BMW Axial Flux Motor: 20% More Efficiency & New Rotor Design

BMW is advancing electric vehicle propulsion with a cutting-edge axial flux motor featuring a specialized rotor design that secures magnets more effectively. This innovation targets higher efficiency, greater torque output, and superior long-term reliability, positioning it as a game-changer for EV performance.

The Shift from Radial to Axial Flux Motors

Traditional radial flux motors dominate current EVs, where magnetic fields flow radially from the center, resembling wheel spokes. These designs rely on a single rotor interacting with a stator to generate motion through alternating currents in copper coils.

Axial flux motors flip this paradigm: magnetic flux travels parallel to the rotor’s axis, enabling a pancake-like structure. This allows for larger active surface areas within compact volumes, yielding higher torque density. Engineers note that the broader diameter provides mechanical leverage on the shaft, amplifying torque at low RPMs without increasing size.

BMW’s approach builds on this by refining rotor construction. In axial flux setups, dual stators often sandwich a single rotor, distributing heat across more surfaces for better cooling via indirect water channels. This contrasts with radial motors’ cylindrical limitations, reducing core and copper losses due to shorter electromagnetic loops.

Breakthroughs in Rotor Magnet Retention

Central to BMW’s design is a novel method for holding magnets in the rotor. Conventional rotors use steel yokes or adhesives, which can degrade under heat and centrifugal forces. BMW’s solution employs a structural innovation that locks magnets firmly, ensuring stability at high speeds and temperatures.

This rotor enhances durability by minimizing magnet displacement risks, a common failure mode in high-performance EVs. The design also supports yokeless architectures, slashing weight and material use. Startups like DeepDrive, backed by BMW’s $16 million investment, exemplify this: their dual-rotor systems eliminate steel yokes, combining axial flux perks with radial manufacturability for 20% efficiency gains.

• Higher Torque Density: Larger flux surfaces double torque output per volume.
• Improved Cooling: Dual-sided stators expand heat dissipation areas.
• Modular Stacking: Central hollows allow easy motor stacking for scalable power.

BMW’s Partnership with DeepDrive

BMW’s investment in Munich-based DeepDrive accelerates axial flux adoption. DeepDrive’s dual-rotor motor merges two units into one compact package. A central stator drives inner and outer rotors simultaneously, boosting active material use and torque while cutting rare-earth magnets by half and iron by 80%.

Projections indicate costs one-third lower than equivalent radial motors. Rare-earth-free options further reduce dependency on scarce materials. BMW integrates this for battery EVs, not just hybrids, aiming for extended range and dynamic performance.

Engineering Advantages of Axial Flux Design

Axial flux motors excel in electromagnetic efficiency. Shorter flux paths cut losses, enabling high torque from standstill—ideal for EV acceleration. The pancake form integrates seamlessly into wheel hubs or central drives, freeing chassis space.

Yokeless designs like YASA’s (Yokeless And Segmented Armature) shrink diameters via advanced materials, reducing mass. DeepDrive’s truss-like copper windings add torsional rigidity and cooling channels, solving stiffness issues in steel-free rotors.

MPP Innovations’ collaboration with Torev Motors yielded a stator one-third shorter than radial equivalents using Soft Magnetic Composites (SMC). This modular setup hit 98% peak efficiency in 150 kW units, with 30% cost savings and weight reduction.

Real-World Applications and Performance Gains

BMW targets passenger EVs with this tech, enhancing range via real-world 20% efficiency boosts. Dual rotors synchronize for balanced fields: north poles align with south across rotors, tightening flux loops.

High power density suits in-wheel motors or AWD systems. Simulations confirm optimized torque at low speeds, vital for urban driving. Lightweight builds improve handling and energy use.

Challenges persist: manufacturing complexity demands precision winding and SMC molding. Yet, scalability via stacking and cost reductions make axial flux viable for mass-market EVs.

Future Implications for EV Industry

Axial flux motors herald lighter, more efficient EVs. BMW’s rotor innovation, paired with DeepDrive, could standardize dual-rotor axial designs, slashing costs and boosting range. Rivals like Turntide emphasize stacking for custom power.

As rare-earth prices fluctuate, material-efficient motors gain traction. Expect integration in upcoming BMW models, pushing industry benchmarks.

FAQs

What makes BMW’s axial flux rotor unique?

It features a novel magnet retention system for superior durability and efficiency under extreme conditions.

How do axial flux motors outperform radial ones?

They offer higher torque density, better cooling, and lower losses via larger flux areas and shorter paths.

What is DeepDrive’s role in BMW’s tech?

DeepDrive supplies dual-rotor, yokeless motors with BMW’s investment, enabling compact, high-torque designs.

Are axial flux motors cost-effective?

Yes, using less material, they promise one-third the cost of radial equivalents for same torque.

When will we see these in BMW EVs?

Development is advanced; expect prototypes and production models soon, enhancing range and performance.