Variable F/R torque split (to 50/50) idea

underscore

Well-known member
MWP":32li2bo6 said:
Actually, it funny you say "Hot AWD versions of FWD cars", because thats what a Celica AllTrac/GT4 is :p

So you are telling me all the Audi RSx cars aren't very good? They are all front engined 4WD haldex systems.
I would happily forget everything to do with Toyotas & Celicas (all ive ever owned) to have a Audi RS4.

Audi TT RS? I dont believe there is a FWD version of that.

The vehicles you're listing are worth vastly more than most Alltracs, whereas the ones mx6er2587 is listing are more at the "average" consumer end of things (ie the ones you'd be pulling hardware from). Don't tell me you plan on buying an AWD system from a Lambo and adapting it to your car because that's ludicrous (and you've got to remember that anything setup MA or RA is the opposite of our car). Just because a Haldex can be good doesn't mean they are all good.

MWP":32li2bo6 said:
Nissan GTR uses electronic clutches to move power around, as does the Mitsu EvoX and Subrau WRX STIs with DCCD.

WRC Corollas (based on ST205 drivetrain) had front & center electronically controlled clutch diffs.

Again, its not the clutches themselves that make the difference, its how they are used.

Correct me if I'm wrong but I believe these aren't running the same style of open front diff as we are, so tossing on half of their system isn't going to make ours work the same way.
 

MWP

New member
underscore":sizbn277 said:
The vehicles you're listing are worth vastly more than most Alltracs, whereas the ones mx6er2587 is listing are more at the "average" consumer end of things (ie the ones you'd be pulling hardware from). Don't tell me you plan on buying an AWD system from a Lambo and adapting it to your car because that's ludicrous (and you've got to remember that anything setup MA or RA is the opposite of our car). Just because a Haldex can be good doesn't mean they are all good.

Yup, thats very true.
I was just trying to prove that all Haldex coupling equipped cars are not "bad", and its not the fault of the Haldex coupling units, but how they are implemented.

They are really quite simple devices.
They simply control how much of the power on the input shaft appears on the output shaft in response to an electronic signal.
How you use the coupling units in/around the gearbox and diffs is what is important.

Of course using one in a GT4 would be a very very simple implementation, controlling only how much power is sent from the front to the rear with a max of 50:50 split.
I believe it'll still have quite large advantages over the viscous center.
 

MWP

New member
This is an example control map for a WRX's DCCD center electric diff.
Similar power split maps couple be implemented if the GT4's viscous center was replaced with a haldex (or similar ) electronic clutch:

mapdccd_2.jpg


Another advantage would be handbrake (e-brake) detachment.
No more loading up a front wheel when applying the handbrake to initiate a slide :)
 

st185-sainz

New member
Hey guys,

I only had a quick overview on your posts and just wanted to clarify a statement of using an EVO gearbox or centre diff - EVO 5 for example has the same visco rating than my uprated unit!
The guy who did my Celica Visco does also rebuild all our EVO units for rallying...

mario
 

athousandleaves

New member
Just from glossing over the OP's original idea it sounds much like the V-Flex AWD system installed in the ST215G/matrix/voltz but electronically controllable.

http://toyota-club.net/files/faq/04-01- ... 15-eng.htm

Might be worth working with those parts before you step into the world of Audi...

-edit-

Also the SV25 Camry with automatic transmission featured a clutch type center diff instead of the viscous coupler... Perhaps this unit could be modified to offer a different split to the front or rear and be electro-hydraulically controlled as well.
 

MWP

New member
athousandleaves":u8nj4kak said:
Just from glossing over the OP's original idea it sounds much like the V-Flex AWD system installed in the ST215G/matrix/voltz but electronically controllable.
http://toyota-club.net/files/faq/04-01- ... 15-eng.htm
Might be worth working with those parts before you step into the world of Audi...

Interesting... i wasnt aware of the G version.
As that page says though, its a worse system than the viscous center diff we have at the moment.
Nothing from that system could be reused to do what im after.
 

athousandleaves

New member
I'm fairly sure that with the automatic Camry that the 4WD button once pressed allows the car to apportion up to 50% to the rear end when it senses a difference in wheel speed.

Its not a full 50% or nothing situation because its a clutch based unit responsible for the transfer and by engaging the 4WD it allows the car to increase/decrease the pressure on the plates until it senses that front and rear wheel speed are the same however due to how the center differential is designed I think that you only ever see about 50% power at the front even with the 4WD disengaged.

So I believe that its F50:R0-50, not exactly the F100:R0/variable ratio that you were looking at with the Audi parts. Could make for a pretty aggressive drag setup maybe?

If you wanted a different ratio like F30:R70 with the Camry parts you would have to change the center differential gearing to bias it to the rear.
 

MWP

New member
athousandleaves":2oxxwuya said:
I'm fairly sure that with the automatic Camry that the 4WD button once pressed allows the car to apportion up to 50% to the rear end when it senses a difference in wheel speed.

