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What is the planetary gear set in an automatic transmission?

The components and function of the planetary gears.

The planetary gears are a set of sun gears, planet gears and ring gears inside the automatic transmission. That is why they get their name. Planetary gears produce the gear ratios that your transmission delivers when the vehicle is in motion and is the main function of the overall transmission in which everything depends upon. The whole device is about 7 to 10 inches and is the main function of the overall transmission.

Think of it as planets rotating with the largest gear on the outside as the ring gear with the core of this centered in the middle as the sun gear and small planetary pinions or gears between those two gears rotating around the sun like a solar system as seen in this illustration. These gears are always engaged and they are all locked together inside one device.

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The sun gear is in the center of them all and the ring gear connects to the planet gears as seen in this illustration. Each gear ratio depends on the state of the planet gears being locked in or unlocked as they move around the center “sun” gear.

Each of the planetary pinion gears have a different function individually delivering what the transmission needs at any given time such as deliver torque or speed. The torque convertors are connected to clutch system which is connected to the planetary gear set and feeds pressurized oil into the gear set. The propelling movement sends in motion the necessary thrust to the output shaft that turns your automobile's wheels.