Motivation: Curiosity as a Starting Point

Sometimes, engineering projects don’t start with a specification sheet – but with a simple question.

After Munro & Associates (Link)published their detailed teardown of the Volkswagen APP550 drive unit, I found myself wondering:

How close can you get to the real machine using only publicly available information?

No OEM CAD, No internal data, No test bench measurements.

Just images, videos – and engineering judgment.

From Images to Geometry: Reconstructing the Machine

The FEM model is based entirely on public sources:

• teardown videos and high-resolution images

• publicly accessible presentations and publications

• pictures of physical cutaway models, including exhibits at PCIM Europe 2024

From these sources, the machine geometry was reconstructed step by step and translated into a 2D – FEA model.
Absolute dimensional accuracy is unrealistic – but a physically consistent approximation is achievable.

Key assumptions used in the model:

• Electrical steel: NO20

• Magnet material: N52-EH

• Magnet temperature: 100 °C

• DC-link voltage: 380 V

These assumptions strongly influence the results and are therefore stated explicitly. Details of the re-engineered geometry you can take from the provided image.

Results: A Calculated Efficiency Map

Using the model, an efficiency map of the electric machine was calculated.

The interesting part came during comparison:

• maximum torque

• base speed and maximum power is reached.

• location of peak efficiency

show strong similarities to the efficiency map published by Alexander Bloch (Link) in his analysis of the APP550 drive unit.

Of course, questions remain:

• Are boundary conditions truly comparable?

• Are material and temperature assumptions correct?

• What role do cooling details play?

👉 Still: The fundamental machine behavior is captured surprisingly well.