Aluminum Torque Tube
05-10-2003, 01:23 PM
#18
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You forget that there is a chromoly 25mm (that's 1 inch) solid driveshaft running through the assembly. For the tube to fail and drop down causing massive, catastrophic failure, the drive shaft will have to fail as well. If the tube does fail, the driveshaft vibration will become so severe that the car will be undrivable long before hitting the ground. In that case, the bellhousing o
If that tube snaps, the transmission will already be starting to rotate up. The transmission mount will instantly break. The drive shaft won't stop it, nor will the driveshaft break (yet)... but there will easily be enough play with the torque tube snapped in 1/2, for a ton of rotation, depending on where the torque tube breaks, before the drive shaft can wedge the two pieces of torque tube.
My guess is that that 1" drive shaft could easily be snapped in the above scenario once that torque tube breaks. The driveshaft is designed for torsional strength, not sheer strength, bending, etc...
The point here is that it has to be real strong.
There's a LOT of force applied to that torque tube.
But hey..... if you get one that survives a ton of abuse.... I'm IN! :-)
You can figure out/imagine the rest of the damage from there.
If that tube snaps, the transmission will already be starting to rotate up. The transmission mount will instantly break. The drive shaft won't stop it, nor will the driveshaft break (yet)... but there will easily be enough play with the torque tube snapped in 1/2, for a ton of rotation, depending on where the torque tube breaks, before the drive shaft can wedge the two pieces of torque tube.
My guess is that that 1" drive shaft could easily be snapped in the above scenario once that torque tube breaks. The driveshaft is designed for torsional strength, not sheer strength, bending, etc...
The point here is that it has to be real strong.
There's a LOT of force applied to that torque tube.
But hey..... if you get one that survives a ton of abuse.... I'm IN! :-)
You can figure out/imagine the rest of the damage from there.
05-10-2003, 03:42 PM
#19
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Tons of newer rear wheel drive vehicles use an aluminum driveshaft. They are also alot thinner than you plan. I don't think you will have any troubles,just be sure any welds are up to the task. You may even think about having them X-ray checked for quality of the welds. Some hard core enthusiasts have run CF driveshafts and foun that they are too stiff and not enough flex. They broke alot of axles, gears and trannys. I realize that you are talking about the tube it's self and not the actual shaft right now. But, when you do come to possibly building a new shaft, remember that some flexability, may save other components. Good Luck
05-10-2003, 05:33 PM
#20
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Hey David, sounds like a great project you have going. My first impression is that a 7000 series aluminum would be a better candidate due to its high tensile and yield strengths. Also, FYI I am almost 100% sure that 5000 series is what is used in pressure vessels. I am a junior in the school of material science and engineering at the University of Illinois, and have more knowledge in polymers then metals. Yet I am surrounded by people with great expertise everyday in regards to what you are working on, and if you have any questions I will gladly get some answers for you.
Nate
Nate
05-10-2003, 05:54 PM
#21
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nine-44
That's a bad analogy.
A drive shaft is not exposed to the same types of loads that a torque tube is.
The torque tube not only deals with twisting forces, but mainly it deals with the rotational forces that act up on it perpendicular to it's length. A drive shaft doesn't have to deal with this.
Example Torque Tube Car: You accelerate a 450ft/lbs turbo car. All 450ft/lbs are transmitted to the torque tube as the transmission tried to rotate itself backwards (that's assuming that you don't "pop" the clutch... in which case the loads are much higher). The torque tube is the only thing that prevents that from happening.
Example Drive Shaft Car: You accelerate a 450ft/lbs turbo car. The rear axle is supported from the twisting force by either a set of suspension links, leaf springs, or a torque arm. In no case, does the drive shaft bare any of the twisting load from the rear axle.
Further... most drag racing requires a safety loop around an aluminum drive shaft when you're over a certain level of performance (and the threshold isn't very high)....
Big difference in between the two above scenarios.
Don't compare apples to oranges.
That's a bad analogy.
A drive shaft is not exposed to the same types of loads that a torque tube is.
The torque tube not only deals with twisting forces, but mainly it deals with the rotational forces that act up on it perpendicular to it's length. A drive shaft doesn't have to deal with this.
Example Torque Tube Car: You accelerate a 450ft/lbs turbo car. All 450ft/lbs are transmitted to the torque tube as the transmission tried to rotate itself backwards (that's assuming that you don't "pop" the clutch... in which case the loads are much higher). The torque tube is the only thing that prevents that from happening.
