The rear planetary gear rack (commonly known as the planetary rack or planetary gear bracket) plays a crucial role in an automatic transmission. It is one of the core components of the planetary gear set and its main functions are as follows:

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 Support and connect the planetary gears
The planetary gear rack is used to fix and support multiple planetary gears (usually 3 to 4), enabling these small gears to be evenly distributed between the sun gear and the gear ring and maintain synchronous rotation.
The planetary gears are installed on the planet carrier through bearings to ensure that they can rotate freely while meshing with the sun gear and the outer gear ring.