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Crowd sourced research: Active differentials

Discussion in 'Microblogs' started by Diamondback, May 31, 2020.

  1. Diamondback

    Diamondback
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    Hey guys,

    I already hinted at it with the 0.19 release and I'd like to ask you all to share your knowledge about and personal experience with active differentials. (active meaning that they are controlled by some software rather than being fully hardware based)

    Electronically controlled differentials are a pretty wide field, there's many different systems and as I have learned over the past years, assuming to know all the quirks of modern cars just doesn't work out. Some manufacturer will always do something weird (and possibly wonderful) that you didn't know about before.

    So what I'd like to do with your help is to gather a nice list of active differential types and in which cars they are used.

    Please note: Unfortunately it's not of much use to me to just list a car and say that it got such a differential, what I'm after is more technical details, control concepts, weird ideas from the OEMs etc.

    Let me give you an example:
    This is basically a clutch based LSD, but the clutch is electronically controlled. Thefore, what the diff can do is locking itself to minimize overly high wheelspin on one side of the diff. It has no means of actively controlling the torque output independently on both sides. Used for example in M3/4 cars. (https://www.bmw-m.com/en/topics/magazine-article-pool/the-active-m-differential.html)

    I'm interested in solutions from all manufacturers, all times and not restricted to road cars. If you happen to have detailed information about WRC active center diffs or other crazy motorsport things, feel free to mention this as well. :)
     
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  2. Justy4WDTURBO

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    https://www.beamng.com/resources/active-differential-pack-for-pessima.1897/

    https://repository.lboro.ac.uk/articles/Vehicle_handling_control_using_active_differentials/9219482

    http://www.autolatest.com/auto-editorial/active-differential-of-the-porsche-959

    http://awdwiki.com

    Go nuts, Diamondback. I love ridiculously complex powertrains like the ADP for the Pessima has. SAE also has a bunch of papers regarding active differentials but they're behind a paywall. (hint: try sci-hub or libgen.io)

    Speaking of active differentials, have you reached out a company like Haldex in Sweden?
     
    #2 Justy4WDTURBO, May 31, 2020
    Last edited: May 31, 2020
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  3. YellowRusty

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    I don't have any personal experience with it, but apparently the electronic differential available on 2014-present Jaguar F-types equipped with the V8 can overheat and disable themselves, particularly if it has been in constant use (say, the driver is doing doughnuts). When that happens, the system shuts down, opening the differential, and the car suddenly gets grip. A warning is also displayed on the dashboard. The vehicle can still be driven as normal, and the electronic differential will come back online after it has cooled down.
     
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  4. Car_Genius

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    It takes a lot to overheat e-diffs in most high-performance cars.
     
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  5. ORIGIN4LFluffy

    ORIGIN4LFluffy
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    I'm not quire sure how detailed you want to be about the specific ways of engagement for active differentials (like whether it uses a computer-controlled cam gear or piston or whatever), but I have found some interesting things about the GM eLSD and its methods.

    The eLSD finds its way into Corvettes, Camaros, and Cadillac V-series cars. My personal car has it equipped and it's a pretty neat system. Changes aggression based on which drive mode the vehicle is in, which isn't extraordinary itself, and if you really pay attention, you can feel when it locks up. Does good donuts and burnouts too.
    TL;DW: GM literally just has a piston set up to press on the clutch pack to lock it up. The computer can account for temperature of tires, the weather, etc. Higher trim Camaros and Corvettes even have a page in the Driver Information Center that shows the slip percentage.

    - This guy explains it pretty simply
    - This is the C8 Corvette hype video specifically about the eLSD, and it may be advertisement, but it's still kinda neat

    https://gm-techlink.com/?p=11291 - This one talks more about the pathway through the computer modules and the various factors affecting how it behaves
     
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  6. The Gas Station

    The Gas Station
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    Hi! I hope this information helps:
    I've had the opportunity to drive an Isuzu D-max owned by a friend. When we were off-road, it turned out to be a pretty capable machine. It has a 4wd transfer case, and a rear "electronic differential". Technically speaking, it's not really the diff that 'limits the slip', but the brakes. It works using wheelspin data from sensors, and I believe it looks for a difference in wheelspin speeds (from my experience it has to be a big difference- pretty much one wheel needs to be above the ground). Then, it stops the spinning wheel with the brakes, so that power goes to the other wheel. I don't know how exactly the sensors work or what is the threshold (and a quick search on google yielded no results). However, I know many cars use similar systems, because they are much cheaper than a proper LSD, and give decent results.
     
