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post #31 of 48 (permalink) Old 03-15-2017, 11:42 AM
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Originally Posted by dhh3 View Post
.... When the rear drive shaft engages, the front clutches in the wet pack begin to spin which heats up the goo inside and engages the rear clutches, which then spin the rear differential, and thus the rear wheels.
Where did you read that goo engages the clutch?

Edit to add: This is what I've dug up in the past.
Disclaimer: I don't have any inside info on this system, only what I've been able to read. Interested in anything other people can contribute and substantiate.

We know that Jeep uses the American Axle EcoTrac system: http://investor.aam.com/phoenix.zhtm...cle&ID=1886076 - "AAM is proud to partner with Chrysler Group LLC in providing this industry-leading technology," said David C. Dauch, Chairman, President & CEO of AAM. "Our new EcoTracTM Disconnecting AWD reaffirms our commitment to technology leadership and we are excited that it has supported Chrysler Group's development of the unique 4x4 systems debuting on the all-new 2014 Jeep Cherokee."

American Axle has a slew of patents on this "Single speed and two-speed disconnecting axle arrangements" design. Everything I've read indicates the "wet" clutch is designed to be fully engaged, slipped, pulsed, and fully disengaged using a hydraulic servo motor and lever. These mechanical clutch manipulations are necessary to enable torque biasing the system is known for.

"The torque transfer device can include any type of clutch or coupling device that can be employed to selectively transmit rotary power from the input assembly to the second differential (i.e. rear end). In the example shown, the torque transfer device is a multi-plate friction clutch that can include an input clutch member driven by the hypoid gear, an output clutch member coupled for rotation with the second differential case, a multi-plate clutch pack having a plurality of interleaved friction plates disposed between the input and output clutch members, and an engagement member that is moveable for selectively applying a clutch engagement force to the clutch pack. The torque transfer device is shown to generally surround a portion of the second differential. The TTD actuator is provided to generate translational movement of the engagement member relative to the clutch pack and can be controlled by control signals from the control system".
https://www.google.com/patents/US898...BgBPwQ6AEIHDAA

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Last edited by Array; 03-15-2017 at 12:34 PM.
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post #32 of 48 (permalink) Old 03-15-2017, 12:16 PM
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The Jeep Active Drive I 4WD uses a fully variable wet clutch housed in the rear drive module. As for the Jeep Active Drive II (available on all three of the aforementioned models), this includes a two-speed PTU with torque management and low range. The system's 4-Low mode locks the front and rear drive shafts for low speed power or towing, while low range provides a 2.92:1 gear reduction for better climbing ability and crawl in off-road conditions. The front and rear driveshafts should have a mechanical connection, not a wet one, IMHO.

The input shaft (drive shaft at the front wheels) and the output shaft to the rear wheels (differential) each carry a series of plates that are alternately intertwined and closely spaced inside the wet clutch housing. All the plates swim in a special fluid (goo) that transfers power from the input to the output plates when needed. If the front-drive wheels begin to slip, their shaft and plates spin more quickly than the others. This speed differential within the housing churns and heats the fluid, which thickens it and more tightly bonds the alternating plates. Some torque is now sent to the grippier wheels until spinning ones regain traction. So, the more the tires slip, the more the clutch plates spin and the hotter the goo (lubricant) gets. If it gets too hot, it disengages until it cools down.

Sad, for a Jeep.

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post #33 of 48 (permalink) Old 03-15-2017, 12:44 PM
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.... The front and rear driveshafts should have a mechanical connection, not a wet one, IMHO.
I hear what you're saying about mechanical connections. However, a big driver to this American Axle system was economy and space/weight conservation. Also, what I've read is the wet clutch is used to improve handling and off road capabilities through its ability to be slipped and pulsed.

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post #34 of 48 (permalink) Old 03-15-2017, 12:48 PM
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Quote:
Originally Posted by dhh3 View Post
....The input shaft (drive shaft at the front wheels) and the output shaft to the rear wheels (differential) each carry a series of plates that are alternately intertwined and closely spaced inside the wet clutch housing. All the plates swim in a special fluid (goo) that transfers power from the input to the output plates when needed. If the front-drive wheels begin to slip, their shaft and plates spin more quickly than the others. This speed differential within the housing churns and heats the fluid, which thickens it and more tightly bonds the alternating plates. Some torque is now sent to the grippier wheels until spinning ones regain traction. So, the more the tires slip, the more the clutch plates spin and the hotter the goo (lubricant) gets. If it gets too hot, it disengages until it cools down.
Is this description specific to the EcoTrac system in the Jeep Cherokee? And if so, can you sight a reference. Thanks.

