ZF Develops Magnet-Free Electric Motor

ZF has developed an electric motor that does not require magnets and that is not on the SESM concept. The I2SM (In-Rotor Inductive-Excited Synchronous Motor) transmit the energy of its magnetic field via an inductive exciter inside the rotor shaft. This makes the motor uniquely compact for its power and torque density.

According to ZF, when compared to common separately-excited synchronous motor (SESM) designs, the I2SM can reduce losses for energy transmission into the rotor by 15 percent. Additionally, the CO2 footprint for production can be reduced by up to 50 percent when compared to the standard permanent-magnet synchronous motors used commonly in today’s electric vehicles. The ZF I2SM design requires no rare earth metals, thus removing one of the costliest and most environmentally unfriendly parts of current EV motor design. The I2SM also eliminates the drag losses inherent in current e-motor design, which would enable better efficiency at higher speeds.

Other advantages to the I2SM design, says ZF, are its allowance for liquid cooling, something that SESMs cannot do. Because the I2SM is so compact, it can easily replace current permanent-magnet motors without much engineering. Another advantage over larger SESM designs.

ZF plans to continue development of the I2SM design towards production maturity. It will offer it as an option in its own e-drive platform at that time and will be available for both a 400-volt or 800-volt architecture.