Stator heat extraction system for axial flux yokeless and segmented armature machines

The torque density of electric motors strongly depends on the performance of the cooling system. In the axial flux yokeless and segmented armature machine, cooling inherently occurs through self-ventilation by both rotor discs. Nevertheless, an independent cooling system remains necessary for most applications. In the axial flux yokeless and segmented armature machine, the individual stator cores with concentrated windings are potted in the stator housing using an epoxy resin. These epoxy resins are relatively bad thermally conductive, and therefore, limit the heat transfer to the surface of the machine. Therefore, radially inward heat extraction fins are introduced in this paper. These fins provide an excellent thermal conduction path from the windings to the stator surface, where they can be abducted by conventional cooling techniques such as forced air or water jacket cooling. The focus of this paper is on the study of the radially inward heat extraction fins using thermal finite element modelling as well as experimental validation on a 4kW axial flux yokeless and segmented armature machine stator. At steady state and for the rated losses, the temperature difference between the winding and stator housing is less than 10 degrees Celcius.