A 3-D CFD Study of the Lubricating Oil Flow Path in a Hybrid Vehicle Transmission System 2024-01-2635

Effective design of the lubrication path greatly influences the durability of any transmission system. However, it is experimentally impossible to estimate the internal distribution of the automotive transmission fluid (ATF) to different parts of the transmission system due to its structural complexities. Hybrid vehicle transmission systems usually consist of different types of bearings (ball bearings, thrust bearings, roller bearings, etc.) in conjunction with gear systems. It is a perennial challenge to computationally simulate such complicated rotating systems. Hence, one-dimensional models have been the state of the art for designing these intricate transmission systems. Though quantifiable, the 1D models still rely heavily on some testing data. Furthermore, HEVs (hybrid electric vehicles) desire a more efficient lubrication system compared to their counterparts (Internal combustion engine vehicles) to extend the range of operation on a single charge. Thus, this paper includes a detailed, transient, three-dimensional CFD analysis of the lubricating oil flow path in an HEV transmission system using the commercial CFD software Simerics-MP+. The modeled transmission system includes scores of bearings, rotating components, and planetary gear systems. Using this modeling framework, we can predict the lubrication state of the various components of the transmission system. Furthermore, this paper reveals the effect of the centrifugal force on the oil distribution and the wetting fraction of different components. Additionally, two different designs of lubricating flow paths inside the roller bearings are explored to study the effect on the wetting of the rollers. The current simulation framework adopts the volume of fluid (VOF) technique to accurately model the two-phase interface development in the rotating systems.