There are 3 types of magnetic motors. Radial, Axial, and Transverse.
Radial Flux Motors (Most EV cars use this radial flux motors)
In short, features of a radial flux permanent magnet motor are designed on the sides. The copper windings are wrapped around slots. The flux is generated perpendicular to the axis of rotation. Flux refers to the magnetic flux which is present in electric motors and is caused by the magnetic field of the permanent magnets. The magnetic flux is measured in unit tesla (T). The magnetic flux is normally imposed by multiple permanent magnets. These magnets are often made of rare earth material, therefore they are called rare-earth permanent magnets.
As an example, traditional radial flux BLDC motors consist of a rotor made of permanent magnets located inside a stator. In this case:
- A stator contains support known as a yoke, which is outfitted with “teeth” containing electromagnetic coils
- The teeth function as alternating magnetic poles
- The rotor’s magnetic poles interact with the alternating magnetic flux of the wound stator teeth, resulting in the motor’s torque.
Axial Flux Motors
An axial flux BLDC motor design has a different geometry from a radial machine.
In axial flux motors, the flux is generated parallel to the axis of rotation because of the way its wound. This carries the advantage of simplifying the fabrication of the motor.
Although this type of electric motor geometry is far from new, it was rarely used in commercial applications due to manufacturability and costs when using laminations. Soft magnetic composite (SMC) materials exclusive to powder metal are allowing designers to exploit the axial topology’s advantages, driving the future of axial flux motors:
- High power density (More on this in a bit)
- Simplified high-current BLDC motor winding design
- Shorter magnetic path
Transverse Flux Motor:
Transverse flux motors (TFM motors) take a different motor stator winding design approach.
Instead of winding copper wire around the stator teeth or the pole, the TFM has coils circumferentially around the axis of rotation.
This setup enables the 3D flow of magnetic flux, where it crosses axially through the stator, circumferentially through the rotor, and radially through the gap between them.
As a result, you can increase low-speed torque and efficiency or even increase the power for particular energy inputs and motor sizes. The TFM design is uniquely suited for SMCs, and with their lower inherent core losses, there’s decreased cooling requirements for this style motor.