Investigation of Stator Cooling Concepts of an Electric Machine for Maximization of Continuous Power

With the automotive industry's increasing focus on electromobility and the growing share of electric cars, new challenges are arising for the development of electric motors. The requirements for torque and power of traction motors are constantly growing, while installation space, costs and weight are increasingly becoming limiting factors. Moreover, there is an inherent conflict in the design between power density and efficiency of an electric motor. Thus, a main focus in today's development lies on space-saving and yet effective and innovative cooling systems. This paper presents an approach for a multi-physical optimization that combines the domains of electromagnetics and thermodynamics. Based on a reference machine, this simulative study examins a total of nine different stator cooling concepts varying the cooling duct positions and end-winding cooling concepts. To ensure the highest possible comparability, the rotor geometry as well as the overall dimensions in terms of outer diameter and length of the electric machine remain unchanged. The stator design is slightly adjusted to achieve same maximum torque and winding cross-section. Initially, the electromagnetic effects of various cooling slot positions are investigated and compared with respect to efficiency and individual loss distribution. Subsequently, the thermal performance is analyzed by means of fluid-dynamical simulations to quantify the heat transfer and assess the cooling effectivity. Eventually, these results are merged in a lumped parameter thermal network model. Accounting for both the distinguished electromagnetic and thermal benefits and disadvantages, a final study is presented evaluating the continuous power capability of the different concepts at equal boundary conditions.