Direct oil cooling of end-windings in torus-type axial-flux permanent-magnet machines

For high power density applications, such as electric or hybrid electric vehicles, heat extraction is a crucial aspect in electrical machine design due to stringent machine volume specifications. In these cases, it is extremely difficult if at all possible, to satisfy the maximum temperature requirement when using conventional cooling systems such as housing fins, shaft-mounted fans or even water jackets, due to insufficiently low thermal resistances. To this end, a novel direct oil cooling system conceived for Torus-type axial-flux permanent-magnet machines, is proposed here. In order to demonstrate its effectiveness, lumped thermal equivalent circuit simulations, finite element analyses and experimental tests are presented. Furthermore, the expected performances of the machine using the proposed direct oil cooling are compared to those obtained using state-of-the-art water cooling.