PEEK gears feasible in an automotive powertrain application

Known for its special capabilities among polymers, Evonik’s VESTAKEEP® PEEK is an already highly sought after material within the evolving automotive industry, valued for its unsurpassed ability to withstand high temperatures as well as its oil-resistance.  The high impact strength, and the dynamic, tribological performance of products made with this material are also key to its use in  demanding mechanical environments. Another benefit is that when running, plastic gears made of VESTAKEEP® PEEK emit several decibels less noise than their traditional metal-based counterparts. Even with the evolution to hybrid- and fully electric-powered vehicles in the automotive sector, this material can benefit the industry for many years to come.

Substituting metal with plastic naturally requires a serious amount of cutting-edge engineering and research. This is true especially when it comes to load-bearing gears in a motorized vehicle’s transmission. To test the capabilities of such an application, the researchers at TUM engineered and incorporated special gears made from Evonik’s VESTAKEEP® 5000 G in the transmission of a Renault Twizy electric vehicle. A one-seater concept car symbolizing the ongoing electric-powered evolution of the automotive industry, the test vehicle was an ideal choice for learning more about the stresses and performance of PEEK in this novel environment, as well as hopefully come to conclusions about whether the material could be used in scaled-up applications sometime in the future.

Made by the experienced plastic gear manufacturer, Werner Bauser GmbH – Kunststoff-Verzahnungstechnik, two VESTAKEEP® 5000 G components were specially designed to allow in principle a replacement of the original metal gears in the electric test-vehicle’s drivetrain. Such a design made it possible to compare whether PEEK gears could act as a viable substitute without major modifications in the existing drivetrain setup.

Due to its molecular properties, one disadvantage of metal compared to plastic is its high density. When smart plastic gear solutions are used in similar applications, a gear made of metal can weigh more than one made of plastic. Finding a way to replace the metal gear by a lighter plastic gear, however, would reduce the overall rotating mass of a transmission and lead to a higher degree of mechanical efficiency. In fact, studies have shown that in passenger cars, one-third of the fuel energy is used to overcome friction in the engine, transmission, tires, and brakes ^[1]. The viable replacement of metal gears with PEEK plastic gears could have the benefit of increasing the energy efficiency of a vehicle – a constant goal in automotive engineering. It would also make the transmission quieter, due to PEEK’s natural noise-absorbing qualities. Additionally, plastic gears might be more cost-efficient due to the injection molding process used to produce polymer parts, which is unique and much more economical than the process commonly used for metal part production.

As for the future of VESTAKEEP® PEEK as a replacement for metal gears in the automotive industry, Evonik has plans to continue engaging in research and development work with key partners.

“With VESTAKEEP®, we truly have an excellent high-performance polymer for tribological applications, such as gear wheels,” said Karl Kuhmann, head of polymer technology development at Evonik’s High-Performance Polymers business line. “VESTAKEEP is extremely resistant to chemicals and high temperature, and it also significantly reduces the coefficient of friction and noise behavior compared to traditional metal gears. Cooperating with great project partners – like the team at TUM– helps demonstrate the amazing potential of this material.”