How does an automatic transmission work?

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There are a few differences between a manual and automatic transmission car. The two most noticeable differences are; an automatic transmission car does not have a clutch and, it also does not have a gear shift. You may be wondering how an automatic transmission car can change gears without being told to and how the car does not stall when it comes to a complete stop, here’s how:

Torque Converter

Automatic transmissions cars have something called a torque converter. This basically does the same thing as a clutch would in a manual transmission car as it allows the car to change gears. The torque converter connects the engine and the transmission to one another.

The torque converter is made up of four main parts;

  1. The impeller
  2. The turbine
  3. The stator
  4. The lock-up clutch

Its job is to briefly disconnect the transmission from the engine which allows the automatic transmission to change gears. These four parts work together in order to make this happen.

The impeller is shaped like a fan and as it turns it causes the transmission fluid to move. This then makes the turbine spin. The stator sits in between these two components and directs the fluid. The clutch is an energy saving element that makes the turbine and impeller move at the same speed. When the car is idling, the turbine stops moving which is why the car does not stall.

Planetary Gears

Planetary gears allow the car to have multiple forward gears and a reverse gear. The planetary gear has four major components;

  1. The sun gear
  2. The planet gear
  3. The planet carrier
  4. The ring gear

The sun gear is in the middle of the planetary gear. There can be three or four planet gears that are positioned around the sun gear and are attached by the planet carrier. The final component is the ring gear. It surrounds the internal gears and is constantly interlinked with the planet gears. The movement of the vehicle is dependant on the movement of the gears within the planetary gear. For example, when a car is just getting started the sun gear and planet gears will move in the opposite direction to one another while the ring gear will remain still.