Aluminum Torque Tube
05-09-2003, 09:12 PM
#1
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Aluminum Torque Tube
I'm nearing completion of the prototype of an aluminum torque tube. It will be totally rebuildable, use the correct C4 clearance bearings, and weigh less. Any interest??
05-09-2003, 10:05 PM
#3
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Not determined at this point. After it's tested, I'll see where I am with materials costs.
The interesting thing here for track guys is I can put any number of bearings in, but I would recommend 5 instead of 4 for a high hp application to eliminate driveshaft flex. I'm also looking into replacing the driveshaft with alternate materials like titanium or carbon.
The interesting thing here for track guys is I can put any number of bearings in, but I would recommend 5 instead of 4 for a high hp application to eliminate driveshaft flex. I'm also looking into replacing the driveshaft with alternate materials like titanium or carbon.
05-09-2003, 10:19 PM
#5
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My engineering pal tells me no, since I'm using 6061T6. If I used a softer alloy in the 2XXX series then it would have to be treated. Either way, the only real test is in a car.
05-09-2003, 10:45 PM
#6
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"Either way, the only real test is in a car."
Of course if it fails the test, not only will the torque tube/drive shaft be broken, but the transmission, bell housing, and probably the clutch, and possibly the crank, be trashed as well...
Of course if it fails the test, not only will the torque tube/drive shaft be broken, but the transmission, bell housing, and probably the clutch, and possibly the crank, be trashed as well...
05-10-2003, 12:40 AM
#7
Drifting
How do you figure?
If the tube snapped, what are the possible damage areas? Input shaft on tranny? Possibility of over-rev?
Realistically, I can't think of other scenarios...
Fill me in.
Aside from that, If Dave is re-using the stock driveshaft, what is the worry? Better bearings?
If the tube snapped, what are the possible damage areas? Input shaft on tranny? Possibility of over-rev?
Realistically, I can't think of other scenarios...
Fill me in.
Aside from that, If Dave is re-using the stock driveshaft, what is the worry? Better bearings?
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05-10-2003, 02:10 AM
#8
I remember reading how hard it was to get the engine behind a pilot on a prop plane due to the length of the drive shaft, it tended to vibrate and it was hard to make a long drive shaft that was light and true. If this doesn't work, I would expect it would have vibration that would be very noticeable long before the unit would fail.
05-10-2003, 02:42 AM
#9
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If you lose the torque tube, the transmission will rotate. The torque tube is a structural member, and all the torque generated by the engine, is secured by the torque tube (which is what keeps the transmission from twisting around when you gas it...).
Also, if you loose the torque tube, and it breaks, hits the ground, and gets hits something, that impact will be directly transmitted to the bellhousing and clutch/crank.
Also, if the torque tube gets pushed down , it will probably snap a part of the bellhousing off.
Pretty serious stuff.
I would probably want a safety loop around the torque tube for the exact same reasons that every sanctioned racing body requires it around aluminum drive shafts.... (and for the same reasons that they require scatter shields around the bellhousings (when used with aluminum flywheels....).
Also, if you loose the torque tube, and it breaks, hits the ground, and gets hits something, that impact will be directly transmitted to the bellhousing and clutch/crank.
Also, if the torque tube gets pushed down , it will probably snap a part of the bellhousing off.
Pretty serious stuff.
I would probably want a safety loop around the torque tube for the exact same reasons that every sanctioned racing body requires it around aluminum drive shafts.... (and for the same reasons that they require scatter shields around the bellhousings (when used with aluminum flywheels....).
05-10-2003, 02:44 AM
#10
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Also...
To clarify.
I'm not saying that an aluminum torque tube can't be done (I wouldn't use an aluminum drive shaft inside it though) safely.
All I'm saying is that it has be be real strong.
To clarify.
I'm not saying that an aluminum torque tube can't be done (I wouldn't use an aluminum drive shaft inside it though) safely.
All I'm saying is that it has be be real strong.
05-10-2003, 03:20 AM
#11
I was thinking why didn't Pcar do this, they did a lot of parts in Aluminum. Tony, your point about safety is well stated and I hope they are applied to the test car. The points of attachment are , bell housing, torque tube, and transmission, am I mising one? Aluminum alloys have come a long way since the time this car was developed. I really hope this pans out.
Dave, what aluminum are you using? Will the overall strenght be the same as the steel tube?
Dave, what aluminum are you using? Will the overall strenght be the same as the steel tube?
05-10-2003, 09:20 AM
#13
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Ok- we've thought out a lot of these issues and-
1) Tube breakinging-
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 on the tranny will be toast anyway since it is attached to the tube. In my design, a short "stub" of the original tube is used to locate and pin the new tube into concentric location with the input shaft. Also, look at the mega-hp drag cars. They use a carbon driveshaft with huge hp numbers and that shaft is unsupported by anything other than its own structure. There are also cf axles for other perfomance applications.
2) Aluminum used-
My tube is 3.5OD 6061T6 seamless tube with 1/4 walls. This is the tube used in steam pressure vessels, I think it will carry a driveshaft. Bearing carriers, flange, and tube coupling (attaches tube to existing tranny bellhousing) are of the same material.
3) Why didn't Porsche do this?- I can only comment from experience with other makes.
First-
Aluminum is very expensive compared to steel. There was already an existing run of other similar cars- late 924, 924 Turbo, 944, early 944. To change would have necessitated changing tooling, upping materials costs, and added expense of another part to the bin. Even Porsche has to consider economics. To manufacture a tube like mine would be cost prohibitive for a relatively short run of cars because of being labor intensive. It is much cheaper to make a steel tube and press fit it into a bellhousing.
