Article explains how an automotive automatic transmission works.
Many automatic transmissions have a service filter in the transmission pan that
should be changed at manufacturer specified intervals. When
servicing an automatic
transmission a complete fluid flush is recommended to clean the valve body,
torque converter and fluid
cooler. The driver selects a mode by maneuvering the gear shift lever, usually placed
on the steering column or next to the driver's seat in the center console. It is
necessary to depress the brake pedal before the gear selector can be moved from
the "park" position.
Gear selection options include (P) park, (R) reverse, (N) neutral, (O) overdrive,
(D) drive. The park or P mode locks the transmission mechanically. This restricts
movement of car in any direction. This is achieved using a metal rod that engages
the output shaft and prohibits movement. An automatic transmission functions by
automatically changing the gear ratios while determining the speed and load of the
engine. Automatic transmissions have been available since the early 1950s.
The automatic transmission consists of: a transmission case, planetary gear-sets,
valve body, fluid cooler (in radiator) and a torque converter. A torque converter
utilizes transmission fluid as a coupling agent allowing the engine to run while
the car is stopped without stalling. Then when the engine speed is increased, re-engaging
the transmission to make the car move. A series of clutches and bands control the
planetary gear sets to provide multiple forward gear ratios. The valve body is the
hydraulic control center that receives pressurized fluid via the main transmission
pump. This transmission gear system is controlled by the computer PCM (power control