Development of high efficiency Axial Flux Motor for Shell Eco-marathon

Abstract

In 2011 Lubna Nasrin designed an optimized in-wheel axial flux motor for the competition Shell Eco-Marathon. A motor was built for the 2012 competition by Fredrik V. Endresen. Testing of this motor showed however that the performance was nothing like the one anticipated by Nasrin?s. The conclusion was that the production methods were not good enough and this was the main reason for the poor result.A new motor was built for use in the 2013 competition. Several design improvements over the old motor which was built in 2010 has been made. Litz wire is used in the stator and Halbach array permanent arrangement in the rotors. Rims, axle and other mechanical parts have also been made brand new this year to try to make the best possible design.The assembly didn?t go without problems, but in the end the motor was fit to the car and tested. It was used in the competition where the team ended up with a third place in the battery electric class.Several tests were performed on the motor to identify how well it performed compared to the FEM results. Question marks have however been raised when it comes to the results of the test due to problems aligning the motor in the test bench. The results indicate rather high rotational losses, but also an induced voltage 35% lower than anticipated. This should not be critical though as the theoretical efficiency, rotational losses discarded, still is 99% with this value.The high eddy current and friction losses measured do however ruin the real efficiency of the machine.