He was beyond my level of understanding, so he was trying to build one specifically for this purpose.seems like defcon 5 was working on something like that iirc...
Hello chaps -
he has to keep those fingers nimble for making little electronic devices!!^^^And that is why I like you Chris, haha (geeez you weren't kidding about the rambling part... I think you just like to type though)...rojectsti.com:
Hello chaps -
formula91 and Gr3en: The short answer is "yes". The real world answer though, is more along the lines of "yeah, but not really..."
The simple switch mod outlined in this thread achieves the maximum possible result with the minimum cost and effort.
Because I like to ramble, I'll answer questions with questions:
Q: Is it possible to control the center "diff" through a potentiometer (knob) of some kind?
Q: Will it be just like the DCCD on the STI?
A: Never in a million years.
Q: Why not?
A: Among other things, the STI's DCCD design allows for the selection of a RWD bias. In contrast, the 4EAT's design lacks the capability to exceed more than 50/50 power distribution between the front and rear axles.
You can dial between FWD (90/10) and 4WD (50/50), but never more than 50% to the rear wheels. This is due to physical restrictions of the 4EAT's design and cannot be overcome without significant modification.
Q: Care to elaborate?
A: Sure! I do love to ramble....
I won't go into how the STI achieves the ability to power the rear wheels - that subject is a small treatise on it's own. Suffice it to say that a fair amount of brilliant engineering and countless hours of research and development went into it's birth - and possibly a small quantity of unicorn tears...
As for the 4EAT, the primary limiting factor is that the center "diff" isn't a diff at all. It's a Multi Plate Transfer Clutch (MPT). By design, a single clutch can only transfer power in one direction, and is limited by the laws of physics to transferring up to 100% of the power supplied to it.
So, power comes from "Point A" and the clutch allows varying amounts of that power to be sent to "Point B". That's it. The point I'm trying to make is that a clutch lacks the ability to multiply torque - that's what gearboxes are for.
So that's the general idea - In our Subaru 4EAT specific example, the power flow goes something like this:
The engine rotates the input shaft of the 4EAT. Inside the transmission a whole mess of hydraulic fluid, torque converters, bands and other stuff make sure the power gets to it's next destination - the front differential - (this is the other limiting factor - more on that later). The front differential then sends the power out to the front wheels and on to the MPT clutch. The MPT clutch is connected to the rear wheels via the rear differential. Under normal operation, the MPT clutch is open and no power is transferred to the rears. If the transmission computer senses excessive front wheel slip, the MPT is closed to allow some power to the rear wheels.
That, in a nutshell is how the 4EAT's AWD system is laid out.
Now, let's discuss that second limiting factor. In the example above, remember that the power goes to the front differential first and then on to the MPT. This means that the front diff effectively drives the MPT. Thus the front wheels will always be powered 100%. No matter how cool you are, the MPT (and the rear wheels that it powers) can never spin without the front wheels spinning too. You can lock the MPT up as hard as you like - weld it, glue it, hold it with clothespins. It just won't matter - the best you can hope for is equal sharing of the work.
This leads me to the final subject - which I get a lot of emails about.
Q: I'm young, ambitious and haven't yet been jaded by the world's indifference - If I really put my mind to it, could I physically modify the transmission to support some kind of true DCCD functionality?
A: Maybe, I'm not sure. But before you get out your die grinders, give this a thought.
If you were somehow able to achieve the desired result, you would still be stuck with a lazy, over geared transmission with rotten shift logic. The fact that you could make it RWD would be completely overshadowed by the fact that it would still shift at the worst times, and even if you manually shift it, the gearing is decidedly non-performance oriented.
As a pure technical exercise, I still think it's a brilliant idea - always have.
I'll still pursue my plans when time and finances allow. If however, performance is your goal - there are better ways to spend your time, money and effort.
I realize that last bit sounds really sour, but don't take it the wrong way. I think the 4EAT is a wonderful little transmission. Heck, it's been around in one form or another since the late 80's - it really is a gem. However - it has limitations. It's intent was to be a plucky little automatic transmission for Japanese economy cars. Not for us lunatics to go four-wheel drifting through country lanes...
Over the years, Subaru's image and heritage changed, but the 4EAT wasn't involved in any of that. Sure they may have made some changes over the years, and put it in some pretty powerful cars, but performance is still the domain of the manual transmission and/or purpose built automatics (in the drag racing world)
So, if your goal is to have the trickest 4EAT out there - knock yourself out. If however you want a reliable, daily driver that can still provide you with some massive grins, all for less than the cost of a boy's night out - read up, cut some wires, learn some new skills, and have a blast. If you get stuck, send me an email (defcon5industriesatgmaildotcom) I'm always happy to help.
I haven't wired it up yet (got finals to work on!) but I will probably next week. I'll let you know the results. You're the only local with another 05 RS AT after all!Formula91,
Were you able to make it work by providing voltage to it instead of cutting it completely?