By Josh Perry, Editor
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Researchers from the Fraunhofer Institute for Chemical Technology (ICT) and the Karlsruhe (Germany) Institute of Technology (KIT) developed a new directly-cooled motor for electric vehicles that allows polymer materials in the housing to reduce weight, increase power density, and improve efficiency.

Sectional view of the electric motor. The core of the motor is a stator consisting of twelve individual teeth, which are wound upright using a flat wire. (Fraunhofer ICT)

According to a report from Fraunhofer, the DEmil (directly-cooled electric motor with integrated lightweight housing) project focused on developing a new design for the motor’s stator, which contains the copper windings that electricity flows through.

With 10 percent of the electrical energy produced by electric motors being lost to heat, the researchers replaced round wires with flat, rectangular wires that can be wound tighter in the stator and increases the space for a cooling channel.

Instead of requiring the heat to be transferred through a metal housing to a cooling channel, this new design places the cooling channel inside the stator. There is also a rotor cooling solution that dissipates heat inside the motor.

By incorporating thermal management at the spot where heat is being created, there was no need for metal housings. Instead, the motor housing was built with fiber-reinforced, thermoset plastics that are temperature-resistant and resistant to the coolants being used.

“The polymer housing is produced in an automated injection molding process using the phenolic molding compound Vyncolit X7700,” the article explained. “The cycle time for manufacturing the prototypes is currently four minutes. The stators themselves are overmolded with a thermally conductive epoxy resin molding compound (Sumikon EME-A730E) in a transfer molding process.”

This manufacturing process should enable the motor to be mass-produced. A prototype motor was built and tested to ensure the process works as expected. Researchers found that it dissipated 80 percent of the remaining heat and that could be enhanced by optimizing the coolant flow.

Watch a video about the motor at https://www.fraunhofer.de/en/press/research-news/2019/february/directly-cooled-electric-motor-made-from-polymer-materials.html.