When the turbine speed is reaching about 80% of the pump speed, the torque multiplication becomes 1.0 i.e. the turbine torque becomes equal to that of the pump torque. From this point on, the converter is working similar to a fluid clutch. A stator freewheel serves to improve the efficiency in the upper driving range, in the torque multiplication range it is backing-up the torque upon the housing, and is released in the clutch range. In this way, the stator can rotate freely.
Function of a hydrodynamic torque converter (schematic view) T P = Torque of the pump wheel T T = Torque of the turbine wheel T R = Torque of the reaction member (stator) From the engine T To the gearbox Starting condition = 0 Machine standing Intermediate condition 1 n T Condition in the coupling point 1 0 1 n T = 0.8n engine 7577APT100 3-5 Pump wheel e P 1 1.5 Rea (stat TR Turbine whe nT ction member 2.5 M or) st