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This post provides a link to an American Axle patent which describes a way to provide torque split between the front and rear differentials in an AWD system: Disconnectable driveline with a multi-speed RDM and PTU.

Jeep provides several videos covering the attributes of each of the Cherokee’s Active Drive 4 x 4 systems. This is an example: https://www.youtube.com/watch?v=KHbRvP7RB6w. These videos describe certain aspects to include how power is variably distributed between the front and rear wheels for each of the systems (i.e. AD1, AD2, and AD Lock). Since the Active Drive systems are based on a FWD platform and the front differential always receives engine power, varying amounts of the power can be distributed to the rear differential when the Torque Transfer Device (TTD – a wet clutch) in the Rear Drive Module (RDM) is variably engaged. When the TTD is fully engaged, the power is approximately distributed front to back at 50/50.

There is a relationship between torque and power, but they are not the same (This is discussed in this post: http://jeepcherokeeclub.com/4-2014-...in-mode-power-distribution-8.html#post1946649. Torque split is a different matter. Jeep’s video linked to above says:

Snow - with a front wheel biased 60/40 split of torque

Sport - with a rear wheel biased 40/60 split of torque

Sand/Mud - with up to 100% of torque available to the rear axle

Rock - with up to 100% of torque available to the rear axle

The question is: How are the fixed torque splits accomplished (i.e. front to back 50/50, 60/40, and 40/60)? This post proposes a possible answer is by overdriving and underdriving the rear differential.

It is believed the Cherokee’s Active Drive systems are based on the EcoTrac system by American Axle & Manufacturing Inc. of Detroit, Michigan. (See post that includes a link to the patent that is probably describing the EcoTrac system: http://jeepcherokeeclub.com/33-engi...146353-ad1-ad2-adl-uncovered.html#post1617785.) American Axle has another patent that includes methods for torque distribution using underdrive/overdrive non-direct speed ratios (Reference: Disconnectable driveline with a multi-speed RDM and PTU). This patent gives a clue as to one way the Cherokee’s Active Drive systems could produce fixed 50/50, 40/60, and 60/40 torque splits. The following is an excerpt from the patent:

The present disclosure is directed to all-wheel drive motor vehicles having a disconnectable power take-off and rear drive module to permit disconnection of various rotary components in an effort to improve fuel economy and extend the service life. In addition, multi-speed range units are incorporated into one or both of the power take-off units to permit selection of at least two different speed ratio drive connections. The multi-speed range units can be configured to provide a direct (1:1) ratio drive connection and a non-direct ratio drive connection. The non-direct ratio can be either an underdrive (i.e., reduction) ratio or an overdrive ratio depending on the desired speed ratios. It will be understood that it is preferable, but not limiting, to match the multi-speed range unit integrated into each of the power take-off and the rear drive module to provide one of the underdrive/overdrive non-direct speed ratios in addition to the direct ratio to meet the desiredtorque distribution requirements of a particular vehicle.
 

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Bringing this topic back from the dead.

So it looks like from what I can tell we still havent figured out if this overdriven underdriven ratio allows the rears to have the higher torque split vs front for a rear wheel bias in sport mode. From the seat I can tell for sure the rear is pushing but how much l have no clue.

When I had a subaru outback previously we @ the forums came up with the idea to read the percentages via a tool software called Freessm. Connected via Vag com obd2 cable to a laptop we were able to see in real time the Transfer duty ratio TDR that the TCU was reading from multiple sensors which applies to the center clutch pack that traafers power to the rear wheels. For example from a dead stop to 20mph moderate throttle the TDR will be at 100% which equates to a 50:50 split then tappers down like 60% 60:30 then less the faster you go and stays at around 50% avg then 0% strictly FWD at highway speeds, light throttle. But if you give it aggressive throttle to make a pass up to 45% is applied to send power to rear wheels in the 60mph plus range. Baisically it was always variable and almost always near 50:50 when under 40mph when throttle is applied but never rear bias becauae the front is directly connected from the trans. Only if front wheel in the air or zero traction up to 100% can go to the rear.

So has this been proven with the active drive? is a rear bias possible?

