Stall Point and Clutch Point


1. Stall point

The stall point refers to the situation in which the turbine runner is motionless. The difference in rotation speeds between the pump impeller and the turbine runner is at a maximum. The maximum torque ratio of the torque converter is at the stall point. (It is generally in a range between 1.7 and 2.5.) The transmission efficiency is 0.


In the stall test described later, the performance of the torque converter and engine output are tested by the engine being run at full throttle (full load) at this stall point.

2. Clutch point

As the turbine runner starts to rotate and the speed ratio increases, the difference in rotational speed between the turbine runner and pump impeller starts to decrease. However at this time, the transmission efficiency increases. The transmission efficiency is at its maximum just before the clutch point. When the speed ratio reaches a specified level, the torque ratio becomes almost 1:1. In other words, the stator starts to rotate at the clutch point and the torque converter to operate as the fluid coupling in order to prevent the torque ratio from falling

below 1.


Stall test

This test is used to check the overall performance of the engine and transaxle (the clutches and brakes of the planetary gear unit). It is carried out by rendering the vehicle immovable, then measuring the engine rpm while shifting to the “D” or “R” range and depressing the accelerator pedal all the way.

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