Note: I added some references to my message #31 above.
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post #35 of 48 (permalink) Old 03-15-2017, 01:02 PM
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The description makes sense as my problem went away when using 4-low which was a mechanical connection and didn't require any slipping of the clutches.
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post #36 of 48 (permalink) Old 03-15-2017, 01:05 PM
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Its basically a description of how a wet clutch works. FCA says it is a wet clutch, but reading American Axle's description, they say that it is a multi-plate clutch pack. Since they don't mention wet, it must be dry, although there would be oil present for lubrication. What American Axle came up with is the most sophisticated way of making a FWD (cross mounted) 4WD with a 2-speed transfer case. A dry clutch pack would be more of a "mechanical" connection than a wet pack, but a dry clutch pack still has the ability to overheat. It would be nice if the connection was gears instead of clutches.

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post #37 of 48 (permalink) Old 03-15-2017, 02:15 PM
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.... FCA says it is a wet clutch, but reading American Axle's description, they say that it is a multi-plate clutch pack.

.... It would be nice if the connection was gears instead of clutches.
American Axle says the EcoTrac uses a wet clutch. "Utilizing a wet clutch in the RDM to gently bring the driveline to proper speed, the PTU will be quickly synchronized and will engage and begin delivering the appropriate amount of torque."
http://www.aam.com/technology/ecotra...ystem-120.html

The wet clutch is most likely used for cooling.

Wet vs. dry systems
A wet clutch is immersed in a cooling lubricating fluid that also keeps surfaces clean and provides smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil), stacking multiple clutch discs can compensate for the lower coefficient of friction and so eliminate slippage under power when fully engaged. The Hele-Shaw clutch was a wet clutch that relied entirely on viscous effects, rather than on friction.
A dry clutch, as the name implies, is not bathed in liquid and uses friction to engage.

https://en.wikipedia.org/wiki/Clutch...s._dry_systems

I think @David_Baker in post #26 nailed it. There should be a temp guage that can be monitored.

James DeLong from Linear Logic LLC was on the forum back in 2015 and worked with several of us. He came up with some nice displays (e.g. gear, PTU state) but was unable to crack the nut on when the TTD was engaged and disengaged. Since the effects of the TTD engage/disengage are very hard to observe given it being hidden in the RDM as well as Brake Limited Differential added to the mix, effort would be required to black box test that system.

Regarding using gears, the PTU does use a gear. However, something has to be able to give otherwise there would be driveline binding across the propshaft to contend with.
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post #38 of 48 (permalink) Old 03-15-2017, 02:27 PM
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The description makes sense as my problem went away when using 4-low which was a mechanical connection and didn't require any slipping of the clutches.
The power still has to go through the TTD's clutch, but what you say makes sense; maybe it closes the clutch pack tight while in 4-LOW. Does it say anywhere to be careful because vehicle will develop bind while in 4-LOW? That would be a dead giveaway.
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post #39 of 48 (permalink) Old 03-15-2017, 02:51 PM
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Would it not help to put the Jeep TH in 4 Lo and put the locker on? You could always disengage the Locker if needed. We have tons of snow right now, courtesy of Stella and I might have to take the TH out and see how things work, but I've never had a problem with my Jeeps in the deep and drifting snow before. Sand is a very different beast. Because of this I generally avoid playing in it, but it's always been beach sand. I have a hard enough time trying to rid the vehicles of salt during and after Winter. Most people here choose to play with the sleds in the deep snow anyhow. Nowhere near as cozy as sitting inside a TH, WK, JK or Commander, but we definitely have a good amount of sled berserkers in the area. With big snows they try and ride to Canada and back around the Eastern section of Lake Ontario.

Not something that interests me these days. Too many hidden obstacles, especially after we had so many trees uprooted or snap from the insanely high winds last week.

I guess Jeep can please some of the people some of the time, but never all of the people, all of the time. Remember that this is a SUV that is generally under $35, without all the electronic bells and whistles.

What system does Mercedes or the newer Land Rover/Range Rivers use?

I know my TH is primarily for safe transport and any play time is a bonus where I try not to damage the Jeep anymore than I can avoid.

Just my $0.02.


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post #40 of 48 (permalink) Old 03-15-2017, 03:21 PM
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Quote:
Originally Posted by Array View Post
The power still has to go through the TTD's clutch, but what you say makes sense; maybe it closes the clutch pack tight while in 4-LOW. Does it say anywhere to be careful because vehicle will develop bind while in 4-LOW? That would be a dead giveaway.




It actually does state in the owners manual to not use 4-low while on high traction surfaces, and from experience I can tell you being in 4-low it is most definitively locked front to rear.
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