2018-01-0400 Published 0 3 Apr 2018 © 2018 SAE International. All Rights Reserved.Effect of Facing Groove Design on Drag Torque of Automatic Transmission Wet Clutches Kazunari Asai and Takanobu Ito Aisin Chemical Co., Ltd. Citation: Asai, K. and Ito, T., “Effect of Facing Groove Design on Drag Torque of Automatic Transmission Wet Clutches,” SAE Technical Paper 2018-01-0400, 2018, doi:10.4271/2018-01-0400. Abstract In recent years, along with growing requirement for fuel economy in relation to reduce CO2 emission, reduction of drag torque from wet clutches has been an important issue. This study observed ATF flow on friction surface under different configurations of facing using high speed camera and investigated the mechanism of drag torque using CFD analysis. Introduction The increase in environment awareness in recent years has led to tremendous growth in the demand to improve fuel consumption of automobiles. The compe - tition to develop electric automobiles has intensified, and it is expected that strict activities to improve fuel consumption will be in demand with respect to automatic transmissions (A/T). Therefore, the reduction of the drag torque from wet clutches used in A/T has become an extremely important issue. Shear stress acting on the automatic transmission fluid (ATF) between the separator plate (S/P) and friction plate (F/P) bonded with paper-based facing is a major factor that influences drag torque and is considered a fundamental element. With wet clutches, torque is measured with a friction evaluation tester to compare the F/P facing shape. Several extant studies have focused on the friction surface area, number of grooves, and ATF supply quantity [ 1]. Previous studies indicated an increase in the drag torque at low speeds owing to the high shearing stress of the ATF film. However, the drag torque decreased at high speeds owing to the discharge effects of the ATF. In this study, ATF flow was observed under different facing shapes, and the mechanism of drag torque was examined from data obtained via CFD analysis. 1.  Test Conditions The test equipment included a SAE No.2 tester, which is a standard friction evaluation tester ( Figure 2 ). The rotation of Shaft causes the F/P to rotate, and torque is transmitted to the stationary S/P through the ATF. It was used with glass plates installed on the front of the tester to allow for the visualization of the interior. The evaluation was performed by coupling three (3) F/P and three (3) S/P alternately and rotating the F/P. The oil temperature was set at 40 °C, and the oil supply from the shaft was at 1,200 cc/min with a clearance of 0.17 mm per F/P. A CFD analysis was conducted for two-phase flow analysis under identical conditions, focusing on a piece of facing of a single F/P.  FIGURE 1   Friction plate and separator plate© SAE International  FIGURE 2   SAE No. 2 Clutch friction test machine© SAE InternationalDownloaded from SAE International by Brought to you by the University of Texas Libraries, Sunday, August 05, 2018 2 E FFECT o F FA CING G R oov E D ESIGN o N D RAG To R qu E o F  Au Tom ATIC T RANS m ISSI o N W ET Clu TC h ES © 2018 SAE International. All Rights Reserved. 2.  Test Results 2.1.  R otational Speed and Drag Torque When shear stress of a wet clutch oil film is theoretically considered, it is expected that shear stress will increase owing to the increase in the rotation speed when test conditions for ATF temperature (viscosity) and clearance are kept constant. Additionally, shear stress decreases with the reduction in facing area. When actual drag torque is evaluated, drag torque increases at a low rotation range because the rotation increases ( Figure 3 ). However, torque begins to decrease and peaks at approximately 1,000 rpm. In order to investigate the cause for this change, the state of oil film on friction surface was observed ( Figure 4 ). At 500 rpm, the facing rotates in a state immersed in the ATF and the oil