The electrifying future of gears

Automotive transmissions play a dominant role for gear industry. The trend towards electrified powertrains has the potential to change the game. The average number of gears in a car with conventional combustion engine amounts to approximately 15 pieces, currently. Electric cars get along with just 4 spur gears or even less. The electrification of mobility is strongly driven by the megatrends urbanization, digitalization and climate change. Consequently, various forecasts estimate that the share of electric cars might reach up to 50 percent by 2030. For someone working in the field of drive technology, such data raises the question, whether the importance of gears in automotive applications is going to change.

On the other side, recent studies and concepts indicate that combining high-speed electric motors with gearboxes introduces opportunities to significantly reducing weight and cost of the drive system. This area of application, however, comes with a bandwidth of challenges: Noise/vibration/harshness (NVH), efficiency and power density. Consequently, these are the focus topics of current research at the Gear Research Centre (FZG).

For future mobility concepts, efficiency is a key topic, since energy consumption and/or CO2-emission is a crucial challenge for our society. Methods for efficiency optimization according to the state of the art, like synthetic and low viscosity oils or reduced oil levels are usually implemented, already. In our research simulation methods offer additional possibilities for further improvement. Thermo-elastohydrodynamic (TEHD) simulations allow to determine the influence of different lubricants or even of coatings on the coefficient of friction. Computational fluid dynamic (CFD) simulations can calculate the flow of lubricants in gearboxes and allow the assessment of the influence of different oil levels on the thermal behavior of the drive system.

Besides efficiency, for future automotive powertrains the NVH-behavior of gears gets more into the focus due to the reduced ambient noise level inside the car. A very promising approach towards this topic on top of classic measures according to the state of the art is to apply periodic flank modifications. This special adaption of the micro geometry offers the opportunity to separately optimize the micro geometry for optimal load carrying capacity and for minimal transmission error.

Finally, the electrification of automotive powertrains will increase the demand for weight saving. High-speed electric motors with high ratio transmissions are a promising approach. Besides, the use of plastic material for power train parts offer favorable properties such as low friction, dry-running capabilities or good damping at minimal costs. High performance plastic material offers the opportunity of substantial improvements, but the limited load carrying capacity restrict their direct application to machine elements. Focused research is required to set the bar higher.

At the VDI International Conference on Gears 2017 more than 144 presentations in total will be presented and discussed in Garching/Munich for more than 600 experts on gears from all over the world on various topics around gears, like the ones described above. For example, a presentation on the research project on optimized gear micro geometry with periodic modifications as mentioned above is given during the Conference on Gear Production, which is accompanying the VDI International Conference on Gears 2017. Additionally, current projects on how to widen the range of application of high performance plastic gears are presented and discussed at the Conference on High Performance Plastic Gears, which is also conducted in parallel to the VDI International Conference on Gears 2017.

I am looking forward to meeting the international experts on Gears at the Conference on Gears, September 13 till 15, in Garching/Munich.

Author of the article

Prof. Dr.-Ing. Karsten Stahl,Full Professor at the Institute of Machine Elements, Head of the Gear Research Centre (FZG), Technical University of Munich (TUM) Boltzmannstrasse 15
D-85748 Garching
tel.: +49 89 289-15805
stahlfzg.mw.tumde
www.fzg.mw.tum.de