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

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

Postby phattyduck » Fri Dec 20, 2013 5:40 pm

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
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'89 Camry LE Alltrac 3S-GTE - SV25/ST205 hybrid
'99 4Runner SR5 4WD 5VZ-FE
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Re: Variable F/R torque split (to 50/50) idea

Postby MWP » Sat Dec 21, 2013 8:21 am

phattyduck wrote: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).
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Re: Variable F/R torque split (to 50/50) idea

Postby phattyduck » Mon Dec 23, 2013 10:50 pm

MWP wrote:
phattyduck wrote: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)

Image

Image

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
'89 Camry LE Alltrac 3S-GTE - SV25/ST205 hybrid
'99 4Runner SR5 4WD 5VZ-FE
Previous: '88 Camry LE Alltrac 3S-GE BEAMS, '90 Camry 3S-GTE, '90 Camry DX
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Re: Variable F/R torque split (to 50/50) idea

Postby MWP » Tue Dec 24, 2013 2:10 am

phattyduck wrote:
MWP wrote:
phattyduck wrote: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.
My collection of GT4 documentation: http://gt4.mwp.id.au
Daily: Celica GT4 ST185 (~170kw/atw)
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Re: Variable F/R torque split (to 50/50) idea

Postby phattyduck » Tue Dec 24, 2013 6:09 pm

MWP wrote: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
'89 Camry LE Alltrac 3S-GTE - SV25/ST205 hybrid
'99 4Runner SR5 4WD 5VZ-FE
Previous: '88 Camry LE Alltrac 3S-GE BEAMS, '90 Camry 3S-GTE, '90 Camry DX
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Re: Variable F/R torque split (to 50/50) idea

Postby MWP » Wed Dec 25, 2013 1:09 am

Ah, fair enough :)

Merry xmas fellas.
My collection of GT4 documentation: http://gt4.mwp.id.au
Daily: Celica GT4 ST185 (~170kw/atw)
Project: Toyota RA28 '77 Celica (1UZ-FE powered)
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MWP
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