[discogodfather]

In my never ending quest to understand AWD technology (and the mitsu AWC system) I have been reading and re-reading a combination of mitsu technical papers and JSAE (Japanese Society of Engineers) papers on active differential theory. It’s uncovered some very interesting information and I wanted to share some of the ideas / concepts.

One thing that keeps me awake at night (yes, I am a geek) is the mechanical limits of the ACD / AYC. Tuning masters have extracted hundreds of HP + out of the 4b11T engine and it seems no one is running a stock Evo. What effect does this added power have on the extremely complicated AWC system?

S-AWC uses three hydraulically actuated clutches (one for center diff control and the other two for rear diff control and torque vectoring). The ACD acts like a nanny ensuring front to rear power distribution is maintained at an optimal level (close to 50:50) while still allowing slip (in order to turn). The AYC system (rear diff) is primarily concerned with artificially inducing a yaw moment (felt by the driver as the phenomenon of oversteer / understeer). Both use clutches similar to what we have in a motorcycle wet clutch or the SST transmission.

Ask anyone who is into the SST tranny what the one of the big debates that has raged since 2007 and they will tell you it’s how much torque the clutches can hold. I have been consumed with a similar interest in how much torque the ACD and AYC clutches can hold. Theoretically, just like with any clutch, if the power max is exceeded it will slip. How does this affect the AWD system? Are we killing the effectiveness of the ACD and AYC by adding more power? Are we overcoming it’s performance capability? Is it dead weight at a certain power level?

So I have been looking for answers in the white papers and have come up with some surprising numbers as far as the AYC is concerned. There are a few engineering equations that describe how the system works in the papers, so I have used them as a starting point and tried to extrapolate some numbers we can all understand:

Old AYC (pre Evo X systems found on JDM and EDM Evo 4 to Evo 9) system:
Max torque of the clutches before slip = 590 foot pounds (800 Nm)
Average torque = 480 foot pounds (650 nm) approx.
S-AYC (Evo X) system:
Max torque of the clutches before slip = 885 foot pounds (1200 Nm)
Average torque = 625 foot pounds (850 nm) approx.

These numbers are calculated from a standing start on a split mu surface. It seems reaction time is a factor with the max coming at 1 second after hydraulic activation, which clues us into how fast the system can react. There is a wobble in the torque transfer initially before the max is achieved. The averages are my best guess at this point. Don't know if this is different in a dynamic (rolling with power at speed) situation.

You have to account for the fact that the power distribution between the front and rear wheels ( statically at 50:50 but moving around quite a bit based on slip) cuts the engine torque number in half theoretically most of the time.

It would seem that we are well within the bounds of what the system can do in terms of active differential control, meaning the system can be effective at very high powers, at least in terms of the AYC. Info on the ACD is much harder to find and I am going back in time on the JSAE papers into the (early nineties) to find more answers, anyone have any ideas??

A note on the calculations: these numbers might not translate well to direct comparison to engine torque), it’s very confusing to me right now. I think these equations predict Nm in the form of energy, like the Joule, rather than the torque function. If anyone knows how to convert these two, it would be helpful. This is an explanation from Wikipedia:
“In this very different usage the metre term represents the distance traveled or displacement in the direction of the force, and not the perpendicular distance from a fulcrum as it does when used to express torque.”

Some interesting notes:
1) The S-AYC actually has the ability to send more power to the right rear wheel (operated by the left clutch) than the left rear wheel (operated by the right clutch)!!! Is this NASCAR, lol! The factor is 2.22x for the LH clutch and 1.8x for the RH clutch). I wonder if this could be measured in a skidpad test in two different directions??

2) The AYC is controlled mostly by a physics based model and not influenced heavily by the various sensors. Engine load (throttle opening), WSS, lateral G, longitudinal G, all influence the operation but not nearly as important as the steering angle sensor. The steering angle is referenced to tables that are based on the physics predictions of trajectory. This is evident in a few JSAE papers that call the AYC a “feed forward control” based system and the ASC as a “feedback control” system, which may give us clues as to the algorithm operation.

