The Ravigneaux gear set is a type of planetary gear set used in automatic transmissions. It consists of two sun gears, a ring gear, and four planet gears. The planet gears are divided into two sets, with each set rotating around a different sun gear. The two sun gears are connected by a carrier, which also holds the planet gears.
The Ravigneaux gear set is used in some automatic transmissions to provide multiple gear ratios using a single planetary gear set. By changing the direction of rotation of one of the sun gears and holding the other stationary, the gear ratio can be changed without the need for additional gear sets or clutches.
The Ravigneaux gear set offers several advantages over other types of planetary gear sets. It is compact, lightweight, and can provide multiple gear ratios. However, it can be more complex and expensive to manufacture than other types of gear sets.

Types of Ravigneaux gear sets, including:

1. Standard Ravigneaux gear set: This type consists of an outer ring gear, a sun gear, and two planetary gear sets. The two planetary gear sets are connected to each other and to the sun gear by a carrier.
2. Double-reduction Ravigneaux gear set: This type has two sets of planetary gears with different sizes. The first set is connected to the sun gear and the second set is connected to the carrier. This arrangement allows for a greater reduction in speed.
3. Compound Ravigneaux gear set: This type has two sets of planetary gears that are connected to each other and to the sun gear by a carrier. In addition, it has a third planetary gear set that is connected to the carrier and to the output shaft. This arrangement allows for even greater speed reduction.
4. Triple-reduction Ravigneaux gear set: This type has three sets of planetary gears with different sizes. The first set is connected to the sun gear, the second set is connected to the carrier, and the third set is connected to the output shaft. This arrangement allows for the greatest reduction in speed.