I just switched from EVO 8 to EVO 9. 9 has the LSD & ACD. I noticed a strange driving characteristic or behaviour with the new car that was not there on the EVO 8.

Assume you are crusing on a straight road. Ahead is a long constant radious bend in the road. Once you turn the steering wheel, holding it in the same position would take you around the bend. However, on the EVO 9, once I had my steering angle for the entire curve I have to readjust it if I either apply more throttle or get off the throttle. If I apply throttle, the car ends up wanting to go straight, so I need to compensate with the steering wheel (just a tiny bit). If I let off the throttle, the car wants to turn into the turn and I have to compensate again with the steering. This is a very weary subtle feeling that I would not want to experience at higher speed (kind of like a twich). Could this be the ACD or LSD in action even when miles away from the car's actual limits?

I had a FWD car with LSD and it did not have that behaviour. I can tell you definitely what it is NOT:
- not oversteer or understeer,
- does not feel like an alignment issue
- it is not a weight trasfer characteristic
- it is not new tire break in as they are the ones I trasfered from my 8.

Changing ACD setting makes no difference. It feels more like something mechanical is happening, like something is steering the rear wheels for me...

Note that I did not WOT it around the bend. This was just cruising @ 50mph around 3K rpm and just applying moderate throttle in 5th and then easing off before full boost kicks in. I have 40 miles on the odomoter so I have not experimented with what happens at WOT and full boost.

So, would this be ACD and or LSD behavior or should I get my new car checked out?

 

Sounds a bit twitchy. I would have said AYC, since you are talking about the rear wheels, but we don't get those anyway...

I have a standard 8, but I've driven one with a LSD and I can't say that twitchy behavior you experienced was exhibited. But, I haven't driven one with ACD, so I dunno about that.

 

I'm not sure either, but I do know that the ACD kicks in while turning.

 

dunno what it could be, i had an evo 8 with acd, and now a 9 with acd, and both car handle great, i never experienced that kind of behavior u are discribing here, both car handle great at the limit, very predictable and smooth. Like warrtalon said the acd kicks in while turning, it uses a g-sensor in the abs module and other inputs.

 

Hmmmmm...Have not noticed that on mine....but next time i drive i will look for it.

 

Yeah, I was not going fast enough to produce any G's on the bends and can reproduce this behavior easily... When I picked up the car it had 4 miles on it, so it is not like someone abused it during test drives or something.... very strange. I'll have try another car and see if it is the same.

Thanks for your inputs.

 

Ok there has to be a scientific explanation...lets rationalize about how the system works...bear in mind i have no previous experience with this, but if it what i say makes sense ill be amazed as much as you are!

so, what we know is ACD transfers the torque front and rear. We also kno from some Sport Compact Car test of the 2005 evo w/acd vs a 2005 STi w/ DCCD that the evo behaves more like a FWD under low torque aka a little bit of throttle.

so maybe whats happening is that when you have your foot off the gas, but in gear, the engine braking "negative torque" gets transferred to inside front wheel via the front LSD, causing it to slow, making the car rotate in more.

then when you apply some gas, there is "positive torque" transferred to the outside front wheel BUT doesn't yet transfer to the rear, causing the car to not turn as fast and showing a bit of FWD understeer effect!!!

wow that even impressed me, what do you think?? dont hesitate to shoot my theory down

 

Why would it ever tranfer more engine braking torque to the inside front wheel?

 

actually the does control front/rear torque distribution...

quote from your link

"If the front wheels are spinning faster than the rear wheels, then the ACD begins to lock the clutches up. If the amount of force exerted by the front wheels is less than the amount the clutches resist, then the slip is stopped and both front and rear spin at the same speed. However, if the force the clutches can resist is less than the force exerted by the slipping set of wheels, then the wheels will slip, but only by how much remaining force the slipping wheels overpowered the clutches with. (1) (9)"

re-read section I-B

second i dunno, but if the front lsd's job is to spin outside wheel faster in a turn while applying gas(torque), could it possibly have the opposite effect when there is no torque and you are engine braking?

 

No it doesn't.

First sentence:

 

All the ACD does is control the speed at which the center diff locks/open depending on a variety of inputs. It does NOT work like Subaru's DCCD system, which, IIRC, actually does control torque distribution from front to rear. The torque distribution in an Evo is always 50/50.

 

so then, what would be the function of the ACD? if not to adjust torque split front/rear it certainly cant do side to side

 

Read my post right before yours.

 

I edited out my statement about torque distribution. I was wrong. Strictly speaking, I think it DOES control torque distribution.

Imagine that the front tires are on a theoretical surface with a coefficient of friction of zero (no traction at all) and the rears are in sand. If the differential is completely open, it must send equal torque to the front and rear. If we ignore the effects of the moment of inertia of the wheels, there will be no torque transferred to the front wheels (refer to Newton's 3rd law - you can't push on something if there is nothing to push back). Consequently the rear tires will receive no torque, so you're stuck.

Now consider that the ACD locks up the center diff. Now the front and rear tires must spin at the same speed, which forces the rears to receive ALL of the torque.

I'm not saying this is exactly how the ACD works, but it shows that the process of locking and unlocking the center diff does change the way torque is distributed.

 

quote from mitsubishi's own press release @ http://media.mitsubishi-motors.com/p...detail992.html

"The Active Center Differential incorporates an electronically controlled hydraulic multi-plate clutch. An ECU optimizes clutch cover clamp load for different driving conditions, regulating the differential limiting action between free (where torque is split equally between front and rear wheels) to locked states. The result is improved steering response together with better traction. ACD operation switches automatically between three modes - Tarmac / Gravel / Snow - to realize quicker control response for changes in road surface. A single ECU provides integrated management of both ACD and Super AYC components."

"locked states", means more torque forward or back