Single Planet Gear Set

A. General
Planet gear sets are used as multi-stage gear trains in automatic car transmissions. The benefits which they offer are:
- Coaxial position of input and output.
- Compact design.
- High efficiency.
- Good Shift properties of the individual gear train elements.

If individual elements of a planet gear set are locked (sunwheel, planet carrier, annulus), it is possible to form various ratios without having 10 move the gearwheels or sliding sleeves.
The gems are always meshed and shift operations consist of hydraulic operation of clutches and brake bands depending on which gear is shifted.


B. Design
A single planet set consists of an annulus (1), the planet gears (2) running in the planet carrier (4). and a sunwheel (3).

To enable a planet gear set to transmit a torque, either the annulus the planet carrier or the sunwheel must be supported against the transmission housing. This is done by operating a brake (brake band or multiple-disc brake). A torque is also transmitted if the net gear set is locked in itself. This requires operating a clutch (multiple-disc clutch).

C. Operating principle

The following gear reduction possibilities are used in automatic transmissions:





Annulus locked
- sunwheel driving
- Planet carrier driven
- produces a relatively large gear reduction.





1. Annulus
2. Planet gear
3. Sunwheel
4. Planet carrier





Sunwheel locked
- Annulus driving
- Planet carrier driven
- produces a relatively small gear reduction.





Planet carrier locked
- Sunwheel driving
- Annulus driven
- produces a reversal in direction of rotation and a gear reduction.

This combination is used with reverse gear.

Two elements locked together
- Planet gear set rotates as complete unit
- produces direct drive.