The conversation surrounding the use of rare earth materials and the environmental impact and cost of using them has led to many in the industry actively working to move away from the use of rare earth metals like cobalt and neodymium. The key challenge for the industry is finding alternatives that produce the same or more levels of efficiency as the permanent magnet motor.
Wanting to understand how or if this could be done, Automotive IQ spoke with Dr. João Bonifácio, Head of System Development Advanced Engineering - Electrified Powertrain Technology at ZF Group to learn insights on reducing rare earth materials, improving efficiency in doing so and what alternatives can be used.
Q: How can OEMs reduce using rare earth materials, or completely remove them from motors while maintaining efficiency?
João
The reduction of rare-earth materials is a very important subject not only due to its cost impact but also due to the possibilities of reducing the CO2 footprint of e-drives and minimising supply risks. We are currently working on two different paths for promoting the reduction or elimination of rare earth materials. The first path to take is the reduction of the heavy rare earth content of magnets in Permanent Magnet Synchronous Machines (PMSM). The other one relates to the use of magnet-free technologies, like the Separately Excited Synchronous Machines (SESM). Both paths have their advantages and challenges, but it is clearly possible to maintain high-efficiency levels on both solutions.
Q: Following on from this, what low-cost material alternatives to rare earth materials are there and why are alternatives required?
João
Alternatives are required due to strategic and economic aspects. Rare earth materials and heavy rare earth elements (HREE) in particular have a significant environmental impact in their mining and processing. Moreover, there are also concerns about supply chain security and price volatility, which could drastically impact long-term perspectives for e-mobility products. For the PMSM, a first step on reaching high efficiencies and power densities with magnets free of the heavy rare earth elements Dysprosium (Dy) and Terbium (Tb) have been demonstrated in our e-drive prototype EVSys800, where a very high torque density (5210 Nm/75 kg) and 75% ratio of continuous and peak power have been reached.
For the SESM, we developed the In-rotor Inductive-Excited Synchronous Machine (I²SM), which features a brushless exciter fully integrated into the rotor shaft and a completely magnet-free rotor. The brushless exciter shows 15% less losses than commonly used exciter technologies and the machine has a superior power density (with up to -90mm axial length advantage compared to benchmark) and very high efficiencies in highway cycles than comparable technologies.
Q: How can alternative technologies be used to reduce costs?
João
These alternative technologies can have a significant cost-reduction impact enabled by using cheaper materials, i.e., copper instead of magnets in one case and the use of cost-optimised magnets in the other. Moreover, if these technologies can be combined with a system-level approach, which
includes optimised cooling systems and various software functions, just to mention two examples, that can enable weight reductions and the use of fewer materials, the reachable cost savings can be further increased. It is also important to mention that the reduced supply-chain risks with, for instance, the I²SM technology can also reduce future cost risks.
Q: How can OEMs incorporate rare earth-free motors into different models?
João
The key to increasing the application range of magnet-free motor topologies relies on their optimisation for reaching the requested performance while minimising the necessary installation space. This was one of the main motivations for developing the I²SM technology. As objectives for this product, we set the same values of the performance indicators efficiency, power, and torque as a state-of-the-art PMSM e-drive system, while keeping the same installation space as the reference machine. This would allow a seamless transition between these two technologies in the available platforms.
Q: What are the challenges related to reducing the amount of rare earth materials in motors, and more importantly, what are the solutions?
João
There are multifaceted challenges at the system level that must be solved to reduce the amount of rare earth materials. To mention an example of challenges we face for the PMSM when reducing the heavy rare earth content of magnets, we also increase their temperature sensitivity and therefore the probability of demagnetisation. To cope with this challenge, the thermal conditioning of the e-drive system must be designed very carefully and the system reactions to special situations like short circuits must be considered as well.
Regarding the I²SM, we are also faced with similar challenges. The cooling system has a significant impact on continuous performance and efficiency, and the functional challenges related to the technology must be addressed with a suitable system design.
Q: What technologies can be used to eliminate the dependency of using rare earth materials?
João
The two previously mentioned technologies have an enormous potential for reducing or eliminating the dependency of using rare earth materials. The scope of application of each one will depend on the exact requirements needed for a particular scenario. Nevertheless, they represent a big leap forward in the direction of building more cost-effective and sustainable e-drives.