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  7. charl

    charl
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    I have a 2000 Subaru Forester which is my car since about a year ago (I'm 16 but quite a car nerd) and the AWD system is functional.
    The All-Wheel-Drive is computer controlled, and if the system fails it latches a solenoid to only deliver power to the front wheels through an open differential. I have not had this happen before but if it does there is an indicator light on the dash saying "FWD". Power goes to the rear through a normal driveshaft which is split near the rear axle with a computer controlled system which I think uses an electric clutch mechanism and some simple fluid coupling. The system senses the speed of each wheel and if one wheel is moving at a lower speed than the others it will close a clutch to that wheel, and if it's at a higher speed to the others, it closes the clutch to the wheels opposite of it. The rear wheels can be computer-controlled individually with varying amounts of grip whereas in the front I think it's just an open differential that can be locked automatically via the computer system. I will update this post if I go peering under my car or on the internet and find more information
     
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  8. btcb48

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    There's a fairly thorough non-primary-source forum post on Mitsubishi's active center diff here, including the differences in the driver selectable modes though there's some disagreement on which mode locks the most and when in non-acceleration conditions.

    Unfortunately, Mitsubishi has scrubbed most of their old resources and doesn't list out the control logic in their more recent official descriptions. Maybe try Subaru's.

    That picture with the 180 degree corner lists some conditions that match up with the 2nd half of the WRC YouTube vid here.

    Also more discussing ACD's surface modes here and there.
     
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  9. Krolfox

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    In addition to the ACD @btcb48 mentioned, Mitsubishi have AYC (active yaw control) in a range of their AWD cars, most notably of course Evolution GSR models since the Evo IV in 1996.

    To qoute their website:

    "AYC(Active Yaw Control) is the system that controls the driving and braking forces between the left and right wheels by judging accurately both driver operation and vehicle behavior based on information from steering angle, yaw rate, driving torque, braking pressure and wheel speed [...]"

    (according to another source the range of data utilized is: Longitudinal acc. sensor, front and rear lateral acc. sensors, steering angle sensor, wheel rotational speed sensor, throttle opening sensor)

    The sensor data is processed and utilized to drive the electrohydraulic actuator which engages the clutches in the diff.

     
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  10. 8coibaf

    8coibaf
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    Ford Focus RS rear differential, basically a locked differential with a clutch for each output driveshaft, if both clutches are opened no torque is given to the wheels, each clutch can be closed progressively to regulate the torque on each wheel, it is possible that 100% of the torque input is transferred to a single wheel by leaving one clutch open. I can see this kind of differential used on the Cherrier to help implement a "Drift Mode"


    Added a small working example that may be useful
     
    #10 8coibaf, Jun 16, 2020
    Last edited: Jun 18, 2020
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  11. Mundy64

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    Yes! Please add this type of traction control, I really want to make some modern 4x4's in the game (opens up possibilities such as old vs new 4WD's), and this is exactally what we need to do that! Also i know this isn't really the right section, but could you guys please add either a modern 4x4, similar to a Land Cruiser 200 series or a Y62 Nissan Patrol, or add independant rear suspension to the d-series/roamer? I would really like to see how the fully independent suspension (IFS and IRS) holds up against solid axles when doing some serious offroading.
     
  12. astonv8

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    So I’m not to sure on the actual mechanic side of it but I have a lot of experience with how they feel and basically in something like a modern rally car it really try’s to pull the car towards the apex of the turn, it almost feels like torque vectoring but I’m pretty sure it’s the actual diff doing stuff like that. On more performance based roads cars you can feel them work a lot in weight transfer like you will feel the inside wheel spin a bit then it locks up and suddenly you can slide but if you start getting a ton of angle it tends to try and keep the car stable. It doesn’t really cut power but you can feel something going on. I know my mustangs diff is active and I’ll mess around with it more tomorrow to see if I can really pinpoint some stuff.
     
