Efficiency and heat balance calculation of worm gears

Worm gears enable compact gear design and high power density due to a high gear ratio within a single gear stage. However, they often show high sliding speeds within the tooth contact, resulting in high frictional heat and increased thermal stresses. Therefore, an exact calculation regarding efficiency and heat balance is essential in the early stages of gear design. Currently, no calculation method is available to automatically analyze worm gears with regard to efficiency and heat balance. The simulation program “WTplus” is widely used to calculate the efficiency and heat balance of gearbox systems containing cylindrical and bevel gears. The efficiency is determined by adding up load-dependent and no-load power losses of gears, bearings, seals and other rotating components. The calculation of the heat balance of the gearbox is based on the heat transfer between the single components, as well as heat dissipation to the environment. A suitable abstraction of the gearbox by nodal points is conducted for an efficient and accurate calculation of local temperatures using a thermal network model. The simulation program WTplus was extended to automatically analyze the efficiency and heat balance of various designs of worm gears. For this, new approaches for the calculation of load-dependent and no-load losses, as well as new algorithms for nodalization and node-linking, were developed and implemented. Moreover, essential formulas describing the thermal resistances were customized. Simulation results were validated with measurements from research and industry showing very close alignment for various operating points and gear designs.