Experimental investigation of the dynamic load sharing of planetary gearboxes

Due to their compactness and power density, planetary gearboxes are used for a wide range of high-performance applications in the automotive, aviation and marine sector. Aerospace applications in particular benefit from a full use of the load capacity potential to meet the requirements for lightweight construction and efficiency. Against this background, the load sharing between the individual planetary gears plays a decisive role. A uniform load sharing enables the design of the single tooth meshes without load increases and oversizing. However, due to manufacturing and assembly deviations, a perfect load sharing is technically not feasible. These load increases are taken into account in the standard calculation of the load capacity of planetary gearboxes by the mesh load factor Kγ. The load sharing in planetary gearboxes is influenced by a number of factors, such as the rigidity of shafts, housing and bearings, the number of planets, the quality of the gear wheels and the operating conditions. Detailed simulations or extensive experimental measurements are required to determine the exact load sharing. For new designs of planetary gearboxes, there are only simplified assumptions available, based on the number of planets and a rough estimation of the operating range. Especially additional dynamic forces, due to operation in high-speed ranges or near resonance frequencies, can lead to a considerable change of the dynamic load sharing compared to the static load sharing and cause an uncertainty in the design. Thus, in this paper the dynamic load sharing behaviour is investigated from 0 to 6800 rpm sun speed for different loads. Based on the experimental data recommendations for the design of planetary gearboxes under consideration of the operating conditions are derived.