An Analysis of Flow Field Characteristics Under the Start-Up Condition of a Subway Gearbox

This study investigates the transient lubrication dynamics of subway gearboxes during acceleration phases through computational fluid dynamics (CFD) modeling. A simplified gearbox model with helical gears, bearings, and oil-guide channels was developed using STAR-CCM+®. Simulations evaluated the effects of three acceleration levels (7.4 m/s2, 4.4 m/s2, and 3.2 m/s2) and three different oil temperatures (−10 °C, 10 °C, and 70 °C) on pressure distribution, churning torque, and oil supply dynamics. The results show that higher acceleration levels intensify transient pressure fluctuations in gear meshing regions and expedite oil supply initiation to bearings. However, the steady-state lubrication performance remains consistent across acceleration magnitudes. Elevated oil temperatures significantly decrease the initial churning torque of a gearbox but increase the steady-state churning torque. There exists an optimal temperature that maximizes the oil supply in the gear meshing zone. In addition, the initial oil supply times for bearings are slightly reduced under lower temperatures. These findings highlight the critical role of transient acceleration and temperature effects in gearbox lubrication optimization, providing insights for enhancing reliability under dynamic operating conditions.