|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Dinamica non-lineare e chaos nei rotismi planetari|
|Titolo in inglese||Nonlinear dynamics and chaos in planetary gears|
|Settore scientifico disciplinare||ING-IND/13 - MECCANICA APPLICATA ALLE MACCHINE|
|Corso di studi||Scuola di D.R. in HIGH MECHANICS AND AUTOMOTIVE DESIGN & TECHNOLOGY / MECCANICA AVANZATA E TECNICA DEL VEICOLO|
|Data inizio appello||2012-03-26|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
I riduttori a planetario sono stati largamente impiegati nelle trasmissioni meccaniche con grandi vantaggi, quali l'elevata coppia trasmissibile, il peso ridotto, l'alta affidabilità ed efficienza. Esempi di applicazioni dei rotismi planetari sono presenti nelle trasmissioni automobilistiche, nelle macchine agricole, negli elicotteri e nei motori di impiego aeronautico.
Planetary gear system, have been widely used in power transmission systems owing to their advantages such as high torque to weight ratios, large speed reductions in compact volumes, availability of multiple speed reduction ratios, high reliability and high efficiency. Examples of application of planetary gears are automotive transmissions, tractors, helicopters, and aircraft engines. The dynamic analysis of planetary gears is essential for reducing noise and vibration problems. The dynamic forces at the sun-planet and ring-planet meshes are the main sources of such problems due to the strong interaction between noise and dynamic transmission error. Planetary gear vibrations produce dynamic loads, cause reduction in the structural life time and generate noise. The main source of vibration is the parametric excitation due to the periodically time-varying mesh stiffness of each sun-planet and ring-planet gear; because the number of gear tooth pairs in contact changes during gear rotation. This thesis presents a full model to simulate the dynamic behavior of a single-stage planetary gear system with backlash. The generic nature of the formulation allows the analysis of a planetary gear set with any number of planets. This dynamic model considers time varying mesh stiffness and backlash, for all sun-planets and ring-planets meshes and bearing compliance. In the present model each element (the sun gear, planets, carrier and the ring gear) has three degrees of freedom; two transverse and one rotational, thus giving a total of eighteen degrees of freedom for the case study system with three planets. The linear averaged equations of motion are solved to obtain the natural frequencies and the nonlinear equations of motion are solved numerically to study the effect of time-varying stiffness and backlash. The proposed model is employed to describe the nonlinear behavior of a planetary gear system. The natural frequency sensitivity to system parameters is investigated for planetary gears. Parameters under consideration include support stiffnesses for symmetric and equally spaced system. Tooth separations at large vibrations introduce nonlinearity in geared systems. The present work examines the complex, nonlinear dynamic behavior of spur planetary gears using a lumped-parameter model. The two-dimensional (2D) lumped-parameter model represents the gears as lumped inertias, the gear meshes as nonlinear springs with tooth contact loss and periodically varying stiffness due to changing tooth contact conditions, and the supports as linear springs. This work examines the complex nonlinear dynamics of planetary gears by numerical method over the meaningful mesh frequency ranges. Bifurcation analysis have been studied to investigate the chaotic and period doubling phenomena. The dynamics of planetary gears show different nonlinear phenomena. Nonlinear jumps, chaotic motions, and period-doubling bifurcations occur when the mesh frequency or any of its higher harmonics are near a natural frequency of the system. At resonance, the resulting vibration causes tooth separation leading to nonlinear effects such as jump phenomena and sub-harmonic resonance.