Wet-Running Current Transmission: Schunk's Key to Efficient and Rare-Earth-Free EESM Motors

While Permanent Magnet Synchronous Motors (PSMs) are still widely used in electric vehicles, EESMs are gaining attention as a sustainable and cost-effective alternative. They don’t require magnets, meaning they avoid the use of rare earth elements – a key factor in reducing supply chain risk and environmental impact. 

However, one technical challenge remains: power transmission to the rotor. Typically achieved through carbon brushes, this step becomes increasingly complex in oil-cooled motor environments – the exact problem Schunk set out to solve. 

As power density increases in electric motors, so do thermal loads. Many OEMs rely on oil-based cooling systems to manage heat – but traditional current transmission systems are dry-running and must be completely sealed from oil. If seals fail or oil enters the system, it can lead to degraded performance or total failure. 

"Our goal was to ensure reliable power transmission even in an oil-filled environment – and to do so over the entire vehicle lifespan," explains Thomas Pichler, Global Account Manager at Schunk Mobility Carbon. 

The new system from Schunk consists of a wet-running slip ring and traction module, specifically designed for use in oil-cooled EESMs. Through a custom material composition, the system remains conductive and stable even under harsh operating conditions. 

Benefits at a Glance: 

• Stable operation in oil-rich environments 

• Improved cooling and motor efficiency 

• Greater vehicle range with the same battery size 

• No use of rare earth magnets 

“We developed a system that performs where others would fail. That’s a critical enabler for future-proof electric mobility,”  says Pichler. 

The technology was developed at Schunk’s Bad Goisern facility, where a cross-functional team brought it from concept to prototype. Initial samples are already being tested by OEMs, with positive feedback confirming its market potential. 

The next step: making the solution commercially viable. 

“We know the system works – now we’re focused on scaling it economically,” says Pichler. “Because even the best technical solution needs to make sense commercially.” 

Externally Excited Synchronous Motors offer real advantages: no rare earths, lower cost, improved recyclability, and less exposure to global material risks. 

With Schunk’s wet-running current transmission, EESMs become even more attractive – offering high efficiency, improved thermal management, and greater resilience under real-world conditions. 

Notably, the innovation was selected as a finalist in the Schunk Innovation Contest – reflecting both its technical merit and its strategic relevance for the future of electric drive systems. 

Schunk Mobility Carbon’s wet-running current transmission system is more than a materials innovation – it’s a key enabling technology for rare-earth-free, efficient, and robust electric motors. What it means for electric mobility: 

• Increased reliability in demanding environments 

• Better thermal management and range performance 

• A scalable path toward rare-earth-free EV drives 

The shift to EESMs is coming – and Schunk’s solution is helping drive that transformation. 

Interested in learning more? Discover all relevant brochures and technical documents on wet-running power transmission and FSM solutions from Schunk.

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