Abstract
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.
Highlights
If torque conversion with high gear ratio, compact installation space and 90-degree axis-crossing angle is needed, often worm gears are used
The subsequent calculation of the heat balance of the gearbox is based on the so-called “Thermal Network Method” (TNM) [11, 15], which is a mathematical method for determining the heat transfer between single components, as well as the heat dissipation to the environment
There are several approaches for the efficiency and heat balance calculation of worm gears, none of them uses an automatic approach to building the TNM
Summary
If torque conversion with high gear ratio, compact installation space and 90-degree axis-crossing angle is needed, often worm gears are used. There are several approaches for the efficiency and heat balance calculation of worm gears, none of them uses an automatic approach to building the TNM They either abstract their investigated gearbox as an isothermal system for which no temperature distribution can be calculated, or they build the TNM statically and for an experimentally considered worm gearbox. This is where the method shown in this paper excels: It describes a method for an automatic efficiency and heat balance calculation for various designs of worm gears
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