New design allows smaller, lighter traction motors

February 04, 2019 //By Christoph Hammerschmidt
Plastic cooling case for lightweight motor
If electric cars are to be lighter, the motor must also be reduced in weight. For example, by manufacturing it from fiber-reinforced plastics. Researchers at the Fraunhofer Institute for Chemical Technology ICT and the Karlsruhe Institute of Technology KIT have developed a new cooling concept that enables the use of plastics as housing material. This also allows power density efficiency of the drive to be significantly increased.

High power density, small installation space within the electric vehicle and high efficiency play an important role in the success of sustainable mobility. In the DEmiL cooperation project, short for “Direct-cooled Electric Motor with Integral Lightweight housing”, researchers from Fraunhofer ICT are working together with the Electrotechnical Institute and the Institute for Vehicle Systems Technology at KIT to develop a new concept characterized by direct cooling of the stator and rotor. "An electric motor consists of a rotating rotor and a stationary stator. The stator contains wound copper wires through which current flows. This is where most of the electrical losses occur. The real innovation of our concept lies in the stator," explains Robert Maertens, scientist at Fraunhofer ICT.

Electric motors already have a high degree of efficiency; typically, they reach more than 90 %. The remaining about 10 % of the electrical power is lost in the form of heat. To prevent the motor from overheating, the heat in the stator was previously dissipated through a metallic housing to a cooling jacket with water. The research teams are replacing the round wire with rectangular flat wire that can be wound tighter onto the stator. This creates more space for the adjacent cooling channel. This optimization allows the heat loss to be dissipated through the internal cooling channel and no longer has to be transported out through the metal housing to a cooling jacket. A cooling jacket is no longer required in this concept. Another consequence is that the motor achieves a higher continuous output and the thermal inertia is reduced. In addition, cooling of the rotor also allows its heat loss to be dissipated in the motor.

Since the heat is dissipated where it arises, the project partners can design the complete motor and the housing in plastic material and thus realize further advantages: They save weight, and plastic housings are also easier to produce than aluminum ones. Even


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