Three main concerns are in the focus of the development of geared transmissions nowadays: load carrying capacity, noise–vibration–harshness (NVH) behavior, and efficiency. Increasing the efficiency of modern gearboxes contributes significantly to the reduction of energy consumption and the saving of resources. Gearboxes are frequently designed conservatively with an oversupply of oil to guarantee operational reliability. An oversupply of oil results in an unnecessarily high amount of oil kept in motion and to high no-load losses. Detailed information on the oil distribution in the early design stages of gearboxes would help to optimize the lubrication and to increase the efficiency. Thereby, CFD (computational fluid dynamics) methods offer a very flexible way to visualize the oil flow inside gearboxes with much fewer restrictions compared to measurements with transparent gearbox designs. In this study, a verified CFD model based on the finite volume method is used to investigate the oil flow in a single-stage gearbox. Different oil viscosities and circumferential speeds are considered. The investigations focus on the oil flow. The gear churning loss, as part of the no-load loss, is additionally considered. Experimental validation is obtained by high-speed camera recordings and measurements at the FZG no-load power loss test rig. The results show very strong agreement between simulation and measurement. The results show that CFD simulations can visualize the oil flow behavior with a very high degree of detail.

Efficiency is becoming a main concern in the design of power transmissions. It is therefore important, especially during the design phase, to have appropriate models to predict the power losses. For this reason, CFD (computational fluid dynamics) simulations were performed in order to understand the influence of geometrical and operating parameters on the losses in power transmissions. The results of the model were validated with experimental results.

The aim of the current research is to develop a gear transmission fluid based on water and plant extract. Up to now, mineral or synthetic oils are used as lubricants in most gear drive applications. These oils are made of fossil raw materials and are non-biodegradable. Lately, there have been some efforts made to develop lubricants as an alternative to conventional lubrication systems such as triglycerides from native oils or synthetic esters. These lubricants are more biodegradable than mineral oils but also show some difficulties during performance like saponification. Within a former research project, the company Carl Bechem GmbH and the Fraunhofer Institute for Process Engineering and Packaging IVV developed a cutting fluid based on water and plant extract. With a model sample of this fluid, which also contained gear typical additives, preliminary experimental investigations for a current research study were conducted. The results confirmed the general suitability of this water-based lubricant for gear drives under certain operating conditions. Using water as lubricants can lead to some improved characteristics due to the very high thermal conductivity and the reduced friction. This paper aims to point out the benefits of using water-based lubricants, share the results of some preliminary experimental investigations on a fluid sample based on water and plant extract, and discuss the challenges, which one has to overcome during the development of such new lubricants.

Bending strength of injection molded polyacetal test gears is investigated in back-to-back testing using oil-lubrication. To validate state of the art calculation methods, tooth geometries with a variable number of teeth are investigated, maintaining a constant center distance and transmission ratio. To enable testing on a constant level of tooth temperature for variable torque loads and speeds, occurring tooth temperatures are measured and considered in latter testing. Test results show that bending strength of tooth geometries with a higher number of teeth stand higher tooth root stresses acc. to VDI 2736, as the calculated tooth root stress is too high due to negligence of load-induced deflections. A modified method for calculating tooth root stress considers load-induced deflections, allowing to trace back the failures of the different tooth geometries to a common stress level. Therefore, a possible approach to consider the actual contact ratio for tooth root stress calculation of steel-plastic spur gear pairings is proposed.