ABB Files Patent for Traction Motor Using Bonded Mn-Bi Magnets with Customized Magnetic Profiles

ABB Switzerland Ltd. has filed a patent application for a “traction motor with bonded magnets,” according to information published by the China National Intellectual Property Administration. The application, published under CN121863729A, was submitted in October 2025.

The filing reflects ongoing efforts by ABB to advance motor design technologies through alternative magnetic materials and optimized rotor structures for traction applications.

Patent Overview

According to the abstract, the invention relates to a traction motor equipped with bonded permanent magnets integrated into the rotor structure.

The motor includes:

• A rotor containing one or more magnet cavities

• At least one magnet positioned within each cavity

• A stator arranged opposite the rotor magnets

• Bonded Mn–Bi (manganese-bismuth) permanent magnets placed inside the rotor cavities

A key feature of the design is that the Mn–Bi bonded magnets are shaped into a desired contour, allowing the magnetic geometry to better match performance requirements.

Technical Focus: Mn–Bi Bonded Magnets

The patent highlights the use of manganese-bismuth (Mn–Bi) based bonded magnets, which are considered a potential alternative to conventional rare-earth permanent magnets.

Compared with traditional rare-earth materials such as NdFeB, Mn–Bi magnets offer:

• Reduced dependence on critical rare-earth supply chains

• Improved thermal stability in certain operating ranges

• Flexibility in shaping due to bonded magnet processing techniques

However, Mn–Bi materials also face challenges, including:

• Lower energy product compared to NdFeB

• Manufacturing and material processing complexity

Design Innovation: Contoured Magnet Geometry

A notable aspect of the patent is the shaping of bonded magnets into a “desired profile.”

This design approach may provide:

• Improved air-gap flux distribution

• Reduced torque ripple

• Better electromagnetic optimization for traction applications

• Enhanced adaptability to rotor cavity geometry

By tailoring magnet geometry, the motor can achieve more precise electromagnetic field control without relying solely on material performance improvements.

Application Context: Traction Motors

Traction motors are widely used in:

• Electric rail systems

• Industrial transport equipment

• Heavy-duty mobility platforms

For these applications, key performance requirements include:

• High torque density

• Thermal stability under continuous load

• High reliability in harsh operating environments

The use of bonded Mn–Bi magnets suggests an exploration of cost and supply-chain diversification strategies in high-performance motor design.

Industry Implications

This patent reflects several broader trends in electric motor development:

1. Material diversification beyond rare earths
   Manufacturers are actively exploring alternatives to NdFeB magnets due to supply volatility and cost pressures.

2. Geometry-driven performance optimization
   Increasing emphasis is placed on shaping and structuring magnetic materials to improve electromagnetic efficiency.

3. Integration of bonded magnet technology
   Bonded magnets enable more complex geometries compared to sintered magnets, supporting advanced rotor designs.

Outlook

While the patent does not necessarily indicate immediate commercial deployment, it highlights ABB’s continued exploration of next-generation motor architectures.

If successful, such designs could contribute to:

• More resilient supply chains

• Improved manufacturability of traction motors

• Enhanced design flexibility in electric drive systems

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