Torque Converters and Fluid Dynamics

The driven part of the converter is the turbine. The turbine spins inside the cover, and is connected directly to the input shaft of the transmission. The fluid coupling energy-created impeller rotation spins the turbine. In between the impeller and the turbine is the thinking part of the torque converter—the stator—or reactor. The stator redirects the flow of fluid between the impeller and the turbine, and is the key to smooth converter operation. The stator creates the multiplication of torque by redirecting fluid as it flows from the center of the turbine.

Fluid Coupling
Power applied to a direct fluid coupling, such as a turbine and impeller with no stator, would quickly bring the coupling to the point where the two parts and the fluid are rotating as a solid mass. This is known as the coupling phase, or the point where the turbine is turning 9/10ths as fast as the impeller. The fins inside the impeller and turbine force the transmission fluid in two directions at once to achieve this coupling. The transmission fluid flows in both a rotary and vortex motion at the same time.


To visualize these forces imagine spinning a half empty bucket of water around and around over your head. Rotary flow and centrifugal force holds the water in the bottom of the bucket. Vortex flow is taking place as the water circulates inside the bucket as you spin it around.


Inside the torque converter, rotary flow forces the fluid to the outside of the impeller and turbine assembly, and creates a centrifugal force that makes it spin ever faster. Vortex flow created by the blades channels fluid in a vortex within the impeller and turbine and helps this situation occur. This forces the fluid to circulate from the outside and back through the centers of the turbine and impeller. At the coupling stage, at 9/10ths, rotary flow overcomes vortex flow and the two halves spin essentially as one. Vortex flow is crucial to get things going with the help of the stator.

Multiplying Reactor
At idle, the stator locks on its one-way clutch, stops turning, and redirects the flow of fluid exiting the center of the turbine. On throttle application, the fluid exiting the center of the turbine hits the blades of the stationary stator. The reason this is key is that as the fluid jets out of the center of the turbine, the vortex is turning the wrong way—against engine rotation. The stator, or reactor, corrects the flow direction of the fluid and multiplies the energy contained within. This helps the impeller to spin the turbine faster by redirecting the fluid from the center of the turbine. The fluid then enters the center of the impeller with engine rotation, and then back out through the outside blades at a higher flow rate.