The state of the art

High efficiency by maximum usage of available space, high gear ratios, best possible efficiencies and a wide range of applications due to the possibility of switching operations, superposition and summation gearboxes, are known properties of planetary gearboxes.

The optimization and effective utilization of these gearbox designs requires a detailed consideration of the loads on the gears in the gearbox. Therefore, standardized calculation methods, such as ISO 6336 or DIN 3990, can be used. To benefit from the full potential of the teeth, while the safety of the teeth can be assured at all times, advanced analysis of load distribution will be necessary.

Because of the need of the universal use of these calculation standards, these methods use approximations that cannot cover the special characteristics of planetary gearboxes and therefore cannot be used to optimize the gears to their full potential. For this reason, computer-aided calculation methods have been developed for planetary gearboxes with spur and helical gears that consider the most important influences on the load distribution, like housing deformation, bearing deformation, deformation of the planet carrier, deformation of the wheel bodies, and the deformation of the teeth themselves. Using this information, a detailed load distribution is possible to reach the maximum capability of the gears.

Research project for double helical gears

It is of vital importance to interpret and use the single calculation results correctly. The different results are given by different methods in analytical and numerical calculations. Regarding a complex assembly like planetary gearboxes, there is an additional fact to consider by having all results for single elements, depending on the behavior of other elements, in the assembly. An iterative calculation algorithm is inevitable.

The need of high rotational speeds and torques in gearboxes leads to high axial loads and therefore high risks for the additional elements in the assembly, for example, the bearings. The solution for these axial loads can be done by using double helical gears where the axial load components compensate each other. Double helical gears, the resulting loads, and the deformation of the wheel bodies with possible influences from one gear side on the other, cause the assembly to have an entirely different behavior than planetary gear stages with spur or helical gears. Detailed load distributions cannot be calculated at the moment, because the results of the existing calculation algorithms are not regarding these specific characteristics, and approximations cannot be made at this point due to the lack of experience.

The present research project describes the algorithm to determine the load distribution of planetary gearboxes with double helical gears. The detailed calculation methods offer the possibility to use the actual assembly design for the necessary finite element analysis; results have shown that approximated models cannot be used to calculate the load distribution accurately. Additionally, analytical calculations for the bearing deformation are presented. As already mentioned, the process of combining the single information to a final result is of major importance. The interdependent elements of the assembly lead to nontrivial correlations, making multiple calculations inevitable. The research project also offers a structured approach for the iterative calculation process that allows to be transferred into a computeraided calculation program. This solution enables the possibility of an effective and detailed calculation process for planetary gearboxes with double helical gears.