Manufacturing of tooth coil winding PM machines with in-slot oil cooling

This paper presents a description of the manufacturing challenges and solutions of two 50 kW radial flux inner-rotor tooth coil winding PM machines with in-slot cooling for vehicle application. The two machines are designed for different DC link voltages, 600 V and 48 V, and to achieve high efficiency and high power density. To enable this, liquid cooling is necessary. In the solution presented, the oil coolant is pushed through the stator yoke and in the slots with the intent of removing the heat close to the loss generation. The cooling channels in the slots are built during the stator potting process using a high thermally conductive potting material. The machines presented in this paper are designed for high speed operation and capable to withstand RMS current densities of 25 A/mm² in continuous operation and 35 A/mm²for 30 s peaks, at 6 I/min oil flow and a inlet temperature of 20°C. It is shown that stator is designed to be compatible with automated manufacturing for high volume production with a set of suggested improvements.