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.

The knowledge of component temperatures during transient operation conditions is essential for an optimal design of a gearbox. This is because critical peak temperatures limit the transferable power as well as the load capacity. Moreover, understanding the thermal behavior of the gearbox is key to improving its efficiency. Therefore, the Thermal Network Method (TNM) of the calculation program WTplus was extended to calculate component temperatures in gearboxes for transient operation conditions. Specifically, the TNM considers the component masses and specific heat capacities of each node modelling the gearbox structure. This enables the algorithm to compute a corresponding system of differential equations and thus determine the temperature change over time. Therefore, WTplus can be used to identify critical gearbox component temperatures during load cycles. The applied method was validated with measurements collected at the FZG gear efficiency test rig.

The circular layout and the kinematics of planetary gearboxes result in characteristic oil flow phenomena. The goal of this paper is to apply a new remeshing strategy, based on the finite volume method, on the numerical analysis of a planetary gearbox and its evaluation of results as well as its validation. The numerical results are compared with experimental data acquired on the underlying test rig with high-speed camera recordings. By use of a transparent housing cover, the optical access in the front region of the gearbox is enabled. Different speeds of the planet carrier and immersion depths are considered. A proper domain partitioning and a specifically suited mesh-handling strategy provide a highly efficient numerical model. The open-source software OpenFOAM^® is used.

Power losses in gearboxes result in frictional heating. Sufficient heat transfer from the gearbox to the environment is required for reliable operation. The heat dissipation from gears is linked to their interaction with fluids in the gearbox. Recent research has demonstrated the use of Computational Fluid Dynamics (CFD) to predict the gearbox fluid flow and no-load losses in an isothermal manner. This study focuses on a numerical analysis of the heat dissipation within a dry-lubricated gearbox under atmospheric conditions. Spur gears and helical gears are investigated. The air flow in the gearbox as well as the heat dissipation over the gear surfaces are evaluated in detail. The results show that the gear geometry and the circumferential speed have a strong impact on the air flow. Especially, the axial inflow of air to the gears has a great influence on the heat dissipation. Conveying effects of helical gears lead to a multidirectional airflow, resulting in higher values of the heat transfer coefficient on the gear surface compared to spur gears.

Geared turbofans need to withstand loss of lubrication due to inevitable off-design conditions. Additionally, loss of lubrication specifications that have to be fulfilled are getting stricter. For a loss of lubrication event, today's geared turbofans are equipped with secondary oil supply systems. Their omission would reduce space and weight, and consequently, carbon emissions. However, this requires geared transmissions to withstand loss of lubrication events. In order to enable this, knowledge of the power loss and damage behavior of gears under loss of lubrication is required first. In this study, power loss and bulk temperature measurements of test gears under loss of lubrication on a FZG gear efficiency test rig are presented. Hertzian pressures in the pitch point up to 1723 N/mm², and circumferential speeds up to 20 m/s were considered. The experimental results show the characteristics of increasing power loss and bulk temperatures under loss of lubrication depending on load and speed. At moderate operating conditions, no damage occurs within 20 seconds under loss of lubrication, whereas a load increase results in slight scuffing, and a speed increase results in severe scuffing. Oil centrifugation has a strong effect on the loss of lubrication performance. Additional experiments under reduced quantity lubrication demonstrate the impact of the remaining oil on the survivability of gears facing loss of lubrication.

The primary design criteria for gearboxes are (i) power density and load capacity; (ii) noise, vibration, and harshness; and (iii) efficiency and heat balance. To meet these design criteria, it is essential to use accurate calculation models throughout the design process. The total power loss can be divided into portions of gears, bearings, seals, and other machine elements, of which the load-dependent gear power loss often makes up the most significant portion. The existing literature provides a number of calculation methods with varying levels of detail for mesh-local models that promise high accuracy; however, these are rarely used, partly due to a lack of validation. This study systematically compares mesh-averaged and mesh-local calculation models using experimental results from a twin-disk tribometer and various cylindrical gears. The study includes a wide range of operating conditions and different gear oils. Three calculation levels I, II, and III are defined. The results show good agreement between the calculated and measured load-dependent gear power losses, with the mesh-local models showing high accuracy. When comparing results for an internal gear, the mesh-local calculation model calculates 30% lower load-dependent gear power losses than the mesh-averaged calculation model, which aligns with initial experimental results. The findings of this study suggest that mesh-local models are viable for wider application.