Electromobility New Motor Without Rare Earths Reduces Resource Dependencies

Related Vendors

Hitachi Astemo Europe GmbH

FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Astemo has developed a motor for electric vehicles that completely eliminates the use of rare earths. The new development is based on a synchronous reluctance motor system.

Electric motors typically use permanent magnets made of rare earths, such as neodymium, in the rotor to generate strong magnetic fields. However, rare earths are associated with significant geopolitical risks, and ensuring a stable supply is challenging. Magnets without rare earths, such as ferrite magnets, are readily available but possess only about one-third of the magnetic strength. To achieve the same performance as their rare-earth counterpart, the motor would need to be designed about three times larger. As an alternative, induction motors and externally excited motors have been introduced, which do not rely on permanent magnets. However, because they generate the magnetic field in the rotor using electromagnets, they require large amounts of copper in the rotor. With the increasing use of renewable energy sources and the growing prevalence of electric vehicles, this poses a potential resource risk for induction and externally excited motors, particularly concerning possible copper shortages.

"Multi-Layer-Flux" Structure

Astemo has therefore developed a new synchronous reluctance motor as a sustainable alternative. The motor generates rotational force by utilizing differences in magnetic resistance (reluctance) resulting from the shape of the rotor core. By developing a "multi-layer flux" structure, the path of magnetic power transmission is divided into several layers. At the same time, the current can be controlled so precisely that magnetic poles are specifically formed in the rotor core. In this way, the strong magnetic force of neodymium magnets can be compensated. The formation of magnetic poles in the rotor core requires a higher current flow through the stator coils. This poses a significant challenge, as the coils heat up more as a result. For this purpose, the company has developed a structure in which the slots and ends of the coils are immersed in cooling oil. This significantly reduced the additional heat generation in the motor.

In terms of performance, the main drive motor, which is continuously in use in an electric vehicle, achieves a power output of 180 kW. It is a magnet-assisted synchronous reluctance motor that uses ferrite magnets as a supporting element. At the same time, the size increase compared to conventional permanent magnet motors with rare earths is limited to 30 percent. For the auxiliary drive, a synchronous reluctance motor was developed that operates entirely without magnets. This is because magnets installed in an auxiliary drive motor could act as braking torque during the coasting phases of the main drive, causing energy losses. The auxiliary drive motor is therefore only used as needed to provide additional power and delivers up to 135 kW. In this way, the overall energy consumption of the drive system can be effectively reduced. (se)