M. Tech. (Department of Metallurgical Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / To meet the ever-increasing demand for maintenance of gear systems, industrial companies have traditionally depended on the shutdown of the machines before processing the fault diagnosis. Nowadays, online monitoring has proven to be effective in terms of machine state analysis and fault prediction. However, the application of such a technique in the analysis of combined multiple nonlinear faults is still a subject of research. The vibration signature of a coexisting nonlinear crack and pit in two-stage gear system is unknown, it can be regarded as one of the most difficult problems to extract and diagnose. Additionally, incorporating both a crack and a pit into numerical models is a time-consuming process that demands a breadth of mechanical understanding. Diagnostics of faulty gears, on the other hand, can be performed in the time and frequency domain or in the Time-Frequency domain, depending on the complexity of the vibration. Non-linear and non-stationary phenomena (Features) occur when repeated pitting and cracking faults occur, reducing the reliability of standard signal processing methods (Gear displacement and Fast Fourier Transform). This thesis solves each of these shortcomings by developing an eight-degree-of-freedom (DOF) gear model with a breathing crack and multiple pitted gear teeth. The identified spur-gear model enabled the investigation of the crack and pitting signatures and their effect on the ensuing vibrations independently of the action of other system components. Additionally, when pitting and cracking coexist, the study was conducted to determine the influence of such a failure on the transmission system. Theoretical results indicated that the presence of pitting and crack in the tooth of the gear resulted in a decrease in mesh stiffness. Additionally, the influence of the breathing pitting and crack results in material fatigue, which results in the generation of a random term in the vibration signal. To corroborate the acquired results, several experimental tests on a spur-gear test rig with a defined pit and crack size range were undertaken under a variety of conditions. In comparison to the presented methodologies, theoretical and experimental results indicate that 3D Frequency-RPM analysis is the most sensitive and resilient method for the early detection and identification of pit and crack faults. Furthermore, when crack or pit faults are studied individually, the STFT analysis yields interesting results. The feature analysis revealed that, when using the Time-Frequency technique, the crack and pit combination in a two-stage gear system is a priori more efficient than the other options.

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A unique multifrequencied transfer matrix method performs three-dimensional harmonic, steady-state response calculations on geared-rotor systems. The full six degrees-of-freedom method includes physical branching to accommodate multiple shafting and frequency branching to simultaneously accommodate multiple frequencies and their interdependence resulting from time-varying mesh stiffness. Areas of emphasis include development of a modified transfer matrix to handle multiple frequencies and shafting; description of the time-varying stiffness tensor representing the involute spur gear mesh based on bending, shear, compression, and local contact deformation; development of the mesh transfer matrix; development of an automatic system solver to allow the engineer to analyze systems of arbitrary construction; and the development of a matrix solver to efficiently handle large systems. A computer analysis demonstrates the significance of terms included in the stiffness evaluation as compared with less rigorous treatment in the literature. An analytical example problem illustrates the automated model generation through complete rotor system dynamic response analysis produced by the current work with special attention to the significance of parametric excitation due to the gear mesh. / Ph. D.

Pour répondre au besoin des clients ainsi qu’aux réglementations gouvernementales, les constructeurs de camions doivent diminuer la consommation et les émissions de leurs véhicules. Une solution-clé est d’améliorer le rendement de la transmission du camion, dont le pont fait partie. Leur design n’a longtemps été optimisé qu’en fonction de critères de durabilité et de bruit. L’objectif de ce travail est donc de caractériser le rendement des ponts de camion. La dissipation de puissance au sein du pont est causée par l’engrènement, les roulements, les joints et le barbotage. Des méthodes permettent d’estimer globalement ces pertes de puissance, mais elles ne sont pas forcément adaptées aux ponts. En effet, l’élément principal du pont est un engrenage spiro-conique ou hypoïde et son importance est étudiée : sa forme influe sur le barbotage, tandis que sa géométrie de denture et sa cinématique gouvernent le frottement à l’engrènement. Il semble ainsi important d’évaluer le frottement de ces couples coniques par une approche locale et d’étudier l’influence des paramètres de denture. Cependant, les pertes de puissance dépendent de la température, via les propriétés de l’huile. Des expériences montrent un important écart de température entre les composants. Il faut donc considérer des températures locales plutôt qu’une température d’huile globale. Le rendement et la durabilité peuvent être impactés par des points chauds. La méthode des réseaux thermiques permet de modéliser les échanges thermiques du pont ainsi que la distribution de températures. Les tests classiques de rendement mesurent uniquement la perte globale et la température d’huile : rien ne permet de confirmer la répartition des pertes entre sources. Une campagne d’essais avec mesures de température est donc réalisée et valide le modèle pour le calcul des températures locales et pour l’estimation des pertes de chaque composant. Ce modèle peut alors être utilisé lors du design de futurs ponts. / To fulfil customer demands, but also government regulations, the truck industry must decrease the fuel consumption and emissions of its vehicles. A key development is to improve the efficiency of the powertrain, which includes the axle. Until recently, optimisation of axle design has mainly concerned durability and noise aspects. The aim of this study is then to characterise the efficiency of truck axles. As for most of the mechanical transmissions, power dissipation in axles is due to gear mesh, rolling element bearings, seals and oil churning. Formulae already exist to estimate these power losses at a global level, but they are not always adapted to axles. Indeed, the main component of axles is a spiral bevel or a hypoid gear set. The influence of these special gears on efficiency is investigated here: their shape drives oil churning losses, while their tooth geometry and their kinematics impact friction at gear mesh. Therefore, the meshing friction of the gear set is also evaluated thanks to a local approach. The influence of some gear parameters is studied. However, power losses are influenced by temperature through oil viscosity. As previous experiments underline non-negligible temperature difference between components, it is necessary to consider local temperatures instead of a global oil temperature. Efficiency but also durability can be impacted by local hot spots. The thermal network method is used to model the thermal exchanges inside and outside the axle and to calculate temperature distribution. Usual efficiency tests on axles measure only global power loss and oil temperature: no evidence allows to confirm a power loss breakdown. Thus, a test campaign with temperature measurements is done and validates the model on local temperature calculation but also on estimation of component power losses. The model can be used at design stage for future development of axles.

