Old technology – new applications: The torque converter transmission is still “in” and is very important in automotive engineering. It is used more frequently in hybrid engines, for example. But how does the technology work and what are the advantages and disadvantages?
1. How does the torque converter transmission work?
“Classic” automatic transmissions are usually based on torque converter technology – it is therefore something like the traditional standard in this area. The whole thing owes its name to the torque converter. This is a construction consisting of a guide wheel, turbine wheel and impellers, which are located in a housing filled with oil and act as a kind of intelligent clutch – in other words, as a connection between the drive and the actual transmission.
A hydrodynamic process takes place inside it: the impeller is connected to the motor and turns at the corresponding motor speeds. This moves the oil in the housing and generates flow energy, which in turn is transferred to the opposite turbine wheel. You could also say that the oil pressure provides the power transmission to the turbine wheel. When it turns, the downstream transmission also moves and, thus, the car.
There is also a guide wheel inside the torque converter, although it does not turn and its task is to increase the torque on the blades of the turbine wheel by redirecting the oil flow. It also directs the oil flow back to the impeller blades.
Exploded view of a torque converter: The oil pressure ensures power transmission.
2. What is the purpose of the technology?
Overall, the torque converter (as the name suggests) is responsible for massively increasing the torque at rather low engine speeds, which in turn makes it easier to start the car. It can also be used to interrupt the tractive force when you want to stop or brake the vehicle, for example.
The individual components of a torque converter.
Incidentally, the subsequent transmission is then a so-called planetary gearbox, the basic structure of which consists of a ring gear, planetary gears and a sun gear. In torque converter transmissions, however, there are several of these designs in a row, which are cleverly coupled together for different ratios.
3. Who invented it?
The German engineer Hermann Föttinger first described a so-called “fluid transmission” (as the torque converter could also be called) in detail in a patent application in 1905. Here he already speaks of turbine wheels for “work transmission between adjacent shafts.” This formulation still applies today.
It was not until 1948 that the “Föttinger clutch” (as it is often called) was used in a production vehicle by General Motors. In the years that followed, torque converter transmissions increasingly conquered the market, giving the invention a considerable boost from the 1960s at the latest. Various refinements over the decades ensure optimized function.
4. What are the advantages and disadvantages of the torque converter transmission?
Perhaps the biggest advantage is immediately apparent to every driver: the automatic gear changes are not really noticeable. There is only a slight interruption in traction. One special feature is the almost proverbial “automatic creep.” The car always starts rolling immediately when the brake is released, because a little torque is transferred from the engine to the transmission even when the car is idling. In addition, the described power transmission via oil protects all the components concerned and wear is low. The torque converter also dampens vibrations in the drivetrain. A typical disadvantage is the problem when towing or pushing – in many models this does not work on the rolling axle.
5. What does the future hold?
Currently, the torque converter automatic is increasingly being used in plug-in hybrid engines, where the drive energy from the combustion engine and electric motor are effectively combined. Incidentally, fewer gears are required overall, as the electric motor takes over the drive of the car in certain driving situations (such as when starting off). As a result, the combustion engine is used less frequently and the number of gears required decreases.
The central components of a planetary gearbox can be machined with EMAG machines.
You can find out more about the planetary gearbox, the subsequent transmission, here.