Which part of the automatic transmission provides multiple gear ratios in a compact form?

The planetary gear set is integral to the operation of automatic transmissions and serves the crucial function of providing multiple gear ratios in a compact design. It consists of a central sun gear, a surrounding planet gear set that is mounted on a carrier, and an outer ring gear. This configuration allows for various gear ratios to be achieved simply by modifying the input and output connections to the gears. As the sun gear is driven, the motion and position of the planet gears relative to the ring gear can produce different gear outputs, allowing the transmission to adapt to the changing speed and torque requirements of the vehicle.

The design of the planetary gear set is significant because it enables a wide range of gear ratios to be compactly arranged within the transmission. This is particularly advantageous in modern vehicles, where space is often limited. The ability to shift between gears seamlessly is crucial for optimizing performance, efficiency, and drivability.

In contrast, the other components mentioned serve different roles within the transmission system. The torque converter primarily facilitates the transfer of engine power to the transmission while allowing for fluid coupling and increasing torque during acceleration. Clutch packs enable gear changes by engaging and disengaging different gears but do not themselves provide the gear ratios. The electronic control unit (ECU) manages the transmission's