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  #49  
Old 09-09-2010, 06:08 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by vonk View Post
...But, could you elaborate about the misnomer? Iím confused....
Even with QuadraDrive, the limited slip diffs only transmit power to one drive wheel at a time at each axle. So, you are really only getting two wheel drive at any point, and not all four wheels pulling. That's where "locker" diffs come in for off-roading, and then both on each axle are transmitting power equally to both wheels, but you need to rely on each tire slipping a bit on any condition other than driving straight ahead. It's also why you need to rely on tire slip when running in 4Lo because the front and rear are at equal speeds and the tires want to run at different revolutions when turning. Your Overland is going to be similar, with most likely excellent traction conditions, but the front slip will be controlled by brake application. The engineers stated the system is about as good as anything they've ever done (except likely the Rubicon - my words), and with QL, you have an adjustable lift kit built in.
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  #50  
Old 09-09-2010, 07:42 PM
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Re: No front ELSD for QD II?

I'm fine with send power to only one wheel. I'm not fine with using the brakes to send whats left to one wheel.
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  #51  
Old 09-09-2010, 09:31 PM
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Re: No front ELSD for QD II?

BUT,,,,how do you know it doesnt work as good?
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  #52  
Old 09-09-2010, 09:48 PM
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Re: No front ELSD for QD II?

Because its robbing the vehicle of torque that could be applied to forward motion and is instead used to inhibit motion.

Dragging a brake cannot be as good as directing full power like quadra drive is supposed to be able to do.
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  #53  
Old 09-09-2010, 10:16 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by Jim Hef View Post
Even with QuadraDrive, the limited slip diffs only transmit power to one drive wheel at a time at each axle. So, you are really only getting two wheel drive at any point, and not all four wheels pulling.
Jim, I donít think that statement is correct. Even open diffs transmit torque to both wheels of an axle, equally on dry pavement, and when one wheel is slipping, proportional to each wheelís traction. Otherwise, how could a slipping wheel spin without torque? However, unlike an open diff, a limited slip diff will internally resist relative axle speeds resulting from one wheel slipping. This is done with fixed or self-actuating clutch-packs (Eaton VariLoc). The resistance may be set from none (open diff) to total (locked), and with any setting each wheel receives torque proportional to its traction.
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  #54  
Old 09-09-2010, 10:52 PM
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Re: No front ELSD for QD II?

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Originally Posted by Scottina06 View Post
BUT,,,,how do you know it doesnt work as good?
Just to name one case: Assume you're rock-crawling uphill. You need all the grunt (wheel torque) you got to make it and just then your left front wheel becomes airborne. An ELSD or self-activating LSD would internally lock the axle and send all the available torque to the right front wheel to lift you over that boulder. But with brake actuation, half the available torque is braced against the external brake, leaving only the remaining half for your right front wheel. That might not be enough.
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  #55  
Old 09-09-2010, 10:57 PM
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Re: No front ELSD for QD II?

No, thats incorrect bro.
If the spinning wheel is braked completely, 100% of that axle's torque is transfered across the diff to the loaded wheel.
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  #56  
Old 09-09-2010, 11:06 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by vonk View Post
Just to name one case: Assume you're rock-crawling uphill. You need all the grunt (wheel torque) you got to make it and just then your left front wheel becomes airborne. An ELSD or self-activating LSD would internally lock the axle and send all the available torque to the right front wheel to lift you over that boulder. But with brake actuation, half the available torque is braced against the external brake, leaving only the remaining half for your right front wheel. That might not be enough.

But you dont know this...or what percentage of tq isnt transferred? How can you be sure its half? The engineers said that it is better than the front elsd in the wk becasue of the advanced computer controls....so its NOT just the brakes.
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  #57  
Old 09-09-2010, 11:17 PM
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Re: No front ELSD for QD II?

direct from the engineers-

Question:
One of the topics most often discussed relating to the new WK is the mysterious "disappearance" of the front ELSD. It's mentioned in the early literature and manuals, it has a part number, yet it never appeared when production started. The off-road community feels a lot of capability has been lost without the front ELSD. What was the reason it was decided to not use it, or will it reappear someday?

Answer:
The front ELSD was not need to make this new Jep the most capable Grand Cherokee yet. The chassis electronics (esp, abs, traction controll) systems are soo fast not that we were able to get amazing traction without a front ELSD. I can tell you from expreience (Moab ect) this Jeep will go anywhere.

Question:
can you explain the elsd a little to us. Weve had deep discussions into how it works on the wk2. aslo how does the front axle handle wheel slip now that the front elsd is gone...for now?

Answer:
The Electronic Locking Slip Differential (ELSD) essentually uses a clutch pack/motor to transfer torque seemlessly right-left. We use the throttle position sensor to monitor driver feedback and the wheel slip sensors to monitor tire traction. The software monitors all system performance and moves torque when needed.

Now...the discussion of the ELSD on the front was a very lengthly internal Jeep team discussion early in the program. We found in our testing that the better BLD software performance, slightly bigger brakes, improved fuel efficiency/reduced friction, and new T-case torque transfer out-weighed the potential front ELSD benefit. Bottom line, we believe the off-road and on-road performance are maximized with our 2011 system.
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  #58  
Old 09-10-2010, 09:04 AM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by Scottina06 View Post
But you dont know this...or what percentage of tq isnt transferred? How can you be sure its half? The engineers said that it is better than the front elsd in the wk becasue of the advanced computer controls....so its NOT just the brakes.
Of course the engineers would say it's better.

Wikipedia has a nice write-up for those who want to get technical. But let me simplify, using their images.







Input torque is applied to the ring gear (blue), which turns the entire carrier (blue), providing torque to both side gears (red and yellow), which in turn drive the left and right wheels. If the resistance at both wheels is equal, the planet gear (green) does not rotate, and both wheels turn at the same rate.







If the left side gear (red) is held still (X) by brake application, the planet gear (green) rotates about the left side gear, in turn doubling the speed of the right shaft (yellow). This means that the right shaft now runs at doubled its original gear ratio. Given the same input torque, we know that when you double the gear ratio of any drive train, the output torque is cut in half.
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  #59  
Old 09-10-2010, 09:44 AM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by vonk;266067[FONT=Verdana
Given the same input torque, we know that when you double the gear ratio of any drive train, the output torque is cut in half.[/FONT]
For the math inclined,

(From http://en.wikipedia.org/wiki/Torque#..._versus_torque )

The question is does this matter in the use case you have described? What other factors are in play such as varying the engine power/rpm?
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  #60  
Old 09-10-2010, 09:59 AM
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Re: No front ELSD for QD II?

Why did they keep the rear ELSD?
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