3) The chart attached shows the influences of torque vectoring on FWD, RWD, and AWD configs. Look at the difference in Lat/Long accel! This is why the Evo X handles so well…..

4) According to the claims in the Mitsu papers, the S-AYC system can transmit 1.8x more torque than the old AYC system can. That isn't quite right in my calculations, it seems a little less, but maybe in the ballpark. Can't explain why there is a difference.

 

[Fede]

Some interesting notes:
1) The S-AYC actually has the ability to send more power to the right rear wheel (operated by the left clutch) than the left rear wheel (operated by the right clutch)!!! Is this NASCAR, lol! The factor is 2.22x for the LH clutch and 1.8x for the RH clutch). I wonder if this could be measured in a skidpad test in two different directions??

The question is why?I'm not following you...

http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2006/18e_03.pdf

I've find the equations ( about torque transfer) and they are fine...

 

[Fede]

There are a few engineering equations that describe how the system works in the papers, so I have used them as a starting point and tried to extrapolate some numbers we can all understand:

Old AYC (pre Evo X systems found on JDM and EDM Evo 4 to Evo 9) system:
Max torque of the clutches before slip = 590 foot pounds (800 Nm)
Average torque = 480 foot pounds (650 nm) approx.
S-AYC (Evo X) system:
Max torque of the clutches before slip = 885 foot pounds (1200 Nm)
Average torque = 625 foot pounds (850 nm) approx.

These numbers are calculated from a standing start on a split mu surface. It seems reaction time is a factor with the max coming at 1 second after hydraulic activation, which clues us into how fast the system can react. There is a wobble in the torque transfer initially before the max is achieved. The averages are my best guess at this point. Don't know if this is different in a dynamic (rolling with power at speed) situation.

Sorry I don't want to put any doubt in your capabilities but... how have you measured the frictional coefficient (to determinate the max torque before slipping) of dry clutches that in reality are wet so the coefficient is another and it changes, pheraps not linearly, with temperature?
I've asked about that because it's the first thing I've thought, but there are also many other problems

 

[Fede]

these numbers might not translate well to direct comparison to engine torque), it’s very confusing to me right now. I think these equations predict Nm in the form of energy, like the Joule, rather than the torque function. If anyone knows how to convert these two, it would be helpful.

I've not read it well...don't take in the wrong way but I'm begging you to stop and wait until this confusion is gone away.
I've got to thank you for your ACD-AYC (what fluid and where) thread because now, it's clear for everyone wich fluid is where, but the thread started in the wrong way, with a lot of confusion and I followed you because I have never played with the sistem in my hands. Thanks to some guru, at the end we discovered the truth and now is easy for everyone to understand...

Now you are speaking about Physic, Math and Mechanic, is science, not supposing or maybe, there's only 1 way the thing will work!Applying the known laws

If you have all this confusion don't try to solve problem like that, because it's going to end up in worse confusion. I try to make it clear but I don't know if in English I'll be able...so, sorry for grammar errors and incorrect translation.

Nm and Joule are the same thing... at least in the SI system.
Torque is a force(F)*application distance(d) and it live also without motion. F=m*a [kg*m/s^2], so F*d=[kg*m/s^2*m]=[N*m]
You can measure also the energy (As work) done by a system...in this case it is Force*displacement but you need to have a displacement to have work (if i can translate in this way)...not as before with torque!

So I don't know on which basis you have done your calculation but don't break your head on things like these ,without knowing very well the instrument to get rid of it.

As written before the equation developed by Mitsubishi, for the ammount of left-right torque, seems fine and right to me.

 

[dboz]

If I break this down, do I get a PhD?

 

[Golden]

Nope. It's barely Undergraduate work.

 

[discogodfather]

Whoa, relax. This is a discussion not a pulpit, this is theory and called theory. I see the Mitsu 2008 paper you posted up, it has nothing to do with the info I am using here, it's much more in-depth in these older papers. The 2003 and 2001 Mitsu papers have more info, and several JSAE papers I had to pay to download from the JSAE.

