Progettazione ed ottimizzazione di trasmissioni ad ingranaggi in ambito automotive: ingranaggi conici, ipoidi e pignone-cremagliera.

The aim of this thesis is to develop tools for the design and optimization of gear transmissions for automotive applications. In so doing, the know-how developed over the last 20 years by the members of the Applied Mechanics Group at the Universit`a di Pisa has been carefully collected, studied and further extended and enriched. Gears are the main component of the transmission assemblies employed in vehicles, featuring one of the most complex geometries among mechanical parts. The focus of the tools presented in this dissertation concerns mostly the geometrical aspects of the design step because gear tooth geometry plays a fundamental role in the mechanics of contact during tooth meshing. In the proposed approach, the manufacturing process is virtually embedded in contact analysis tools to provide a computational pipeline which can be profitably be driven optimization. Furthermore, some tribological investigations are performed in order to obtain a reliable tool that can estimate, with sufficient accuracy, the friction-induced efficiency losses. Moreover, during the operating life of the mating gears, wear can drastically affect the micro-topography of the flanks. Therefore, a wear simulation methodology has been detailed in order to provide an accurate estimation with minimal amount of computational resources. Other geometrically complex gears are often employed in some advanced, purely mechanical steering mechanisms for vehicles. Those gears are usually referred to as variable transmission rack-and-pinion drives. The rack in this application presents continuously variable tooth profiles that instantaneously comply with a pre-defined rack gain function. The theory of gearing, despite its generality, may be challenging to implement robustly and efficiently in those cases. Alternative generation methods, based on Boolean operations, are proposed in this thesis in order to overcome numerical difficulties of the envelope theory while designing complex gear geometries.