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In this paper, the cooling airflow in a unidirectional ventilated open-type motor for electric vehicles (EV) was studied. Numerical fluid analysis was performed on the airflow in the motor through a ventilation path outside the stator iron core inside the frame. It is confirmed that there was a flow separation where air did not flow along the path surfaces. This was observed in a flow visualization experiment using water instead of air. We propose a new structure to prevent air separation and confirm its effectiveness by a visualization experiment. It is also shown that another structure with paths both inside and outside the stator iron core in the frame improves the motor's cooling performance. These structures are effective for EV motor downsizing. Index Terms--Airflow, downsizing, electric vehicle (EV), flow analysis, flow visualization experiment, main motor, unidirectional ventilation, weight reduction.

This paper studies the cooling performance by axial fans with forward-swept and inclined blades and a structure with low ventilation resistance for large-capacity open-type motors. The ventilation resistance of axial fans for motors is much greater than that of common fans for creating draughts. Flow separates remarkably on the blades' surfaces and fluid noise is large. We reduced the ventilation resistance inside an electric motor and adopted axial fans with forward-swept and inclined blades. We confirmed by wind tunnel experiment that the flow rate with this combination increases remarkably compared with the conventional ventilation structure and axial fans. Numerical fluid analysis was performed on the flow around the blade at this flow rate. It was confirmed that no flow separation appeared for the air flow along the blade surfaces. This was also observed in a flow visualization experiment. Furthermore, an actual motor with both the low-ventilation-resistance structure and axial fans with forward-swept and inclined blades showed that the flow rate of cooling air increased by 80% compared with that of conventional machines, and the average temperature rise of stator windings decreased by 30%. Thus, the cooling performance was greatly improved. Index Terms--Cooling, fans, fluid flow, motors, numerical analysis, temperature measurement, ventilation, visualization.