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The only reason I think that others in the GM fleet might not have TOD could be that it isn't beefy enough for the torque output of the big V8s? Heck I even have a guage on the dash that shows within a 10% range how much power is going to each axle at all times, this is very useful to know that the system is working properly and also for off-road to know if you need to go to low-range based ont he torque split.
On the smartrack, I wonder if anyone has messed with the electronics to see if there is a way to trick the computer into transferring some torque to the front at all times? Some of the Trooper guys are in touch with Borg Warner and are working on an override switch to lock in the TOD unit at 50/50 so that we will have:
2wd (locked 0/100)
4-hi (locked 50/50)
4-lo (locked 50/50 low range gears)
TOD (15/85 variable up to 50/50)
Right now in hi-range we only get the variable TOD working.
-mike
-mike
I think it'll be a cold day in hell that they let you change things like that, for liability reasons.
o "other than the X5, you're not going to see any off the beaten path. "
I doubt that even the X5 goes near anything more than a dirt road
o "Maybe I'm just a technogeek, but I would love those features!"
That makes 2 of us, I've always wanted to have an LCD screen for a dash and be able to make my own guages via a config screen
-mike
Could it be the extra wear on the front drivetrain or concen about fuel inefficiency? Also, I take it that all these systems have open front end diffs to ensure smooth steering at slow speeds.
My bet would be that that the smarttrack is trying to save on fuel efficiency, the wear is the same even if not engaged because the front CVs and driveshaft and diffy are all turning.
-mike
-mike
-mike
-mike
Just heard the news... It's in the latest issue of Motortrend! Maybe we'll see some changes yet to the Smarttrak AWD system!
-juice
-juice
-mike
Just one of the reasons I now own an RX300 AWD.
It's perfectly normal. Just don't use 4WD on non-slippery surfaces.
Full-time AWD can be used in dry conditions because they have a center diffy that allows for at least some slip.
-juice
Looking through the smoke and mirror (Uh, media hype), what is the technology behind this system? Is it as effective as advertised? Also, per our host's definition, which type is the Aviator's AWD system? Thanks.Aviators with all-wheel drive that are paired with the optional AdvanceTrac™ traction and stability enhancement system need only one wheel with traction to get under way because the two systems combined allow torque to be shifted side-to-side and front-to-rear.
This is all pure guessing based on what you posted above. The center may not be a viscous coupling though, it could be open differntial as well.
-mike
IMO and based on my experience with 4wd vehicles, the best combination of designs for a 4wd system would be one with AWD delivering a guaranteed minimum amount of torque to all 4 corners using LSD's and a visc ctr coupling, combined with the 4wheel traction control setup of the Sequoia.
My guess is that that is the approach Ford is taking. In simple terms its AWD w/ traction control. If it offers a 4wd lo gear ratio it would also provide a strong traction design for off-roading.
My personal favorite would be lockers front and rear with a TOD-like system in the middle that provides a 15/85 torque split like the Trooper, in addition an ability to lock it in 50/50 in hi-range would be nice addition to a 50/50 lock in low range as well as a variable 15/85->50/50 lock in low range.
-mike
-juice
I bet we find the Ford system is nearly identical to the AWD system from GM, and all the other AWD manufacturers combined with 4 wheel electronic traction control. I would also bet as more and more high end suv consumers shop for expensive suvs, awd systems with no interaction on the part of operator will become the standard as the owner's of these types of vehicles will almost never go off-road.
-mike
So, if I follow your thinking correctly then my GS300 doesn't deliver torque to both rear wheels (absent intervention by the VSC/TRAC/ABS) since there is only an open diff'l to apportion torque between them.
So which rear wheel does it drive?
The left one of the right one?
The answer to your question is rather simple if the GS has a open rear diff as you state. If the traction system were disengaged as in your example the torque could be fully allocated to EITHER wheel.
It works like this. If you hammer the accelerator with the traction control off, whichever tire slips first will quickly draw all of the torque from the engine away from the other tire. As more torque is directed to the tire "consuming" it, the differential will direct even more and so on. Until one tire has no torque and the other is melting away leaving itself on the road as a skid mark. It can occur with either tire, its just a matter of which one slips first.
The traction control continuously monitors the wheel slippage and prevents further slippage thereby forcing torque to remain on the other side or transferring more, if its available. In simple terms its a slip, check, transfer approach to managing torque.
If the GS had an LSD in the rear combined with the traction control, it would be a transfer, slip, check, transfer more setup which would be a more responsive way to distribute power to the road. A more expensive setup because of the cost of the LSD but maybe for the consumer's of GS' Toyota doesn't think it matters.
Open diffs split torque 50/50, not 100/0 or 0/100, but 50/50. Whether one is spinning faster than the other or not the split IS 50/50.
http://www.howstuffworks.com/differential5.htm
It's on the first line of this article. I am not denying a problem with open diffs (one needs to apply the brake which means less power is available, if one is at WOT).
