ABSTRACT 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). INTRODUCTION In the past, automatic transmission (AT) planetary gearset failures have been reported and investigated [ 1]. Due to thesliding contact between elements a large amount of heat is produced in the domain. The lubricant that is used in an AT performs the two important functions of lubricating the sliding interfaces to reduce friction, and also to act as a coolant and carry away heat - thereby preventing an extreme rise in temperature. While many systems in automobiles use pressurized fluid lines to ensure coolant access, this is not possible inside a planetary gearset due to the nature of the geometry and rotating elements. The flow path in the input gearset of an automatic transmission is shown in Fig.1. The planetary gearset is splash lubricated and the lubricant is essentially sprayed into the domain from the turbine shaft, and thus can end up not reaching the intended locations. While several patents [ 2,3,4] have been published proposing novel designs of flow paths to ensure better cooling and lubrication, they have been based on inferences from first principles rather than on computer based simulation. An AT planetary gearset has several sliding interfaces. The major sources of friction as well as heat are: a) The meshing teeth between gears (sun/planet, planet/ring), b) thrust washers, c) thrust bearings and d) needle bearings. When an inadequate amount of lubricant is provided to a particular sliding interface, heat buildup occurs in the region thereby taking the temperature of the material above its critical temperature and reducing its load bearing capacity significantly, thereby causing failure. Thrust washers and needle bearing failures have been reported and investigated [1]. Some such component failures are illustrated in Fig. 2. Lubricant Flow and Temperature Prediction in a Planetary Gearset2011-01-1235 Published 04/12/2011 Sujan Dhar, Amit Rawool and Sudipto Ray GM Technical Center India Ltd. - General Motors Company Fanghui Shi General Motors Company Copyright © 2011 SAE International doi:10.4271/2011-01-1235Downloaded from SAE International by Purdue University, Monday, August 20, 2018The present method has been developed using techniques from computational fluid dynamics (CFD). The method has a potential to provide the designer of the lubricant path inside any AT with a detailed picture of the flow inside the domain. It aims to provide a fully quantifiable measure for the amount of lubricant flow reaching its intended targets - the load