Electric motors in current e-cars mostly work with permanent magnets inside. That has disadvantages. Other manufacturers such as BMW and Renault use current-excited magnets. Supplier ZF has now further developed this principle and is bringing a separately excited synchronous motor with a revolutionary design.
Separately excited (= current-excited) electric motors basically have the advantage that they do not require rare earths, metals that are not only rare but also expensive and sometimes obtained under inhumane conditions. Compared to permanent magnet motors, however, those with brush or sliding contacts need more installation space, and they are also less efficient, explained ZF CEO Holger Klein at an event of the German Car Awards, where he presented the jurors present with the motor that his company had devised: the In-Rotor Inductive-Exited Synchronous Motor (I²SM). In a new development, the magnetic field is transmitted without contact via an inductive exciter inside the rotor shaft instead of being generated from the outside. Transmission losses are said to be 15 percent lower than in conventional separately excited motors. In addition, the company from Friedrichshafen promises a particularly compact design: Compared to conventional FSM engines, the ZF innovation requires up to 90 millimeters less axial installation space. “This makes the engine uniquely compact with the highest power and torque density,” promises Klein. The size of the I²SM corresponds to that of a PSM motor. Test drives in a Porsche Taycan equipped with the I²SM did not reveal any differences when driving. Things get interesting when the reduced space requirement can be factored into the design of the vehicle. In addition, the CO2 footprint in production, which occurs in PSM-E motors in particular through magnets with rare earths, can be reduced by up to 50 percent. as well as 800 volt systems.
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