DCCD Torque Split

[A1337STI]

Yes it really is Torque split (on both cars)
Perhaps you've never read this Car and Driver article ?
http://www.caranddriver.com/features...different.html

[Dean]

Originally Posted by A1337STI

Yes it really is Torque split (on both cars)
Perhaps you've never read this Car and Driver article ?
http://www.caranddriver.com/features...different.html

I wish they had gone back to the track and tried some more testing to make the STI better...

[MikeK]

Originally Posted by Dean

I wish they had gone back to the track and tried some more testing to make the STI better...

You mean playing with the DCCD mid-turn?

[Dean]

Originally Posted by MikeK

You mean playing with the DCCD mid-turn?

No, read the last paragraph of the article...

[A1337STI]

Yes just maybe if you turn the dial Enough while cornering, in each corner... Er wait a minute ...

lmao

i have found if you adjust it and try different settings you prove Dean very correct in stating the subaru engineers really know their stuff. That doesn't mean it can't add fun to your fun runs though

Also the owners manual does state it won't harm anything to adjust it as you drive as long as there is no wheel spin. And during wheel spin if you are in a manually selected locking rate it is Okay to select Auto. Which i've also done from time to time when playing around in the snow with the dccd

[sperry]

Originally Posted by A1337STI

Yes it really is Torque split (on both cars)
Perhaps you've never read this Car and Driver article ?
http://www.caranddriver.com/features...different.html

Yeah, 'cause C&D is an engineering bible.

The torque split ratio is defined by the mechanical properties of the open center diff. The DCCD clutch simply limits wheel spin. You cannot, under any circumstances (except perhaps if you change the laws of physics) get different than 35f/65r torque split out of the STi's center-diff ('04-'05, the split I hear is different on the '06, but it's still *fixed*).

Originally Posted by C&D article

Now, we're simplifying things a little because it would take pages to describe exactly when those center-diff clutches operate,

Here are those pages:

http://velozt.com/elements/tech/sti/.../DCCD_FAQ.html

Read it carefully, and you'll see that no matter what you're doing with that knob, the center diff ratio is *always* fixed at 35/65. The clutches allow you to send power to the wheels that aren't slipping, but that's go nothing to do with the diff's ratio.

[A1337STI]

you do know in that link you sent me it has a Chart that show Actual Front and rear Torque being different At different locking rates? which says in a nutshell that YES the torque gets moved around.

Did you even read that or did you just post it thinking 'ya i'm right, and this proves it' ? cause it proves you wrong.

It also has a lot of wrong stuff in there things like 'if your traction will only permit 100 ft lbs of torque to be put down with out wheel spin the engine never produces more than 100 ft lbs of torque. Wow that's so wrong i don't know where to begin. If that's how physics worked no one would ever spin their wheels because as in that explation your motor can't produce more power than your wheels can put down (WRONG!!!!)

maybe they meant you can't transmit more torque to the ground than your wheels will permit traction wise and when your motor produces Over that amount your tires spin.

If you Re-read that article Carefully it says when a center diff is fully open the torque split never changes, But if you can Lock it some how... than it does.

Reading comprehension is our friend

[A1337STI]

i'm trying to find a PDF Produces by the subaru engineers that explains it. it had it on my old work machine. it even explains the conditions that envoke various amounts of lock.

such as as you get on the brakes it uses less lock, as you turn the steering wheel , less lock, as you get back on the gas and straighten out it dials up the lock. just can't find the damn thing. its got a tag like Driver-controllable center differential .pdf and since it came from engineers and not 1 guy piecing together his understandings from way things work and nasioc, its bound to be a lil better.

[A1337STI]

This from the article you linked sums it up the best

So what should you remember from Part 1 of this article?

1. With an open diff the torque split is always fixed by the gearing of the planetary gearset. With the STi, it is 65R/35F.

2. When the diff is locked the answer to “what is the torque split” is: It depends. It is not always 50:50.

IT DEPENDS ON THE LOCKING RATE

http://www.purepwnage.com/media/Kyle...ng%20noobs.mp3
good track

[sperry]

1) You are a crackhead... three rambling, blubbering posts in a row.

2) You may have read the article, but you certainly don't understand it. I specifically said, "Read it carefully". Your comments indicate you blew over it, and didn't bother to comprehend what's written in there. This especially shows your incompetents regarding the topic:

Originally Posted by crackhead

It also has a lot of wrong stuff in there things like 'if your traction will only permit 100 ft lbs of torque to be put down with out wheel spin the engine never produces more than 100 ft lbs of torque. Wow that's so wrong i don't know where to begin. If that's how physics worked no one would ever spin their wheels because as in that explation your motor can't produce more power than your wheels can put down (WRONG!!!!)

