ZF Magnet-Free Electric Motor without Rare Earths

ZF receives major CLEPA innovation award for electric motor without rare earths

Motor of The Future Without Rare Earths

Frank Thoma, corporate media editor at ZF has reported that electric mobility is closely linked to the use of rare earth metals. Since their origin and mining can prove problematic, ZF adopts a three-pronged approach to make its product portfolio as responsible as possible.

What the combustion engine was for the mobility of the 19th and especially the 20th century, the electric motor is for current and future mobility. According to estimates from the International Energy Agency (IEA) in its Global EV Outlook 2023, the share of electric vehicles worldwide will reach the 35 percent mark in 2030. If the emissions caused specifically by the fuel are problematic in the combustion engine, the permanent magnets normally used in the electric motor are regarded as its Achilles heel. These magnets contain large quantities of the rare earth metals neodymium, praseodymium and dysprosium, which are expensive to mine. The electric driveline of a passenger car contains up to five kilograms of these metals, while a wind turbine generator has between 300 and 550 kilograms.

Rare Earths: so Important, so Problematic

The group of rare earth metals (rare earths for short) includes 17 metals. Although large quantities of these metals are usually present, mining is only feasible if the ore in the ground has a sufficiently high content of rare earth metals. Consequently, today’s known and developed deposits are limited to a handful of regions around the world. China currently produces between 70 and 80 percent of all rare earths for the global market. This creates a strong dependency for all customers and poses the risk of trade barriers. As with other raw material chains, monitoring occupational health and safety and human rights due diligence is also challenging for rare earth metals. In addition, the mining of rare earth metals involves processing enormous quantities of rock. The need to use toxic chemicals also risks contaminating soils and water.

The above gives rise to three obligations to act for ZF. ZF must ensure that the rare earths used in electric motors, for example, are produced ethically and ecologically. It is equally important to promote recycling of these valuable materials. The best way and thus ZF’s goal is to dispense with rare earth metals in its own products, replacing them with new technical solutions.

“Our suppliers of rare earth-containing products are also required to adhere to the standards defined by ZF for environmental protection and human rights.”
Olga Schick-Scheider, Head of Supply Chain Sustainability at ZF

Let’s turn to point one, regarding the responsible procurement of rare earth metals. ZF does not purchase these in raw form, but they will have already been processed into intermediate products, especially as permanent magnets for electric motors. The products come from various countries, mainly from China and Japan. “As with all products we purchase, our suppliers of rare earth-containing products are required to adhere to the standards defined by ZF for environmental protection and human rights. We evaluate our suppliers’ sustainability performance and support them in their sustainability journey,” says Olga Schick-Scheider, Head of Supply Chain Sustainability. In addition, the Group uses various tools to evaluate the sustainability performance of its suppliers.

Recovering Rare Earths

Recycling is another way of dealing with the critical material “rare earths” more sustainably. ZF is currently working on strategic partnerships with suppliers of recycled magnets. However, larger quantities of recycled metals will not be recovered for several years yet until large numbers of electric motors and wind turbines have reached their end of life. Although recycling will primarily improve the product carbon footprint of customers such as ZF in the future and is another important step toward a circular economy, increased reprocessing will of course not alter the highly uneven geographic distribution of useable natural deposits.

Recycling of rare earths is about to take off in a big way. Initiatives that promote this special recycling are therefore in demand worldwide. An EU-funded research project SUSMAGPRO stands for “Sustainable Recovery, Reprocessing and Reuse of Rare Earth Magnets in a European Circular Economy.” According to SUSMAGPRO, the recycling rate for rare earth metals is currently less than one percent worldwide. By 2027, it should be 25 percent in Europe. One of SUSMAGPRO’s goals is to develop a recycling supply chain for rare earth magnets in Europe. To this end, 19 companies from different industries have come together, including ZF.

Recycling-Compliant Development

One aspect addressed by ZF within SUSMAGPRO, is how products can be developed in order to enable efficient disassembly at the end of product life. More generally: “Optimising designs to make best use of critical rare earth materials, using magnet-free designs where appropriate, and ensuring rare earth metals where used aren’t lost at the end of a product’s life all contribute to a truly sustainable future.” notes Dr David Moule, Electric Drives Technical Specialist from the ZF Servo Drives Centre of Competence.

The insights gained by ZF designers from SUSMAGPRO are incorporated into the new design of motors. This is primarily about their improved recyclability, which in turn supports ZF’s sustainability strategy.

Avoiding Rare Earth Metals

The I2SM (In-Rotor Inductive-Excited Synchronous Motor) is one example of how this is feasible particularly with today’s standard permanent magnet-excited synchronous motor (PSM) with its relatively large amount of rare earth metals. ZF presented I2SM, an enhanced, production-ready variant of a separately excited synchronous motor (SESM), in late summer 2023. Unlike other magnet-free concepts for separately excited electric motors, ZF’s I2SM transmits the energy for the magnetic field via an inductive exciter within the rotor shaft. Compared to common SESM systems, the losses during energy transmission to the rotor are 15 percent lower in the I2SM due to the inductive exciter.

