ABSTRACT The purpose of this paper is to study the flow field of a lockup clutch inside a torque converter. The performance of a torque converter has been one of the most important areas of improvement for an automobile equipped with an automatic transmission. Improving the torque converter's performance and efficiency are key contributions to saving fuel, which is an important consideration with the recent increase in environmental awareness. Moreover, the lockup operation- or slipping control- of an automatic transmission is another good opportunity for improving fuel economy. INTRODUCTION The torque converter is a major component of an automatic transmission and transfers power from the engine to the transmission gearing system. The torque converter has been used in automatic transmissions for numerous applications such as passenger cars, trucks, buses and trains. There are two important roles for the torque converter. One such role is the reduction of vibration, or noise, from the engine by means of the automatic transmission fluid. The second important role is the multiplication of engine torque. Fig. 1 illustrates a cut-away view of an automatic transmission. Fig. 2 shows a typical automotive torque converter cross-section. Figure 1. Automatic transmission Figure 2. A typical torque converter cross-section Transient Flow Field Analysis Around a Lockup Clutch Inside a Torque Converter2012-01-2001 Published 09/24/2012 Takeshi Yamaguchi Aisin AW Co. Ltd. Kazuhiro Tanaka Kyusyu Institute of Technology Copyright © 2012 SAE International doi:10.4271/2012-01-2001Downloaded from SAE International by Univ of California Berkeley, Tuesday, July 31, 2018There has been much research carried out to predict hydrodynamic performance and to understand the flow field inside a torque converter either experimentally or analytically using Computational Fluid Dynamics (CFD) [ 1,2,3,4,5,6]. In order to improve the efficiencyof an automatic transmission, it is often desired to engage the torque converter lockup clutch as soon as possible to conserve the power flow from the engine. However, early engagement of the lockup clutch is associated with a larger slip velocity against the front cover, making it increasingly important to manage the heat transfer on the friction paper. Moreover, sudden engagement of the lockup clutch causes vibration and noise within the engine. Most research has focused on these issues of either heat management of the lockup clutch or the shudder mechanism. The torque converter lockup system is controlled by hydraulics. Understanding from a fluid dynamics perspective how the flow field around the lockup clutch influences its behavior is a key factor in both preventing shock and improving engagement time. However, only a few studies have focused on the lockup clutch, and all of the numerical research was solved at steady state conditions [ 7, 8]. In this paper, not only was a transient solution applied to solve the flow field, but also two new techniques were attempted: “virtual weight” and “moving mesh.” By using these techniques, the lockup clutch was set in motion by the imbalance of its own weight and the opposing pressure acting on its surface. With this approach, the lockup clutch engagement time- or the responsiveness of the lockup clutch- could be estimated. DESCRIPTION OF THE MODEL AND COMPUTATIONAL METHOD The modeled torque converter has diameter of 272mm and a maximum width of 62mm for the torus area (i.e., pump, turbine, stator area). ANSYS CFX Ver.14 is used for the CFD solver, with two major domains in the CFD model. One domain is the torus area. The other domain is the lockup clutch area, where a “moving mesh” is applied. The two domains are connected by the CFX GGI (General Grid Interface) function. The whole torque converter CFD model and a detail view of the lockup clutch CFD model are shown in Fig. 3 and Fig. 4, respectively. Fig. 5 shows the boundary conditions for inlet and outlet pressure