Of course the motor makes over 100ftlbs, that's what causes wheelspin. If you actually read the article, you'd understand that the example cases are to demonstrate torque distribution (which had nothing to do with changing the ratio of the torque split) without the wheels slipping. If the motor were making more than 100ftlbs, the wheels would slip, and the torque at each end would instantly revert to the fixed 35/65 ratio instead of applying torque to the wheels with grip.

3) THE CENTER DIFF USES A PLANETARY GEAR. THE RATIO IS FIXED. NO AMOUNT OF LOCKING OF A CLUTCH CAN CHANGE THE NUMBER OF TEETH IN THE GEAR. This of it this way: if the motor makes a maximum of 300ftlbs of torque, you will *never* get more than 105ftlbs to the front wheels and never more than 195ftlbs to the rear wheels. When traction is limited, you can distribute the power to the wheels with more traction via the DCCD clutches, but not in a manner that exceeds the fixed ratio of the diff. That DCCD knob does not make the car into a rear-wheel drive car, the ratio is FIXED at 35/65. Period.

4) Go read the article again. And again. And 5 more times. Until you understand it. Then come back here and talk shit to me again.

[MPREZIV]

Ahhh... this is where it gets good! Where's the smilie with the little dude eating popcorn?

[MattR]

I need an adult! I need an adult! Wow. i should forward this thread to Allon so we can get some feedback from that side.

[Dean]

Originally Posted by sperry

3) THE CENTER DIFF USES A PLANETARY GEAR. THE RATIO IS FIXED. NO AMOUNT OF LOCKING OF A CLUTCH CAN CHANGE THE NUMBER OF TEETH IN THE GEAR. This of it this way: if the motor makes a maximum of 300ftlbs of torque, you will *never* get more than 105ftlbs to the front wheels and never more than 195ftlbs to the rear wheels.

Scott, I realize Alex's posts were rambling and while your above statement may be true in ideal conditions on paper as was my "Pin locking brake system" , perhaps you should read your referenced article again...

A differential allows for differing speeds on each of the output shafts. The ratio of the gears in a planetary differential related to output torque is only absolute when it is fully open.

As the article clearly points out, under partial to full locking, the actual amount of torque at each end is a function of a number of different factors.

What is the torque split when the LSD clutch is fully engaged and the driveshafts are turning at the same speed? Note: This question only applies to a clutch style LS mechanism. A viscous LS mechanism cannot transfer torque without a speed difference.

The answer to this question is: It depends. The answer is neither “35:65” nor “always 50:50”. Often literature (Subaru’s and others) will mention something like "equal torque distribution" but this is an inaccurate simplification of a much more complex process. A more considered answer would be:

It depends on:

1. The front/rear weight distribution of the car
2. Any dynamic loading of the axles (due to acceleration or deceleration)
3. The available friction at the tires, which depends on the surface under the tire (ice snow gravel tarmac) and the tire itself
4. The amount of lock (the clutch engagement force)
5. The torque being output by the engine

[sperry]

Dean, part of the problem is that the article uses the term "torque split" inconsistently. The "torque split" of the differential is not the same thing as the "torque split" seen at the wheels.

People have this misconception that adjusting the DCCD changes the way the differential splits torque between the wheels, which is patently not the case. The differential cannot send more than its fixed ratios of torque to the wheels. What the clutches can do however, is allow the differential to send power to wheels that have traction.

Think of it this way: if the rear wheels have little traction, the clutch can engage and act as resistance in place of the resistance that should be provided by the ground, allowing the front wheels to see up to their full 35% of the engine's output. The torque distribution in that situation will appear like there's more torque to the front half of the differential, but that's not the case, because the "missing" torque at the rear is actually being gobbled up by the clutch to prevent wheel spin.

The article is a pain to read and understand, but if you've read it 100 times over the last 2 years like I have, it will start to make sense.

[Dean]

I agree, with you, but by definition, a twisting motion that is not applied is not torque...

So, the gotcha becomes are we talking about torque at the wheels which is after the clutches on the output shafts of the whole "DCCD" differential unit, or on the output shafts of the internal planetary diff gears within the case which is a subset of the whole "DCCD"?

Without clearly identifying which, you can argue this forever with many parties being correct...

Just because an engine is capable of producing 300 ft/lbs of torque doesn't mean it is. If the maximum torque that can be absorbed by the tires and assorted drive line losses including DCCD clutches is 200ft/lbs, that is all the maximum measurable torque that the overall system will attain...

Can you point me to any diagrams of the actual internals of the DCCD? It would be interesting to see if the clutches are strictly on the output shafts or internal to the planetary diff itself.

[MikeK]

Originally Posted by Dean

Can you point me to any diagrams of the actual internals of the DCCD? It would be interesting to see if the clutches are strictly on the output shafts or internal to the planetary diff itself.

I have a file called "DCCD technicians reference booklet" that has diagrams of everything, but I can't seem to attach it. I can email it to you if you want.

[sperry]

Originally Posted by Dean

I agree, with you, but by definition, a twisting motion that is not applied is not torque...