The math is very confusing to me right now, I'd like to post it up here. All this info is coming from a series of JSAE papers and I am a little afraid if I post them I'll get into copyright issues.

The only math I did was to try and determine the total transferring torque on a road surface, it does seem funky to me the more and more I look at it.

All other info is just reading and paraphrasing the articles. It's clearly stated in the 03 Mitsu paper that the application of a planetary gear in the rear diff had the side effect of uneven capacity, see below.

Anyone have any ideas or want to actually discuss the concepts? How much torque can the clutches hold without slipping? If the math is not good, is there a real world test to find out, etc?

I've not read it well...don't take in the wrong way but I'm begging you to stop and wait until this confusion is gone away.
I've got to thank you for your ACD-AYC (what fluid and where) thread because now, it's clear for everyone wich fluid is where, but the thread started in the wrong way, with a lot of confusion and I followed you because I have never played with the sistem in my hands. Thanks to some guru, at the end we discovered the truth and now is easy for everyone to understand...

Now you are speaking about Physic, Math and Mechanic, is science, not supposing or maybe, there's only 1 way the thing will work!Applying the known laws

If you have all this confusion don't try to solve problem like that, because it's going to end up in worse confusion. I try to make it clear but I don't know if in English I'll be able...so, sorry for grammar errors and incorrect translation.

Nm and Joule are the same thing... at least in the SI system.
Torque is a force(F)*application distance(d) and it live also without motion. F=m*a [kg*m/s^2], so F*d=[kg*m/s^2*m]=[N*m]
You can measure also the energy (As work) done by a system...in this case it is Force*displacement but you need to have a displacement to have work (if i can translate in this way)...not as before with torque!

So I don't know on which basis you have done your calculation but don't break your head on things like these ,without knowing very well the instrument to get rid of it.

As written before the equation developed by Mitsubishi, for the ammount of left-right torque, seems fine and right to me.

 

[Fede]

Hey disco,
as I said before, don't take in the wrong way...I'm not trying to do something for discredit your work!To be honest you spend a lot of time on it...
But Math is the only way to go when you have all the variables of the problem and you have to know how to use it.
In my paper deltaTorque is easy to see, I don't know which equations have been used in your...if the clutches are the same and also pressure on them perhaps there are unbalanced gear ratios used in the carrier

 

[Fede]

You can't define for sure how much torque can be transfered in the S-AYC until you try with FEM, but you won't able to define all the variables.
Also if you'll do it, then, in reality, things can be different from calculations because there are a lot of unpredictable things...
How the oil will respond to the same stress after degradation?If outside temp is 10 degree different, it will influence extreme deltatorque transfer, calibration of sensors isn't the same for every single evo and so on...

 

[Frankiago]

Talk about dork vectoring....

That diagram is cool. Proves that FWD sucks and RWD is inferior.

 

[Fede]

That diagram is cool. Proves that FWD sucks and RWD is inferior.

Yes, dogs are faster than us off the line...perhaps our legs can compete with a RLegsD dog :bowlol:
Joking

 

[Golden]

Does the amount of torque transferred really matter? It's not like a 1000 HP Evo X is going to try to take a corner and put down all 1000 HP at the same time. Even trying to put down all 300 HP of the stock car's power and taking a corner is a bit of a crazy idea.

The car can only corner so fast, so it is its own limiting factor.

 

[dkevox]

I love your posts. thanks for the info!

 

[dave]

Why doesn't the RWD have more longitudinal grip than the FWD?

 

[X-Factor]

I'm so goddamn confused.

 

[Frankiago]

Does the amount of torque transferred really matter? It's not like a 1000 HP Evo X is going to try to take a corner and put down all 1000 HP at the same time. Even trying to put down all 300 HP of the stock car's power and taking a corner is a bit of a crazy idea.

The car can only corner so fast, so it is its own limiting factor.

Golden, serious question... do you get much track time?

 

[CountIT]

I'm so goddamn confused.

:+1:

 

[Golden]

Golden, serious question... do you get much track time?

Yes.

Let me also add, the torque in 1st gear is killer compared to 5th.