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YOUR RESEARCHC4S in snow videos, what's up?
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Use of the electromagnetic coupling clutch
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Suggestion
So most modern day "light" F/awd systems, and many R/awd systems, make use of the electromagnetic coupling clutch.
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The R/awd 911's using the VC, Viscous Clutch, to couple drive torque to the front wheels is mostly non-functional...PERIOD.
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I've seen a bunch of videos on youtube of guys in C4S cars driving like idiots in snow. They spin their back wheels like crazy, but the fronts never seem to spin. Since the car is AWD (and I know it is not a 50/50 split or a positive coupling between front & rear), why don't the front wheels seem to be spinning at least a little bit? Do they have the PSM turned off? Would that even matter? What gives?
If PSM is turned off, one wheel will spin, losing all torque for the entire axle... The brake system needs to be activated (via PSM) to stop the wheel with no traction... Do the videos show both sides of the car?
Without diff locks any 4WD is one wheel drive if a wheel looses traction. If this guy was to put the handbrake on two clicks, he would have had both rear wheels working together. Gentle application of the foot brake as well would probably get maybe 3 or 4 wheels working together. And then you drive out - maybe...
i have thought about this also. this is my understanding (please correct me if need be). the viscous coupling transfers 5% to 40% of torque to front axle. is does so via a fluid that as it heats up becomes thicker and causes the two sets of plates in the clutch to couple more closely, transfering power to the front. there is no direct connection so you will not typically get front wheelspin. rather the front wheels will just pull forward while the rears spin away. i dont really know how quickly the fluid heats up, and is the car in the video cold? have a look a this video and look when he is doing the doughnuts. if the front wheels were not pulling i believe that he would get stuck.
You Tube
Heres a rwd video, as much as the C4S has awd is barely drives the front wheels but it does. The C4S can't do the same degree of donut because the front wheel does pull your out into the direction the wheels are pointed.
PSM like in the wet grass and deep snow will hinder and power transfer to the front wheels. Turn it off if your stuck or in deep snow.
The video attached by Vange above is one of the ones I saw. It does show both sides of the car (not at the exact same time), and both sides do appear to be spinning the rear wheel. Re Spender above, the rears seem to be losing more than enough traction compared to the fronts to send drive torque to the fronts.
Seems that PSM would prevent such disproportionate spinning, so it must be turned off.
It just doesn't look like I would expect an AWD with stability control to look...
As I understand it, the AWD in the 996 Porsche models (and just about every viscous coupling awd car on the market) is based on the awd viscous coupler design that Subaru developed, perfected, and patented.
If you watch videos of other sports cars with a viscous coupler doing snow burnouts, what do they look like?
Well that is the issue with a viscous system. It really is not a "modern awd system" If you want awd the 997.1 TT and then the 997.2 4/4S/TT model have an electronic awd system. Unfortunately the 996 is mechanical and in reality is predominately a rwd drive car.
The R/awd 911's using the VC, Viscous Clutch, to couple drive torque to the front wheels is mostly non-functional...PERIOD.
To freely spin the rear wheels like that requires that you turn TC off.
With the advent, REQUIREMENT of TC and with predominantly FWD or F/awd Subaru was forced to abandon the VC as a functional entity. Except for "after the fact" (wheelsin/slip already present) TC activation, the new WRX is simply a ONE wheel drive car.
VC, absent an extended period of wheelspin/slip, disparate front verus rear driveline rotational rate, NEVER came online, functional. Obviously with TC "interferring" that's no longer very likely to be happening.
So most modern day "light" F/awd systems, and many R/awd systems, make use of the electromagnetic coupling clutch. Newer 997's and Cayenne's, for instance.
Early on in the video I assumed that one, or two, of the wheels we couldn't see were spinning, but no, this guy's clutch was burning up.....because he has the e-brake engaged???
