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Daido Steel & Honda develop neodymium magnet free of heavy rare earth elements; Honda Freed hybrid first to adopt resulting new motor

Daido Steel Co., Ltd. and Honda Motor Co., Ltd. have developed a practical hot deformed neodymium magnet containing no heavy rare earth elements (REE) that still delivers the high heat resistance properties and high magnetic performance required for the use in the driving motor of a hybrid vehicle.

Honda will first apply this hot deformed neodymium magnet with absolutely no heavy rare earth elements to the Honda Sport Hybrid i-DCD (Intelligent Dual Clutch Drive) system, a system Honda will use in 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.

Neodymium magnets (NdFeB, an alloy of neodymium, iron and boron), have the highest magnetic force among all permanent magnets and are used for the drive motors of electric vehicles including hybrid and full-electric vehicles. Thus, demand for neodymium magnets is expected to grow exponentially in the future.

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

Summary of the rare earth elements of most interest to industry, contained within the light (LREE), medium (MREE) and heavy (HREE) groups. Source: Technology Metals Research. Click to enlarge.

However, major deposits of heavy rare earth elements are unevenly distributed around the world, and also are categorized as rare metals; thus, the use of heavy rare earth elements carries risks from the perspectives of stable procurement and material costs. As a result, 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.

GM’s approach to reducing REE; ferrite
GM’s first-generation Voltec system used NdFeB magnets in both motors. In the second generation, to optimize the EV range of the system, motor A was designed with a Ferrite magnet rotor while motor B was designed with an NdFeB magnet rotor. (Earlier post.) The Gen 2 system transmits most power through motor B under typical driving conditions, while motor A is used to augment power at high loads.
Each motor design was optimized to match its distribution of operating points. Since motor A rotates during most operating conditions but is mostly at zero torque, it was designed with weaker magnet flux to minimize speed related losses.
Although using ferrite magnets in a motor is not a new idea, most of the machines designed with these types of magnets are intended for use in industrial applications in which the requirements of size, torque density and wide operating temperature range are not as extreme as in automotive traction applications.
GM engineers developed other ways to increase the torque capability of the ferrite-magnet machine using a topology referred to as Permanent Magnet Assisted Synchronous Reluctance Machine (PMASRM).

Daido Electronics Co., Ltd., a wholly owned subsidiary of Daido Steel, has been mass-producing neodymium magnets using the hot deformation method, which differs 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 that is approximately ten times smaller than that of a sintered magnet, which makes it possible to produce magnets with greater heat resistance properties.

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, for the first time, 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.

Honda also designed a new motor to accommodate 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.

Left. Heavy rare earth-free magnets. Right. A rotor for the i-DCD drive motor. Click to enlarge.

As a result, the hot deformed neodymium magnet that contains absolutely no heavy rare earth 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.

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.

With the newly-developed hot deformed neodymium magnet, Daido Steel will make a new entry into the market for magnets used for drive motors of hybrid vehicles, which has been basically monopolized by sintered neodymium magnets.

Starting in August 2016, Daido Electronics will begin the mass-production and shipment of this magnet using a new production line that the company built in its factory (located in Nakatsugawa City in Gifu Prefecture in Japan) using a subsidy received from the Japanese Ministry of Economy, Trade and Industry (METI).

Daido Steel will continue pursuing the development of heavy rare earth-free magnets with further improved properties.

Furthermore, Daido Steel has been procuring magnetic powder, the raw material for magnets, from Magnequench International Inc. (located in Toronto, Ontario, Canada), and Daido Steel will work together with Magnequench to develop new types of raw magnetic powders for the purpose of realizing enhanced magnetic properties.


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