Ravigneaux theorem
A Ravigneaux set is a special type of double planetary gear commonly used in automatic transmissions . It is named after the French inventor Pol Ravigneaux, who introduced it in Neuilly-sur-Seine in the mid-1930s .
Components
It consists of:
- a common ring gear (gray), which is connected to the drive wheels via the differential
- a common planet carrier (red)
- two different sized sun wheels (green and dark green)
- short (dark red) and long (light red) planetary gear sets
function
The Ravigneaux set is the basis for most four-speed automatic transmissions. Supplemented with other planetary gear sets, it can also be found in many automatic transmissions with 5, 6, 7 or 9 gears. As with the simple planetary gear set, the various gear ratios are achieved by driving and braking certain parts or by blocking the entire planetary gear set. The output can either be guided via the ring gear or the planetary gear carrier. The drawing shows an output via the ring gear. To shift gears, the large (green) sun or the planetary gear carrier ring (red) must be held in place with the brakes and the motor shaft (white gearwheel) connected to one of the sun gears or the planetary gear carrier via clutches. This results in six useful combinations according to the gear table, which result in four forward gears, one reverse gear and one idle.
| Neutral | 1st gear | 3rd gear |
|---|---|---|
|
|
The achieved ratios can be changed by varying the number of teeth of the gears involved. Third gear is a special feature. There, any two clutches are engaged at the same time, so that the gearbox is locked and the gear ratio is always one, regardless of the number of teeth.
Usually three short and three long planet gears are used. However, other numbers would also be conceivable. The number of planets has no influence on the gear ratio, but it does have an influence on the maximum transferable torque.
Web links
- Description with illustration
- Explanation and animation of how a Ravigneaux movement works
- Animation of a Ravigneaux movement in all courses
Individual evidence
- ↑ Malcolm James Nunney: Light and heavy vehicle technology . 4th edition Butterworth-Heinemann, Oxford 2007, ISBN 978-0-7506-8037-0 , page 331 [1]