Experimental and simulation investigation on lubricant flow allocation in high-speed planetary transmissions

Planetary gear transmission (PGT) is widely used in vehicle transmission systems. The complex internal lubrication structure and kinematic relationships within vehicle PGT lead to an uneven distribution of lubricant flow among the planetary gear sets (PGS), compromising transmission efficiency and reliability. This study investigates lubricant flow allocation in a multi-stage PGT through an integrated experimental and numerical approach. A visualization test bench was developed to measure the flow rate to each PGS, and a Volume of Fluid (VOF)-based computational fluid dynamics (CFD) model was established and validated experimentally. The effects of inlet oil pressure, temperature, and rotational speed on lubricant flow allocation to sun gears and planetary bearings were analyzed. Results reveal that lubricant flow allocation among PGS components is uneven, with planetary bearings receiving a higher proportion than sun gears. Increasing inlet pressure generally enhances flow rates across all PGSs, except for the PGS₂ planetary bearings at 12000 r/min, where a decrease is observed. Elevated oil temperature promotes flow rate to the sun gears, while its effect on bearing flow varies with rotational speed. Within the planetary bearings, oil distribution is governed by both oil passage flow rate and bearing’s speed. As speed increases, the oil volume fraction at the inner ring decreases significantly, showing a reduction of 86.16% at 12888 r/min compared to 3222 r/min. This indicates a risk of lubrication starvation under high-speed conditions. These findings provide quantitative insights for the lubrication design of multi-stage planetary transmissions.