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post #21 of 35 (permalink) Old 03-13-2017, 12:36 PM
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Originally Posted by dhh3 View Post
I am unaware that it automatically goes into 4WD below 40 degrees. I thought that just to PTU engages to be ready for 4WD, if needed.

Is this TH specific?
FCA has not released the official workings of this, probably a trade secret type thing. Member @Array investigated this as much as he could. What we do know, and there is an official Cherokee video that quickly describes this, is that a few parameters do *engage* something in the AWD system, and this is for all AWD systems, not just AD-Lock (TH). Power is sent to the propeller shaft, but not to the rear wheels directly. In other words, it's an AWD-ready state. Parameters that trigger this : 40F and below, inclines (unknown trigger angle), rain, heavy engine load / towing (unknown specifics) and probably one or two more I'm forgetting. These all do the same thing at PTU level. Engine load does increase because of this, impacting fuel economy.

Some will describe it as added/invisible security while I see it as overly aggressive and costly (fuel).
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post #22 of 35 (permalink) Old 03-13-2017, 12:52 PM
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If the TTD is a wet clutch pack, which auto engages, is it possible that the drive shaft is not spinning? Every wet pack clutch that I have seen has a series of discs connected to one side, and another set connected to the other side. Once one side starts spinning, the goo heats up and expands pushing all the spinning discs together to form a connection. I don't see how this wet clutch would work if the drive shaft is spinning.

When Ford got rid of the manually connecting front hubs, when the 4WD button was pushed, this would engage the front drive shaft. This turning motion would engage the front hubs: presto, 4WD. To unlock the front hubs, you had to back the vehicle up at least a full cars length.
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post #23 of 35 (permalink) Old 03-13-2017, 01:01 PM
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If the TTD is a wet clutch pack, which auto engages, is it possible that the drive shaft is not spinning? Every wet pack clutch that I have seen has a series of discs connected to one side, and another set connected to the other side. Once one side starts spinning, the goo heats up and expands pushing all the spinning discs together to form a connection. I don't see how this wet clutch would work if the drive shaft is spinning.

When Ford got rid of the manually connecting front hubs, when the 4WD button was pushed, this would engage the front drive shaft. This turning motion would engage the front hubs: presto, 4WD. To unlock the front hubs, you had to back the vehicle up at least a full cars length.
This stuff exceeds my knowledge bank. @Array may be able to comment though. And to make this all a little more fun, I think AD1 and AD2/AD-Lock have different clutch packs for the rear...
The *official* promo video says AWD is engaged when the above parameters are detected, but they don't/won't go as far as decribe what is really going on.
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post #24 of 35 (permalink) Old 03-13-2017, 02:15 PM
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If the TTD is a wet clutch pack, which auto engages, is it possible that the drive shaft is not spinning?
The way the AD1/AD2/ADL systems operate is to first engage the TTD (Torque Transfer Device) to spin up the drive shaft to wheel speed. When a PTU sensor indicates the PTU's input and output are synched, the PTU's dog clutch is engaged. At this point, and under computer control when in Auto Mode, the TTD clutch may release, thus having the system in a ready state but not in connected AWD. Under computer control, the TTD (wet clutch) can be engaged or slipped or pulsed to accomplish torque biasing affecting drive characteristics.

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post #25 of 35 (permalink) Old 03-13-2017, 04:00 PM
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I read your link, and was looking for something that says that a given temperature will set things in motion. I didn't find a specific temperature, but I did find this:

The system operates on 2 sets of parameters:
1. First Sensors: The group of first sensors 152 can be arranged within the motor vehicle 10 to sense a vehicle parameter and responsively generate a first sensor signal. The vehicle parameter can be associated with any combination of the following: vehicle speed, yaw rate, steering angle, engine torque, wheel speeds, shaft speeds, lateral acceleration, longitudinal acceleration, throttle position and gear position without limitations thereto.
2. Second Sensors: The group of second sensors 154 can be configured to sense a driver-initiated input to one or more on-board devices and/or systems within the vehicle 10 and responsively generate a second sensor signal. For example, the motor vehicle 10 may be equipped with a sensor associated with a mode selection device, such as a switch associated with a push button or a lever, that senses when the vehicle operator has selected between vehicle operation in a two-wheel drive (FWD) mode and an all-wheel drive (AWD) mode. Also, switched actuation of vehicular systems such as the windshield wipers, the defroster, and/or the heating system, for example, may be used by the controller 150 to assess whether the motor vehicle 10 should be shifted automatically between the FWD and AWD modes.

