Magnetics Business & Technology - May/June 2023 - 44

INDUSTRY NEWS
Halbach Magnet Array Key to In-Wheel Drive by Hitachi & Honda
By placing the permanent magnets in a Halbach array and using
flat coils, Hitachi and its joint venture partner Honda have
developed a powerful yet lightweight direct-drive system for
electric vehicles that combines the motor, inverter and brake
into a single unit which can be installed in the wheel. The new
motor transmits the high drive force necessary to run an EV directly
to the wheels, and its lightweight design with world-class
2.5 kW/kg power density significantly limit the weight increase
traditionally associated with in-wheel motors, the companies
said.
Increasing the number of magnetic poles is effective in improving
a motor's drive force but also can reduce the proportion of
magnetic flux that can be effectively used, requiring more coil
weld points and welding space, they explained. By placing the
magnets in a Halbach array, however, the Hitachi and Honda
engineers improved the drive force by increasing the effective
magnetic flux of each magnetic pole and made the motor lighter
by using beam welding to create a high-density array of flat
coils. This limits the in-wheel weight increase of the EV, and
avoids the increased energy consumption that is characteristic
of conventional, heavier in-wheel systems.
Sometimes called a one-sided flux structure, a Halbach array
(pictured at right) has the magnets arranged to create a
stronger field on one side while reducing the field on the other
side to near zero. The magnets are oriented so that their poles
are out of phase, typically by 90 degrees, essentially re-routing
the magnetic field below the structure to the plane above it,
strengthening the magnetic field of the working surface.
Adopting an in-wheel unit does not require a substantial change
to the existing configuration of the suspension and other components,
they note. Driveshafts and other indirect mechanisms
have been eliminated, allowing motor power to be applied
directly to EV operation, reducing energy loss by 30% and
increasing the range on a single charge compared to existing
EVs. The system also enables more expansive interior and battery
space.
It uses direct-cooling technology. High-insulating cooling oil
directly cools the power semiconductors and is cycled to the
44 Magnetics Business & Technology * May/June 2023
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motor to directly cool the coils. This combined with the singleunit
drive system-which integrates a motor, brake and inverter
significantly reduces the space taken up by cooling pipes and
enables in-wheel installation without having to significantly alter
the existing configuration of suspension and other components.
The system was jointly developed by Hitachi and Hitachi Astemo,
which is a joint venture with Honda set up as a technology
company that develops and manufactures automotive and
transportation components as well as industrial machinery and
systems. Hitachi Astemo said it plans to apply the new directdrive
system to its already extensive, global EV product lineup.
For more info, see www.hitachiastemo.com.
http://www.hitachiastemo.com http://www.MagneticsMag.com
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