Japan’s Daido Steel Co., Ltd. and Honda Motor Co., Ltd. have announced the development of heavy rare earth-free magnets that will now be used for the first time in the driving motors of hybrid electric vehicles. Hot deformed neodymium magnets, containing no heavy rare earths, are reported to offer the high heat resistance properties and high magnetic performance required for motor applications and will be used in Honda’s new FREED vehicle, scheduled to go on sale at the end of 2016.
Neodymium magnets are used for the drive motors of electric vehicles, including hybrid vehicles, due to their high magnetic properties. These 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, due to regional restrictions on the production and supply of these heavy rare-earth elements, a reduction in their use has been one of the major challenges to using neodymium magnets for the drive motors of hybrid vehicles.
Daido Electronics Co., Ltd., a wholly owned subsidiary of Daido Steel, has produced 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 realise a fine crystal grain structure that is approximately ten times smaller than that of a sintered magnet, which makes it possible to produce magnets with greater heat resistance properties.
In developing the new neodymium magnets Daido Steel further evolved its hot deformation technologies and Honda, using its experience in the development of drive motors, revised the shape of the magnet. Through these joint development efforts the two companies achieved, for the first time in the world, a practical application of a neodymium magnet which contains absolutely no heavy rare earth elements yet has high heat resistance and high magnetic performance suitable for use in the drive motor of hybrid vehicles.
In addition to the shape of the magnet, Honda revised the shape of the rotor to optimise the flow of the magnetic flux of the magnet. As a result, the hot deformed neodymium magnet became usable for the drive motor, demonstrating torque, output and heat resistance performance equivalent to those of a motor that uses the conventional type of magnet.