling in the inactive zone, under a TEHD regime has been developed and validated by comparing the predictions to the test results of the literature and of the test benches of Safran Transmission Systems. The results obtained show a double pressure field in the hydrodynamic bearing of the epicyclic reduction gearbox, due to the strongly deformed film thickness, which greatly affect the dynamic behavior of the bearing. In addition, the influence of the centrifugal force on the oil pressure in the oil film was also examined.