Even without permanent magnets, this motor has an extreme power and torque density and is still unusually small. “This uniquely compact electric motor without magnets is impressive proof of our strategy of making electric drives more resource-efficient and sustainable, especially by increasing efficiency,” says Stephan von Schuckmann. the person responsible on the ZF Board of Management for electrified drive solutions. Expressed in figures, this more resource-saving approach allows ZF to massively reduce its CO2 footprint in production with I2SM, by up to 50 percent compared to the classic electric motor with rare earth magnets. This is just one example of the technology company’s efforts and associated investments in sustainable technical solutions to make mobility more climate friendly.

 

ZF makes magnet-free electric motor uniquely compact and competitive

• Inductive current transmission unit inside the rotor enables ultra-compact e-motor design
• Performance data on par with permanent-magnet synchronous machines, currently the most common form of drive for e-vehicles
• Advantages: no magnets or rare earth materials, increased security of supply, and better sustainability and efficiency

2023-Sep-01 – Friedrichshafen, Germany. ZF has developed an electric motor which does not require magnets. In contrast to the magnet-free concepts of so-called separately excited synchronous motors (SESM) already available today, ZF’s I2SM (In-Rotor Inductive-Excited Synchronous Motor) transmits the energy for the magnetic field via an inductive exciter inside the rotor shaft. This makes the motor uniquely compact with maximum power and torque density.

This advanced variant of a separately excited synchronous motor is thus an alternative to permanent-magnet synchronous machines (PSM). The latter are currently the motors most frequently used in electric vehicles, but they are based on magnets which require rare earth materials for their production. With the I2SM, ZF is setting a new standard for making e-motors both extremely sustainable in production and highly powerful and efficient in operation.

“With this magnet-free e-motor without rare earth materials, we have another innovation with which we are consistently improving our electric drive portfolio to create even more sustainable, efficient and resource-saving mobility,” said Dr. Holger Klein, CEO of ZF. “This is our guiding principle for all new products. And we currently see no competitor that masters this technology as well as ZF.” Compared to common SESM systems, the inductive exciter can reduce losses for the energy transmission into the rotor by 15 percent. In addition, the CO2 footprint in production, which arises with PSM e-motors in particular due to magnets including rare earth materials, can be reduced by up to 50 percent.

“This uniquely compact electric motor without magnets is impressive evidence of our strategy to make e-drives more resource-efficient and sustainable, primarily through efficiency improvements,” said Stephan von Schuckmann, Member of the Board of Management of the ZF Group.

In addition to the benefits of eliminating rare earth materials in a compact and powerful package, the I2SM eliminates the drag losses created in traditional PSM e-motors. This enables better efficiency at certain operating points such as long highway trips at high speed.

Advanced rotor design makes e-motor very compact

To ensure that the magnetic field in the rotor is built up by current instead of magnets, the conventional SESM concepts currently still require sliding or brush elements in most cases, which force compromises: A dry installation space, i.e. not accessible for oil cooling and with additional seals, is necessary. As a result, conventional SESMs take up around 90 mm more space axially. As a result, manufacturers generally cannot flexibly vary between PSM and SESM variants in their model planning without additional effort.

In order to offer the advantages of separately excited synchronous machines competitively, ZF has succeeded in compensating for the design-related disadvantages of common separately excited synchronous machines. In particular, the torque density has been significantly increased compared to the state of the art thanks to an innovative rotor design. The space-neutral integration of the exciter into the rotor means that there are no axial space disadvantages. In addition, an increase in power density in the rotor leads to an improvement in performance.

Inductive excitation as a key technology

The technological prerequisite for the ZF innovation is that energy is transferred inductively, i.e. without mechanical contact, into the rotor, generating a magnetic field by means of coils. Thus, the I2SM does not require any brush elements or slip rings. Furthermore, there is no longer any need to keep this area dry by means of seals. As with permanently magnetized synchronous motor, the rotor is efficiently cooled by circulating oil. Compared to common separately excited synchronous motor, the ZF innovation requires up to 90 millimeters less axial installation space. In terms of power and torque density, however, the ZF innovation operates at the level of a PSM.

ZF plans to develop the I2SM technology to production maturity and offer it as an option within its own e-drive platform. Customers from the passenger car and commercial vehicle segments can then choose between a variant with 400-volt architecture or with 800-volt architecture for their respective applications. The latter relies on silicon carbide chips in the power electronics.

About ZF

ZF is a global technology company supplying systems for passenger cars, commercial vehicles and industrial technology, enabling the next generation of mobility. ZF allows vehicles to see, think and act. In the four technology domains of Vehicle Motion Control, Integrated Safety, Automated Driving, and Electric Mobility, ZF offers comprehensive product and software solutions for established vehicle manufacturers and newly emerging transport and mobility service providers. ZF electrifies a wide range of vehicle types. With its products, the company contributes to reducing emissions, protecting the climate and enhancing safe mobility. With some 165,000 employees worldwide, ZF reported sales of €43.8 billion in fiscal 2022. The company operates 168 production locations in 32 countries.