h a l f b a k e r y"This may be bollocks, but it's lovely bollocks."
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I have already seen this idea put to use on an off-road car; I think it would work great on a street car too.
The off-road car used a four-cylinder Honda engine and automatic transmission mounted in the middle of a space frame chassis. Instead of being mounted transversely, the engine was longitudinally
mounted, with driveshafts coming out where the halfshafts would normally be and leading to two solid axles.
I propose modifying a front-wheel drive car, such as a Cadillac with the Northstar V8. You would take out the engine and transaxle and rotate it 90 degrees. Try to mount the engine so its weight is best distributed left/right and so the output shafts are more or less at the centerline of the car.
Then add a differential, subframe, and suspension on the front of the transmission, and a driveshaft out the back to the rear axle. The differential in the stock transmission acts as the center differential. You might have to modify it to change torque split, otherwise it would be 50/50.
This might work best by putting the FWD engine/transmission in a rear-wheel drive chassis or a custom mid-engine platform like the offroad machine. A problem with any layout would be the lopsidied shape of the drivetrain which would cause bad weight distribution and torque steer. Also, there would be a slightly higher center of gravity.
Some problems could be overcome, but it would probably be better to just ditch the transaxle and use a regular AWD system.
(?) Rhino Off Road Industries
http://www.rhino-offroad.com/index.cgi
the original inspiration for this idea [discontinuuity, Feb 02 2007]
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Brilliant use of existing hardware [raspberry], but it would be really difficult to remount the engine in an existing chassis. I know it's just a matter of hoses, but all of the plumbing underhood would be radically rerouted. That's just details, though, and any dedicated gearhead could probably make it work. |
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Two big points regarding the CV shafts running fore and aft: |
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What's wrong with a 50-50 split? Except under hard acceleration, that would be the preference for most driving. And if the vehicle is already equipped with traction control, that capability should still exist, serving the front and rear axles. Sensitivity will probably drop. |
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The halfshafts are already running at a significant gear reduction; running them through another differential into the new halfshafts will reduce them yet some more, giving you something like a permanent 4-low drive ratio. You'll get some of the top end back by running highly oversize tires, and some back if you run high-speed diffs, but still I think this would be pretty buzzy on the Interstate. |
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Sounds like great homebrew for light rockcrawling, though. [+] |
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It sounds innovative enough that I have to wonder why some major car manufacturer hasn't already attempted something like it. |
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Hybrid cars with an electric motor turning the rear differential would be the answer. The computer could be utilized to verify that the rear wheels were turning at the same speed as the front wheels via the ABS sensors. When rear power was not required, the rear motor would become a generator and charge the battery "bank". |
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I like BMCUE's idea. That sounds
like something a competent
engineer could whip up out of
stock parts. Ideally, you'd want to
find a car that came in a front-
and rear-drive version under the
same body, so you'd have more
stock parts to work with. |
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I can't imagine the NVH problems this thing would have. |
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I've been mentally playing with a variation of this, which would give differntial properties better suited for one-road performance driving. 50/50 split isn't really ideal for that--too much torque to the front causes power-on understeer |
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Anyway, what you do is weld the transaxle diff solid, then place a hydraulic torque converter (like for an automatic transmission) on the shaft leading to the front of the car. You'll get essentially rear wheel drive normally, with the torque converter slipping in tight corners to avoid tire scrub. If the rear wheels spin, as in oversteer, the torque converter will start sending more power to the front, correcting it. |
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I *think* this is sort of how the new AWD Lamborghinis work, based on qualitative descriptions--dedicated drive to the rear, and a hydraulic coupling to the front. But I've got nagging doubts about the whole thing--putting the engine between the front and back might make things act oddly, I know the Lambo doesn't do it that way. Thoughts, anyone? |
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i made this setup last year. but for 4x4 ability i welded the spider gears in the fwd differential , it worked well,the fwd diff had a 3:1 ratio and top speed was approx 70kph .biggest problem was finding somwhere to sit, making another one this year with a mitsubishi fwd v6 motor and mounting it pulleys to the back (last motor was a toyota and had pulleys forward) |
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I think that the setup used in the link and by [tristanp] would work well for offroading, where you want the front and rear axles spinning at the same rate. The way that [5th Earth] describes it would work best for a high-performance car. I think the way I originally described it would work well on an everyday road car or for a CUV/soft-roader type car. If you didn't always want all of the wheels being driven with the same torque, it would be good to put some kind of torque converter or cutch on one of the output shafts, though. |
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