Together with the a few-passage torque converter, two passages are utilized for transmission oil (ATF) circulation in the torque converter and for clutch cooling, though the 3rd passage is utilized independently to manage the lock and unlock in the clutch. A torque converter can not realize 100 percent coupling efficiency. https://torque-converter-clutch43085.dailyhitblog.com/39401584/detailed-notes-on-torque-converter-clutch