Unique air-cooled direct-drive system expands Astemo's lineup for in-wheel EVs; is compact, lightweight and efficient
The air-cooled 12-inch model achieves a continuous rating of 5.5 kW.
Together with the oil-cooled 16-inch and 19-inch models, they enable a wide range of in-wheel EV applications, from small cars to SUVs

12-inch air-cooled direct-drive system

Tokyo, May 16, 2025- Astemo, Ltd. (hereafter “Astemo”) has developed a 12-inch air-cooled direct-drive system for in-wheel EVs, which are gaining attention as the next-generation mobility with the enhanced EV performance, convenience and the ability to be installed in compact vehicles such as Kei cars. Directly transferring the driving force of the built-in motor to the wheels, the system achieves a continuous rating of 5.5 kW, which is ideal for everyday driving. Employing a simple air-cooling system, it achieves compactness, light weight, and high efficiency. Combined with the 16-inch and 19-inch systems, Astemo is aiming for direct-drive system deployment in various EV sizes, slated for implementation in around 2030.

Various companies are developing in-wheel EV direct-drive systems as a technology that will expand future mobility applications. Astemo has been collaborating with Hitachi, Ltd.’s (hereafter “Hitachi”) R&D group to develop an oil-cooled direct-drive system^* for 19-inch and 16-inch wheel applications. However, oil-cooled systems require cooling piping and ancillary components, posing an issue for small cars and motorcycles that have significant packaging and cost constraints. On the other hand, air-cooling presents another challenge in that the small wheel size constrains the heat dissipation area needed for cooling.

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  News release dated September 30, 2021, “Compact, Lightweight Direct-Drive System To Make In-Wheel Electric Vehicles Closer To a Production Reality”

• https://www.astemo.com/en/assets/pdf/news/20210930-01.pdf

The newly developed 12-inch direct-drive system has overcome such issues by adopting a new air-cooling structure that uses the rotation of the motor in the wheel to increase heat dissipation. Specifically, the rotary-fin structure, in which heat-dissipating fins are arranged on the entire outer surface of the motor's rotating parts, has greatly improved heat dissipation performance. As a result, it achieves a continuous rating of 5.5 kW per wheel, which is top class for its size, and a maximum output of 13 kW. When mounted on four wheels, it can meet the drive performance requirements of Kei car EVs.
This new air-cooled structure—developed in collaboration with Hitachi's R&D group—is simplified compared to oil-cooled systems, helping to eliminate issues such as layout complexity and increased costs. In addition, this system uses “easy disassembly concentrated coils,” which were developed through Green Innovation Fund Projects / Next-Generation Motor Development (JPNP21026) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Achieving higher motor efficiency and designed to be recyclable, these coils have a high space factor and are easy to disassemble. In addition, they will also be applied to the 16-inch and 19-inch systems as a common technology. With the three model applications, the direct-drive system can be used for EVs of various sizes.

The newly developed 12-inch air-cooled direct-drive system will be exhibited at the Automotive Engineering Exposition 2025, to be held at Pacifico Yokohama from May 21, 2025.

Astemo will contribute to realizing a sustainable society and enriched lives through the development and provision of advanced technologies that enhance the value of automobiles, including direct-drive system for in-wheel EVs.

Main specifications for in-wheel direct-drive system

Main specifications for in-wheel direct-drive system