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  1. #11
    Senior Member Lundefaret's Avatar
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    Quote Originally Posted by itix View Post
    This makes me even more confused... What would then be a passive center diff? To me it sounds like a standard limited slip diff pretty much.
    Hello again Itix

    A passive, or mechanical, centre diff is for example a "normal" LSD diff which relies on real time speed differences between the shafts on each side of the clutch plates to generate friction to get the diff to lock.
    In a diff like this you adjust the locking mainly by the number and type of friction plates, and ramp angle (on throttle and off throttle.) A steeper ramp angle will generate a higher treshold for the diff to lock, and vica verca.

    On an active diff the locking of the diff is not relied on real time shaft speed differences, but by sensor generated input. So you can program the diff to lock/open when you want, no matter differences in shaft speed etc.

    In its simples form it would kind of be like programmable ramp angles and preload.

    If you take a "simple" road car active diff system like the electronically opperated BMW Xdrive, you could theoretically send all power too one wheel (three active diffs, front, centre and rear). That system is working with electroniv servo motors opening and closing the clutch plates.
    A rally active diff works in much the same way, but by using hydraulics instead of electronics to do the locking/opening.
    (Edit: BMW Xdrive might not be the best example according to Mirek)

    (BTW, its open for any engineer/expert to correct me if Im wrong.)

    Edit 1: Added "preload" to the programmable example.
    Last edited by Lundefaret; 7th December 2016 at 10:33.
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  2. #12
    Armchair General Mirek's Avatar
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    X-Drive itself can not send 100% of torque on one wheel because it's an electo-magnetic center clutch. Only some cars which have active DPC rear diff can distribute 100% on either one of rear wheels. To my knowledge BMW doesn't use torque vectoring on front axle.
    Stupid is as stupid does. Forrest Gump

  3. Likes: itix (20th December 2016)
  4. #13
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    You are right Mirek, I know that the Mitsubishi 2005 has some difference comparing to the other cars but can't remember what exactly was. Thanks for the correction!

  5. #14
    Senior Member itix's Avatar
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    Took me a while to get around to answering to this one. Sorry about that.

    So basically, unless I'm retarded, the old active WRC diffs according to Warmbold, Mirek and Ole-Martin were basically what I thought they were. Actively lockable diffs (I had read the Warmbold article before but forgotten about it).

    The diffs as explained by all three of you would mean that power (or torque if I'm allowed to be pedantic) gets sent to the wheels which have grip. They weren't torque vectoring diffs like the rear diff on newer Evos, some Lexuses etc etc. A torque vectoring diff basically locks a clutch pack with a positive or negative gear ratio on it to force one wheel to turn faster than the other (or one axle in the case of a center differential... Although I have yet to hear of a torque vectoring center differential). The Mitsubishi AYC system is a well documented example of this. Some diffs use planetary gears to achieve this (sort of like in an automatic gearbox) although I will admit I haven't fully grasped how yet.

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    Mitsubishi acd (active center diff) and ayc rear diff (active yaw control) have both clutch packs which activated hydraulically and planetary gears with crown and pinion.
    Mitsubishi diffs are active diffs.
    torque vectoring diffs we use to name(as same Ford names) the plated clutch of focus rs ie.

  7. #16
    Senior Member itix's Avatar
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    The Mitsubishi ones work differently from one another. Basically the center diff locks up (like having no diff at all if you don't factor in clutch slip etc) and the rear one locks up two different gear sets that send torque to the opposite drive shaft forcefully (through increase and decrease in speed on the other drive shaft).

    It is true that the Evo 10 (all models) have planetary gears, but the old ones (European and Japanese models) had just a straight gear set with clutch packs and torque distribution level is controlled via clutch pressure.

  8. #17
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    Active diff in that case simply controls the amount of lock between the front and rear axle. Depends on speed difference between those two axles (slip) or throttle position, speed, brake position, etc, etc. It's relatively simple, just mapping of it it's what makes the difference.

  9. Likes: itix (21st December 2016)
  10. #18
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    Quote Originally Posted by itix View Post
    The Mitsubishi ones work differently from one another..
    no, all evos work the same, with very little differences.I talk about Evos from 2001 (evo 7) till evo X.

    Quote Originally Posted by itix View Post
    and the rear one locks up two different gear .
    no there is not 2 different gears.

    Quote Originally Posted by itix View Post
    It is true that the Evo 10 (all models) have planetary gears, but the old ones (European and Japanese models) had just a straight gear set with clutch packs and torque distribution level is controlled via clutch pressure.
    all evos,whatever domestic market they have been build,have at center and rear diff clutch packs AND planetary gears with crown and pinion. Except some versions,usdm and rs versions that have plated limited slip diffs from factory at rear.

  11. #19
    Senior Member itix's Avatar
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    Quote Originally Posted by br21 View Post
    Active diff in that case simply controls the amount of lock between the front and rear axle. Depends on speed difference between those two axles (slip) or throttle position, speed, brake position, etc, etc. It's relatively simple, just mapping of it it's what makes the difference.
    Like I thought all along. People started saying that was not an active diff and that started making me confused. Thanks!

  12. #20
    Senior Member itix's Avatar
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    Quote Originally Posted by dimviii View Post
    no, all evos work the same, with very little differences.I talk about Evos from 2001 (evo 7) till evo X.
    I mean that the ACD and AYC diff work differently from each other.

    The ACD simply lock up with a clutch pack whereas the AYC have two different clutch packs with different function (to send torque either to the right wheel or the left one).

    Quote Originally Posted by dimviii View Post
    no there is not 2 different gears.
    At least in the old AYC diff there was two separate gear ratios, separate to the pinion and crown plus worm gears and whatever else all the components are called. The separate gear set was spinning freely until you lock either of up the respective clutch packs forcing more torque to one wheel or the other. I don't know the details of the new planetary gear AYC's but yes, the principle is the same. At least the 7 had the old type AYC... I'm pretty sure the 8 and maybe the 9 too had them. If the Evo isn't spec-ed as S-AWC it doesn't have the planetary model (I'm talking about European models now... US ones were never fitted with them for some reason until the Evo X which has the planetary gear AYC).

    Quote Originally Posted by dimviii View Post
    all evos,whatever domestic market they have been build,have at center and rear diff clutch packs AND planetary gears with crown and pinion. Except some versions,usdm and rs versions that have plated limited slip diffs from factory at rear.
    I have never seen or heard of a planetary gear center diff. Planetary gear sets take up quite a lot of space and the center diff plus transfer case has not changed design on the outside as far as I'm aware.

    I'd happily change my mind if I'm proven wrong though.
    Last edited by itix; 21st December 2016 at 05:15.

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