Electric motors used in both electric vehicles and hybrid vehicles require a steady improvement to enhance their performance. Output power, motor weight and size, rotational speed and power consumption are main requirements for engine performance. However, an increase in rotational speed can lead to higher power output and inturn larger windage power loss will be generated by the rotor.
In a collaborative research between Tokyo University of Science and Denso Corporation in Japan, researchers proposed a new spiral groved viscous vacuum pump combined with an aerodynamic step thrust bearing in reducing the wintage power loss of a high speed rotating motor. The research is now published in journal, Precision Engineering.
To reduce the windage power loss of a high speed motor, two methods were suggested in the past this include the use of flywheel generator system, where flywheel were rotated in a vacuum container to reduce the windage loss of the flywheel. The other method investigated the windage power loss of a flywheel in a housing filled with H2 and SF6 gas mixture and confirmed that proposed gas mixture could reduce the power loss compared with air. The research team observed the need of vacuum pump and gas compressor for the previous researcher work to continue and also space for their devices.
To address the limitations, another method in this study was proposed to reduce the pressure in a laser scanner housing using viscous vacuum pump with herringbone groves. This method reduced the windage power loss of scanner motor by 50%. In another work, a viscous vacuum pump using spiral groves that function as an aerodynamic thrust bearing was used. By applying this method the team realized the gap of the viscous vacuum pump could be easily kept constant, due to its output power and the size of the laser scanner been small. The disadvantage of this work was inability of the mechanism to adjust the gap of the viscous pump by itself during a high speed motor with large output power.
To improve further, the research team came up with a viscous vacuum pump combined with an aerodynamic step thrust bearing that is capable of adjusting gap by itself under developed structure will pump out air from within the seal space of the motor housing by using the pump effect of the spiral grooves and a reduced windage power loss of the rotor will be achieved.
They used a divergence formulae DF method in a boundary fitted coordinate system to investigate the pumping characteristics of the viscous vacuum pump. In reducing the windage power and of high speed motor, they considered the time needed to get to the final pressure. While the transit pressure variation in sealed space was obtained through calculation.
This study found that the windage power loss can be reduced by decreasing the pressure in the rotor environment. The newly developed method can reduce the pressure in the sealed space of the motor housing to 0.02Mpa at 30,000rpm at a gap of 10um. The authors confirmed the work by comparing 10,000rpm calculated result with the experimental results and found out that their proposed structure was very useful in reducing windage power loss of a high speed motor.
Fumiya Asami1, Masaaki Miyatake1, Shigeka Yoshimoto1, Eitaro Tanaka2, Takuma Yamauchi2 , A Method of Reducing Windage Power Loss of a High Speed Motor Using a Viscous Vacuum Pump, Precision Engineering 48 (2017) 60–66.
1Dept. of Mech. Eng., Tokyo University of Science, 6-3-1 Niijuku Katsushika-ku Tokyo, 125-8585, Japan.
2 Corporate R&D Div.2, Denso Corporation, 1-1, Showa-cho, Kariya-shi Aichi-ken, 448-8661, Japan.
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