INTRODUCTION The demand of low fuel consumption car is increasing day by day due to the aspect of protection of the global environment. The regulations of fuel efficiencies of passenger cars in many countries have been established and become gradually stringent. Therefore, lowering fuel consumption is an urgent issue. Fuel efficiency can be improved by reducing the energy loss a power train and others. Some estimates shows that about 14%-30% of the energy from the fuel gets used to move a car down the road and 5-6% energy is lost due to drive train[1]. Therefore, a potential improvement of power train components can lower the fuel consumption significantly. Fig.1 shows an image of an automatic transmission. During the operation of a transmission, some of the clutches are engaged for power, while the rest of clutches remain disengaged. Due to the engagement and disengagement process, a frictional heat is generated which leads to some damage to clutches. Therefore, it is necessary to cool down the disks to increase the service life of clutch. An automatic transmission fluid (ATF) is delivered in between the friction disks and separator plate to cool them. Since the friction plates and separator plates are always in relative motion to each other, a shear force is generated on the fluid in the gap between the disks. This shear force generates a DT which is considered as a loss. This undesired DT reduces the efficiency of power transmission and increases the fuel consumption of a car. Therefore, it is of interest for transmission engineers to understand the physics of this kind of flows and identify design variables and parameters that dictate the loss mechanism so as to minimize the loss in engineering practice. Fig.1. An automatic Transmission which consists of multiple numbers of clutch disks and clutch plates For more than several decades, a lot of researches have been done to understand the DT in disengaged wet clutches. In 1984, Hashimoto et al.[ 2] presented the governing equations for the flow in a thrust bearing subject to centrifugal force. These equations describe the flow between two adjacent flat rotating plates facing each other at an angle. Though this work is not directly applicable to clutches, it laid down a framework Multiphase Drag Modeling for Prediction of the Drag Torque Characteristics in Disengaged Wet Clutches Shahjada Pahlovy, Syeda Faria Mahmud, Masamitsu Kubota, Makoto Ogawa, and Norio Takakura R&D Center, Dynax Corp. ABSTRACT The undesired Drag Torque (DT) which is developed due to the shearing of fluid film in between the disk and separator plate reduces the efficiency of a transmission and increases the fuel consumption of a car . In order to minimize the transmission loss, the physics of the fluid flow mechanism inside the clutch should be understood well and the factors influencing the DT should be identified. In this paper, a model is proposed to predict the drag torque of a disengaged wet clutch at different rotation speeds, clearances, disk sizes and oil temperatures. The model explains well how the DT changes for the no groove disk, grooved disk and different ATF properties. The proposed model is validated by several experimental results conducted by a visualization tester and images of the fluid film taken during the test. Results show that there is a good degree of agreement between the DT trends derived from the proposed model and the test results for the same condition. CITATION: Pahlovy, S., Mahmud, S., Kubota, M., Ogawa, M. et al., "Multiphase Drag Modeling for Prediction of the Drag Torque Characteristics in Disengaged Wet Clutches," SAE Int. J. Commer. Veh. 7(2):2014, doi:10.4271/2014-01-2333.2014-01-2333 Published 09/30/2014 Copyright © 2014 SAE International doi:10.4271/2014-01-2333 saecomveh.saejournals.org 441Downloaded from SAE International by Brought to you by the University of Kansas (Technical reports: 1998 to Present), Sunday, August 26, 2018for the modeling of DT for