Design and Manufacturing Limits of a Thermoset Composite Overmolded Electric Traction Motor Implementing an Internal Cooling Concept in a Hairpin Winding Stator

This study investigates the potential of using composite overmolding technologies to realize internal cooling concepts for increasing the continuous power density and peak power availability of electrical machines, while simultaneously reducing cost and improving resource efficiency. To this end, a general concept has been developed and engineered for a high continuous power traction motor with distributed hairpin winding. Utilizing highly heat conductive thermosetting composite materials enables the realization of an indirect slot cooling close to the areas of heat generation caused by copper and iron losses. These electrically insulating indirect slot cooling designs can make use of water-based coolants, enhancing cooling efficiency, reducing cost on a system level and improving resource efficiency. However, limited design space introduces a conflict between electromagnetic design, thermal design and manufacturing limitations which leads to challenging optimization of the system design that must be considered. This research paper focuses on a thermosetting composite overmolding concept realized by applying a transfer molding manufacturing technology. Having the possibility of realizing thin-walled cooling channels between the hotspots and the cooling fluid can be beneficial for ensuring short thermal paths, allowing for a high slot filling factor and reducing the overall amount of overmolding materials required. In contrast to the potential benefit, thin wall structures are more susceptible to small defects and cracks in the overmolding. This can compromise electrical insulation and prevent safe operation of the machine. Therefore, analysis results of test specimen, which highlight various aspects of this concept, are presented to identify design and manufacturing limitations.