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Active Drive Selec-Terrain

Discussion in 'Compacts: Renegade, Patriot, Compass, Caliber' started by npaladin2000, Feb 5, 2017.

  1. npaladin2000

    npaladin2000 LOAD "*",8,1
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    Ok, so I like the idea of the system, but I'm wondering if we can get a little more info about it. I got the following info off of the Allpar page for the Compass: 2018 Jeep Compass: here it is!

    Auto:
    Automatic mode

    Snow:
    Second gear launch; slick-surface brake controls; locked in AWD; up to 60/40 front/rear power split; ESC full on

    Sand/Mud:
    Off-road brake controls; locked in AWD; partial ESC

    Rock:
    Increased brake lock differential capacity; no ESC

    Since Sand and Mud are different modes, I'd love to know the difference between them, if any.

    I was also looking at the Renegade's section on ActiveDrive/Selec-Terrain (2015-2017 Jeep Renegade: the mini-Jeep) since the systems are supposed to be the same, It lists the following:

    • Standard mode is automatic, staying in front wheel drive most of the time, but splitting torque as needed.
    • Sport limits traction control, increases stability-control thresholds, and targets a front/rear torque split of 40/60 for a rear-drive feel.
    • Snow starts in second gear, sets brake controls for slick surfaces, and goes into full time 4x4, preferring a 60/40 front/rear split.
    • Mud/Sand is similar but has modified brake controls, and prefers rear wheel drive.
    • Rock, on Trailhawk only (because it is only available in low gear), is similar to Mud/Sand but increases brake lock differential capacity, and locks the differential.
    As I recall, the Renegade didn't have a Sport mode, that was in the Cherokee. I'd love to HAVE a sport mode, if at all possible. And mud/sand are combined here too. I'm just a little confused.
     
  2. Rick Anderson

    Rick Anderson Well-Known Member

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    All the manufacturers do a dismal job at explaining their technology, it seems they assume the consumer is too stupid to understand it; but honestly I think its the Marketing department that doesn't understand their own technology and try to explain it in marketing terms and gee whiz claims. They have to have the engineers dumb it down to just what happens at the end of the line.

    Not familiar with the mechanics of the Active Drive system, nor that much with the electronics.

    But, it seems to me the mode selection is just user input into the electronic control of the 4WD system. I'm sure in testing they found they could make some simple changes to optimize the 4WD systems reaction to perform better for each different surface. So instead of trying to average out all those different factors in the programming to do as best as possible on all different surfaces, they added a mode switch that told the electronic control that would select the best factors for a particular surface.

    The description itself pretty much says that.

    AFA sand/mud modes being combined, while they may be very different surfaces, perhaps the electronic control optimization is the same. And even if there are several factors that would argue the 4WD system should react differently for sand vs mud, they may still be able to combine the modes because the system can recognize it and react properly on the fly.
     
  3. Rick Anderson

    Rick Anderson Well-Known Member

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    I'd like to know how the Active Drive can direct more torque to the rear of the vehicle than the front?

    As I understand the clutch packs used in some of the other systems, especially the transverse FWD systems that use a Power Take-Off/Transfer Unit, the clutch pack can engage with various pressures on the clutch pack, that will or will NOT allow slip. So if you pressurize the clutch pack fully and not allow any slip you'd at best can get a 50/50 split of torque, pressurizing partially could allow slip for turning like a differential or allow for a torque split less than 50/50.

    But the torque split less than 50/50 would always be Front Biased. Remember this a FWD transaxle that taps off power to the rear, thus you could let the coupling slip a bit to reduce the amount of torque going to the rear. But how do you get transaxle to direct more torque through the tap off to the rear than its does to the front CV shafts?

    Only thing I can think of myself, they tap the power off of the starboard side output of the transaxle differential, so there isn't a center differential in a conventional sense in these systems. So perhaps a clutch pack or differential paired with the transaxle differential might be able to do some weird things to accomplish this. But I can't figure that out off the top of my head.
     
  4. npaladin2000

    npaladin2000 LOAD "*",8,1
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    My big confusion point is that Sand/Mud are combined in the descriptions, but they're seperate modes on the selector switch. So I'm trying to figure out the difference between the two settings.

    My understanding is that the Jeep system can direct almost (but not quite) 100% of power to one axle or the other but I might be mistaken on that.

    I also want to whine about not having a sport mode with AWD launch and 60/40 bias on the Compass but you can ignore that part. ;)
     
  5. BobbiBigWheels

    BobbiBigWheels I'm likely at work...
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    In my experience sand/mud perform identically, I've played around with both Cherokees and Renegades in different conditions. I found the only notable difference was that sand started out in first, whereas mud started out in 2nd gear.
     
  6. Rick Anderson

    Rick Anderson Well-Known Member

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    I see what you're asking now. My guess, the programming for sand and mud is the same, have the same features enabled, but might differ in the thresholds it engages different aspects of the programming.

    You don't want to start off spinning wheels in sand if you can avoid it, mud you do want to start out spinning wheels a bit. Same features control that, its just how soon will the traction control come on to prevent spinning wheels? Much sooner when sand is selected to limit spinning wheels, much later when mud is selected to allow spinning wheels right away. BobbiBigWheels mention mud starting off in 2nd gear while sand starts in 1st, make sense to me, you want to crawl along in sand if you can, you have to spin and slip & slide in mud.
    Well, you can have 100% torque to one axle by disengaging the other axle, which most Jeep 4WD systems can do (but not all, look at Quadra Train/Drive) but to pick either front or rear axle to send 100% is quite a feat, which I have trouble understanding.

    A transaxle has the differential for that axle built into the transmission, and they started off as just FWD axles, so exactly how do you redirect power away from the front differential and direct all of it toward the rear differential?

    Again, not read up on the Active Drive, IIRC, the PTU is rather complex with dog clutches engaging and disengaging the rear drive shaft, it even completely disengages the rear drive shaft so it doesn't spin at all to eliminate parasitic drag to improve fuel economy. But I still can't see how it could direct all torque to rear bypassing the front differential, that is built into the trans with the pinion being the end of the output shaft from the trans, that would require an insane redesign of the transmission.

    With two differentials side by side, perhaps there's a way to direct more torque toward the 2nd differential down the line than the first differential upline, so front/rear split 40/60 might be possible. Are you sure the Active drive isn't limited to 100% to the front axle with any combination up to front/rear 40/60% split? That would make sense to me. And it would even more sense if it was limited to a range of 100% front to 50/50%.
    Perhaps the Compass is small enough that AWD launch doesn't offer any improvement, probably more likely simply cost, for the Compass segment they have to keep price down and thus can't afford to equip it with the more complex (usually means more expensive) PTU that the more premium segment vehicles come equipped with.
     
  7. npaladin2000

    npaladin2000 LOAD "*",8,1
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    I don't think the differential in Jeep's system is in the transaxle, I think it's in or adjacent to the PTU. That's the only way I can figure that they can send 95% to the rear axle. It seems like a pretty complex system, I wonder how much it weighs. That might also explain why they still offer 4x2: if everything is seperate it can be easily left off.

    Your explanation on the sand and mud modes make more sense than anything I've found. I don't particularly see myself ending up in sand, but one never knows. Mud and snow, yeah.

    It's too bad we can't throw a switch and get a rear-biased drive mode. But they bothered putting it into the 500x, and that's a very similar system. In fact it's probably the same except for software tweaks.

    We really should try and get more information on this stuff. Not that that will be easy, the stuff that makes it out to the public is marketing rather than technical.
     

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