Simpson planetary gearset

A Simpson gearset delivers three forward gears and one reverse, plus neutral, and is commonly employed in three and four ratio automatic transmissions.

The second carrier is locked so its ring motion causes the common sun to spin retrograde.

The retrograde spin reduces the first carriers reaction to its ring motion thereby doubling the reduction of the first set and output.

Sprag clutches mitigate roughness when a shift requires a combination of bands to be released or actuated.

GM's Turbo Hydra-Matic 350 and 400 transmissions utilized overrunning clutches in both the low and intermediate gears, allowing for fully progressive shifting with no "overlap".

Turbo Hydra-Matic mates a torque converter to a Simpson planetary gearset
Simpson Planetary Gearset Schematic Diagram