Lubrication Effectiveness Determination for Wet-Sump Transmissions using Multiphase Computational Fluid Dynamics Modeling 2024-26-0298

Wet-sump transmissions are widely used in heavy duty and medium duty vehicles. As these transmissions do not have a dedicated forced lubrication system, it is important that the gear train, shafts, and enclosure are designed appropriately so that enough oil splashes to critical locations to ensure sufficient lubrication. The lubrication effectiveness of such transmissions can be studied through detailed tests or numerical simulations.

Often, the vehicle, and therefore the transmission, encounters some severe operating conditions, such as climbing on an incline, driving downhill, etc. Studying these conditions through tests is an expensive process and this imposes the need for an analysis first approach. In this paper, the 3D multiphase Volume of Fluid (VOF) method is used to examine two such extreme cases: an 8-degree tilted installation of transmission in a vehicle, and an inclined condition of transmission during a 10-degree uphill climb. By studying the oil volume fraction on gears and splash patterns, inertia and reverse gears in the first case and headset gear in the second case are found susceptible to oil starvation. The effectiveness of a simple and easily deployable solution of increasing the transmission oil level is then assessed. Results show that increasing the oil level improves the lubrication effectiveness in the first case, but only slightly in the second case. However, both cases show higher churning losses. This calls for a trade-off between lubrication effectiveness and power/torque consumption. Present work demonstrates how the developed methodology can help identify oil-starving locations and evaluate potential solutions for extreme cases, eliminating the need for testing multiple prototypes before arriving at a suitable solution.