Thermal Modelling of a Liquid Cooled Traction Machine with 8-layer Hairpin Windings

This paper describes the conjugate thermal analysis performed on an traction electric motor for electric vehicle (EV). The machine considered adopts hairpin windings and the cooling is achieved by combining an external water jacket and internal oil spray on the end-windings which is delivered by high pressure nozzles. The thermal characterization was performed in two stages; in the first stage the thermal performance of the original design was investigated whilst in the second stage some solutions were proposed to enhance the cooling effectiveness. Due to the heavy computational cost of the analyses, performed by the means of Computational Fluid Dynamics (CFD), fluid flow and conduction heat transfer were investigated separately. The results produced have shown that despite the good overall cooling capabilities of the spray, some issues may arise when the motor operates at low speed-high torque condition as the number pin layers increases. In this scenario droplets might struggle to penetrate through the conductors, leading to localized hotspots. It is also found that minor adjustments of the position of the nozzles may considerably improve the heat transfer rate. The realistic 3D representation of the conductors has allowed to further improve the accuracy of the analyses carried out.