How the converter works
Automatic Hydraulic Clutch
In Reverse, low and second gears, the converter operates in hydraulic or soft drive conditions. In hydraulic drive, the converter functions as an automatic clutch (when the car is stopped) and as a torque multiplier (when engine load requires more torque).
The engine drives the impeller mechanically.
The turbine is driven hydraulically by the impeller.
The turbine drives the tube input shaft for input to the gear train.
Impeller Pumps Fluid
The purpose of the impeller is to put the fluid in motion. Inside the impeller housing many curved vanes, along with an inner ring, form passages for the fluid to flow through. The rotating impeller acts as a centrifugal pump. Fluid is supplied by the hydraulic control system and flows into the passages between the vanes . When the impeller turns, the vanes accelerate the fluid and centrifugal force pushes the fluid outward so that it is discharged from openings around the inner ring . The curvature of the impeller vanes directs the fluid toward the turbine, and in the same direction as impeller rotation
Rotary Force on the Turbine
As shown in View B (above), the turbine vanes in the turbine are curved opposite to the impeller. The impact of the moving fluid on the turbine vanes exerts a force that tends to turn the turbine in the same direction as the impeller rotation. When this force creates a great enough torque on the transmission turbine output shaft to overcome the resistance of motion, the turbine begins to rotate.
Now the impeller and turbine are acting as a simple fluid coupling, but we have no torque multiplication yet. To get torque multiplication, we must return the fluid from the turbine to the impeller and accelerate the fluid again to increase its force on the turbine.
Vanes Reverse the Flow
To get maximum force on the turbine vanes when the moving fluid strikes them, the vanes are curved to reverse the direction of flow . Less force would be obtained if the turbine deflected the fluid instead of reversing it. At any stall condition, with the transmission in gear and the engine running but the turbine standing still, the fluid is reversed by the turbine vanes and pointed back to the impeller. Without the stator, any momentum left in the fluid after it leaves the turbine would resist the rotation of the impeller.
At this point, we have a simple fluid coupling that will cause the turbine to drive the input shaft with no torque multiplication. To gain multiplication, we must add the reaction member or stator.