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-   -   Can someone explain QTII a little better to me? (http://www.jeepgarage.org/f109/can-someone-explain-qtii-a-little-better-to-me-32297.html)

SightSeeker 12-09-2011 08:43 AM

Can someone explain QTII a little better to me?
 
I have read the 4x4 systems on the jeep site and I understand that QDII has the electronic differential. What I don't understand is what is going on with QTII when you select the different modes.

So if I am in deep snow, in snow mode, and I floor it will all 4 tires have power or does 1 wheel in the back and 1 wheel in front get power? From what I understand the brakes get applied to the slipping tire but I wasn't sure if all 4 wheels can potentially get power or just one front and one back.

2nd question is if in sport mode I see the traction control goes off but does that mean I am in 2x4 and it won't go 4x4 even if I slip? So if I was in snow and I floor it will I get a 4 tire spin or just the rear?

ColdCase 12-09-2011 08:59 AM

Re: Can someone explain QTII a little better to me?
 
All the jeeps have brake traction control which applies pulsating brakes (ABS style) to any wheel that is spinning faster than it should in relation to the others. So when you floor it all the four wheels will have power and spin at about the same rate, hopefully one or more of them will have some traction.

The QT II transfer case is computer controlled in that it will apply a clutch to send more power to the axle that is spinning least which reduces the power loss through brake traction. But all wheels will receive some power.

In sport mode, the traction control indicator should be illuminated. That means the the computer is directing the QT II case to direct most of the power to the rear axle and change the way brake traction works to give the Jeep more of a rear wheel drive feel that some like. If you floor it on slippery surfaces, all four wheels will spin, the fronts probably slower than the rear.

SightSeeker 12-09-2011 09:26 AM

Re: Can someone explain QTII a little better to me?
 
Okay that makes sense then. So the main difference is that QDII can put 100% of torque to one tire opposed to a whole axle right?

ColdCase 12-09-2011 10:54 AM

Re: Can someone explain QTII a little better to me?
 
Its not a full lock system that's set up for 100%. QT II can put about 90% of engine power on one axle or the other. QD adds a limited slip to the rear dif (90%), so eventually about 80% of the engine power is delivered to one rear or the other when the other wheels are off the ground. Limited slip is not available for the front, so the max front tire power is 45% when all other wheels are off the ground.

Brake traction has about a 50% power loss. So with a completely open QT I system, the max power to any one wheel when the others lose traction is about 25% of the engine power (50% in the axle, 50% transfer case). For the QT II system, with its limited slip transfer case, it is about 45% of engine power to the wheel with traction. For QD, rear wheels its about 80% of the engine power, front wheel about 45%. The rest of the engine power is used to make brake heat.

So QDII has an advantage getting engine power to the ground on steep slopes, negotiating rocks, or deep stuff, other things being equal. In the real world, things are rarely equal. Good tires and driving will make more of a difference.

BTW, QTII and QDII have a transfer case lock position so full 100% of torque can go to the axle with traction instead of the 90%.

You may ask why not full lock transfer case and difs as that will get you 100% of the power to the wheel with traction... that is a dangerous vehicle to drive where there is good traction. It takes quite a bit of driver skill to operate full lockers safely and to get the most out of them.

These are rough numbers for illustration. There are numerous other factors, like speed of detecting spin, sensitivity... etc that also make a difference in the real world.

Sparro 12-09-2011 10:25 PM

Re: Can someone explain QTII a little better to me?
 
Nice write up. Thanks for the info.
The V8 has QDII with front ELSD correct? Does the V6 have QTI or QTII?

jgc4ever 12-09-2011 10:42 PM

Re: Can someone explain QTII a little better to me?
 
The V8 can have either QTII or QDII with rear ELSD only.

The V6 can have either QT1 or QTII.

ColdCase 12-09-2011 11:43 PM

Re: Can someone explain QTII a little better to me?
 
Unlike previous models, front ESLD is not available on any 2011 or 2012 GC.

Rear ELSD is available only on V8 models and, for 2012, only with the ORA II or the Summit package. You can't get the ELSD on a V6. We joke that the V6 doesn't have enough power to spin the tires anyway :)

Overlands have QT II regardless of power plant, perhaps also limiteds. Laredos have QT I with QT II as an option.


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