Three-Dimensional Design and Optimization of the Liquid Cooling System for the FITGEN E-Axle

The H2020 funded FITGEN project aims to deliver a fully integrated e-motor-inverter-transmission power unit for next generation electric vehicles. This paper describes the design and optimization of a liquid cooling system for the e-motor. Three variants of a three-dimensional conjugate heat transfer model, based on the Reynolds-averaged Navier-Stokes (RANS) and energy equations, are used to carry out the design process: a CFD model of the liquid cooling system to assess candidate configurations, a CFD and heat transfer model of the full e-motor to calculate heat transfer boundary conditions, and a CFD and heat transfer model of a reduced geometry including liquid cooling system to carry out optimization and sensitivity studies. The design process identifies a promising cooling system configuration made up of axial and circumferential ribs, satisfying requirements for inlet and outlet position, volumetric flow rate, overall pressure drop, manufacturability and maintainability. An optimization study is carried out on the size of a mandatory gap, between the ribs and the outer part of the e-motor external housing, through which coolant is allowed to flow. Sensitivity studies are carried out to assess the effect of off-design variation in the aforementioned gap and the rib width. The results provide insight into the fluid dynamic and thermal behaviour of the cooling system, the optimal sizing of the rib-outer housing gap, and the effect of off-design variation on temperature and pressure drop. A design for the liquid cooling system is proposed.