Automatic transmission - Mechanical system

In the Automatic transmission mechanical system there are three main components.

• Gear sets (usually planetary) Used to create different speed ratios that the transmission can produce.
  
  - Sun gear, This is the gear which is located in the centre of the gear set and which the other smaller gears rotate around.
  
  - Ring gear, These are the gears around the outside of the gear set.
  
  - Planet carrier, This gear is located between the outer ring gear and inner Sun gear. It connects to both these gears and is mounted on Planetary pinions.
  
  Any of these gears can be held stationary (one at a time) and the other gears will still rotate around the stationary gear.
• Multi plate clutches
  - Used to hold two rotating planetary gear set components. Consists of a forward clutch and a direct clutch. They engauge steel plates and transfer the torque of the engine. Also lets the drive manually change gears at times.
• Band type brakes- Used to hold planetary gear set components to the transmission case. Located around the outer edge of the direct clutch drum. Takes very little space in the in the transmission housing and has a big surface area to ensure a strong holding force.