My interpretation of this is the system is either in FWD or AWD; there is no "ready" position for AWD unless Jeep specifically added something to the mix, since this "white paper" is written by American Axle. The "Temperature Actuation" comes into play with signals sent from the HVAC or wipers.
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post #26 of 35 (permalink) Old 03-13-2017, 04:06 PM Thread Starter
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I'm thinking the same as dhh3. I can understand the mileage hit for engaged 4wd, but a "4wd ready" condition doesn't seem like it would sap that much power/fuel.
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post #27 of 35 (permalink) Old 03-13-2017, 05:38 PM
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Originally Posted by dhh3 View Post
My interpretation of this is the system is either in FWD or AWD; there is no "ready" position for AWD unless Jeep specifically added something to the mix, since this "white paper" is written by American Axle. The "Temperature Actuation" comes into play with signals sent from the HVAC or wipers.
This is a patent document filed by American Axle regarding its EcoTrac AWD system. It does a good job describing the hardware and how it can be controlled. It is computer controlled and I presume Jeep did the programming. Answers to logic questions are difficult to come by since they are locked in software that Jeep most likely holds as proprietary. Black box testing could reveal some of this logic.
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post #28 of 35 (permalink) Old 03-13-2017, 05:59 PM
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Originally Posted by dhh3 View Post
My interpretation of this is the system is either in FWD or AWD; there is no "ready" position for AWD unless Jeep specifically added something to the mix, since this "white paper" is written by American Axle. The "Temperature Actuation" comes into play with signals sent from the HVAC or wipers.
Your guess is as good as any regarding the logic. However, the sequence of engagement is TTD, PTU synch, PTU engage.

EcoTrac™ allows the AWD vehicle to utilize its primary drive system, the front wheels, when AWD is not needed.

When the vehicle senses that AWD may be necessary due to conditions, the system will passively and automatically engage, seamlessly and without disturbance to the driver.

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.

When conditions allow, the vehicle will revert back to an economical mode, conserving fuel and reducing emissions.


http://www.aam.com/technology/ecotra...ystem-120.html

Other members have reported when the drive shaft spins. This was based on bad bearings where the spinning drive shaft could be heard from the cabin. This goes to my comment about black box testing.
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post #29 of 35 (permalink) Old 03-19-2017, 09:59 PM
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Just busted 5000 miles in my V6 TH and thus far have averaged 20.7mpg according to my entries at Fuelly. I commute 4 days a week in fairly early morning (6-7AM) and later evening (6-7PM) Seattle traffic, so it is not that bad most the time. I'll be curious to see if it improves as the weather gets better as all my previous cars saw a minor improvement.

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post #30 of 35 (permalink) Old 03-20-2017, 09:37 AM
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Getting 19mpg city, 23 hwy on my V-6 TH. The mileage isn't a big deal, especially with 100% gasoline hovering around $2.20 gallon.

Just wish it had a bigger fuel tank like my Subaru (18.5 gals). I can easily go over 500 miles on a tank of gas in the Subaru.
23 highway for the V6 is horrible but many factors go into that number mostly speed. 19 mpg city is good. That is basically where I am.
I find that anything over 62mph will decrease mpg. Over 70mph and its horrible.
I am envious of your $2.20 for 100% gas. By me its usually .15-.20 more a gallon over 10% ethanol. Only one place sells it, that is 87 and 92 octane.
.15 is the breakeven to be worth the use vs the cost. But it does add 1.5-2.0 mpg. I use to use it all the time when the difference was only .10 gallon in my V8 Grand Cherokee.
In my location I am confined to 55-65 mph maximum so I am able to maximize my mpg. If I am on the interstate hwy only at 70mph I will be in the 28-29 range.
If you have to deal with urban smog gas during the summer that will lower that number also. My trips to Chicago I avoid like the plague filling up within 100miles of that City because of the gas.

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