Reducing mass while improving the operational behavior: form optimization of planetary gearbox housings

The optimization of load sharing between planets is one of the most important goals in planetary gearbox design. Unevenly distributed load will cause locally higher flank pressures and therefore, less durability of gears and bearings. Furthermore, unevenly distributed or fluctuating loads can cause excitations in the gear mesh and structural vibrations. The load sharing in planetary gear stages depends on the individual stiffness conditions in each mesh position. The stiffness is not only influenced by the gear geometry but also by the surrounding structural elements like shafts, housings and torque arms. In wind industry these components are often designed very stiff in order to reduce their effect on the operational behavior.

Within this paper, a method is presented, which allows combining the structural optimization process with a tooth contact analysis for planetary gearboxes. By means of this combined approach, it is possible to optimize the housing structure of the ring gear in terms of mass reduction while keeping the operational behavior in focus. With a weighted design objective function, it is possible to decide whether the main objective should be load distribution, excitation behavior, low mass or a balanced design.