A concept model of the in-wheel motor exhibited by NSK
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The layout of the motor
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NSK Ltd exhibited a concept model of the "Wheel Hub Motor Fit" in-wheel motor at Tokyo Motor Show 2017, which was open to the public from Oct 28 to Nov 5, 2017.

Incorporating two motors and a compact transmission, the in-wheel motor realizes smooth acceleration, according to NSK. With the embedded transmission, it becomes possible to reduce the size of motor and ensure a high torque, the company said.

By arranging the two motors in the diameter direction and employing a combination of pinion gears and internal gears, NSK reduced the size and thickness of the in-wheel motor.

"We reviewed and improved the structure so that it can be contained in a limited space inside a wheel," the company said.

The output and maximum torque of each of the two motors is 12.5kW and 850N·m, respectively. The motor is expected to be embedded in the front wheels of compact cars. In that case, the maximum speed will be 130-140km/h (approx 81-87mph).

In general, in-wheel motors that are not equipped with a transmission change speed just by controlling motors, requiring a large-size motor that supports a wide speed range. On the other hand, with an embedded transmission, it becomes possible to use a compact, high-speed motor, enabling to reduce the size and weight of an entire in-wheel motor unit, NSK said. The company expects to reduce the weight by about 30%.

Original Japanese article