An experimental investigation of a self-vacuuming action of a gear pair for the purpose of reducing windage loss (Interior vacuum level, power losses, and temperature rise)

Windage loss may become more than 10% of all losses when large sized gearing runs fast. In order to reduce the windage loss, it needs to vacuum a gear box because it is proportional to the density of ambient air. The study proposes a helical gearing unit in which interior air is discharged due to mesh process as like as a gear pump, and investigates the performance experimentally in terms of depressure level, power loss and temperature rise due to heat generation. The pressure in the gear box got to - 0.08MPa under appropriate condition, but the temperature rose up to about 200°C. Losses were measured and found to consist of four types in self-vacuuming: mechanical loss, windage loss, pressure difference loss, and turning flow loss. Among them pressure difference loss was the most marked part which is due to the gears rotating against pressure difference between high and low pressure atmosphere, or the beginning of engagement and end of it, respectively, in the gear box. Furthermore existence of turning flow loss was confirmed due to circulation flow in the wide exhaust opening volume, and it was eliminated by changing the exhaust port to such as an axial narrow hole. The temperature rise was proven to the effect of adiabatic compression and corresponding energy dissipation. It was verified by the calculation based on the typical thermal dynamics at tooth space which consists of isovolumetric, isobaric, and adiabatic changes. By calculating the required kinematic work of this cycle, the result matched with the pressure difference loss. Furthermore a small external vacuum pump can collaborate to assist reducing this pressure difference loss.