Investigation of Modal Parameters on Planetary Gearbox using Finite Element Analysis to Minimize Vibration

The advantage of a planetary transmission is determined by load distribution over multiple planet gears. It is thereby possible to transfer high torques utilizing a compact design. The designed transmission system comprising two degrees-of-freedom compound planetary gear train with two conjoined planetary gear trains and four torque-transfer devices. The different combinations of states of various torque-transfer devices yield multiple modes of operation. Planetary gears have problem of vibration. Since a planetary gear has internal and external meshes in several gear pairs, power distribution is unequal in gears, and loads can be concentrated in a specific planet gear. These vibrations are transferred to the gearbox casing through shafts and bearings. As the gearbox is coupled to engine, there are more probabilities of coincidence of natural frequency of engine and gearbox which causes resonance and leads to damage in gearbox. The natural frequencies and mode shapes are important parameter in the design of a structure for dynamic loading conditions. Subsequently, it is necessary to investigate modal parameters of gearbox and study the dynamic characteristics of gearbox. In this work, modal analysis is done using Finite Element Analysis and results shows range of frequencies obtained is suitable for gearbox which can avoid maximum amplitude of vibration and hence resonance. Dynamic analysis in ANSYS is used to solve the vibration problem, by using the modal analysis method of dynamic analysis; natural frequencies and mode shapes of systems are found out. The fundamental frequency obtained by the analysis is 87.015 Hz which is far away from the forcing frequency which is engine frequency in the range of 30-50 Hz and avoids resonance. Results of modal analysis after structural modification are also presented which shows enhancement in rigidity of the gearbox.