Secondly anyone made any attempts to read the module to see what percentages are being applied to the clutches for bias purposes like my example with the Subaru?
 

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I like this topic because it's always a brain bender. Bear with me, I'm wordy...

First of all, consider that torque really doesn't "exist" unless there's something to torque against. Turn an imaginary air doorknob. Don't really feel any torque right? Go turn a real one and you do.

I think of torque split defined two ways... static and dynamic. Static would be, for the purposes of this discussion, a situation where traction is very high and there is no realistic chance of breaking traction. Pretty much describes the reality of driving around on dry paved roads.

Any AWD system CANNOT, in a static condition like that, distribute less that 50% of torque to the "primary" axle without some trickery. By primary I mean the front axle in the KL and other FWD based systems, or the rear axle in something like a truck with an "auto 4wd" mode. As we know, each type has a clutch to variably connect the secondary axle to take up the slack when the primary one loses traction. What I'm getting at is there is NO WAY to mechanically REDUCE what goes to the primary axle.

Trick one would be a special clutch pack sitting between the transmission output and the axles , or TWO clutch packs, one for each axle output. The key would be said clutch(es) are the FIRST STOP after the transmission, so they can affect what goes where. I believe Subaru kinda does this but I'm not entirely sure.
Two would be some kind of specially geared Torsen-style differential. Again, its input would be the first stop and would have one output per axle. I think Audi does this, or used to.

Either of those also kinda takes away the concept of primary/secondary axles.

The key here... the KL has neither of those. The clutch in the RDM is not the first stop after the transmission. The front "primary" axle is. The imaginary line drawn from the transmission to the front wheels does not cross that clutch.

Those over/underdrive ratios between the PTU and RDM cancel each other out because the front and rear axle speeds must match going in a straight line. If they didn't the RDM clutch would be in a constant state of slip when engaged and would wear out/overheat really fast.

It's a regular old FWD based AWD system with 3 party tricks: 1) really good brake based traction control 2) the Trailhawk rear diff lock and most importantly 3) an RDM clutch strong enough to send ALL power to the rear axle. I'm pretty sure every other FWD based system on the market can't do that.

That's how you get "up to 100%" rear in sand/mud/rock modes. BUT that only happens when the front axle loses all traction and can accept 0%. Pulling a wheelie up a rock face? There's your 100% rear. Those modes apply basically full power to the RDM clutch making the system behave like standard 4wd. Both axles locked together, always turning at the same speed. Torque just goes to wherever the traction is with the brakes (or locker) helping influence that between wheels on a given axle.

"But is says 40 front / 60 rear in sport mode." I call that... misleading. Sounds good for marketing though. But it's not meaningless. Misleading because until you break traction on the primary axle. Recall there is NO WAY to REDUCE what goes to that axle. So, no 40%.

That's where "dynamic" torque split comes in. Say your front wheels are on gravel in sport mode. They might only take 40% of what you're applying with your right foot. I like to think that in that situation, the RDM clutch is ready to send that 60% to the rear but again, that doesn't actually happen until the front axle "gives up". If that gravel still provides enough traction then sorry, that front axle is not getting less than 50%. Maybe the front only gives up 2%... then it's a 48/52 split. It's controlled by available traction at the front until said traction drops to that 40% threshold, not by what the RDM clutch is doing. Below that threshold, the RDM clutch instantly is sending that full 60% to the rear. And the computer can in theory choose to do even more.

Fun sidenote, if that clutch never goes above the 60% mark, and the front loses all traction, the total torque in the system is only that 60%. Remember the doorknob. Torque really isn't there with nothing to push against.

Snow mode is similar and arguably not misleading because it's not claiming less than 50% to the front axle. 60/40 makes it less likely to kick the rear end out when the front loses traction.

That 40F/60R number is also not meaningless with regards to driving behavior. ANY percentage of RDM clutch engagement will influence the rear axle, making it feel more rear wheel drive-ish. That's because in a corner the front axle will travel the longer distance and thus spin faster. That in turn spins the RDM input faster than the rear axle, and the clutch applies some torque through to the rear axle trying to drag it up to speed. Don't ask me to figure out what the % exactly is but it ain't 60%, because remember, you have no way to "take" more than 50% from the front.

