Design and Verification of In-Slot Oil-Cooled Tooth Coil Winding PM Machine for Traction Application

Tooth coil windings, in particular when using a double layer structure, present opportunities for in-slot liquid cooling. Since the windings are not overlapping, access to the slot from the end section for coolant liquids is enabled. In this article, a solution for in-slot and in-stator direct oil cooling for a tooth coil winding machine is presented. The coils are prewound on bobbins and inserted on the stator teeth. The novelty of the design consists in the integration of the cooling, using a thermally conductive epoxy resin to create the channels within the slot as well as the positioning of the stator yoke cooling channels. A 50-kW machine for an automotive traction application is designed, manufactured, and tested. Conjugate heat transfer simulations are used in the design process in combination with finite-element analysis for the loss mapping. The thermal model is verified with measurements at 6-L/min oil flow and 17.5 A/mm $^2$ continuous and 35 A/mm $^2$ 30-s peak. The thermal model is then used to establish a continuous operating point at 25 A/mm $^2$ .