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4WD and AWD systems explained

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  • ateixeiraateixeira Posts: 72,587
    I really liked that new one when it debuted. I will definitely check it out this auto show season, even though I'm not likely to buy a truck.
  • Hi there,

    I was wondering if you had found out the problem with your transfer case / 4WD system. I also have a 96 cherokee with the exact same problem you described in your post. Whining sound and hesitates on the disengage with a "thud."

    Your post is the only thing I have found while spending awhile searching for a possible solution to this problem.

    Were you able to get your Jeep fixed and what was the problem?
  • >> There's no torque vectoring on the rear axle, I think that's pretty clear. If it could Mitsubishi would mention it.

    Mitsubishi says Outlander has Active Front Differential and Active Center Differential, and based on illustrated PDF file I’ve seen, the Active Center Differential is integrated with its rear differential and using electronically controlled coupling to transfer torque to the rear wheels. Outlander AWD system is still as advanced as it gets. Top slalom speed and “ice walk test video” validate that.

    I am not sure about rally/exotic cars, but it appears that no car in $100k price range has both front and rear active differentials, and very few cars have active center differential.

    Both new torque vectoring-capable Audi A4, A5 and Q5 and BMW X6, X5M have only one active differential on rear axle, conventional mechanical center differential, and conventional open front differential:
    * BMW / ZF “Vector Drive"
    * Audi / ZF “Active Sport Differential"

    Since 2009 Mercedes appears to use side-to-side torque transfer based on 4-wheel active braking, which according to online source is limited to 50% of torque transfer.
    Mercedes calls it “Torque Vectoring Brake system"

    Acura’s SH-AWD, and few other manufacturers also utilize single axle active differential.

    In nineties Mitsubishi implemented the Initial version of its torque vectoring S-AWC based on rear axle active differential. In addition to Active Center Differential, Active Rear Differential and Helical Front LSD Differential, Mitsubishi EVO S-AWC uses four-wheel independent Active Braking system on all 4 wheels (not to confuse with a typical ABS/stability control) ; another S-AWC article

    image
  • ateixeiraateixeira Posts: 72,587
    Mitsubishi says Outlander has Active Front Differential and Active Center Differential, and based on illustrated PDF file I’ve seen, the Active Center Differential is integrated with its rear differential and using electronically controlled coupling to transfer torque to the rear wheels

    So ACD works front to rear but not side-to-side on the rear axle, else they'd say it had an Active Rear Differential.

    The ice walk test video is nice but it shows the Outlander can climb smoothly if at least two wheels have traction. Others have shown they can do the same task with just one wheel.

    C&D has an article in this month's issue about Porsche Torque Vectoring, which is on the rear axle.
  • Can someone help me understand the CX-9's supposed fulltime AWD system?

    I have seem a schematic in the service manual which shows the normal front wheel drive etransmisson and a rear differential. I believe it runs normally with a 90-95% front bias and progressively routes up to 50 front / 50 rear during slip conditions. Is this possibly like any of Subaru's systems?

    Some website posts have referenced Borg Warner's ITM 3e as similar, but that doesn't seem to gibe with the service department's schematic I saw.

    I'm looking to purchase for mostly pavement driving very soon - please help!
  • ateixeiraateixeira Posts: 72,587
    A good person to ask would be aviboy97. He works at a Mazda dealership and usually attends dealer training events, so he'd have the inside story as well as some background knowledge.

    I haven't seen him around in a while, however.
  • kdshapirokdshapiro Posts: 5,751
    I've come to the conclusion the type of AWD/4WD drive only really matters in the marketing literature unless the vehicle is faced with extreme racing conditions or extreme trail conditions. For most people slogging through the weather without getting stuck and flipping switches is the most important thing.

    After the recent winter storm and before the snow was way above the bumper, I took the trusty XT out on unplowed roads. XT was as surefooted as mule. What else could one ask for? I didn't care if the front/rear bias was fixed, was 90/10, 80/20, 50/50 or 100/0. I didn't care if it had an active center differential or not, full time/part time, side to side, one wheel, two wheels etc. All I know it worked.

    The small percentage of people who scrutinize the drive train and make a decision on only the drive train before buying a car, have to be in the minority.
  • ateixeiraateixeira Posts: 72,587
    Well said.

    My kid went sledding with a little buddy and his mom got stuck on their way home in an Odyssey. Steep, long hill.

    The next day she asked if I'd pick him up to take them sledding. No problems. Even with uneven surfaces it just went straight up, no hesitation.

