I believe there is no clutching for the rear at all. I drove one with no front driveshaft installed. I bet it has a planetary set fixed to the input shaft and rear output shaft. Then has a chain to a front clutched ball ramp setup similar to bmw xdrive. Even the configuration settings show the vehicle as permanent rear wheel drive with no center differential installed

 

The piece I would want to experiment with is how it handles the somewhat common urban case of pulling out onto a main route where there are at times a bit of gravel and a need for rapid acceleration which doesn’t match the typical soft accelerator use. In other words does it prep the front axle disconnect at a stop or does it leave it disconnected then face a wheel spin event under throttle? In a full time awd system it will handle this situation with no drama. In a part time system like this you would have to chop the throttle and wait for the pieces to engage before applying it again. With a focus on mpg you definitely don’t want to be accelerating these front end pieces every time if not needed. Perhaps that extra front clutch is at play in this scenario to avoid a potential banging shock load like I have experienced with a GMC and their simplified disconnect.

 

Active Driveline always activates AWD when you accelerate from a stop. In fact, it is always activated under 21 mph, over 100 mph, below 37°F and when you are off-road. It is constantly monitoring grip levels and driver inputs 100 times a second to properly distribute torque between the front & rear axles. It is also a proactive system, so things like whether the lights and wipers are activated will affect the AWD system's operation.

 

Glad to hear that they didn’t take a step back here with this change. The extra clutches in that front axle to me means that JLR is showing their different focus here vs the simplified GMC system I mentioned. Perhaps they needed those due to the many extra scenarios that they proactively apply the system.

Related to all of this that video comparing the base Defender 90, Bronco, and Wranglers really drove home how much better the system works (as well as how far a proper brake biasing system can take a vehicle with limited traction compared to the old school 4x4 systems.

 

Don't most GM AWD systems require you to manually select AWD? I rented an Equinox and an Acadia within the past year, and on both you had to press a button to activate AWD.

 

Indeed you have to enable the "AWD" mode ... overall the system is very suboptimal--especially when combined with the G80 rear locker which requires excessive wheelspin to activate and a stability control system that cuts throttle aggressively on any wheel slip. I frequently found my 1500 AT4 almost worthless and stuck on slight grades in the winter on snow until I remembered to put its drive mode in "off-road" mode so it would allow some slip. To top if all that truck had such a meager payload capacity that with 4 adults and a topper you would be nearly maxed out before adding any signifiant cargo let alone a trailer--my little D90 has 60% more payload! Best day ever was when I sold that truck off, it was a huge mistake. </rant>

 

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If the variable locking was at 100%, could you theoretically drive in FWD? I'm sures there's some software that would alter this. I know on D1/D2 you can lock the center diff and drive in FWD or RWD, which has come in handy too many times to count. At least know you can carry 1 front spare axle rather than 2. I used to carry a front driver side axle, hoping that if one were to break it would be that one. I know very little about the new systems. I'm curious to learn more, not trying to question your knowledge.

"Active Driveline always activates AWD when you accelerate from a stop. In fact, it is always activated under 21 mph, over 100 mph, below 37°F and when you are off-road. It is constantly monitoring grip levels and driver inputs 100 times a second to properly distribute torque between the front & rear axles. It is also a proactive system, so things like whether the lights and wipers are activated will affect the AWD system's operation."

Curious to why its always on under 21mph. I get from a stop, as power to all the wheels would reduce wear on the rear wheels. I had no clue it would activate due to temperature and take input from the lights and wipers. Sick technology imo. Everything being interlinked does have some perks!

 

My guess is that it is activated because in most low-grip scenarios, you are travelling at low speeds, and would make sense just to always have it activated. Plus, fuel economy doesn't really matter under 20 mph anyway. No idea why exactly it is activated, but I wouldn't be shocked if that's the reason why. I reached out to my buddy who was a development engineer at JLR who worked on Discovery 5 and Defender. He was part of the team that did aero/cooling systems, but might be able to provide some further insight.

UPDATE: He didn't have an answer for me, but he said that my theory is logical and could be one of the reasons why it is activated under 21 mph.

 

@CincyRovers Nice you have some internal contact to gain more information than most of us here. Could you help to clarify if our Defender with iAWD can drive with in FWD mode?

 

Like I said above, he can't answer questions regarding the drivetrain, as he was part of the team that worked on the aero/cooling systems. But no, it can't operate in a FWD mode. It is a rear-biased system and the rear wheels are always driven. A maximum of 50% of the torque can be sent to the front axle. So, when driving the torque split can vary from 0:100 F/R, 50:50, or anywhere in between.