Reducing windage loss can be achieved by vacuuming the gear box. This study examines the possibility of implementing a gear pump characteristic with a working helical gear pair inside the gear box itself. An air-tight gear box is constructed and its vacuuming ability, windage loss, and temperature rise in speed range up to 60 m/s are investigated. The vacuuming ability is satisfactory, as it can reduce the pressure to less than 0.02 MPa (absolute), but large heat is generated by adiabatic compression associated with the temperature elevation of about 200°C. This presents excess loss and is due to the pressure difference before and after mesh engagement. Since this loss is proportional to the speed, further higher-speed condition will make total loss smaller than the expected windage loss which is proportional to the third power of the speed. In addition, this self-vacuuming ability can be improved with the assistance of a small vacuum pump to maintain the interior pressure at the beginning of engagement as small as possible. Finally, the feasibility of lubricant feeding is also examined.

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