Anyway I think it's important to understand the static vs dynamic difference and that you need specific hardware to actually change static torque split. Without it the split numbers are mostly fluff until you enter a dynamic situation.

The KL system is pretty pedestrian. Those party tricks I mentioned are what make it so capable. The reality is the system just works (very well) and this is kinda pedantic. And maybe I'm a little nuts.
 

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OK. Now I think I've got it. My Jeep Commander had QudraDrive II, which consisted of 3 ECLSDs (Electronically Controlled Limited Slip Differentials). This system could send 100% of the torque to one wheel. The American Axle System in the KL seems to be similar, but with only 2 differentials.

This tells me that the TTD can operate in 2 modes: one, set by the controller, say in 40/60 Torque Spit and the other: Locked > 100%:


The high-range torque transfer device, hereinafter H-TTD 152, includes a friction clutch pack 168 and a H-TTD actuator 170. The friction clutch pack 168 can include alternately interleaved inner and outer friction plates coupled to the sun gear shaft 166 and a drum extension 172 extending from the ring gear 158. The H-TTD actuator 170 can include a hydraulically-operated piston 174 that is disposed in a high-range pressure chamber 176 for sliding movement relative to the clutch pack 168. A flow channel 178 communicates with the pressure chamber 176 and is supplied with pressurized fluid from the actuator assembly 134 in response to control signals from the control system 22. The H-TTD 152 is operable in a first or "released" mode when the clutch pack 168 is released to permit relative rotation between the sun gear 156 and the ring gear 158. The H-TTD 152 is also operable in a second or "engaged" mode when the clutch pack 168 is frictionally engaged by the piston 174 to inhibit relative rotation between the sun gear 156 and the ring gear 158.

This tells me how it works:

When it is desired or necessary to operate the vehicle 10 in an all-wheel high-range (AWD-H) drive mode, the control system 22 can be activated to initially signal the H-TTD actuator 170, 170A to shift the H-TTD 152, 152A into its engaged mode for synchronizing the speeds of the primary driveline 16 and the secondary driveline 20. Thereafter, a four-wheel drive connection between the powertrain 12, the primary driveline 16 and the secondary driveline 20 is established by shifting the disconnect mechanism 42 into its connected mode. Thereafter, the H-TTD actuator 170 can be controlled to vary the torque transmitted through the H-TTD 152, 152A to the second wheels 124L, 124R.

Side Note: Someone here on the Forum put his Jeep on Jack Stands to disprove how Jeep was advertising the Active Drive II/Lock system with its various Modes (Torque splits). Putting the vehicle on jack stands is like putting it on a frozen pond with no snow cover: no traction > confused computer (the control system).
 

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QuadraDrive II is very likely a better system with its actual smart diffs. KL can definitely do 100% to one rear wheel (guaranteed by 100% to the rear in the right mode + locker). Not sure if the brake based TC can help get close to 100% to a front wheel (or rear without the locker). Well it probably "can" but who knows if it actually does.
 

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QuadraDrive II is very likely a better system with its actual smart diffs. KL can definitely do 100% to one rear wheel (guaranteed by 100% to the rear in the right mode + locker). Not sure if the brake based TC can help get close to 100% to a front wheel (or rear without the locker). Well it probably "can" but who knows if it actually does.
On the 2011+ QuadraDrive II models I believe it's more like smart diff (singular) since from that year on they did away with the ELSD on the front and went to brake-lock differential. In that case there would seem to be very little functional difference between QDII and ADII Lock (?)
 

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On the 2011+ QuadraDrive II models I believe it's more like smart diff (singular) since from that year on they did away with the ELSD on the front and went to brake-lock differential. In that case there would seem to be very little functional difference between QDII and ADII Lock (?)
I believe that they removed it from the Transfer Case as well. QD II was awesome. There was a you tube video of a Commander backing up an incline on one wheel! :surprise:
 

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I believe that they removed it from the Transfer Case as well. QD II was awesome. There was a you tube video of a Commander backing up an incline on one wheel!
Shouldn't ADII Lock be able to do that as well? If the rear diff is locked then you are well covered if only one rear wheel has traction, and if only one front wheel has traction BLD should be able to supply power to that wheel (in the case of the front, perhaps not quite as smoothly as an ELSD but the job should get done nonetheless.)
 

