Comparison of four liquid-cooling strategies for in-wheel motors

Electrification of powertrains has seen rapid development over recent decades. Industrial and governmental incentives have driven research into improving electric traction machines, particularly with regard to power and torque density. Additionally, weaning reliance on the inclusion of rare-earth elements in the production of electric machines constitutes a significant goal. The present work focuses on the thermal management of direct-drive in-wheel motors (IWMs). Indeed, a comparison is made regarding three direct liquid-cooling strategies on an IWM, with respect to a benchmark water jacket design. The studied IWM is experimentally verified in the literature. Duct cooling in the stator back-iron with ducts located beneath slots in one solution as well as ducts located beneath teeth in another are studied. Both feature immersed end-windings. An additional evaluated solution consists of channels placed in the slots. Steady-state and transient thermal analyses are made based on simulations in an electromagnetic-thermal coupled model. It is noted that strategies incorporating immersed cooling displays reduced hydraulic and electric losses, thus larger efficiency, combined with low hotspot winding, and magnet temperatures.