Gear Selector

The most common type of automatic transmission uses hydraulic power to shift gears. The torque converter connects the engine to the transmission and uses pressurized fluid to transfer power to the gears. This apparatus replaces a manual friction clutch and lets the vehicle come to a complete stop without stalling.

As the engine transmits power to the pump of the torque converter, the pump converts this power into transmission fluid that powers the turbine of the torque converter. This apparatus increases the power of the fluid and transmits even more power back to the turbine, which creates a vortex power rotation that spins the turbine and the attached central shaft. The power created by this rotation is then transmitted from the shaft to the transmission's first planetary gear set.

This type of transmission has what is called hydraulic control. The transmission fluid is pressurized by an oil pump, which allows the speed to change depending on the vehicle's speed, tire revolutions per minute, and other factors. The gear pump is placed between the planetary gearset and torque converter, where it pulls and pressurizers transmission fluid from a sump. The pump input leads directly to the housing of the torque converter attached to the flexplate of the engine. When the engine is not running, the transmission does not have the oil pressure needed to operate and thus the vehicle cannot be push-started.