First Hybrid Vehicle eMotor Magnet Free of Heavy Rare Earth Elements

Daido Steel Co., Ltd. and Honda Motor Co., Ltd. became the world’s first companies to achieve practical application of a hot deformed neodymium magnet containing no heavy rare earth^*1 and yet with high heat resistance properties and high magnetic performance required for the use in the driving motor of a hybrid vehicle. This heavy rare earth-free hot deformed neodymium magnet will be applied first to the all-new Honda FREED, scheduled to go on sale this fall.

Background of the Neodymium magnets

Neodymium magnets have the highest magnetic force among all magnets in the world and are being used for the drive motors of electric vehicles including hybrid vehicles, and therefore demand for neodymium magnets are expected to grow exponentially in the future.

For use in the drive motors of electric vehicles, neodymium magnets must have high heat resistance properties as they are used in a high temperature environment. Adding heavy rare earth (dysprosium and/or terbium) to the neodymium magnets has been a conventional method to secure such high heat resistance.

However, major deposits of heavy rare earth elements are unevenly around the world, and also are categorized as rare metals; thus, the use of heavy rare earth carries risks from the perspectives of stable procurement and material costs. Therefore, a reduction in the use of heavy rare earth elements has been one of the major challenges needing to be addressed in order to use neodymium magnets for the drive motors of hybrid vehicles.

New development to remove heavy rare earth

Daido Electronics Co., Ltd., a wholly owned subsidiary of Daido Steel, has been mass-producing neodymium magnets using the hot deformation method, which is different from the typical sintering production method for neodymium magnets. The hot deformation method is a technology that enables nanometer-scale crystal grains to be well-aligned in order to realize a fine crystal grain structure. This structure is approximately ten times smaller than that of a sintered magnet, which makes it possible to produce magnets with greater heat resistance properties.

This time, Daido Steel and Honda jointly developed new neodymium magnets while Daido Steel further evolved its hot deformation technologies and Honda leveraged its experience in development of drive motors and revised the shape of the magnet. Through these joint development efforts, the two companies achieved a practical application of a neodymium magnet which contains absolutely no heavy rare earth yet has high heat resistance and high magnetic performance suitable for use in the drive motor of hybrid vehicles.

Moreover, Honda designed a new motor which accommodates this new magnet. In addition to the shape of the magnet, Honda revised the shape of the rotor to optimize the flow of the magnetic flux of the magnet. As a result, the hot deformed neodymium magnet became usable for the drive motor of a hybrid vehicle, demonstrating torque, output and heat resistance performance equivalent to those of a motor that uses the conventional type of magnet.

Benefit of this technology

Adoption of this technology enables a break from the constraints associated with heavy rare earth, which had been one of the challenges to expanding the use of neodymium magnets. This technology will make it possible to avoid resource-related risks and diversify channels of procurement.

Next steps

Honda will first apply this hot deformed neodymium magnet with absolutely no heavy rare earth to the Honda SPORT HYBRID i-DCD^*2, a hybrid system Honda will adopt for the all-new FREED scheduled to go on sale this fall. Honda will continue expanding application of this technology to new models in the future.