  13. Brett3801

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    i have a AWD vehical with Active diff front and rear, basicly my system uses brakes to control wheel slip off road E.g. mud sand etc, It stop Open diff from sending full power to a wheel with no traction sending that power back to the wheel that dose have traction.

    It used it wheel speed sensors to tell if one wheel is spining to Fast comapred to others

    I have a Holden Adventura with the V6
    They use breakes to control slip etc no fancy diffs
    See PDF for and overview on the system
    crosstracflyer0.pdf
     

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  14. ItsTheLittleAcura!

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    The same principle is used by Acura's SH-AWD. I'd like to see SH-AWD style torque vectoring in the game.
     
  15. OAK Petrolhead

    OAK Petrolhead
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    On Isuzu D-max uses Traction Control to act as a limited-slip diff but It doesn't work as good as Toyota Hilux which has an advance traction control called A-TRC (which available on many 4x4 Toyota) it brakes slipping wheels so hard and send power to the opposite wheel phenomenally. :)
     
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  16. rottenfitzy

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    IIRC this sounds like a normal traction/stability control system, and not an active diff.

    If you want to get scientific papers for free, just directly contact the authors of it. They don’t get paid money from the paywall, so they’re just as happy to give it to you for free in a lot of circumstances.
     
  17. default0.0player

    default0.0player
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  18. 2010rrsupercharg

    2010rrsupercharg
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    I think a lot of active differentials are very similar the biggest differences are the tuning (when they lock and how much locking force is generated).

    You have pretty much got locking active differential, which are similar to mechanical LSDs but use electronically controlled clutches to lock at variable level of slip and at variable level of strength. These diffs can transfer more torque to the wheel with the most traction, but basically they are just limiting the amount of of slip the unloaded spinning wheel has. These are commonly referred to as E-Diffs or Electronic-Differentials. That's the type of diff the M3/M4 has. Its also what you would find in a wide range of other cars. You will find them on the back of Grand Cherokee SRTs, Range Rovers, Camaros, Ferraris, and bunch of other cars. This set up makes a lot of sense on high HP cars because you can keep wheel speed relatively similar maximizing traction. For example the 640 HP 2016 Cadillac CTS-V has an E-Diff can go from being completely open to locking with up to about 1500 nm of force depending on the situation, to help prevent the lose of traction that comes from wheel slip, making it actually very controllable for a RWD car. Compared to torque vectoring diffs which can independently adjust torque and wheel speed at each wheel. Car and Driver has an excellent article on them right here (https://www.caranddriver.com/featur...-we-put-torque-vectoring-to-the-test-feature/). You can also find them on BMWs (the X5 M) for example and the back end of a lot of AWD vehicles like Acuras, Audis and strangly the Chery Traverse and Honda Pilot. You can also find them on the RWD Lexus RC-F and GS-F. But those are the two basic types of active rear differentials.
    --- Post updated ---
    When it comes to active center differentials the most common kind isn't actually a differential at all, its a multiplate clutch pack, which you can find on everything from a 95 Explorer to latest supercars like the Audi R8 as well as the new M5s. Those examples are all RWD biased meaning that primary drive goes to the back wheels and there is an electronically controlled clutch pack which can progressively lock to make it more AWD, or 4WD if it locks completely. So you will find them on certain versions of all the half ton trucks (the ones with 4WD auto anyways). The nominal torque split ranges from 100 rear to 50/50%. These systems can not create a front biased torque split. But as the clutch locks up the actual torque split becomes variable, dependant on traction. So you have a system that can practically range from 100% rear to 100% front depending on traction,. Butthe rear axle will either spin faster or the front and rear axles with spin at the same speed, the front axle will never spin faster than the back. I think this is why its used in so many performance AWD systems, like GTRs, Porsches, and both the E63 AMG and M5. FWD based AWD systems work the same but backwards. The better versions of these systems are smart enough to transition from 2WD to AWD before you lose traction and can provide better traction than full time AWD systems. But they can also be way worse as well, if the clutch pack is to weak and not quick enough to engage. Personally I'd really like to see this type of center diff implemented in Beamng drive for the Roamer. Both GM an Ford full sized SUVs used this for there auto 4WD systems.
     
    #18 2010rrsupercharg, Sep 21, 2020
    Last edited: Sep 21, 2020
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