High-Performance Rotor Cooling with Ducted Liquid in Completely Cold-Formed Modular Motor Shaft

TL;DR

The study tackles rotor thermal management in high-performance electric motors by introducing a tooth-guided liquid-cooling shaft manufactured via cold forming. Four shaft geometries are evaluated with CFD (SST turbulence model) to quantify heat-transfer rates, outlet temperatures, and pressure drops under varied rotational speeds, flow rates, and inlet temperatures. Results show substantial cooling improvements over hollow shafts, notably up to 110% at low speeds, driven by increased surface area and controlled vortex formation; Shaft Model 3 often achieves the best balance between heat transfer and pressure. The design is manufacturable with standard cold-forming processes and end-plug assemblies, offering potential gains in motor power density and potential cost reductions through material substitutions, with significant implications for induction and PM machines alike. Overall, the work provides a practical pathway to more efficient motor cooling through geometry-driven thermal optimization and modular manufacturing.

Abstract

This paper suggests a novel rotor-cooling shaft concept for high-performance electric motors that increases the effectiveness of cooling and is yet simple and cost-effective to manufacture. 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 solve the high churning loss of conventional cooled rotor shafts due to internal vortex formation and their still limited heat transfer. Therefore, we optimize heat transfer efficiency and pressure management by incorporating cold-formed internal channels that restrict vortex formation beyond a degree that improves heat transfer. We evaluated key performance metrics, including heat transfer rate, outlet temperature, pressure drop, and velocity profiles, under varying rotational speeds, inlet flow rates, and coolant temperatures. Computational fluid analysis demonstrates that the tooth-guided design outperforms conventional hollow shafts and achieves up to 110% higher cooling efficiency at low rotational speeds, while it maintains comparable pressure levels. These findings provide practical insight into geometry-driven thermal optimization and offer a path toward improving the performance and durability of electric motors.

Figures (21)

• Figure 1: Illustration of the tooth-guided liquid-cooling shaft design and its application in motor thermal management.
• Figure 2: Different shaft geometries.
• Figure 3: Shaft specifications.
• Figure 4: Schematic of the first shaft model along with the boundary conditions applied in ANSYS Fluent.
• Figure 5: Schematic of the second shaft model along with the boundary conditions applied in ANSYS Fluent.