Ce travail de thèse, réalisé dans le cadre d’une collaboration avec la société Hispano-Suiza (groupe SAFRAN) porte sur la modélisation et l’analyse des vibrations et surcharges dynamiques sur les engrènements d’un réducteur aéronautique multi-étage constitué de plusieurs cascades d’engrènements situés dans des plans décalés. Une modélisation originale est proposée qui repose sur le couplage entre la résolution des équations du mouvement et la prise en compte des conditions de contact instantanées sur l’ensemble de tous les engrènements. Le modèle gère les phases relatives entre engrènements ainsi que l’influence des modifications de corrections de forme des dentures. En s’appuyant sur de nombreux exemples d’application, il est montré que des corrections de profil linéaires et symétriques adaptées permettent d’abaisser très sensiblement le niveau de surcharges dynamiques sur une plage de vitesse de rotation importante. Il est également confirmé que les efforts dynamiques sur les engrènements sont fortement corrélés aux amplitudes des variations temporelles des erreurs de transmission locales pour un fonctionnement quasi-statique sous charge. Considérant différentes architectures de transmissions, des optimisations conduites grâce à un algorithme génétique montrent que les paramètres optimaux de corrections de profil sont à choisir au voisinage d’une ‘courbe maîtresse modifiée’, initialement définie pour un seul engrènement et dont les propriétés semblent pouvoir être extrapolées à des systèmes avec plusieurs engrènements simultanés. Les résultats de simulations prouvent que l’ensemble des corrections sélectionnées sur les courbes maîtresses modifiées améliorent sensiblement le comportement dynamique des systèmes d’engrenages multi-étages. En revanche, pour des systèmes soumis à des niveaux de charge différents, des corrections optimales courtes semblent plus adaptées en termes de dynamique de l’engrènement tandis que des corrections optimales longues semblent plus efficaces en ce qui concerne le niveau de contraintes en pied de dents. / This research work, conducted in cooperation with Hispano-Suiza (SAFRAN group), is focused on the modelling and analysis of vibrations and dynamic loads in aeronautical multi-mesh gears comprising several spatial gear arrangements (idler gears, several pinions on one shaft). An original model is presented which relies on the simultaneous solution of the equations of motion and the instant contact conditions for all the tooth contacts and all the meshes. The phasing between the various meshes along with tooth shape modifications are integrated in the simulations. Based on a number of simulation results, it is shown that linear symmetric profile modifications can substantially reduce dynamic tooth loads over of broad range of speeds. It is also confirmed that dynamic mesh forces are strongly correlated with the time-variations amplitudes of local quasi-static transmission errors under load. Considering several gear arrangements, tooth profile optimisations have been performed using a genetic algorithm which indicate that optimum reliefs always lie in the vicinity of the so-called ‘modified Master Curve’ initially defined for a single pinion-gear pair. This finding suggests that the concept of Master Curve can probably be extended to more complex gear systems. The simulation results prove that all the optimal profile modifications on the Master Curve improve the dynamic tooth loading conditions in multi-mesh gears. However, for systems submitted to several load levels, short optimal reliefs seem preferable whereas long optimal reliefs are more effective in terms of root stresses.

