Advanced tooth-guided liquid-cooling shafts for active rotor cooling in automotive electric motors: A comparative CFD study

This study proposes a novel rotor-cooling shaft concept for high-performance electric motors, which increases the effectiveness of cooling and is yet simple and cost-efficient to manufacture. In that context, we investigate the thermal performance of four shaft geometries for rotor cooling in automotive applications. The proposed tooth-guided liquid-cooling shaft design aims to reduce the large churning losses of conventional hollow cooling shafts caused by internal vortex formation while enhancing heat transfer. To this end, the design uses cold-formed internal channels that guide the coolant flow and suppress unfavorable large-scale vortical structures. We evaluate key performance metrics, including heat transfer rate, normalized heat-transfer metrics, outlet temperature, internal pressure level, and velocity profiles, under varying rotational speeds, inlet flow rates, and coolant temperatures. Computational fluid dynamics results demonstrates that the tooth-guided design outperforms conventional hollow shafts and that Shaft Model 3 achieves a heat-transfer improvement of up to 125% relative to the hollow reference shaft, while maintaining comparatively low internal pressure levels among the enhanced designs. These findings provide practical insight into geometry-driven thermal optimization and offer a path toward improving the performance and durability of electric motors.