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):441-447, 2014, doi:10.4271/2014-01-2333.
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.