I posted this in a few places. I thought it may be appreciated here.
The torque converter is one of the least understood components in an automatic transmission equipped vehicle. I will attempt to explain what it does and how it does it.
The torque converter has a few different functions.
We first need to understand that there is no direct link between the crankshaft and the transmission input shaft (except in the case of a lock up style converter, but we'll talk about that later). This means that the first function of the converter is to connect the crank and the input shaft so the engine can move the vehicle, this is accomplished through the use of a fluidic coupling effect.
The torque converter also replaces the clutch that is required in a manual transmission, this is how an automatic transmission vehicle can come to a stop while still being in gear without stalling the engine.
The torque converter also acts as a torque multiplier, or extra gear ratio, to help the car get moving from a stop. In modern day converters this theoretical ratio is anywhere between 2:1 and 3:1.
Torque converters consist of 4 major components that we need to concern ourselves with for the purpose of explanation.
The first component which is the driving member, is called the impeller or "pump". It is connected directly to the inside of the converter housing and because the converter is bolted to the flexplate, it is moving anytime that the engine moves.
The next component is the output or driven member and is called the turbine. The transmission's input shaft is splined to it. The turbine is not physically connected to the to the converter housing and can rotate completely independently of it.
The third component is the stator assembly, its function is to redirect the flow of fluid between the impeller and the turbine, which gives the torque multiplication effect from a standstill.
The last component is the lock up clutch. At highway speeds this clutch can be applied and will provide a direct mechanical link between the crankshaft and input shaft, which will result in 100% efficiency between the engine and trans. The application of this clutch is usually controlled by the vehicle's computer activating a solenoid in the transmission.
Here's how it all works. For the sake of simplicity, I will use the common analogy of two fans which represent the impeller and the turbine. Let's say that we have two fans facing each other and we turn one of them on, the other fan will soon begin to move.
The first fan, which is powered, can be thought of as the impeller that is connected to the converter housing. The second fan- the "driven" fan can be likened to the turbine, which has the input shaft splined to it. If you were to hold the non-powered fan (the turbine) the powered one (the impeller) would still be able to move- this explains how you can pull to a stop with your automatic without the engine stalling.
Now imagine a third component placed in between the two which would serve to alter the airflow and cause the powered fan to be able to drive the non-powered fan with a reduction of speed- but an increase of force. This is essentially what the stator does.
At a certain point (usually around 30-40 mph), the same speed can be reached between impeller and the turbine. The stator, which is attached to a one way clutch, will begin to turn in conjunction with the other components and around 90% efficiency between the crank and the input shaft is achieved. The rpm at which this occurs under full throttle is often referred to as "stall speed".
The remainder of the slippage between the engine and trans can be eliminated by connecting the input shaft to the crankshaft through the application of the lock up clutch that was mentioned before. This will tend to lug the engine, so the computer will only command this in higher gears and at highway speeds when there is very little engine load present. The main function of this is to increase fuel efficiency and reduce the amount of heat that is generated by the converter.
I hope this helped to explain a relatively simple device that has a complex set of functions.
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it's unprofessional because both kits seem to be quality, and it's easy to confuse comparisons with trash talking or advertising...aka the "blatant self promotion".
that's why 3rd parties present comparisons, because any kind of talking down from one competitor towards another makes most people feel as though they just watched an election campaign ad...makes everyone look shady, even though both parties are of the highest quality.
it's unprofessional because both kits seem to be quality, and it's easy to confuse comparisons with trash talking or advertising...aka the "blatant self promotion".
that's why 3rd parties present comparisons, because any kind of talking down from one competitor towards another makes most people feel as though they just watched an election campaign ad...makes everyone look shady, even though both parties are of the highest quality.
-sean
All I want is the facts so I can compare apples to apples.
Without a true comparison it's like he/they are saying "trust me".
I did say - "As long as you don't bad mouth the competitor or give away any trade secrets you are O.K."
Third party "feelings" are not going to help me make a buying decision.
At a certain point (usually around 30-40 mph), the same speed can be reached between impeller and the turbine. The stator, which is attached to a one way clutch, will begin to turn in conjunction with the other components and around 90% efficiency between the crank and the input shaft is achieved. The rpm at which this occurs under full throttle is often referred to as "stall speed".
Transdude: Reread this and see if you want to make any changes. It doesn't look quite right to me. The last sentence doesn't seem to go with the rest of it.
__________________ ADDING POWER HAS NEVER BEEN SO FAST!
Last edited by Dude Boy; 06-11-2004 at 01:54 AM.
Reason: spelling problems!
Transdude: Reread this and see if you want to make any changes. I doesn't look quite right to me. The last sentence doesn't seem to go with the rest of it.
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
__________________ ADDING POWER HAS NEVER BEEN SO FAST!
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
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.
I'm quite used to seeing the torque converter stall RPM on my truck under the following circumstances: High altitude: elevations over 9000 feet where the engine can make only about 50% (or less) of its sea level power. Load: 500lbs of people/cargo in the truck and a 3700 lb trailer in tow. Grade: 15% to 20% (or higher) such as a campground exit or secondary mountain road.
What happens: I floor the throttle, the engine RPMs rise to about 2200 and stabilize (TC stall) and then the truck slowly, but ever so slowly begins to move. Under the above conditions it typically requires around 10 to 20 seconds just to get up to 20 mph (time depends on the exact altitude, air temp/density, and road grade). Engine RPM begins to rise above stall RPM when the truck finally gets up to around 10 mph. My truck is the Tundra V8 BTW.
I might add that acceleration in general is glacially slow even on a level road when towing at high altitude...at WOT a zero to 60 acceleration requires around one to two minutes...and nearly a mile of road. At the end of a typical Interstate on-ramp I've often only managed to attain 45 to 50 mph so merging can be rather interesting in even moderate 75 mph traffic.
Torque Converter Operation Explained
unprofessional
Linear Mode
