Planetary Gear Analysis : deformation induced misalignment and optimization

Abstract: A handheld heavy-duty nut runner, commonly used to assemble windmills and oil pipe lines, and capable of producing 4100 Nm of torque, experiences low cycle fatigue and usually fails after 20 000 cycles at the specified torque. A full assembly Finite element model of the last stage of the four-stage planetary gearbox is constructed and simulated over one complete load cycle. The results from the simulation is compared with, and used to verify a KISSsoft simulation of the same model. Using the Finite Element model, a parametric optimization is performed using a full factorial design. The results show that misalignment issues are difficult to prevent due to the planetary gearbox design. Comparing the two models shows similar characteristics and stress levels but that local differences are common. A proposed design improvement results in better load distribution in the planet – ring interaction, which was previously impaired compared to the planet – sun interaction due to deformation induced misalignment. The result shows that by balancing the rotational stiffness of the side 1 and side 2 carrier pin mountings, it is possible to reduce the contact misalignment and improve the load distribution in the gearbox.