How does an automatic transmission work?

Most people understand and comprehend how a manual transmission in an automobile works; the majority of people are baffled when it comes to explaining how an automatic transmission functions. The sheer number of automatic transmission parts makes these assemblies hard to understand.

Regardless of the type of transmission, it connects to the rear of the engine with a bell housing. In the case of a manual transmission, the bell housing contains the clutch; in the case of an automatic transmission the bell housing is where a torque converter is located. A torque converter is actually a fluid coupling that connects the engine to the transmission. Important automatic transmission parts are the planetary gears; these gears are what provide various ratios.

The torque convertor function:

When the engine crankshaft rotates, the housing of the torque convertor rotates as well. The torque converter connects and disconnects the engine output to the load via the transmission.

The torque converter is made up of a host of parts, the impellor which is connected to the housing, the turbine, stator and lock-up clutch. The fluid coupling, as the name implies, is full of fluid. Basically, the engine turns the impellor; the impellor forces the fluid under pressure to the turbine which imparts torque to the transmission.

The planetary gears:

A planetary gear set is that which changes gears as the engine speed increases. The complete set consists of a sun gear which sits in the middle of the assembly, planet gears that are driven by the sun gear and an outer ring gear. Certain ring gear components can be prevented from moving using complex automatic transmission parts, this feature allows the input and output system to change gear ratios.

The highest gear ratio depends on the transmission design. If the ring gear is fixed, the gear ratio is very different than when the sun gear is fixed.

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