So, the gotcha becomes are we talking about torque at the wheels which is after the clutches on the output shafts of the whole "DCCD" differential unit, or on the output shafts of the internal planetary diff gears within the case which is a subset of the whole "DCCD"?

Without clearly identifying which, you can argue this forever with many parties being correct...

Just because an engine is capable of producing 300 ft/lbs of torque doesn't mean it is. If the maximum torque that can be absorbed by the tires and assorted drive line losses including DCCD clutches is 200ft/lbs, that is all the maximum measurable torque that the overall system will attain...

Can you point me to any diagrams of the actual internals of the DCCD? It would be interesting to see if the clutches are strictly on the output shafts or internal to the planetary diff itself.

It's a messy subject. But the easy way to think about it is: the torque split is 35f/65r, so that's what's going to the ground when you have traction. The clutch can help prevent loss of traction by effectively taking power away from the wheels that are slipping allowing the wheels with grip to get their full share of the engine's power. The DCCD allows the driver to adjust the sensitivity of the clutch's engagement, from no engagement at all (the wheels are free to turn at any speed relative to each other) to full lock (the wheels must turn the same speed).

I get the feeling that I'm going to see the internals of a DCCD center diff sooner rather than later... mines not working.

[sperry]

Originally Posted by MikeK

I have a file called "DCCD technicians reference booklet" that has diagrams of everything, but I can't seem to attach it. I can email it to you if you want.

Send it to me too.

[MikeK]

I sent it to you and Dean. Can you put it on the site somewhere? I can't attach it to a post for some reason.

[cody]

Zip it first and then upload it maybe Mike?

[sperry]

Originally Posted by cody

Zip it first and then upload it maybe Mike?

I'm about to add it to the tech section.

edit: http://www.seccs.org/tech

[Dean]

Originally Posted by sperry

It's a messy subject. But the easy way to think about it is: the torque split is 35f/65r, so that's what's going to the ground when you have traction. The clutch can help prevent loss of traction by effectively taking power away from the wheels that are slipping allowing the wheels with grip to get their full share of the engine's power. The DCCD allows the driver to adjust the sensitivity of the clutch's engagement, from no engagement at all (the wheels are free to turn at any speed relative to each other) to full lock (the wheels must turn the same speed).

A quick look at Mikes' doc of the internals make it appear that it does change from 35/65 to 50/50 assuming sufficient traction is available to reach those levels by effectively locking the planetary gears. It appears there is only a single clutch that appears to control the locking between the input and output shaft in effect overriding the mechanical gear ratios of the diff.

This makes complete sense IMHO. A locked set of planetary gears results in the equivalent of a solid shaft which has a 50/50 split. The clutch slips between the geared ratio of 35/65 and the locked up 50/50.

I am continuing to read and look at pictures. The reduction of clutch engagement on braking may be why I am finding left foot braking to be less effective than I would expect while cornering...

[sperry]

Originally Posted by Dean

A quick look at Mikes' doc of the internals make it appear that it does change from 35/65 to 50/50 assuming sufficient traction is available to reach those levels by effectively locking the planetary gears. It appears there is only a single clutch that appears to control the locking between the input and output shaft in effect overriding the mechanical gear ratios of the diff.

This makes complete sense IMHO. A locked set of planetary gears results in the equivalent of a solid shaft which has a 50/50 split. The clutch slips between the geared ratio of 35/65 and the locked up 50/50.

I am continuing to read and look at pictures. The reduction of clutch engagement on braking may be why I am finding left foot braking to be less effective than I would expect while cornering...

I'm having a bitch of a time visualizing what's going on in there, but it doesn't sound to me like there's anything changing the ratios of the gears.

It seems like the clutch engages, adding drag between the planetary carrier and the differential's case, thus providing drag torque allowing an opposite force for the front wheel side of the diff to push against in order to raise the torque seen at the front wheels.

I'd kill for a cutaway 3D animation of this beast in action.

[MikeK]

Originally Posted by sperry

I'd kill for a cutaway 3D animation of this beast in action.

I'll make you one if you kill Dean.

(that sweet SM trophy will be mine!)

[Dean]

Originally Posted by sperry

I'm having a bitch of a time visualizing what's going on in there, but it doesn't sound to me like there's anything changing the ratios of the gears.

It seems like the clutch engages, adding drag between the planetary carrier and the differential's case, thus providing drag torque allowing an opposite force for the front wheel side of the diff to push against in order to raise the torque seen at the front wheels.

I'd kill for a cutaway 3D animation of this beast in action.

So would I. What I am seeing is that the clutch acts in parallel with the planetaries. The clutch effectively provides friction between the same two surfaces the planetaries rotate between. That friction allows the torque split to be varied from 35/65 when the clutch is disengaged to 50/50 when fully engaged/locked.

There is another interesting statements in the last two paragraphs on page "81" that seams to imply the maximum split in auto is 45/55...