ZF’s newest electric motor: less CO2, no rare-earth metals

At the IAA Mobility in Münich, automotive supplier ZF puts the spotlights on a new type of motor for electric cars. The I²SM is a variant in the externally excited synchronous family. Still, ZF has found ways to cut its CO2 footprint in half during production and reach interesting levels of sustainability and efficiency.

The externally excited synchronous e-motor (SESM) is a significant step away from the permanent-magnet (PSM) versions widely used in current-generation battery-electric cars. Their independence from magnets lifts the value chain’s strain, specifically the mining for rare-earth metals like neodymium or cobalt – a geopolitical worry.

Power in a small package

With the I²SM (for In-Rotor Inductive-Excited Synchronous Motor), ZF wants to raise the externally excited synchronous e-motor standards. Its compact housing sets it apart from other FSMs while retaining a comparable output and torque density to PSM motors. ZF has achieved this by an inductive energy transfer inside the rotor.

As mechanical contact is absent, the I2SM does away with the brushes, coils, and slip rings still found on comparable SESM motors where they generate current. This uses space, making it a headache for car makers to switch as the platform design doesn’t allow such alterations.

As the energy inside the I²SM is transferred through induction, the more convenient packaging allows for better integration into (existing) e-cars. Further advantages of ZF’s solution are a 15% lower loss during energy transmission, compared to SESM, and a 50% reduction of carbon footprint compared to PSM versions. The motor also eliminates drag losses, which are typical for the latter. This means it runs more efficiently at higher speeds during more extended travels.

400 and 800 volts

According to the company, the concept is unique and set to contribute to substantial progress in EV development. “We currently see no competitor that masters this technology as well as ZF.”, said the CEO of ZF Holger Klein in an official statement.

The I²SM is still a concept, but ZF is preparing the motor for production, claiming it will be offered in 400-volt and 800-volt versions, ready for use in passenger cars and commercial vehicles.