Which flux type are our motors – radial or axial flux?

With axial flux motors surfing on a bit of hype right now, we frequently get questions on the flux type we are using to design Elaphe high-performance motors and the thought process behind it.

Our team takes these questions very seriously, so we even reached out to other companies in the in-wheel motor space to see, how others in the industry view this topic.

In order to help you, our readers, get insight into our process, here we lay down the reasons for deciding primarily for radial-flux style in our in-wheel motors and our objectives around it.

 

Image: From left to right – Elaphe RFM motor // Elaphe TFM motor, industrialized by Domel for e-scooters (12% more efficient than nearest competition) // Example of a state-of-the-art axial flux e-motor

FACT #1 – The motor design comes out of requirements, based on holistic state-of-the-art analysis.

We have chosen a multiphysics design approach where one looks at all sorts of requirements needed for the desired outcome.

When we started, we considered all sorts of layouts in concept. Radial flux, axial flux and TFM and their variations with regards to the rotor, stator configuration, winding type, magnet distribution, number of phases and others.

We were not driven by the e-machine design, but rather by the requirements of the in-wheel application such as the nature of the majority of loads, the shape of the design space, the required robustness, other components that need to be fitted in the wheel, the ability to achieve higher pole pair count machines and of course simplicity and cost.

FACT #2 – Data provides a clear tradeoff and overall assessment to meet the required objectives.

The radial flux motor clearly came on top based on requirement analysis. Then, in subsequent development, we also refined other details with regards to the component layout to guarantee maximum performance with minimum changes to the mature and critical components such as brakes, rims and suspension (an important consideration for packaging in our target applications).

FACT #3 – Sometimes there is a clear topology winner. Sometimes it’s down to details.

Depending on the customer application, either axial flux or radial flux can be a good solution, especially, when the desired requirements drive the choice of technology and not the other way around.

While we have not chosen to pursue axial flux as topology in our solutions, for now, that doesn’t mean that great axial flux in-wheel motors are not possible. But rather, it means that we (so far) did not find it as practical from our requirement point of view.

Nevertheless, in-wheel motors will certainly differ in the future, depending on the vehicle mission profile and introducing new innovations that can open the ways towards even higher compactness and motor performance.

OUR TAKEAWAY

For now, the biggest issue we see with axial flux motor type is the inevitable axial forces unbalance, which tends to have a runaway effect. As soon as the bearings start wearing out a bit, the unbalance grows and in no time the bearing gets worn out. Also, based on our experience, axial flux motors can be very hard to cool in demanding cycles, such as those of EVs.

With radial flux type in-wheel motor systems that we can offer today, we are proving that what was once a concept is now realized in a real product, successfully addressing all requirements of the in-wheel application in automotive requirements. We are continuing to push the envelope of the radial flux configuration and pursuing building the most compact, robust and performant in-wheel motor solutions.

We are an in-wheel technology team – and we believe that great things are ahead for the distributed drive paradigm.

And as you know best yourselves, the best way to predict the future is … to create it!

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