Contribución al estudio del comportamiento dinámico de transmisiones mecánicas en régimen no estacionario= Contribution to the study of the dynamic behavior of mechanical transmissions under non-stationary conditions

Abstract

Research developments devoted todynamic behavior characterization of mechanical transmissions is always an interesting topic since there is a continuous need to decrease vibration and noise while keeping high compactness and efficiency. Most studies were focused on transmissions running under stationary condition where speed and load are assumed constant. However, repetitive run ups, time varying loading and speed conditions are very common in many industrial applications which imply non stationary operations. The work presented through this thesis aims to a better understanding of the dynamic behavior of planetary gears running under non-stationary operating conditions. Typical use of such gear sets is in wind turbines, new generation aircraft engines, hybrid car transmissions�In order to fulfill the objectives, a planetary gear test bench with mechanical power recirculation which has been particularly analyzed through numerical simulations and experimental tests. A modal analysis has been done on the available test bench in order to determine the natural frequencies, modal deflections and modal kinetic and strain distributions. A lumped parameters model of the corresponding test bench with three degree of freedom for each component was used for this purpose. Numerical results are compared with those obtained through experimental modal analysis done on the test bench. The dynamic behavior is investigated firstly in stationary conditions with constant speed and load. The objective is to highlight the amplitude modulation in the time signals measured on ring gear induced by the individual influence of the passage of each planet near the measurement point. Asymmetric sidebands around meshing frequency and harmonic are observed in both simulations and experimental results The next part of the thesis is dedicated to the study of the transmission in non-stationary operations. For this purpose, several operating conditions have been considered, such as time varying load and speed, as well as run-up and run down regimes using numerical simulation and experimental tests. The simultaneous amplitude and frequency modulation are emphasized using time frequency analysis based on Short Time Fourier Transform. Moreover, studies on the Load Sharing between planets has been done taking into account the interaction between meshing gears, the gravity of the carrier and the planet position errors in stationary condition. In addition, the effect of speed on the load sharing behavior is studied during the run up regime. Finally, a Transfer Path Analysis approach called Global Transmissibility Direct Transmissibility is used to study the propagation of vibration in planetary gears in the stationary and non-stationary conditions. The directed transmissibilities between the components of the planetary gear test bench are computed from the measured transfer functions.