The aforementioned friction bands and clutches are managed employing automatic transmission fluid (ATF), that's pressurized by a pump and afterwards directed to the appropriate bands/clutches to obtain the needed equipment ratio. Mostly, the automatic gearbox works by using a roller clutch for plan upshifts/downshifts. It operates similar to a ratchet. https://gearboxauto86296.bloggazza.com/32770367/gearbox-auto-for-dummies