Mostly, the automatic gearbox uses a roller clutch for schedule upshifts/downshifts. It operates similar to a ratchet. It transmits the torque only in one path by free-wheeling or overrunning in another. The advantage of this type of clutch is always that it removes the potential for concurrently implementing the clutch https://kylermljgb.blogrenanda.com/40073011/gearbox-auto-an-overview