    Experiences like mine (and yours) are why the Forester wins in owner loyalty for the category. I'm on my 2nd. :shades:
  • who on here can explain ( viscus couplers) in the transfer cases of the 1999 jeep grand Cherokee Laredo 4x4 and can you drive them with the front drive-shaft removed without damaging the transfer-case?
  • Have a question about the 4X4 system on my 2010 Grand Cherokee Limited 5.7L

    To be exactly it is a 2010 Grand Cherokee Limited Standard plus Customer Preferred Package 25H. This package includes 5.7L Hemi, Quadra-Trac II 4X4 system and several other things.

    - The window sticker says the 4X4 system on this vehical is Quadra-Trac II (which is part of the Customer Preferred Package 25H)

    - However the badge on the center console (between the gear shifter and the cup holders) reads Quadra-Drive II

    Quadra-Trac II and Quadra-Drive II are different 4X4 systems. I contacted the dealer as well as Jeep support but none of them can tell if the 4X4 on my vehical is indeed Quadra-Trac II or Quadra-Drive II.

    Is there an easy way to figure out whether it's Quadra-Trac II or Quadra-Drive II?

    Thanks,
    OIIIIIIIO
  • rshollandrsholland Posts: 19,658
    Maybe in the serial #? They often denote what drivetrain the vehicle has. You may have to go to the dealer to get it translated, unless it's somewhere in the owner's manual?

    Also, this site focuses on Chrysler products. Maybe they can help.

    http://www.allpar.com/

    Bob
  • almost all the information you will ever want to know about AWD and 4WD systems in small SUV/sedan platforms

    http://www.youtube.com/watch?v=ooQRxlChvMw

    cliff notes

    Honda CRV--- basically FWD, 4WD is just badge
    system relies on loss of traction to give some power to rear wheels and as you can see it gives very little so you would be better of with FWD vehicle with LSD than this

    Toyota Highlander --- no better than CRV, i suspect Rav-4 to have same/similar system
    about same process as CRV

    Subaru, symmetrical AWD all wheels get same amount of power/torque all the time

    VW - as you can see is also really good but not the best

    these vehicles were tested because manufacturers claimed full time 4WD or AWD.

    Acura SH-AWD is 3.5WD system where front get ~70% of power until slip is detected.

    Infiniti ATTESA - all models that have "x" in the end of the model name. "part time AWD" when driving only rear wheels get power, if torque loss at the wheel is detected (no slip yet) and sends power to front also. capable of up to 50:50 distribution. this is a very short version as the system is very complicated and probably the best you can get for street performance. Inifiniti vehicles are not intended to be used off road

    Nissan Intelligent AWD, Rogue for example provides 50-50 power split between front and rear wheels when accelerating from a stop. As the vehicle gets to cruising speed, that basis will revert back to full front wheel drive . I-AWD predicts potential problems and automatically transfers to a 70-30 bias when taking moderate to sharp turns. The system still reacts to traction loss and sends power where needed, but it’s improved over the standard brainless AWD systems. Now rather than waiting until a traction loss and adapting as quickly as possible, the vehicle is already prepared by having that power bias already set
  • ateixeiraateixeira Posts: 72,587
    FWIW Toyota has been installing an upgraded system and it's trickling in to more models. The 2011 AWD Sienna's system is better than the 2010's, for instance.

    Cool vid, though. Even the most basic Forester is able to send enough power to either axle to climb that ramp.
  • kdshapirokdshapiro Posts: 5,751
    Subaru, symmetrical AWD all wheels get same amount of power/torque all the time

    This has been the topic of hundreds of posts. Bottom line, the statement as a generalization is not true, but exactly what happens under the covers can't seem to agreed on. At least reference STI with the VCCD? Probably don't have the acronym correct.
  • on the first page about the 4WD/AWD classification, should we have one more type called auto-AWD or part-time AWD ? During normal condition it is 2WD (mostly front), it transfers power to the other axle only after slippery. It is different from full-time AWD since full-time AWD at least has 5-10% power to the other axle. Examples are CR-V, Pilot, RAV4,...
  • Most Truck are part-time 4WD. 4W H or 4W L can not be used in dry/wet pavement.

