How BMW’s Rotor Design Enhances EV Motor Efficiency
In recent months, General Motors, Porsche, Mercedes-Benz, and Hyundai have all submitted patents for improved rotor designs for electric motors in the quest to improve power and efficiency. BMW has now also submitted an application with the European Patent Office for a rotor design for an axial flux electric motor. It goes about it in a different way, proposing a rotor in which the permanent magnets are embedded in a metal package to optimize magnetic flow.
BMW’s Rotor Secures Magnets Under High RPM Stress
Being a central part of the motor core, rotor design is critical to motor performance and efficiency. Because electric motors can spin at up to 20,000 rpm and even more, the permanent magnets have to be securely embedded in the rotor so they don’t become dislodged under high centrifugal loads, which can cause catastrophic motor failure.
To this end, BMW secures the magnets in a sheet-metal package in special pockets, and an axial stop is incorporated into the rotor design that prevents any radial movement by the magnets. The magnet package also features air gaps that reduce stray fields and optimize magnetic flow.
What Sets BMW’s Patent Apart from Other Rotor Designs
This patent isn’t too dissimilar to some other rotor patents out there, but BMW’s rotor design is unique in the way it uses an axial stop to restrain magnet movement, as well as a sheet-metal package to hold the magnets. The magnet pockets and air gaps to optimize magnetic flow and control stray fields are also uniquely configured in this rotor design.
Advantages Of BMW’s Rotor Design
BMW says its rotor design holds several benefits:
- Optimized magnetic flux flow
- A reduction in stray fields
- Secure magnet placement with no radial movement, even at high motor speeds
- Improved motor performance
- Long-term motor durability
BMW’s patent improves rotor design in several ways, but other automakers are also experimenting with anisotropic rotor materials, the placement of wire and rod conductors, and others. Many of these best practices will likely converge into a commonly accepted rotor design, so don’t regard this as the final frontier by a long shot, as motor design still improves considerably with every new iteration as we edge closer to an electrified future.
