Selec Terrain mode power distribution - Page 2 - 2014+ Jeep Cherokee Forums
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post #11 of 96 (permalink) Old 02-23-2014, 12:22 PM
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What I'm saying is this is a front drive vehicle with rear wheel assist.
Front wheels are driven the same regardless of mode.
Rear axle is driven only when needed to, with the rear clutch pack engaged.
Terrain select adjusts how aggresively the rear clutch pack engages.
There is never an instance when the rear wheels are getting more power than the front. It is absolutly immposible. There is no drivetrain design possible of doing that. And that is a fact.
So in conclusion, always 100% front drive. 0-100% available to transfer to back end, up to the point of matching what the front end is getting for torque. Giving up to 50/50 power distribution. Never rear biased.
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post #12 of 96 (permalink) Old 02-23-2014, 12:34 PM
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Except power distribution is handled by the PTO in the front transaxle and not at the rear axle. There is a rear axle disconnect to reduce the rotating mass by not driving the driveshaft when in front wheel drive only mode.

For the low range there is a seperate gear reduction for each axle.

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post #13 of 96 (permalink) Old 02-23-2014, 12:44 PM
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Quote:
Originally Posted by Hudsonhawk View Post
Except power distribution is handled by the PTO in the front transaxle and not at the rear axle. There is a rear axle disconnect to reduce the rotating mass by not driving the driveshaft when in front wheel drive only mode.

For the low range there is a seperate gear reduction for each axle.
The ptu does not have a front differential dissconect built into it! For that, it would require a wet clutch pack between it and the front differential. All the ptu is, is a pto (power take off) with a dog clutch built in to disconnect the rear axle. so they call it a ptu (power transfer unit).
The center drive shaft dissconects when not needed, when needed, the rear clutch pack engages, allowing the dog clutches to synch up and then they engage. Then the rear clutch pack varies torque to the back end when needed.
This is a simple slip and grip system! Same basic principle that all vehicles have when built from a front drive platform.
I would like to add that power distribution is handled by the rear axle. The wet clutch pack is electronically controlled. It, and the dog clutch in the ptu dissconect when the rear drive shaft is not needed.

Last edited by Tiefy; 02-23-2014 at 01:15 PM.
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post #14 of 96 (permalink) Old 02-23-2014, 02:43 PM
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I'm still not understanding your assertion... If the ptu up front sends 60% of the power to the rear, that would leave 40% up front. Right?
What you are saying conflicts with math and jeep engineers the way I read it.

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Last edited by clew; 02-23-2014 at 02:58 PM.
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post #15 of 96 (permalink) Old 02-23-2014, 03:17 PM
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I don't think engineers have anything to do with it, I think its sales trying to hype this up as the most advanced system of its type. Personally I would think they only way they came up with 40% front and 60% rear is because the weight balance would be 60% front 40% rear. Just a numbers game and sounds better than 50/50 split.


From everything I have read, torque is normally split 100/0 front to rear. Then there's the ability to transfer torque to the axle with traction. That varies from 100 % front 0% rear to 0% front 100% rear. BUT 100% rear does not mean rear wheel drive. it just means the front tires are already spinning and have 0% traction, so 100% of the torque is going to the rear, that has traction.
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post #16 of 96 (permalink) Old 02-23-2014, 03:29 PM
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Well...one of the head engineers has explained it the same from a video I saw on YouTube. 40/60 has nothing to do with weight, it is torque bias. If it was weight that wouldn't change from sport which is 40/60 to snow which is 60/40.

What you are talking about sounds like a standard awd system that has a 100% fw bias until it starts slipping. That's not how the cherokee operates, at least not in non-auto modes (maybe it does in auto when the rear is connected due to various stimuli). Someone correct me if I am wrong here?

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Last edited by clew; 02-23-2014 at 03:32 PM.
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post #17 of 96 (permalink) Old 02-23-2014, 03:51 PM
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It is a standard awd system with 100% fw bias until it starts slipping. Moving your terrain select to snow, or sport uses tricks to keep the rear clutch engaged at a stop, so the front doesn't spin before engagement. Or slight clutch engagement to always give slight torque to the rear.
Picture a jeep wrangler transfer case. In the 4 hi position front and rear drive shafts are locked together so they turn the exact same speed. Do they transfer torque to the axle with the traction? They sure do. If the front wheels are in the air, it transfers 100% of the torque to the rear wheels. If the rear wheels are in the air, it transfers 100% of the torque to the front wheels. Everybody knows they lock the front and back equally though so there's no reason to use fancy terms to sell them.
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post #18 of 96 (permalink) Old 02-23-2014, 03:54 PM
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Ok...I guess I am saying...in non auto, however they are getting it done, it is not 100% fw bias. Many AWD cars arent that way either. Subaru for instance has symmetrical awd that is 50/50 biased by default.
Hopefully someone else can chime in on this and clear it up.

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Last edited by clew; 02-23-2014 at 04:06 PM.
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post #19 of 96 (permalink) Old 02-23-2014, 04:20 PM
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Subaru and Audi/VW are the only true AWD systems as far as I know. Subaru uses a viscous coupling system to send power where it's needed, and normally splits something like 54% front 46% rear. The Audi/VW system is a mechanical system that I am not familiar with the specifics.

Most AWD cars are FWD and send power to the back as needed. The difference between 4WD and AWD if I'm not mistaken is that the AWD systems can assign power to independent wheels, whereas with 4WD the separation is strictly front/rear.

On Active Drive systems like the Cherokee, they operate much the same way as the previous Ford 4x4 system used on the Escape. FWD until the front axle spins faster than the rear, then power gets transferred back to compensate. What separates Active Drive from the Ford system is the ability to select the different modes, which have varying power distribution between front and rear depending on mode used. Also, the Active Drive II owners get the 4LO, where the front and rear axles are electronically locked.

I don't claim to be an expert so take what I say for what it's worth, but Active Drive is a 4WD system, not AWD. It's a long way from 4HI/4LO and locking front hubs, but it's still technically 4WD and not AWD.
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post #20 of 96 (permalink) Old 02-23-2014, 08:48 PM
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Quote:
Originally Posted by Tiefy View Post
I don't think engineers have anything to do with it, I think its sales trying to hype this up as the most advanced system of its type. Personally I would think they only way they came up with 40% front and 60% rear is because the weight balance would be 60% front 40% rear. Just a numbers game and sounds better than 50/50 split.


From everything I have read, torque is normally split 100/0 front to rear. Then there's the ability to transfer torque to the axle with traction. That varies from 100 % front 0% rear to 0% front 100% rear. BUT 100% rear does not mean rear wheel drive. it just means the front tires are already spinning and have 0% traction, so 100% of the torque is going to the rear, that has traction.
Unfortunately, everything that you have stated clearly contradicts everything that Jeep has published and advertised. The Cherokee's 4x4 System is very different than what you are basing your posts on. It seems like you are more or less referring to a CRV's or Rav4's "AWD" system with 100% power up front until the system detects wheel slip. The Cherokee's system is very different and can automatically send power to the rear BEFORE wheel slip. I can personally vouch for how the system works as I have taken mine off road and used all modes at different times wheeling SPECIFICALLY to see what each mode does. Check out some of Jeeps Video's on their website and other youtube videos.
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