Second-
Porsche is known for incremental improvements. Look at the 911 line. It has evolved over the years to a watercooled engine, the air-cooled guys were screaming heresey until this car proved itself. The 924/44/51/68 line was being phased out in favor of the Boxster so not much extra development was going to be done there past improving the engine and tranny. The torque tube was not high on the improvement list.
Third-
Look at the example of Iceshark's light kit. Porsche could have done this, they didn't though. It took an enthusiast looking to improve the existing problem to make a better "mousetrap". I was looking at T-Tube rebuild cost- nearly $600 if you have it done, less if you DIY. Either way, you are using bearings with the wrong clearance for the job. Porsche specified the C4 clearance bearing, try to get it. It is obsolete, but the bearing houses will be glad to make you some, just so long as you order a 1000 pc minimum. At $25+ per, that's a bit out of reach. The solution is start over and make something that can use an existing stock size with the proper clearance. Want sticker shock, go check on a tube price from Porsche, about $2500 is what I was quoted. A further advantage of this approach is now we have the freedom to have a new driveshaft material considered. I can put any number of bearings for support in for any driveshaft material. You can't do that with the original. That's my next subject for investigation, carbon fiber driveshaft for rotating mass reduction. From what I've been able to find thus far, the only real problem has been the OD of the shaft in the stock tube, I've eliminated that.
4) Aluminum losing Temper during welding-
From what I've learned, the loss of temper is a direct result of being heated (annealed). This looks like a problem except when considering that the welding process introduces additional materials (alloys) into the weld (wire, rod, etc) that maintains the temper. Think that every stretch of welded pipe in a boiler is heat treated after the joints are welded while the boiler is being constructed? Also, aluminum welds properly done are shielded from oxygen by an inert gas shield to prevent oxygen from getting into the weld which would make it brittle.
Like I said before, it will be being tested here shortly. If I can't find a track type to try it, I will in my 951. My car is stock though and would present only a so so test. I would like to see someone track this beast to see how it holds up under racing type conditions. I have two spare trannys to use for the cause and two spare clutch bellhousings. This thing has been some time in development and lots of email between me and several others has been sent about the subject. Almost track time.
1) Tube breakinging-
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 on the tranny will be toast anyway since it is attached to the tube. In my design, a short "stub" of the original tube is used to locate and pin the new tube into concentric location with the input shaft. Also, look at the mega-hp drag cars. They use a carbon driveshaft with huge hp numbers and that shaft is unsupported by anything other than its own structure. There are also cf axles for other perfomance applications.
2) Aluminum used-
My tube is 3.5OD 6061T6 seamless tube with 1/4 walls. This is the tube used in steam pressure vessels, I think it will carry a driveshaft. Bearing carriers, flange, and tube coupling (attaches tube to existing tranny bellhousing) are of the same material.
3) Why didn't Porsche do this?- I can only comment from experience with other makes.
First-
Aluminum is very expensive compared to steel. There was already an existing run of other similar cars- late 924, 924 Turbo, 944, early 944. To change would have necessitated changing tooling, upping materials costs, and added expense of another part to the bin. Even Porsche has to consider economics. To manufacture a tube like mine would be cost prohibitive for a relatively short run of cars because of being labor intensive. It is much cheaper to make a steel tube and press fit it into a bellhousing.
Second-
Porsche is known for incremental improvements. Look at the 911 line. It has evolved over the years to a watercooled engine, the air-cooled guys were screaming heresey until this car proved itself. The 924/44/51/68 line was being phased out in favor of the Boxster so not much extra development was going to be done there past improving the engine and tranny. The torque tube was not high on the improvement list.
Third-
Look at the example of Iceshark's light kit. Porsche could have done this, they didn't though. It took an enthusiast looking to improve the existing problem to make a better "mousetrap". I was looking at T-Tube rebuild cost- nearly $600 if you have it done, less if you DIY. Either way, you are using bearings with the wrong clearance for the job. Porsche specified the C4 clearance bearing, try to get it. It is obsolete, but the bearing houses will be glad to make you some, just so long as you order a 1000 pc minimum. At $25+ per, that's a bit out of reach. The solution is start over and make something that can use an existing stock size with the proper clearance. Want sticker shock, go check on a tube price from Porsche, about $2500 is what I was quoted. A further advantage of this approach is now we have the freedom to have a new driveshaft material considered. I can put any number of bearings for support in for any driveshaft material. You can't do that with the original. That's my next subject for investigation, carbon fiber driveshaft for rotating mass reduction. From what I've been able to find thus far, the only real problem has been the OD of the shaft in the stock tube, I've eliminated that.
4) Aluminum losing Temper during welding-
From what I've learned, the loss of temper is a direct result of being heated (annealed). This looks like a problem except when considering that the welding process introduces additional materials (alloys) into the weld (wire, rod, etc) that maintains the temper. Think that every stretch of welded pipe in a boiler is heat treated after the joints are welded while the boiler is being constructed? Also, aluminum welds properly done are shielded from oxygen by an inert gas shield to prevent oxygen from getting into the weld which would make it brittle.
Like I said before, it will be being tested here shortly. If I can't find a track type to try it, I will in my 951. My car is stock though and would present only a so so test. I would like to see someone track this beast to see how it holds up under racing type conditions. I have two spare trannys to use for the cause and two spare clutch bellhousings. This thing has been some time in development and lots of email between me and several others has been sent about the subject. Almost track time.
05-10-2003, 10:21 AM
#15
Drifting
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Dave,
Am I correct to understand that you are asking for a track test dummie? If so, could you give us a rundown on your expectations for and the responsibilities ($) of this track test dummie?
I guess I'm applying for the job, it you haven't found anyone yet.
Am I correct to understand that you are asking for a track test dummie? If so, could you give us a rundown on your expectations for and the responsibilities ($) of this track test dummie?
I guess I'm applying for the job, it you haven't found anyone yet.