Hitachi believes it has the formula to deliver in-wheel power

TOKYO — In-wheel motors are a long-standing dream for electric vehicles. They hold the potential to transform car design by moving motor hardware to the wheels, freeing up valuable real estate for cabin space.

But the systems are still clunky, heavy and lacking in power. Commercialization is a long way off.

Japanese electronics giant Hitachi and its automotive unit Hitachi Astemo are now touting a breakthrough that brings this long-sought technology one step closer to reality.

Hitachi's newly developed direct-drive system reduces the weight and size of an in-wheel motor setup for EVs while also increasing its power.

The prototype combines the motor, inverter and brake in a single unit that fits in a 19-inch wheel hub and generates 60 kilowatts of power. The in-wheel setup can be arrayed in a two-motor or four-motor layout for total output of up to 240 kW, Akeshi Takahashi, manager of Hitachi's Mobility Drive Systems Research Department, told Automotive News.

The key advance is achieving a power density measured at 2.5 kW per kilogram, which exceeds the 2 kW per kilogram performance of a normal e-axle system, Takahashi said.

Maximizing power density is key for a couple reasons. As proposed, in-wheel motors add weight because instead of having one centralized unit, they require multiple motors and inverters. And to move a C- or D-segment vehicle, each motor needs an output of at least 25 kW, which is quite large.

But by increasing the power density, Hitachi was able to reduce the size of the motor, permitting engineers to also install the inverter and brake inside the wheel as a combined unit.

The company is testing prototypes of its direct-drive motor for reliability and production engineering. It is also working to further reduce cost, Takahashi said, which means the technology could still take years to be market-ready.

But by their very design, in-wheel motors can offset the cost of traditional electric motor setups because they don't require a reduction gear or drive shaft to transfer power.

"We are optimistic because our in-wheel motor system doesn't need any mechanical systems," Takahashi said. "The design is really simplified."

Hitachi's trick is arranging the magnets of the motor in what is known as a Halbach array, widely used in home appliances, which improves the magnetic flux on each magnetic pole and increases the drive force. And Hitachi sheds weight from the system by using beam welding and high-density flat motor coils.

The flat coil approach uses fewer welding points and saves space by condensing the wires. The new coil is made by punching out flat coil from copper plating.

"We eliminated the gaps between the coils, and that leads to weight reduction," Takahashi said.

Hitachi also adopted a direct cooling design that uses oil to cool both the motor and the inverter. Normally, cooling oil is used for the motor, not the inverter.

Hitachi's approach allows it to ditch the bulky water jacket for the inverter while also improving cooling efficiency. Doing so also helped reduce the packaging.

Hitachi does not yet have any committed customers for the new system, Takahashi said. And it's not the only company pursuing in-wheel technology. Japanese motor-maker Nidec is among the rivals that have also announced a prototype.

But Hitachi thinks it can leverage its technological breakthrough.

"It's our challenge to reduce the cost and weight and increase the efficiency," Takahashi said. "This is the fundamental competition."