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I suppose any Cherokee with ADII Lock could be using one wheel drive at any time while off-road in challenging conditions, the drivetrain should take it. But yeah, I wouldn't want to climb Pike's Peak that way.
 

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You can't compare Quadra Drive 2 to the KL system. QDII is a RWD based system which is always powering 4 wheels, the KL system is not. For people wanting to see how the KL AWD system works when there is zero traction up front, search on here I already did tests with both my KL's. Long story short front wheels lose traction power always goes to the rear. Here is the thread

The 2014 (which is a bit different in its behavior because of PTU replacement)

http://jeepcherokeeclub.com/33-engi...ement-behavior-after-ptu-rdm-replacement.html

My 2016

http://jeepcherokeeclub.com/33-engi...terrain-front-rear-power-transfer-videos.html

As for the sport sending less power to the front, the system defaults to the front ass you can see in the videos. The long and short of it is that the system sends power to the rear wheels nearly all the time and its seamless.

This is not a high performance AWD system like something in an Alpha Romeo or similar. Its designed around ease of use and superior offroad traction. Go out to a racetrack and you won't find the limitation of the system being able to send power to the rear it would be more the weight balance of the vehicle (more weight on the front to cause understeer) and since there is no torque "vectoring' other than what the brake based traction control can do. I don't have access to a roadcourse but I do plan on doing autocross in the upcoming year and testing out the various modes to see what is best.
 

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OK. Now I think I've got it. My Jeep Commander had QudraDrive II, which consisted of 3 ECLSDs (Electronically Controlled Limited Slip Differentials). This system could send 100% of the torque to one wheel. The American Axle System in the KL seems to be similar, but with only 2 differentials.

This tells me that the TTD can operate in 2 modes: one, set by the controller, say in 40/60 Torque Spit and the other: Locked > 100%:


The high-range torque transfer device, hereinafter H-TTD 152, includes a friction clutch pack 168 and a H-TTD actuator 170. The friction clutch pack 168 can include alternately interleaved inner and outer friction plates coupled to the sun gear shaft 166 and a drum extension 172 extending from the ring gear 158. The H-TTD actuator 170 can include a hydraulically-operated piston 174 that is disposed in a high-range pressure chamber 176 for sliding movement relative to the clutch pack 168. A flow channel 178 communicates with the pressure chamber 176 and is supplied with pressurized fluid from the actuator assembly 134 in response to control signals from the control system 22. The H-TTD 152 is operable in a first or "released" mode when the clutch pack 168 is released to permit relative rotation between the sun gear 156 and the ring gear 158. The H-TTD 152 is also operable in a second or "engaged" mode when the clutch pack 168 is frictionally engaged by the piston 174 to inhibit relative rotation between the sun gear 156 and the ring gear 158.

This tells me how it works:

When it is desired or necessary to operate the vehicle 10 in an all-wheel high-range (AWD-H) drive mode, the control system 22 can be activated to initially signal the H-TTD actuator 170, 170A to shift the H-TTD 152, 152A into its engaged mode for synchronizing the speeds of the primary driveline 16 and the secondary driveline 20. Thereafter, a four-wheel drive connection between the powertrain 12, the primary driveline 16 and the secondary driveline 20 is established by shifting the disconnect mechanism 42 into its connected mode. Thereafter, the H-TTD actuator 170 can be controlled to vary the torque transmitted through the H-TTD 152, 152A to the second wheels 124L, 124R.

Side Note: Someone here on the Forum put his Jeep on Jack Stands to disprove how Jeep was advertising the Active Drive II/Lock system with its various Modes (Torque splits). Putting the vehicle on jack stands is like putting it on a frozen pond with no snow cover: no traction > confused computer (the control system).
the jack stand videos did not confuse the computer at all. Everything functioned as normal with no check engine lights or anything else like that, they showed a problem which was nearly zero traction at the front end and the rear end was on the ground so not all 4 tires were in the air (so not like a frozen pond) to see how it shifted power to the rear, nothing funny there.

