Torque converter: what is it and how does it work?

Now that we have told you which are the main gearboxes on the market and what their characteristics are, we are going to continue with one of the elements found in them that plays a very important role: the torque converter. To do this, we are going to explain what it is and what function it has inside an automatic gearbox.

The torque converter is a hydrodynamic transmission that is additionally coupled to the automatic gearbox. This mechanical element was invented by the German engineer Hermann Föttinger, who patented it in 1905, and it was first applied in shipbuilding. Logically, the torque converter was also adopted by other sectors such as aviation, industrial machinery, trains and automotive. In the automotive sector, which is the one we are concerned with here, it was introduced in the early 1930s, when it was adopted by buses and heavy machinery from the English company based in Coventry, Daimler Motor Company.

As you can see, it is not precisely a modern component. Over all these years it has had enough time to be refined, but this does not mean that its components and its operation have changed. The torque converter is a mechanical component used in automatic gearboxes to replace another component that these gearboxes do not have: the clutch. Its job is to connect the gearbox to the engine and therefore transmit engine torque to the gearbox. The torque converter is made up of the following elements that make its operation possible, each of them with very important functions:

• Torque converter housing or pump: This element rotates together with the engine, so it starts working from the moment the engine is started. The pump, also called the torque converter housing, consists of vanes that generate a centrifugal force, throwing the oil it contains towards the turbine.

• Turbine: The oil thrown by the pump strikes the curved blades that make up the turbine, basically enabling the vehicle to move, since the turbine is directly connected to the transmission. The turbine blades receive the oil from the pump in the direction opposite to their rotation, so the oil must change direction and, when it returns to the pump, it has to return to its original direction of rotation so that excessive power losses do not occur.
• Stator: The stator is the element responsible for sending the oil back to the pump, changing the direction of the flow thanks to a bearing mounted on it that only allows it to rotate in one direction. In this way the oil changes its direction of rotation just before reaching the pump again, thus increasing the efficiency of the torque converter.

• Lock-up clutch: This element is common in modern automatic gearboxes and can lock up the torque converter as needed, as it is controlled by the vehicle’s control unit. This is because, in the clutch phase, when the torque ratio is 1:1, the torque converter operates with efficiency losses that can reach as much as 95% in high-power engines, whereas for power transmission a slip of more than 3% should never be exceeded. It is coupled to the pump and is pressed against it by oil when engine torque is applied, so that a rigid drive without slip is achieved, similar to that of a normal clutch.