Ravigneaux planetary gearset

The Ravigneaux gearset is a double planetary gear set, invented by Pol Ravigneaux, who filed a patent application on July 28, 1949, in Neuilly-sur-Seine France. This planetary gear set, commonly used in automatic transmissions, is constructed from two gear pairs, ring-planet and planet-planet.

The Ravigneaux set has two sun gears, a large sun and a small sun, and a single planet carrier, holding two sets of planetary gears, inner planets and outer planets. The carrier is one sub-assembly but has two radii to couple with the inner and outer planets, respectively. The two sets of planet gears rotate independently of the carrier but co-rotate with a fixed gear ratio with respect to each other. The inner planets couple with the small sun gear and co-rotate at a fixed gear ratio with respect to it. The outer planets couple with the large sun gear and co-rotates with a fixed gear ratio with respect to it. Finally, the ring gear also couples and co-rotates with the outer planets in a fixed gear ratio with respect to them.

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:

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.

The Ravigneaux improves upon earlier planetary automobile transmissions, such as the Simpson, which has two complete planetary gearsets. As originally invented, the Ravigneaux puts two planetary gear trains on a single planet carrier. It has two sun gears, two ring gears, and two sets of planet gears on a single carrier. Using a single carrier makes the Ravigneaux smaller, lighter, and less expensive to make, because the carrier is usually the largest and most expensive part of a planetary gearset.

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