I'll refer you to this video which shows a KL with only a single wheel having traction, and it passes with flying colors


Notice how in every mode the front wheels always start spinning? There is no way for the system to send less power to the front when its a fwd based system. Again fancy marketing by Jeep, and further more i've also proven that while jeep says the vehicle stays in FWD on flat surfaces in warm weather. My tests prove otherwise. Jeep isn't going to get overly technical trying to explain things to the general public
 

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You can't compare Quadra Drive 2 to the KL system. QDII is a RWD based system which is always powering 4 wheels, the KL system is not.
QDII and ADII Lock are indeed very different systems, which is why I used the term functionally equivalent in the sole respect that they can both supply power to even a single wheel with available traction. The AD system is not full-time 4WD and it wasn't designed to be, part of the idea being to 'turn less stuff' and increase efficiency on dry pavement when 4WD is not required. For my part I was only pointing out that ADII Lock has a similar ability when off-road (and the correct operating mode selected) to supply power to any individual wheel.
 

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tThere is no way for the system to send less power to the front when its a fwd based system.
I'm an absolute novice when it comes to these things, so please don't think my question is a disagreement. Just trying to learn. That is an excellent video, btw. However, in regards to the comment quoted above, I don't understand that conclusion (at least using this video as evidence). We see both the front and rear tires spinning but there is no way to identify the rpm of the individual tires to determine power ratio between front and back. I do notice that the front wheels never stop spinning in any mode while "a" back wheel stops in every mode (just before coming off the rollers). I assume this is evidence of the Brake Lock Differential on the rear allowing the opposite rear tire with traction to push the vehicle forward. What confuses me is that you don't see the same behavior when the only tire getting traction is a front tire. The opposite front tire never stops spinning. Unfortunately they only did the "front tire with traction" test in Auto Mode.
 

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Sadly you'd need something like a Dynapack dyno (one torque measuring device for each wheel) with the ability to simulate low traction on an individual wheel basis, or an actual torque meter built into each CV axle to see that "power ratio". Wheel RPM isn't an indicator... depending on traction a wheel can spin at 1000 RPM whether 5 ft-lbs is being put through it or 500.
 

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I'm an absolute novice when it comes to these things, so please don't think my question is a disagreement. Just trying to learn. That is an excellent video, btw. However, in regards to the comment quoted above, I don't understand that conclusion (at least using this video as evidence). We see both the front and rear tires spinning but there is no way to identify the rpm of the individual tires to determine power ratio between front and back. I do notice that the front wheels never stop spinning in any mode while "a" back wheel stops in every mode (just before coming off the rollers). I assume this is evidence of the Brake Lock Differential on the rear allowing the opposite rear tire with traction to push the vehicle forward. What confuses me is that you don't see the same behavior when the only tire getting traction is a front tire. The opposite front tire never stops spinning. Unfortunately they only did the "front tire with traction" test in Auto Mode.
I do have a video with the rear tires disables (via fuse) showing the front tire spinning and then being braked by the brake lock differential. You are right in understanding how the BLD functions. Short of a dyno it will be hard to measure what force is going to each wheel but my guess is that at most 50% of engine power will go to the rear axle. Any application of throttle even in auto mode sends power to the rear. Under full throttle conditions my guess is that the vehicle sends equal torque to the rear. I have access to a dyno but it's not AWD
 

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Is there anytime when your in a little bit of hard going in low traction areas that you should not use rear locker or it’s not a benefit. My thought is it just gives you a extra level of traction?


2019 Trailhawk Elite
Build date May 2019
 

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Is there anytime when your in a little bit of hard going in low traction areas that you should not use rear locker or it’s not a benefit. My thought is it just gives you a extra level of traction?


2019 Trailhawk Elite
Build date May 2019
I think I've only used the locker a few times. Once to blast through 18" of fresh powder on my street, and the other was a fairly steep loose rock and sandy climb. Maybe a couple other times for a brief time to get out of a situation.. 😎
 
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