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by supermatt 1269 days ago
> A 4x4 with a locked center diff and open front and rear diffs acts just like many AWD implementations.

Thats simply not true. It wouldnt be AWD if it cant adjust the power supplied to each axle. Thats the primary distinction.
1 comments
brookst 1269 days ago
Not all AWD implementations can adjust power per axle. The vast majority just use a center diff that is either open or limited slip. Both of those configurations are also used in some 4WD systems.

The primary distinction is that AWD is full time, while 4WD is part time and vehicles run in 2WD until the transfer case connects the second diff/axle.

Actual torque vectoring AWD systems are fairly rare and expensive compared to the AWD that has existed for 50 years, though they are becoming more common.

Here’s a good illustration of the different AWD implementations; I think you’ll find that a simple open center diff is still considered AWD and is still pretty common: https://www.caranddriver.com/features/a15102281/best-all-whe...

link
supermatt 1269 days ago
To clarify, your initial statement said "a locked center diff" would be a valid form of AWD, which is what i was contesting.

All the differentials mentioned in your link allow for variable power distribution to each axle. Thats the whole purpose of a center differential.

Of course, not all AWD are created equal. Some apply equal torque to all wheels (i.e. open), some prefer a single axle (e.g. limited slip), some aren't controlled by the wheels but by the ESC (e.g. electronically actuated clutch packs). I suppose in electric cars where each axle is driven independently they dont even need a center differential (but I have no knowledge there).

But its an interesting link nonetheless - it was certainly educational - so thanks!

I do agree, however, that a full-time 4WD (which have a central diff, unlike part-time 4WD which generally do not) are effectively indistinguishable from an AWD with a simple open center diff. Of course, those are the least effective types of AWD - but the 4WD at least has the ability to lock that diff and likely has a multi-speed transfer case :)

link