Per the owners manual this is completely normal.

 

Can somebody please clarify whether the torque split is 50:50 or if it varies? I know the ACD does not change the torque split but in this Tech Article which was referenced the article mentions two torque splits, 30:70 and 50:50 front:rear. In a few of the other articles it mentions the base split is 50:50 (meaning it can change from the base split?). Does that mean then that the ACD unit is auto-controlling the torque split between 50:50 through 30:70 as it sees fit? at the same time it is "(un)locking" the differential as well?

 

If the clutch pack isn't engaged it's 50:50 at all times. If the clutch pack is engaged to any degree, it varies. The torque is not magically shipped off to one end of the car or the other at that point, i.e. the car/diff doesn't "decide" where to send torque. It is split depending on traction levels at the wheels (to a degree set by the force clamping the clutch pack together).

 

Take a look at the tech article you saw in there. Sections 2.1 and 2.2 explain why there's mention of a 30:70 and 50:50 split.

Basically, what it says is that a 30:70 split provides emphasis on maximizing cornering. 50:50 is for when you want to emphasis on traction and stability. Therefore, they decided to go with a 50:50 split.

The split numbers they are referring to is the base split of the gears. I.e. the teeth on the center diff gears provide a 50:50 split.

I hope this makes more sense for you.

Terry S

 

Both of the last 2 posts -- -- I agree.

EVOlutionary

 

Can I ask....

So then the ACD is in 'full lock' it's at 50:50 F:R.

When the ACD is 'free' (eg when initiating a turn) does the car become for that instant a FF or FR?

 

no

 

I think I worked it out...

In locked mode it becomes 50:50

In free mode it becomes an open diff - the torque goes to where ever it needs to go eg to the front/rear wheel pairs are free to spin independently (since the front tyres have more distance to travel than the rears)..... the rear diff looks after the L & R rear torque split.

So it's always AWD - just distributed differently.... never FF or FR for an instance unless you have both rear wheels off the ground or something

 

Not really. Think about it like this - when the ACD is open torque is sent to the front and rear at a 50:50 ratio. When it is locked, more than 50% of the torque can be applied through whichever end has more traction. . .

Just like an open rear diff on a RWD truck is not Left or Right drive, an open center diff on the EVO does not really make the car front or rear drive.

 

Trying to get my head around this....

So when the ACD is open (eg turning), the diff is free to function, so it allows the front and rear wheels to spin at individual rates - why is the torque that fixed at 50:50?

When the ACD is locked, doesnt it suppress the diff function and therefore not allow the rear and front wheels to spin independently hence a 50:50 torque distribution?

http://www.driven2modify.com/showthread.php?t=5436

hmmm confused!

 

ok going to read the mitsu scientific publications (from that link above) about the ACD tomorrow to get my head around it....

 

I think it's just that those convenient little front/rear ratios and percentages don't really apply here. When it's open during normal driving, there is no wheel spinning or intelligent power distribution going on. When it locks up after sensing a bit of spin, it's just locked and there is no intelligent power distribution going on either...although I think it is safe to say there is a 50:50 power distribution during this time.

Just my opinion, and I could be wrong.

 

You guys are getting this totally backwards.

When the clutch pack is not engaged, you have an open differential as your center differential. Go to www.howstuffworks.com and read about open differentials. An open differential geared to 50/50 like ours is will ALWAYS have equal amounts of torque on each side of the diff no matter the difference in wheels speeds. It's all about how gears work. You are confusing wheel speed with torque I think, and they are not the same thing.

Weld the center diff together so you have a solid axle between the front and rear, ie, there is no center diff OR look at it like the clutch packs have locked together (both scenarios are the same thing). Where is the torque going to go if the front is on tarmac and the rear is on ice? All of it will go to the front, because THAT IS WHERE THE GRIP IS. If the situation is reversed, all the torque will go to the rear. While the front wheels and the rear wheels are spinning at the same speed in this scenario and it "LOOKS" like the end on ice is doing something, really the end with the grip is doing all the work. There is no computer moving the torque around. It's all mechanics/physics. Get it?

 

Here is another way to think about it:
If the rear wheels are on a low traction surface with the diff open, whatever little bit of torque is put to the ground in the rear will also be evenly applied at the front. For example, if the car can only put down 100 ft# due to low traction in the rear, it will put down an even 100ft# to the front also.

If the rear wheels are off the ground (zero traction) with the closed diff, ALL of the torque (100%) will be put to the ground by the front tires, at least up to the clamping limit of the diff.

In reality, though, the car never exists in either of these states. It is always shifting and moving around as wheels gain and lose traction and the diff locks and unlocks. . .

EVOlutionary

 

so....

free ACD = open diff
torque is 50:50
but the diff allows the wheels to spin at different rates (like a LSD)
so in cornering allows the front wheels to travel more than the rears


locked ACD = supressed open diff function = in equivalent like having no diff
torque still 50:50
so hard braking/accelerating adds stability by varying the degree of 'freeness' of the ACD to balance fulltime AWD stability vs allowing the wheels to spin at different rates....