The torque converter clutch arrives into action to mitigate the inherent inefficiency of the fluid coupling at bigger speeds. The stator sends the fluid getting back from the turbine towards the pump. This increases the performance on the torque converter. Notice the spline, that's connected to a a single-way clutch https://torque-converter-clutch40616.ja-blog.com/34336998/top-torque-converter-clutch-secrets