Aluminum Torque Tube interest?
06-23-2003, 12:07 PM
#16
Racer
Join Date: Jun 2002
Location: ventura ca
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Question is,
Why didn't the fabulous Porsche engineers do this?
We know they were very weight conscious. Magnesium engine parts and aluminum body panels attest to the fact.
I don't have an answer but some things to consider are fatigue failure resistance and flexural modulus of Al vs steel.
The tube may meet stress requirements, but was it analyzed for deflection? Some adjustments may need to be made to wall thickness to reduce torsional deflection to the levels that steel would provide. Weld integrity is also an issue as there will be significant stress concentration. Especially since the welds didn't look consistant. Might I suggest some cleverly placed plug welds to assist the primary welds?
BTW, the tube is a structural member, although not a chassis member as Brendan was trying to point out. A structural member is a member which provides structure. The TT definately structures the transmission to the engine. It may even see some chassis loads when the chassis is twisted significantly due to heavy cornering or the like.
Why didn't the fabulous Porsche engineers do this?
We know they were very weight conscious. Magnesium engine parts and aluminum body panels attest to the fact.
I don't have an answer but some things to consider are fatigue failure resistance and flexural modulus of Al vs steel.
The tube may meet stress requirements, but was it analyzed for deflection? Some adjustments may need to be made to wall thickness to reduce torsional deflection to the levels that steel would provide. Weld integrity is also an issue as there will be significant stress concentration. Especially since the welds didn't look consistant. Might I suggest some cleverly placed plug welds to assist the primary welds?
BTW, the tube is a structural member, although not a chassis member as Brendan was trying to point out. A structural member is a member which provides structure. The TT definately structures the transmission to the engine. It may even see some chassis loads when the chassis is twisted significantly due to heavy cornering or the like.
06-23-2003, 06:28 PM
#17
Three Wheelin'
Join Date: Nov 2001
Location: Northern Kentucky
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The tube obviously takes a beating in the driveline. Yes, the mounts support the engine weight, but a rather large portion of the engine torque is transmitted to the outer tube and back to the trans housing.
I would not be so much concerned with strength as I would be about deflection and most importantly design for long fatigue life...that could be the biggest issue with an aluminum unit. For example, will it cycle over and over again without fatigue failure? Typically, aluminum can't offer the infinite fatigue life steel can offer. You get too far out on the stress vs. no. cycles curve and the life is then exceeded.
Provided the tube is massive enough and has enough material to make it to a reasonable fatigue life, it would be a good deal. After all, the engine castings seem to last forever, so why not an aluminum torque tube?
I would not be so much concerned with strength as I would be about deflection and most importantly design for long fatigue life...that could be the biggest issue with an aluminum unit. For example, will it cycle over and over again without fatigue failure? Typically, aluminum can't offer the infinite fatigue life steel can offer. You get too far out on the stress vs. no. cycles curve and the life is then exceeded.
Provided the tube is massive enough and has enough material to make it to a reasonable fatigue life, it would be a good deal. After all, the engine castings seem to last forever, so why not an aluminum torque tube?
