The new motor developed by Hitachi and Hitachi Industrial Equipment Systems
The new motor developed by Hitachi and Hitachi Industrial Equipment Systems
[Click to enlarge image]
The "laminated iron core structure" was employed for its iron core.
The "laminated iron core structure" was employed for its iron core.
[Click to enlarge image]

Hitachi Ltd and Hitachi Industrial Equipment Systems Co Ltd co-developed a permanent magnet synchronous motor with an efficiency of 93% without using a neodymium (Nd-Fe-B) magnet, which contains a rare-earth material.

The efficiency of the motor is equivalent to "IE4," which is the highest rank in the motor energy efficiency guidelines of the "IEC60034-31" international standard. The motor has an output power of 11kW and is targeted at industrial motors such as of large fans for sending air and fluid pumps.

With the new technologies, it is possible to realize an industrial motor whose performance is equivalent to that of a neodymium magnet-based motor at lower costs, the companies said. As one of the solutions to address the export restriction imposed by China, which accounts for 90% of the rare-earth materials produced in the world, and the rising prices in the wake of the restriction, Hitachi aims to start volume production of the new motor in fiscal 2014.

This time, the companies used an amorphous metal for the iron core of the stator and a ferrite magnet, which is cheaper than a neodymium magnet, for the rotor. Compared with magnetic steel sheets, which are commonly used, the amorphous metal has about 10 times higher magnetic permeability, and its energy loss (iron loss) as a magnetic material is about 1/10, making it easy to improve motor efficiency.

As for the structure of the motor, Hitachi and Hitachi Industrial Equipment Systems employed an "axial gap method" that uses two rotors to sandwich a stator in the direction of the axis of rotation in the aim of increasing the amount of ferrite magnet used for the motor. In 2008, the two companies used a similar technique to prototype a motor with an output power of 150W and an efficiency of 85% (See related article).

Furthermore, Hitachi and Hitachi Industrial Equipment Systems made improvements to the structures of the motor and the iron core to increase the output power and efficiency of the motor. For the motor, they improved its resistance to torque reaction force at the time of increasing output power by using a resin whose fracture toughness is as high as 3.1MPa√m for the stator. And they changed the structure of the rotor so that it can withstand high centrifugal forces.

In regard to the structure of the iron core, the two companies changed the method of processing the amorphous metal. The amorphous metal is as thin as 25μm and has a higher strength than a magnetic steel sheet. Therefore, in the past, they used the "rolled iron core structure," which forms an iron core by rolling the amorphous metal without cutting it. With this method, however, a remaining stress is generated inside the material by bending it, increasing iron loss.

This time, Hitachi and Hitachi Industrial Equipment Systems developed a technology to cut the amorphous metal and employed the "laminated iron core structure," which laminates the metal. As a result, they prevented iron loss from being increased by the process.