Flow Field Analysis Around 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 automatic-transmission equipped automobile. Improving the torque converter’s performance and efficiency is key to saving fuel consumption, which is an important consideration with recent environmental awareness. Moreover, the locking up operation or slipping control of an automatic transmission is another good opportunity for improving fuel economy. For this reason, there 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). Most of the research to date has focused on the inside of a torque converter torus. In recent years, the usage of a lockup clutch has expanded, and the lockup control system has become more complex. Understanding the flow field around the lockup clutch has become a very important issue. Only a few studies have focused on the lockup clutch, and most of the numerical research was solved at steady state conditions. In this paper, not only was an unsteady solution applied to solve the flow field, but also two new techniques were attempted. One was “virtual weight” and the other was “moving mesh.” By using these techniques, the lockup clutch was moved by the balance 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. The flow field calculated by a transient solution was found to be different from the flow field calculated by a steady state solution. The transient solution also revealed that the lockup engagement time and the lockup clutch moving speed were dependent on the lockup engagement pressure and rotation speed.