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Magnet-free electric motor tech is award winner

BorgWarner won an R&D 100 Award in partnership with the Department of Energy's Oak Ridge National Laboratory (ORNL) for their work on a rotary-transformer-based wireless excitation system for electrically excited synchronous motors (EESM). The honor was celebrated at a ceremony on Nov. 20, 2025, in Scottsdale, AZ.

BorgWarner and ORNL's advanced development project powers an electromagnet-based rotor, eliminating the need for rare earth magnets and reducing supply chain risks. The transformer-based approach also eliminates brushes and sliprings, which tend to wear out over time, enhancing overall reliability in passenger and commercial vehicle applications and reducing the size of the motor by 15%.

The partnership began in 2021 and focused on designing a solution that delivers greater efficiency, lower costs, enhanced robustness, and ease of integration -- all of which were achieved. Additionally, while competing concepts are restricted to certain drivetrains based on their designs, this rotary transformer is highly compatible with all forms of drivetrains and compact gearboxes.

"This partnership brought strong collaboration and significant technological advances, including nine patent applications," said Harry L. Husted, chief technology officer, BorgWarner Inc. "By combining BorgWarner's traction motor expertise with Oak Ridge National Laboratory's wireless power transfer capabilities, we developed a technology that matches the performance and exceeds the power density of rare earth-based motors -- without using rare earth materials. This is a substantial accomplishment."

The rotary transformer system wirelessly transmits power to the rotor with 92 to 95% efficiency, and it can spin faster than 20,000 revolutions per minute. High-speed power density of the brushless EESM motor can be 25% higher than rare earth magnet motors.

The annual R&D 100 Awards is a global science and innovation competition that has been hosted by R&D World magazine since 1963. The competition is judged by industry professionals from across the world and evaluates nominations based on "impact, novelty, and practical application" in a variety of fields and categories. BorgWarner and ORNL were awarded in the IT/Electrical category.

Learn more about BorgWarner electric drive motors at:
borgwarner.com/technologies/electric-drive-motors.

You can read the ORNL paper on this technology development at:
https://www.ornl.gov/publication/polyphase-rotary-transformer-field-excitation-electric-machines. Published in 2024 IEEE Energy Conversion Congress and Exposition (ECCE).
Abstract:
This paper presents the magnetic design of a high-frequency three-phase rotary transformer for Wound Rotor Synchronous Motors (WRSM). The traditional DC field excitation of the WRSM is highly challenging as it relies on the brushed connection. The brush/slipring-based connections need cooling, sealing and prone to wear and tear requiring regular maintenance. The proposed three-phase rotary transformer replaces the traditional brushed excitation by a high-power density polyphase wireless excitation. Furthermore, compared to a traditional single-phase rotary transformer, the proposed three-phase rotary transformer significantly enhances the power density, and reduces the eddy current losses and the output voltage ripples.

Source: BorgWarner

Published February 2026

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