The torque converter consists of three parts: a pump (or the leading part), turbines (driven part) and a reactor (stator). The pump blades are made in the torque converter housing. The internal cavity of the torque converter is filled with oil. The turbine and reactor are also located in the torque converter housing. The torque converter housing is attached to the engine flywheel.
When the engine is running, the pump rotates at the crankshaft speed and works as a centrifugal pump. Oil is supplied to the central part of the pump and is thrown out between the blades by centrifugal force.
The shape of the pump cups and blades is selected in such a way that the oil is thrown to the turbine blades clockwise, causing it to rotate. The pump and the torque converter turbine are not mechanically connected to each other and the rotation of the pump is transmitted to the turbine only due to the energy of the oil. The turbine is connected by a splined connection to the hollow shaft of the turbine, which transmits torque through a sprocket and chain.
When the engine is idling, the torque converter pump speed is low. The energy of the oil leaving the pump and, therefore, the torque transmitted to the turbine are extremely small. This ensures that the engine is idling, but the car may "pull" slightly. As the accelerator pedal is pressed, the torque converter pump speed increases and the energy of the oil ejected onto the turbine blades, which creates the torque, increases.
After energy is transferred to the turbine, the oil is discharged through its blades in a counterclockwise direction.
Since the energy absorbed by the turbine is sufficient to change the direction of oil circulation, the turbine increases torque.
If the counterclockwise ejected oil were to enter the torque converter pump directly, it would come into contact with the inner surface of the pump blades in the opposite direction to its rotation, which would result in a complete loss of torque gain. To prevent this, a reactor (stator) is installed between the pump and the torque converter turbine.
The reactor gives the oil returning to the pump the same direction of rotation as the pump.
Since the oil leaving the reactor does not impede the rotation of the pump, the torque of the engine is added to the torque of the oil as it passes through the pump, and this cycle is repeated each time.
The oil returning to the turbine tends to rotate the stator clockwise. The reactor is mounted on a freewheel clutch and can only rotate clockwise. Therefore, when the pump rotates at low speed, the oil ejected from the turbine acts on the blades of the reactor, tending to rotate it counterclockwise, and blocks the freewheel clutch, which does not allow the reactor to rotate.
(Text copied from an online resource: opelbook.ru)
As the turbine speed increases, the direction of the oil flowing out of it changes, acting clockwise on the blades of the reactor. Since the reactor prevents the oil flowing to the pump, the freewheel clutch is unlocked, allowing the stator to rotate freely on the shaft. The reactor stops participating in the process of increasing the torque in the torque converter. Since the pump and turbine rotate at the same speed or in a 1:1 ratio, the torque converter begins to function as a fluid coupling.
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