Product tolerancing decisions made in product design have a significant effect on manufacturing environmental and cost performances by strongly influencing both the selection and operation of processing machinery. These decisions however are typically made without quantitative knowledge of their effects in manufacturing. With estimates of environmental and cost performances of manufacturing processes required to achieve specific part designs earlier in the product design cycle, designers may make more informed, and potentially better, design decisions with respect to manufacturing environmental and cost performance goals. In this thesis a method for quantifiably relating product tolerancing decisions to environmental and cost performances in manufacturing in order to provide decision support for cost and environmentally conscious design for manufacturing is developed. The method is instantiated as an Excel-based tool and exercised by two illustrative examples of increasing complexity, as well as a study of the manufacture of automotive transmission pinion gears with differing tolerance requirements. Uncertainty analysis is performed through the use of @RISK software; the uncertainty of parameters associated with manufacturing operations and machinery is captured through the use of probability density functions and Monte Carlo simulation is performed. Simulation results provide insight into the uncertainty of performance estimates and the risks associated with ensuing decision making. This method may be useful to product designers, as well as process planners, to support decision making efforts related to cost and environmental consciousness in the manufacturing phase of the product life cycle.

High strength secondary hardening lath martensitic steel is a strong candidate for high performance and reliable transmission systems in aircraft and automotives. The fatigue resistance of this material depends both on intrinsic microstructure attributes, such as fine scale (M2C) precipitates, and extrinsic attributes such as nonmetallic primary inclusions. Additionally, the aforementioned attributes are affected by processing history. The objective of this research is to develop a computational framework to quantify the influence of both extrinsic (primary inclusions and residual stresses) and intrinsic (martensite laths and carbides) microstructure attributes on fatigue crack formation and the early stage of microstructurally small crack (MSC) growth that dominate high cycle fatigue (HCF) lifetime. To model the fatigue response at various microstructure scales, a hierarchical approach is adopted. A simplified scheme is developed to simulate processing effects such as shot peening that is suitable to introduce representative residual stresses prior to conducting fatigue calculations. Novel strategies are developed to couple process route (residual stresses) and microstructure scale response for comprehensive analysis of fatigue potency at critical life-limiting primary inclusions in gear steels. Relevant microstructure-scale response descriptors that permit relative assessment of fatigue resistance are identified. Fatigue crack formation and early growth is highly heterogeneous at the grain scale. Hence, a scheme for physically-based constitutive models that is suitable to investigate crack formation and early growth in martensitic steel is introduced and implemented. An extreme value statistical/probabilistic framework to assess the influence of variability of various microstructure attributes such as size and spatial distribution of primary inclusions on minimum fatigue crack formation life is devised. Understanding is sought regarding the relative role of microstructure attributes in the HCF process, thereby providing a basis to modify process route and/or composition to enhance fatigue resistance. Parametric studies are conducted to assess the effect of hot isostatic pressing and introduction of compliant coatings at debonded inclusion-matrix interface on enhancement of fatigue resistance. A comprehensive set of 3D computational tools and algorithms for hierarchical microstructure-sensitive fatigue analysis of martensitic gear steels is developed as an outcome of this research; such tools and methodologies will lend quantitative and qualitative support to designing improved, fatigue-resistant materials and accelerating insertion of new or improved materials into service.

This diploma thesis is focused on compiling a computational model of the transmission of a Zetor Forterra HSX tractor in the Multibody software MSC ADAMS environment. It analyses the issue of creating gears in terms of vibration and noise. The thesis describes the creation of computational model which is used for simulation of the load conditions during tractor operation. The methodology is applied to a single-stage gearbox in which is verified. Then it is used on a model of a real tractor gearbox. The response of the input load conditions is projected during the forces in the engagement of the gears which are transmitted to the bearings.

This graduation thesis dwells on a worm gear design for an elevator mechanism in an already existing wheel case with actuator unit S3 for elevator type BOV 320/0,63. The work includes dimensional and control calculation for the worm gear and as an attachment you will find spiral worm and worm gear drawing documentation, including its specific location.

This thesis deals with a design of new dot-wheels gearing. These wheels serve for closing of paper covers of tea bags. First of all the suggested spare options of the gearing shape are compared with the original. On the basis of the comparison results the gearing is solved as a substandard kind of involute gearing. The involute gearing is designed by the method of generalized parameters. For the gearing design the program GEARING – symetrical profile version 1.5. was used. Consequently this program was adapted for the case of the change of the instrument shape by the user. The kind of wheels material was designed. Further the way of wheels production for single-piece and batch production was also designed. At the end the economic evaluation of the wheels production with newly designed profile was done.