    We got lots of snow in New England area. But they put sand/salt pretty fast on highway, so during/after snow, it is wet or with little bit snow or ice. How do we drive a truck on this road? Do we use 2WD, or 4WD H? If 2WD, then what is the advantage of truck. I saw lots of truck on highway that are running fast during/after snow. While small cars with 2WD just follow the traffic slowly.
  • I have a 2004 suburban 1500 LS 4WD. I bought it with 40K & had to have the transfer case rebuilt at 54K. The 4WD has been used maybe 10 times in 4H on snow only & never driven above 40-45mph. The vehicle now has 113K & I was going up the mountain & had it in 4H when I heard some metal on metal noise & a loud clunk come from either underneath or the front. I took it out of 4H & left it out. Put it in 4H while stopped & drove it 25ft with same metal noise. Ran in 2WD until got home when I tried to put it back into 4H and now the electronic switch defaults to AWD & won't actually engage the front. Put it up on racks, transfer case was a little low on fluid but no metal shaving or debris. When i try to change it to anything other than 2WD the electronic switch just blinks then defaults to AWD & front will not spin. The transfer case was serviced as scheduled at 90K. My question: Is there a common problem with this year of suburban & the 4WD or is it limited to mine. Rebuilding the transfer case twice seems ridiculous considering the minimal light use. Any thoughts?
  • wwestwwest Posts: 10,706
    "..Subaru, symmetrical AWD all wheels get the same amount of power/torque all the time..."

    I sincerely doubt that to be a TRUE statement. No automative design engineer, given a choice, would wish to allow a high level of torque to remain on the front wheels in a turn, tight turn, or even an accelerating turn, certainly not a tight accelerating turn.

    The tighter the turn or the harder acceleration being used in a turn the lower the torque delivered to the front should be.

    "..I-AWD predicts potential problems and automatically transfers to a 70-30 bias when making moderate to sharp turns..."

    I-AWD = Intelligent AWD...??

    NOT...!!

    Simply PRE-EMPTIVE, NOT inteligent by any means.

    An IDEAL, "INTELLIGENT" AWD system would incrementally reduce the engine torque to the front wheels as the turn becomes tighter and/or the acceleration level increases, all the way to 0-100 if need be.

    Since that cannot be easily done with ANY base FWD vehicle the best that can be done to help alleviate, reduce, the potential for loss of directional control in these instances is to partially REDUCE the level of engine drive torque to the front wheels.

    That's where the advantage goes, DRAMATICALLY so, to the SH-AWD system. The rear "diff'l" is over-driven by 7%(?) so the F/R torque distribution can be as high as 30/70.
  • wwestwwest Posts: 10,706
    "..if torque loss at the wheel is detected (no slip yet).."

    To my knowledge, limited as well as it might be, no such system is available. Torque loss at the wheel is ALWAYS the result of wheelspin/slip.

    That's why we now have so many PRE-EMPTIVE F/awd systems in the marketplace today. There is as yet no method of predicting that wheelspin/slip will occur as a result of application of too much engine torque for conditions. So manufacturers are choosing the alternative, most especially F/awd vehicle manufacturers.

    The alternative is to PRE-EMPTIVELY remove engine drive torque away from the front wheels at the times when wheelspin/slip is most likely to occur. That is: During acceleration from a stop, low speed acceleration, or when turning wherein directional control is often threatened due to wheelspin/slip. In a tight turn or accelerating turn due to the buildup of centrifical forces much of the front tire's roadbed cohesion will needed for lateral stability, directional control.

    Today's FWD vehicles, and in the past many F/awd vehicles, compensated for this problem via quickly dethrottling the engine should the VSC's yaw detection and stearing wheel position indicate that the front tires's traction coefficient would/might be exceeded.

    But there is a serious short-coming, design flaw, in these new pre-emptive F/awd systems. They engage the rear drive capability, in effect locking the center "diff'l", even on the roadbed surfaces with the highest tractive coefficient possible.

    That, of course, except when by pure happenstance the roadbed actually is slippery, results in a dramatically serious level of driveline windup and/or tire scrubbing. Stress and HEATING of the driveline components and early tire tread wear out/off.

    Look at the history of these new pre-emptive F/awd systems, the Ford Escape being one of the earlier adopters. "Pre-mature" PTO and rear diff'l drive clutch failures are/were the rule of the day. And the Acura MDX VTM-4 system, transaxle lockup failures as a result.

    The rumor is that the new 2011 Ford Explorer's F/awd system (no, that isn't a typo the new Explorer is a base FWD vehicle) uses water cooling for the PTO and the rear diff'l in an effort to abate the premature failures of these components resulting from the coupling of front and rear wheels even on high tractive conditions.

    Why not have a simple switch that the driver can use that enables the rear driving torque ONLY in known slippery conditions...?
  • wwestwwest Posts: 10,706
    Pine, "Soft", wood 1X2's inserted through all four wheels in such a way as to prevent wheel rotation absent breaking the 1X2's. My F/awd 2001 RX300 would break the front 1x2's with the slightest application of gas with the rear 1x2's remaining completely intact.
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