Planetary Gear Trains
In contrast to a Ravigneaux, a simple planetary gear train has two central gears, one or more planets, and one arm carrying the planets. Usually, one of the central gears has external teeth and is called a sun gear, and the other central gear has internal teeth and is called a ring gear. The carrying arm is usually called the planet carrier. Planet gears are usually not directly coupled, leaving three components that are directly coupled:
- Sun gear
- Ring Gear
- Planet carrier
This provides for two inputs and one output. Usually, in an automatic transmission, one component is held fixed, while another component is input, and the remaining component is used for output. By choosing a set of components for held, input, and output, the planetary gear will increase or decrease speed and change direction.
A Ravigneaux differs from a simple planetary gear train, in that it has two sun gears, which results in three inputs and one output. The additional sun gear allows more combinations. A single Ravigneaux can provide a complete set of speeds in an automatic transmission.
Read more about this topic: Ravigneaux Planetary Gearset
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