Which one of the parts below is primarily responsible for providing forward, neutral, and reverse gears?

The planetary gearset is essential in automatic transmissions as it facilitates the selection of forward, neutral, and reverse gears. This component consists of a sun gear, planet gears, and a ring gear arranged in a manner that allows for various gear ratios and directions of rotation.

When the transmission control system engages different clutches within the planetary gearset, it alters the way the sun gear interacts with the planet gears and the ring gear, effectively allowing the vehicle to move forward, stand still in neutral, or move backward in reverse. The ability to achieve multiple gear ratios and directions makes the planetary gearset a pivotal component in automatic transmission design and function.

Understanding the role of the planetary gearset highlights its uniqueness in enabling the fundamental operation of an automatic transmission system, as opposed to the converter piston, governor assembly, or accumulator assembly, which serve different functions within the overall system. The converter piston primarily aids in torque converter function, the governor assembly monitors vehicle speed to regulate transmission shifting, and the accumulator assembly helps control hydraulic pressures but does not directly affect gear selection.