Lubricant Flow and Temperature Prediction in a Planetary Gearset

This study introduces a method to examine the flow path of the lubricant inside a planetary gearset of an automatic transmission. A typical planetary gearbox has several load bearing elements which are in relative sliding motion to each other which causes heat to be released. The major sources of friction as well as heat are the meshing teeth between gears (sun/planet, planet/ring), thrust washers, thrust bearings and needle bearings. The lubricant performs the vital function of both lubricating these sliding interfaces and cooling these sources of heat, thereby preventing failure of the gearbox.

The exact flow path that the lubricant takes inside a planetary gearset is unknown. Since the gearset is primarily splash lubricated, it is also not known how much lubricant reaches critical areas. A method is developed using computational fluid dynamic techniques to enable comprehensive flow and thermal analysis and visualization of an automatic transmission assembly. The method captures the effect of rotation of the gears and shaft in an automatic transmission. Lubricant/Coolant is driven into the planetary gearbox domain from a rotating turbine shaft. Once the lubricant is sprayed into the domain, it forms a mixture of very small droplets of lubricant suspended in air. The method simulates the flow physics of oil air mixture forming inside the transmission. The temperature map of the entire planetary gearbox is modeled using conjugate heat transfer (CHT).