In an open diff here is what I recall happens...
Normal driving conditions there is a 50/50 split. As soon as a wheel begins to slip, the power is shifted to the wheel with the least resistance, in other words the slipping wheel gets the power. That is why if you take an old american car for example, and floor the gas out of a stop sign making a right turn, your inside wheel the right side one will spin and spin until you let off the gas. An LSD or "Posi-rear" would instead shift the power to the wheel with the most resistance, in this example the outside wheel, the wheel that is gripping.
On the GS above, the VSC senses the slipping and applies the brake to that inside wheel tricking the open differential into thinking that the right wheel is not slipping and therefore continues to apply some power to it. That is how the ML and the Sequoia work when in AWD mode.
-mike
LSDs still delivers power to the slipping wheel, but it can support delivering several times (usually between 2 to 6, depending upon the product and how it's operating) that amount to the opposite wheel. So the spinning wheel gets amount b of torque and the opposite wheel gets amount 2-6 times b of torque.
Lockers don't care what torque is applied to either wheel. They just keep the rpms fixed of both. If one wheel slips, all of the excess power goes to the opposite wheel.
-mike
-mike
avlv "MY 2003 Lincoln Aviator" Mar 27, 2002 5:20pm
Looks like both AWDs are rear biased Fulltime-AWD. First one is similar to the BMW AWD, permanently engaged with rear bias in normal driving. The one with AdvanceTrac is more of a proactive TOD system, which may have fuel milage and handling advantages over the first one.I got this from a Ford Web site..
Traction Anytime, Anywhere
Aviator uses two all-wheel-drive systems, neither of which requires driver intervention. A permanently engaged all-wheel drive system that uses a viscous coupling to transfer torque fore and aft is fitted to vehicles without the optional AdvanceTrac interactive vehicle dynamics system. In normal driving, 35 percent of engine torque is directed to the front wheels and 65 percent to the rear.
Vehicles equipped with AdvanceTrac (late availability) use an electronically controlled single-speed torque on demand transfer case. On most surfaces, this system operates in rear-wheel drive, but if wheel slip occurs, a clutch pack can send up to 100 percent of torque to the front wheels. The system monitors front and rear driveshaft speeds and throttle position, and can anticipate rear wheel slippage and redirect torque before traction is lost.
All-wheel drive Aviators equipped with AdvanceTrac need only one wheel with traction to move because AdvanceTrac monitors wheel speed at each corner and uses the anti lock brakes and engine management to control wheelspin. This allows engine torque to be directed both fore and aft and side-to-side without heavy locking differentials.
Is my understanding correct here?
-mike
One of the Trooper guys is actually working with B&W to find out which wire on the TOD harness needs to be tapped to do a 50/50 lock in 4wd Hi range which would be nice. Also on the Troopers since we have the corporate 10-bolt front differential and the old isuzu impulse used the same 10-bolt corporate diffy in the rear of them, we can actually swap out the impulse LSD to the front of the troopers and then have front and rear LSDs which would be the closest thing to having front and rear lockers.
-mike
Yeah, that's right. The wheel that is not spinning has the same amount of torque going through it though.
HP = torque * RPM / 5252
Example, do not confuse these numbers with real numbers:
A vehicle with one wheel spinning at 100 rpm, but with 1 ft-lb of torque is supplying 100*1/5252 hp. It's opposite wheel isn't spinning and is just rolling along the ground at 1 rpm. It's torque has to be the same (50/50). Therefore it is only delivering 1*1/5252 hp. Hey, that explains alot to me. Thanks for making me do that exercise Paisan. So while they each get 50% of the torque, the amount of power isn't split at 50/50. Now I understand :-)
http://www.off-road.com/4x4web/faqs/diffs.html
for some more confusing info
Oh yeah, torque starts you off, but power keeps you going!
-mike
Lockers maintain rpm, there torque/hp split is based upon something else though. I don't want to think about it to much at the moment
LSD, yeah it's somewhere in the middle.
-mike
So, following die's math, wouldn't be correct to say that since traction control (the type that applies the brake) limits wheelspin, if one wheel has no traction, then the car just sits there since neither wheel has power? Or have I missed something?
Rpm is the same for both
Torque isn't known
Therefore HP isn't known
two unknowns and one equation whereas with the open, it was two unknowns and two equations (torque is split at 50/50)
If one wheel is off the ground and one wheel is on the ground then the split is 0/100, even though rpms are the same. Now if they are both on the ground is the torque split at 50/50, is the HP split at 50/50 (they are the same at the same rpm). I don't think the split is at 50/50 all the time if both tires are not slipping, but I have no way of proving one way or the other. Perhaps someone else knows.