audi8k

Yes. I think that supports what I said. Or do you have another interpretation? The TORSEN diff doesn't really "lock". Instead it instantly binds (using internal friction) up to the maximum torque bias ratio.

NorthwestB9

How are they mistaken? They are slightly off on their numbers, as the real numbers are 85/15 and 30/70 rear/front, but they are not mistaken. Every source mentions that the A4's quattro system is able to redirect most torque to one axle or the other. You contended it can only do 50/50 or 40/60, which is incorrect. I've found no sources at all that support your conclusion. At most, they can be criticized for having slightly the wrong numbers of 70 (correct) and 80 (off by 5) or for lacking precision, but they aren't wrong.

Here's another one (2017 Audi A4 review and road test with price, horsepower and photo gallery):
"The torque split usually runs at 40/60 front to rear, throwing up to 85 percent of the power to the back if necessary."

rsilvers129

Well I am not sure. I am asking for help to sort this out.

https://en.wikipedia.org/wiki/Quattr...l-drive_system)

This link says that for Crown Gear, up to 70% can go to the front, and up to 85% for the rear. So I thought maybe they were using Crown Gear numbers for the T3 system. That link does not say how much can go to the front axle, other than saying it can send up to 80% to "one axle." Does that mean the Wikipedia is claiming it can go up to 80% front or up to 80% rear but defaults to 40/60? Why would it be the same 80% max for both front or rear? Seems odd. Also, Wikipedia doesn't say what the default split is for the Crown Gear. Maybe someone who really knows this stuff can update that page.

audi8k

In the wiki you linked, it is the part "The Torsen type "C" (T3)" that is valid for the TORSEN diff in B8 and I believe B9 (but not sure). The nominal and maximum torque split range has always been described with the same numbers for the T3 and "Crown Gear" diff.
I never understood Audi press text when introducing the Crown gear diff that said the crown gear reaction is faster (T3 is instant but Crown gear clutch packs are described to need compression which can't be instant).
Further I haven't understood how the "rotational speeds ..result in an increase in axial forces that force the clutch plates to close".
The text about " Once closed, the output shaft is locked .." does apparently not mean "locked" because the torque split should then be able to put close to 100% to one axle if the other is in the air.
From the drawing of the Crown Gear diff it can be seen that the point of contact to the front and rear crown wheels are at different radius. This creates the asymmetric nominal torque split (40/60).
It can also be noted that there are many more clutch discs to the rear which allows the maximum torque split to be higher to the rear than to the front before the clutch begins to slip.

superswiss

My understanding is that Audi's current diff while based on the Torsen T3 is Audi's own design. It also uses friction discs. Below is a short video that shows the makeup of the diff. I haven't found a similar video that describes how it works like the Crown Gear video.

audi8k

The discription from autozine
[AutoZine Technical School] clarifies how the nominal torque split in a TORSEN T3 ("C") is achieved. The planetary gears 'outer' side drives the rear output at a larger radius than the 'inner' side that drives the "sun gear" to the front. It is still not clear to me if the "friction" is constant or changes depending on the counter forces from the outputs.

rsilvers129

"Like Torsen C differential, the crown gear differential is default to 40:60 torque split between front and rear axles under normal condition, so it is able to deliver a handling characteristic more akin to rear-drive cars, or in other words, to be less troubled by understeer. When the front axle loses traction, it may send up to 85% torque to the rear. When the rear slips, it transfers up to 70% torque to the front. Such locking range is much wider than the case of Torsen C differential, so it should deliver superior handling, especially when mated with torque-vectoring electronic rear differential as the rear axle now has more torque to play with. Moreover, the crown gear differential is simpler in construction and weighs 2 kg less than Torsen C."

I wonder why they don't put Crown Gear in more cars? I assume it costs more, though this says it is simpler in construction.

rsilvers129

Torsen designs do lock instantaneously.

rsilvers129

ropuff

Very educational videos, thanks.

Makes me want to break out the Lego Technics sets I still have somewhere and play with gears...