Continuing with the write-ups that I am doing, here is an explanation of the 3 4WD systems that are in the WK2. One is technically an AWD system, but I will not berate Jeep for calling it a 4x4 because the system uses fancy magic to make it the most capable AWD I have seen (more capable than many 4x4 systems on the market).
The order that I will follow for this is from least capable to the most capable. As always, feel free to comment or suggest improvements. I would like to think of this as a living guide that is capable of changing and updating to match the current available and specifications available.
* No shift lever or driver interaction required.
* Full-time 4-wheel drive provides smooth operation and vehicle stability under all conditions because torque is constantly being transferred.
* Torque distribution provides traction to maintain forward motion under most conditions.
* The Brake Traction Control System (BTCS) works in tandem with full-time 4 wheel drive. BTCS provides resistance to any wheel that is slipping to allow additional torque transfer to wheels with traction.
* Robust design and improved sealing enhance reliability.
* No maintenance required.
This is my interpretation of how the system works based on the data I have compiled from Jeep and technical descriptions:
As mentioned above, this is a single speed transfer case that offers no locking center differential (part time 4wd setting usually known as 4 High on vehicles like the Wrangler). This allows the system to be used on the road in any conditions and traction quantities. In order to supply power to the wheels that do have traction, the ABS sensors determine when a wheel is slipping and apply the brakes to that side. I still can't find a good explanation of how exactly the system works so here is my best effort:
The differentials of the WK2 are open. This means that the wheels are all allowed to spin at any speed irregardless of the power being sent or the speed of the other wheels. If one wheel were to loose traction, all power would go to that wheel, and you would be stuck. With the brake locking differentials, the ABS system detects when a wheel is spinning too much faster than the other wheels and applies the brake to that wheel. By applying the brake, it forces resistance to that wheel which allows the power to be sent to other wheels that have more traction.
These brake locking differentials do a great job of moving the power. Here is a perfect video of it in action on a patriot (different 4wd system, but it is still making the climb because of the BLD). Watch the tires of both the passenger and driver's sides to see when the brakes grab:
The only other bit of information with the QT I is the torque split between the front and rear axles. Because the differential is open, it is always changing the amount of torque that is being sent to the front and rear drive shafts. Some sources say that the split is 48/52 where 52% of the power is going to the rear to give the Jeep a sportier feel. One site claims that the split happens to be 50/50. According to the Jeeps website (http://www.jeep.com/en/4x4/how_syste...k/quadra_trac/
) The system just transfers torque as necessary.
* Active, on-demand four-wheel drive requires no driver input.
* Instantly anticipates slip and preemptively redirects torque as needed.
* Vehicle stability under all conditions because torque is constantly being transferred.
* 4WD Low operation mode provides an advantage over vehicles equipped with a single-speed all-wheel drive transfer case.
* Electric shifting between 4WD Auto and 4WD Low provides smooth operation and improved NVH control compared to systems with mechanical linkage.
* Enhanced traction and stability provided by the Traction Control and Electronic Stability Program (ESP) working in tandem with four-wheel-drive.
* A robust design and sealing for reliability.
* A neutral mode permits flat towing.
The basics if this 4wd system are similar to those of the QT I, however, they are expanded upon. There is an electronic clutch pack that has the capability of transferring 100% of the power to either the front axle or the rear axle depending on which one has more traction. This is active when the vehicle is in The QT II offers a low range and neutral position. The neutral position allows you to flat tow the vehicle. With the low range, the toque is multiplied by 2.72. This extra 2.72:1 gearing provides the extra power needed to traverse more difficult terrain. When the system in in 4 low, the transfer case locks the front and rear drive shafts together so that both axle gets an equal amount of torque.
* Fully automatic, high range for year round driving in all conditions
* Active electronic transfer case and rear electronic limited slip differential
* When traction is lost torque can be sent to wheel or wheels with the most traction
* System works progressively and on-demand
* Works together with brake traction control
* Torque can be sent front to back or side to side
* 4 Low mode locks front and rear driveshaftsfor low speed power/rock crawling or towing
* Includes Selec-Terrain
* Neutral position for flat towing
The QD II uses the same setup as the QT II. The only difference between these two systems is that QD II has an electronic limited slip rear differential. Due to the nature of BLD, the rear brakes tend to wear a bit fast on vehicles equipped with QT I and QT II. By using a limited slip, the QD II is able to provide a more solid foundation for transferring the torque (because it is a set of gears forcing the power to be transferred rather than brakes locking wheels which can be overridden). The QD II package also comes with skid plates for the transfer case, fuel tank, suspension skids, and front axle. This system also comes with hill decent control which automatically applies the brakes for a slow controlled decent down steep terrain.
If anyone wants further explanation on any part of this, please feel free to ask. I spent a lot of time working on this at times when I should have been sleeping, and am sure that stuff is missing (like the fact that the SRT 8 version is a 2wd verson of QT I that disconnects the drive shaft for 2wd, and reconnects it when there is wheel slip or when throttle input is anticipated).