Probably the most classic automatic is the converter automatic. The torque converter is a fluid coupling and connects the engine to the transmission, which consists of planetary gear sets. If the vehicle is idling, the converter is a kind of separate clutch and transmits no or only a very small torque. If the driver operates the gas pedal, the engine rotates faster than the transmission. The converter works in this phase as a continuously variable transmission. If there is a large speed difference between the gearbox and the engine, the torque is increased. When the acceleration is completed, the gearbox and engine are back on the same footing. The differential speed and the torque increase are then gone. The converter works as a closed and normal clutch. In the transmission, the planetary gear sets are coupled together. Connecting, disconnecting or braking results in different translations. Clutches and brakes work hydraulically. Activation of the control was also hydraulic at the beginning, and very complex. At the present time, electronic control units are entrusted with this work.
The converter is compared to a manual transmission, the clutch and disconnects or connects the transmission and the engine. As a result, the torque is amplified and a gear is engaged, the vehicle creeps. The converter needs oil for a good function. This is rotated by means of impeller and paddle wheels. With the gear housing, the stator is connected and this freewheel, the oil is diverted to the turbine wheel. The turbine is powered by the oil. It is firmly connected to the transmission input shaft. As a visual idea, a watermill is very good. Instead of water, the oil is simply used. The planetary gear set gets its name because its gears are arranged as in the solar system. The wheels are around the sun gear. They are connected by a housing and a ring gear, which is present outside. The various translations are achieved by holding one component or joining two together.
The built-in pump generates the necessary oil pressure and is driven by the engine. The pump also ensures that the switching elements are actuated and that lubrication of the gearbox is ensured. By means of the freewheel, the circuits are controlled. For example, the sun gear may turn in one direction, but the opposite direction is blocked. Therefore, the transmission can not slip during a gear change. The switching elements are very important. The planetary gear sets and the sun gear are connected by means of clutches, for example. The switching elements connect in this way parts of the planetary gear set.