How a Torque Converter Works

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Torque converters are everywhere. All over the world, in different makes and models of vehicles, the torque converter has changed the way we live our lives. For an automatic transmission to work, it requires a torque converter. A torque converter replaces the traditional flywheel and clutch plate. That means that about 90% of all vehicles have a torque converter. Like most revolutionary inventions — TV, refrigerator, microwave — the majority of people have no clue how they work. Here is a simple guide to what a torque converter does, and how it does it.

Inside a torque converter there are 4 things: the pump, the turbine, the stator, and automatic transmission fluid.


Inside the torque converter there is a centrifugal pump, or impeller. Centrifugal pumps are used to change rotational kinetic (moving) energy to hydrodynamic (forced fluid) energy by transporting fluid through its turbines. These kinds of pumps are used commonly with water, petroleum and sewage. As the flywheel spins, fluid is flung to the outside of the converter by the engine torque. As the inner space is emptied it creates a vacuum that draws more transmission fluid to the center. 


The turbine is similar to the pump; it has an output shaft that connects to the transmission. When the impeller ejects the automatic transmission fluid, it is thrown against the outside of the turbine. Similar to a waterwheel, this causes the turbine to revolve. The more the engine turns, the more this process is repeated. Little by little, as the power of the engine increases, it is converted into power for the transmission. With the directional blade of the pump, the turbine has blades that change the direction of its rotation, and push the liquid back to the center.



There is a lot of force propelling the outermost edge of the impeller and the turbine. Because they are rotating in opposite directions, passing fluid between them would counteract what each one is doing. This would inevitably decrease the engine torque and waste power. This is where the stator comes in. The stator sits in the very center of the torque converter and acts as a buffer between them. It helps to change the direction of the fluid before it gets pummeled by blades going the opposite direction. This makes the transition between the rotating wheels smooth and seamless. The stator has a very unique job to perform. The stator is connected to the same shaft as the transmission. So, as the fluid hits it going the opposite direction, it has no choice but to change direction. This is very vital until the vehicle reaches about 40 miles per hour. At that speed, the pump and turbine are rotating at nearly the same speed. This causes the fluid to enter the pump in the same direction it was already going, essentially bypassing the stator.


The fluid is the key to making all of this work. Fluid has revolutionized the conversion of power in machinery. Just look at hydraulics. Automatic transmission fluid is thick and red. Without it, none of this would work.

Now you know a bit more about what is in your car. Share the knowledge, and for goodness’ sake, make sure you have enough transmission fluid.

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