Thermal limitations in air-cooled axial flux in-wheel motors for urban mobility vehicles: A preliminary analysis

The idea of having electric personal urban mobility vehicles that can be better supported within an urban infrastructure has been suggested for some time. Air-cooled in-wheel motors are preferred as they allow more passenger space and remove any plumbing requirements within the vehicle. This paper shows a preliminary analysis of the thermal limitations for axial flux internal rotor (AFIR) and axial flux internal stator (AFIS) machines. It is shown that AFIR type air-cooled machines favours low speed machines with traction power between 3.75kW-5kW and motor diameters between 13" and 15". This forces the traction power to be distributed on 3 or 4 wheels. Conversely the dependence of the cooling on the rotational speed in AFIS air-cooled machines favours high speed geared motors motor powers up to 7.5kW for a motor diameter of 15". This enables the traction power to be distributed on 2 wheels or more.