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Originally Posted by Dude Boy
John:
That was a really concise explanation of how a torque converter operates. The part that I question is the term "stall speed" being related to the RPM at full throttle, in which the stator begins to spin along with the impeller and turbine. You may very well be correct on this, but I've always heard that term defined as the RPM that the engine will develop at full throttle while the turbine is held stationary. I can see where the stator would start spinning and "getting out of the way" at 30-40 MPH under light throttle in high gear, but if you were at WOT, that would occur at a much higher speed, right? I know that if the something goes wrong with the one-way clutch and the stator stays locked, it can really create a drag much like the brakes being on.
I was with some guys that were hill climbing with 4x4's several years ago and an F-250 would not climb the hill, and it wasn't because of wheel spin. It gradually came to a stop even though he was using WOT in 1st gear. It stalled out and would no longer move up the hill. Wasn't this an example of "stall speed?" Under those conditions, the stator would have been locked and the torque multiplication at max (as well the potential for heat build up.)
Bob
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Sorry for the confusion, I was using that particular sentence as an opportunity to segue into a brief explanation of the term stall speed.
Understand that the term "stall speed" usually refers to the *maximum* rpm at which the components in the converter will turn almost as one.
Because of the way that a converter works, the rpm at which the converter components rotate as one is variable based on the amount of torque that is input into the converter- at lower throttle openings it happens much earlier, at full throttle, what is normally referred to as full stall speed is achievable.
The phase where all of the components try to rotate as one is more accurately referred to as "rotary flow"- as opposed to "vortex flow", which occurs during the torque multiplication phase. Again, this can happen at a variety of speeds and rpm's based on engine output.
I was just attempting to make the explanation of a complex device as simple as possible.The mention that I made to 30-40 mph is just an example of what will happen under normal driving with moderate throttle openings.
Regarding the Ford truck stalling while trying to climb a hill, that would really have nothing to do with what stall speed is- stall speed is just the speed at which the rpms stop climbing with the turbine (input member) held stationary. Occasionally, I have seen vehicles' engines stall under these conditions, but it is usually due to the extreme load that the motor is exposed to.
You are also correct in saying that maximum heat is generated at maximum torque multiplication with the stator and turbine locked.
I hope I was able to clarify to everyone what I was trying to describe.
-John