quattro in reverse?

Yes.

Yes.

-- C.R. Krieger (Been there; done that)

Is there even such a thing as a uni-directional differential?

No, but there are all-wheel drive systems that use electronically controlled clutches instead of differentials, and I'd imagine that these might not operate in reverse. It could be that the OP doesn't know or understand the difference.

-- Mike Smith

Exhaust pipes at the back, and the seat with the round hand-rail faces the front?

;o)

(Semi-non-facetious bit: like brakes, clutches only operate in one rotational and one linear dimension. Direction is irrelevant, just the outcome. A bit like a politician.. ;o)

Yes, but that's only *if* the clutch engages. Given that they're electronically controlled in such systems, the electronics could easily be programmed not to engage the clutch while in reverse.

-- Mike Smith

But /why/ would someone do that..? Why would a rational engineer increase the cost of a product in order to reduce the performance, efficiency and safety?

It makes no sense.

H1K

What makes it cost more to disable the clutch operation? It's all software anyway. It probably looks something like this (just a wild-ass-guess example):

if (wheelslip > THRESHOLD) { if (speed < CUTOFF) engage_clutch(MODE_ONE); else engage_clutch(MODE_TWO); }

...uh, or something. If they allowed operation in reverse, they might very well have to add more code, like this:

if ((wheelslip > THRESHOLD) or (wheelslip < REVERSE_THRESHOLD)) { if ((speed < CUTOFF) and (speed > REVERSE_CUTOFF)) engage_clutch(MODE_ONE); else engage_clutch(MODE_TWO); }

That's a little bit more code that someone has to write, someone has to maintain, someone has to test, one more thing to screw up, etc. Maybe it's just simpler (and better for the bottom line) to disallow operation of the clutch pack while in reverse gear.

-- Mike Smith

You've made my point, but then missed it. How about if you replace the code with:

Which seems even easier to design, code, and maintain ;o)

H1K

Then how does the system determine when to engage?

-- Mike Smith

But the heart of quattro in all Audi's except for the TT is a Torsen differential which is purely mechanical. No wet plate clutches in it.

Same as when moving forward - you just have to take the modulus of the speed (i.e. remove the +/- sign)

H1K

ee coughed up the following:

And just to chime in with the obvious----it would be absolutely HORRID if it didn't!

Having a 2 wheel car when you're trying to back out of a snow covered ditch?