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This paper investigates an oil-based shaft cooling system as applied to a 30,000 rpm automotive traction motor. Firstly, iron and air friction losses are identified over a range of operating speeds. Analytical and numerical approaches are then proposed to estimate thermal performance of steady and dynamic states, respectively. Finally, experiments are conducted to evaluate the impact characteristics of this cooling system, such as the rotational speed, the inlet coolant velocity and the amount of heat loss. Based on simulation and testing of prototype, the shaft rotational velocity can significantly enhance the heat exchange between coolant and internal surface of the hollow-shaft, across whole length of the shaft. However, when the rotational velocity reaches 30,000 rpm, the effect of high rotational velocities on heat exchange weakens due to the flow becoming saturated.

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