ACD questions.

2687 Views 4 Replies 4 Participants Last post by Warrtalon, Aug 2, 2005

Fourdoor

Discussion Starter · Jul 31, 2005

OK guys, I am new to the Active Center Differential and have some questions.

I know that it acts as an open differential with variable lock up controled by the ACD computer with 3 modes. When the emergency brake is pulled the ACD decouples the rear wheels completely leaving you with a 100/0 torque split front to rear. The other end of the spectrum would be fully locked up at 50/50 torque split.

Now before any newbies chime in that you can send have a 30/70 split or 0/100 split with a rear bias, let me just say up front that is not correct and in fact is impossible with our setup. I don't even dare ask this question on EVOm because I would have people arguing with me over that point for 10 pages and never get any useful information.

What I am wondering is how the different modes change the lock up characteristics of the ACD. I suspect that tarmac leaves you with an open diff most of the time unless it sees a reason to lock up or partially lock up the center diff, gravel is more likely to give you partial or full lockup, and snow is partially locked most of the time with full lock up part of the time. This is all speculation and I have no idea if it is close to the truth or not.

Does anyone know, or have a link to a good source of information about our setup?

Thanks,

Keith

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turbolarry

· #2 · Jul 31, 2005

Damn. That's a good question. I can't find sh!t as far as when full or partial lock up occurs in the different modes.

With all the sensors it looks like there's a lot of variables and a lot AYC-ECU control/programming.
http://www.lancerregister.com/faq_g04.php

... and then there's this;
http://www.mitsubishi-motors.co.za/lancer/Models/EVOVIII_2005/Lancer_perf.asp

"In Tarmac mode, AWC is tuned to fully extract Super AYC's potential to make the car more responsive on dry surfaces. Super AYC and ACD control is feed-forward compensated for driver inputs to realise better straight-line speed and feedback compensated for car behaviour to improve straight-line stability. The result is that car behaviour is more predictable and corresponds to the driver's intentions and expectations instantly."

More front bias...

"In Gravel mode, AWC delivers the best balance between drive and steering traction - crucial on wet surfaces. Compared with Tarmac mode, Super AYC and ACD feed-back gain is increased to improve traction and stability, while Super AYC provides less turning assist, to deliver cornering characteristics appropriate on wet surfaces."

More rear bias...

"In Snow mode, AWC bias is tuned for greater stability and thus makes the vehicle more competitive over snow-covered surfaces. Super AYC and ACD control bias is tuned for greater stability than the Gravel mode, while Super AYC delivers an appropriate degree of turning assist."

More 50/50...

I'll keep looking.

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Fourdoor

Discussion Starter · #3 · Jul 31, 2005

If you notice, just about all of that info applies to cars with AYC as well as the ACD.... so most of the info will be different for the 05 and up Evolutions.

Keith

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ldstang50

· #4 · Aug 1, 2005

You guys are forgetting, our evo's never came with AYC, so any and all responses regarding or relating to AYC are irrelevant. Our's (later years) only had the ACD.
From my understanding of it from what I've read is in "snow mode" the diff is locked up to 50/50 thus equally distributing the power to all 4wheels. Gravel from what I understood was 60/40 and tarmac was 65/35. Thats right, our cars are front wheel bias. Makes you wonder why we are still able to oversteer doesn't it?
Car and driver did a really good test of the 05 MR vs the 05 Subbie and they talk about the ACD in the car and how our car is primarily FWD but yet it still oversteers where as the STi is primarily RWD and understeers.
I'll see if I can't find the article and post it up.
http://www.caranddriver.com/article.asp?section_id=15&article_id=9052&page_number=1

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Warrtalon

· #5 · Aug 2, 2005

ldstang50 said:
You guys are forgetting, our evo's never came with AYC, so any and all responses regarding or relating to AYC are irrelevant. Our's (later years) only had the ACD.
From my understanding of it from what I've read is in "snow mode" the diff is locked up to 50/50 thus equally distributing the power to all 4wheels. Gravel from what I understood was 60/40 and tarmac was 65/35. Thats right, our cars are front wheel bias. Makes you wonder why we are still able to oversteer doesn't it?
Car and driver did a really good test of the 05 MR vs the 05 Subbie and they talk about the ACD in the car and how our car is primarily FWD but yet it still oversteers where as the STi is primarily RWD and understeers.
I'll see if I can't find the article and post it up.
http://www.caranddriver.com/article.asp?section_id=15&article_id=9052&page_number=1

It's actually 50/50 all the time, but the different settings change the point at which the diff locks. It never actually changes the bias from 50/50, though.

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