Traction Motor Cooling Systems: A Literature Review and Comparative Study

More efficient cooling systems are an enabler for the increase in power-density in an electric traction motor. Contemplating to existing reviews, this paper presents a comprehensive collection of heat transfer mechanisms for the different heat removal techniques used in electric traction motors. In the first section, an overview of various cooling concepts in existing and future traction motors is presented and the cooling approaches are compared. The following literature review compiles geometry-based calculation formulas of the different mechanisms of cooling heat transfer applied in motor-technology. Furthermore general heat transfer phenomena appearing in electric traction motors are reviewed and compiled for easy access. Various specifically relevant aspects, including rotor shaft cooling, different spray cooling concepts, different air convection phenomena, bearing heat transfer and the stator-housing-contact, are examined in more detail. For validation of the review result, based on a well-known motor design a thermal analysis and comparison of the different cooling methods is carried out. Modeling is done with a lumped parameter thermal networks (LPTN). The paper concludes demonstrating the advantages and disadvantages of the different cooling concepts based on the collection of modeling data.