First Gear

In first gear, the smaller sun gear is driven clockwise by the turbine in the torque converter. The planet carrier tries to spin counterclockwise, but is held still by the one-way clutch (which only allows rotation in the clockwise direction) and the ring gear turns the output. The small gear has 30 teeth and the ring gear has 72, so referring to the chart on this page, the gear ratio is:

Ratio = -R/S = - 72/30 = -2.4:1 So the rotation is negative 2.4:1, which means that the output direction would be opposite the input direction. But the output direction is really the same as the input direction -- this is where the trick with the two sets of planets comes in. The first set of planets engages the second set, and the second set turns the ring gear; this combination reverses the direction. You can see that this would also cause the bigger sun gear to spin; but because that clutch is released, the bigger sun gear is free to spin in the opposite direction of the turbine (counterclockwise).

Planetary Gearset Contains :

• The sun gear
• The planet gears and the planet gears' carrier
• The ring gear

How Automatic Transmissions Work

• There is no clutch pedal in an automatic transmission car.
• There is no gear shift in an automatic transmission car. Once you put the transmission into drive, everything else is automatic.