Its not a full 50% or nothing situation because its a clutch based unit responsible for the transfer and by engaging the 4WD it allows the car to increase/decrease the pressure on the plates until it senses that front and rear wheel speed are the same however due to how the center differential is designed I think that you only ever see about 50% power at the front even with the 4WD disengaged.

So I believe that its F50:R0-50, not exactly the F100:R0/variable ratio that you were looking at with the Audi parts. Could make for a pretty aggressive drag setup maybe?

I think you are getting yourself confused here.
You cant have 50% of power sent to the front, and none sent to the rear. If thats the case, where does the remaining 50% go? ;)

Front % split + Rear % split always = 100%.
 

athousandleaves

New member
The other 50% is sent into the transfer case and the parts just spin aimlessly. They specifically tell you in the manual to never drive with the 4WD button disengaged unless its being towed.

Edited my last post after you saw it too...

The car was no faster accelerating with the button off or on...
 

phattyduck

New member
I drove my auto Alltrac Camry a bunch in the snow... It is a 50-50 torque split, just like all the other manual trans Celica/Camry Alltracs.

In the snow, one tire/axle would spin for a bit (half-second ish), then you'd feel the diff lock up and it would drive away. In my case, this was almost always the front because I had (and have) an ST205 torsen rear diff on there. There are speed sensors on the front and rear outputs of the center diff and there is a center diff lock control as part of the ECT ECU. The clutch system may or may not be powerful enough to transfer all the torque to the front or rear. Anyways, the system as implemented in the Camry is only good for getting you out of slippery situations, it doesn't help for performance or handling in any way.

Also, we have to be careful when we are talking about these things. A 50-50 torque split is different than a 50-50 power split. (power is torque x RPM). So, open diff is ALWAYS 50-50 torque, but more power goes to the wheel that is spinning. If the two outputs of the diff are going the same speed, then the torque split and power split are the same.

-Charlie
 

MWP

New member
phattyduck":3vkt4ima said:
I drove my auto Alltrac Camry a bunch in the snow... It is a 50-50 torque split, just like all the other manual trans Celica/Camry Alltracs.

No, you are wrong there IMHO.
The center diff does not act like an open diff.

The center diff transfers all torque to the front wheels (100:0 FR split) until the rear wheel speed is slower than the front wheel speed.
When this occurs, torque is applied to the rear up to a maximum 50:50 split (depending on F/R speed difference).
 

phattyduck

New member
MWP":jvq5ig3u said:
phattyduck":jvq5ig3u said:
I drove my auto Alltrac Camry a bunch in the snow... It is a 50-50 torque split, just like all the other manual trans Celica/Camry Alltracs.

No, you are wrong there IMHO.
The center diff does not act like an open diff.

The center diff transfers all torque to the front wheels (100:0 FR split) until the rear wheel speed is slower than the front wheel speed.
When this occurs, torque is applied to the rear up to a maximum 50:50 split (depending on F/R speed difference).
I'm not sure why you are stuck on this. It is 50/50 just like the manual, with a computer controlled clutch on the center diff. It is packaged slightly differently compared to the manual transmissions, with the front diff and the center diff in different locations (so the center diff and transfer case can both be in gear oil instead of ATF)

540-01-500x470.png


Alltrac01.jpg


Or here:
https://translate.google.com/translate? ... indow.html
(compare the A540H in section 1-1 vs. the later style 1-5 section that is FWD until needed)

-Charlie
 

MWP

New member
phattyduck":3w1onswe said:
MWP":3w1onswe said:
phattyduck":3w1onswe said:
I drove my auto Alltrac Camry a bunch in the snow... It is a 50-50 torque split, just like all the other manual trans Celica/Camry Alltracs.

No, you are wrong there IMHO.
The center diff does not act like an open diff.

The center diff transfers all torque to the front wheels (100:0 FR split) until the rear wheel speed is slower than the front wheel speed.
When this occurs, torque is applied to the rear up to a maximum 50:50 split (depending on F/R speed difference).

I'm not sure why you are stuck on this. It is 50/50 just like the manual, with a computer controlled clutch on the center diff. It is packaged slightly differently compared to the manual transmissions, with the front diff and the center diff in different locations (so the center diff and transfer case can both be in gear oil instead of ATF)

Ok... you are confusing the issue by talking about the older non-viscous ST165 and Camry Alltrac 4WD or Auto trans systems.

It is not relevant at all to this discussion which is about improving the 4WD capability of our viscous centered 165/185/205's.
 

phattyduck

New member
MWP":14vaztq7 said:
Ok... you are confusing the issue by talking about the older non-viscous ST165 and Camry Alltrac 4WD or Auto trans systems.

It is not relevant at all to this discussion which is about improving the 4WD capability of our viscous centered 165/185/205's.
athousandleaves brought up the auto trans Camry Alltrac transmission. I was just correcting his misconception and pointing out that it isn't a good system to add to this discussion. I swapped to an ST205 transmission in my previously auto Camry Alltrac for a reason...

-Charlie
 
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