Example Drive Shaft Car: You accelerate a 450ft/lbs turbo car. The rear axle is supported from the twisting force by either a set of suspension links, leaf springs, or a torque arm. In no case, does the drive shaft bare any of the twisting load from the rear axle.
Further... most drag racing requires a safety loop around an aluminum drive shaft when you're over a certain level of performance (and the threshold isn't very high)....
Big difference in between the two above scenarios.
Don't compare apples to oranges.
05-10-2003, 06:17 PM
#22
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I would also like to point out that the tranny is held in by only 4, four, 10mm bolts, attached to the rubber tranny mount. I don't think that the tube will endure too much more flex with aluminum v steel. The walls on the steel tube are about 3/32 thick. (I need to check again on the tube that has been cut up.) My tube has 1/4 walls. That's .094 v .25. Also, if we find that aluminum does flex a little too much, then the system can be beefed up with solid tranny mounts, but at this time I don't think that'll be necessary. As for using 7XXX series aluminum, as you get harder, the metal, while stronger, also becomes more brittle and subject to fracture. We use steel in our tooling that is about 40Rockwell, with a cutting edge of about 60Rockwell. We can use up to 75Rockwell, but it fractures easily under stress and flex. The same analogy holds for aluminum. It is better to accept a level of flex to ensure the material doesn't develop stress fractures and catastrophically fail. Pictures, weight and test results will be forthcoming.
05-10-2003, 08:19 PM
#25
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TonyG, Have you ever had your torque tube out before? All the 944/951s Ive seen have cross braces very similar to a driveshaft loop, only beefier. They are tied into the structure of the car also, not just sheet metal. Porsches and Drag Racing, isn't that pretty much apples and oranges too? 
05-10-2003, 11:32 PM
#27
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Dave951M
Yes the tranny mount brace is strong. But the rubber tranny mount itself is not.
If you take the torque tube out, and mount the tranny, which I have, you'll see that the tranny moves quite a bit.
The only thing that holds it secure is the torque tube.
The tranny mount is only to provide vertical lift.
The torque tube controls all rotation (or lack of) in all 3 axis.
Yes the tranny mount brace is strong. But the rubber tranny mount itself is not.
If you take the torque tube out, and mount the tranny, which I have, you'll see that the tranny moves quite a bit.
The only thing that holds it secure is the torque tube.
The tranny mount is only to provide vertical lift.
The torque tube controls all rotation (or lack of) in all 3 axis.
05-11-2003, 12:17 AM
#28
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> The torque tube controls all rotation (or lack of) in all 3 axis.
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">This is correct. Concerns about a lack of torsional rigidity from a material that has something like a third of the stiffness of steel are legitimate. That being said, those kinds of problems(torsional rigidity) have been long ago solved in the performance bicycle world.
Your either have to increase the diameter of the tube or the wall thickness or some combination of the two. Dave's using a wall thickness that's 1.5 times thicker than the steel torque tube. I can't tell you if that's sufficient, but I bet somebody out there with about a minute of spare time and a calculator
can.
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">This is correct. Concerns about a lack of torsional rigidity from a material that has something like a third of the stiffness of steel are legitimate. That being said, those kinds of problems(torsional rigidity) have been long ago solved in the performance bicycle world.
Your either have to increase the diameter of the tube or the wall thickness or some combination of the two. Dave's using a wall thickness that's 1.5 times thicker than the steel torque tube. I can't tell you if that's sufficient, but I bet somebody out there with about a minute of spare time and a calculator
can.
05-11-2003, 01:06 AM
#29
NKN84944 : Thanks for the fast reply. Assume a standard steel as a base line. When I pulled my TT it had a rough finish and had rust to boot so it looked like common steel to me. Please ask if there is a way of determining steel strength without destructive testing. I would like to see some numbers that can determine the thickness of the new TT to meet or exceed the old steel TT. Senior project material?
05-11-2003, 01:23 PM
#30
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Dave951M
What ever you do... make the torque tube strong enough to do the job WITHOUT the use of any solid mounts.
If you use solid mounts, then the thing only becomes usable in a track only car as the vibration and noise transmitted to the car would be too much for a street car.
Remember.... it's got to be strong in it's rigidity, as well as it's torsional strength.
It has to be very stiff with no flex, and no twist.
What ever you do... make the torque tube strong enough to do the job WITHOUT the use of any solid mounts.
If you use solid mounts, then the thing only becomes usable in a track only car as the vibration and noise transmitted to the car would be too much for a street car.
Remember.... it's got to be strong in it's rigidity, as well as it's torsional strength.
It has to be very stiff with no flex, and no twist.