xDrive
 

Hey everyone! Long time, no post....

So I was reading about the e70 X5 in last month's Roundel, and it described the functioning of the xDrive system exactly the same as it is in the face-lifted e53, and the X3.
I thought I'd read somewhere (on this forum, probably) that the e70 was going to get xDrive "II", where the electronic diffy could vary torque not just between the front and rear axles, but side to side as well (as opposed to calling upon ABS to limit wheel spin within a given Axle) I guess this new system didn't make it into the e70 (?)

Also, the article briefly mentioned the role DSC and DTC play in the functionality of xDrive... and how it's possible to disengage DSC (which we all know is done by pressing the DSC button on the center console) - which leaves xDrive operating with only the DTC. But apparently you can also disengage the DTC and let xDrive manage traction on its own.
I seem to remember reading (also, probably on this forum) that this can be done in the e53 too... something about holding down the button for 3 seconds maybe (?) Anybody know the details?

xDrive II is stated for release in the middle of the E70's lifecycle. Just as the E53 went from a DSC based 4 wheel drive system to xDrive in the middle of its lifecycle.

I'd look for the new xDrive to debut at the time of the new next-gen X3's unveiling. BMW will bring the X5's spec up to date with X3 spec...

OK, so xDrive II will be introduced the same way the current xDrive was - that makes sense...

Any ideas about the DSC/DTC question?

just press the button and hold it for more than 10 sec

Will there be another indicator showing when both have been disabled?

Also, I'm assuming that X-drive is more effective when you leave the DSC button engaged?

I'm new to the X-drive camp arriving from Quattro and giving it a little boot with the throttle would ensure the EDL's would get engaged to get you out of a really tight spot. From what I'm reading about X-drive, the torque has to rely on traction control to brake the spinning wheel and transfer torque to the other? Not as effective as a locking differential, but works nontheless. If one could point me to a technical description of X-drive I'd appreciate that as well.

try this http://www.janixworld.com/x5/misc/X5%20xdrive.pdf

courtesy of the homepage :thumbup:

thanks, newbie alert here!!

i'm a newbie too :thumbup:

That was a good read where, but I'm still left with a few questions. I see how the torque can be shifted fore and aft by the center diff, as well as from side to side by engaging a particular wheel's brakes.

So what happens if you push the DSC button once? I assume that this only disables stability control which really reacts to excessive yaw rates (ie oversteer or understeer)? I think I have that right?

What happens if you push and hold DSC down for >10secs? That disables DSC AND traction control? Hence that essentially disables sensors from distributing torque from side to side AND front to rear? That confuses me a bit thinking that it may disable X-drive altogether and go to a 100% rear drive car? If that's the case, I can see some rear-wheel drive enduced oversteer in my future, but I'm guessing this is not the case. I need to go out and experiment a bit :)

oooo....i'm interested to know that too...

The description of xDrive II that you cited is actually a description of xDrive I first introduced on the 2004 X3's and X5's. Here's the quote from Wikipedia describing the 2004 X5:

"For 2004 the X5 was refreshed with new headlights, a few new exterior colors, a new four-wheel drive system and upgraded engines. The exterior touches kept it fresh and gave the X5 a more aggressive look. The grilles were enlarged, as well as their actual slats being modified in a 'flame surfaced' style. In keeping with the E39 refresh of 2001, the 2004 X5's headlights got "angel-eyes" (rings or halos around all front headlamps). The taillights also got an E39-style refresh treatment and the exterior glass went from a "dotted" pattern to a cleaner one of "lines". BMW invented a new four-wheel drive system dubbed xDrive shared both in the X5 and X3 in 2004. Instead of using the previous X5 system which consisted of power being split 60-40 (rear wheels-front wheels) and DSC to brake wheels losing traction, xDrive could variably cut off power to the front or rear axles in a matter of milliseconds, while transferring 100% of the engine power to either, thus allowing the vehicle to regain traction quickly."

I haven't found a formal description of what exactly changed with xDrive II. I'm guessing it might be stronger, lighter, and faster, but from a functional design standpoint, pretty much the same as xDrive I.

I hate audi but have to admit there awd system is better than bmws. Quattro is one of the best sytems out there.

i know audi's famous for it...how does the quattro system work?

Well I believe it has LSDs all around and can transfer 100% of power to the one wheel that has most power not relying on the traction control at all. It can also transfer power form front to back side to side and diagnally if I remeber correctly. My wifes A6 has awesome traction in all conditions. You can feel the difference. But Xdrive is getting closer and im sure Xdrive2 will be as good if not better than quattro but thats 3 years away,

The DSC button does not disable the X-Drive system components, it simply makes them less aggressive. BMW has a nice (IMO) habit of providing buttons in their rides that change existing functionality. Anyone who has hit the SPORT button in a E46M3 knows what I mean.

I just hope BMW takes a page from Audi on how to design AWD systems....Audi is unstoppable.

Google is your friend: one search on Audi Quattro System

http://en.wikipedia.org/wiki/Quattro...l_drive_system)

http://en.wikipedia.org/wiki/Quattro...rive_system%29

i wonder why i didn't think of wiki...:doh:

thanks :thumbup:

Yeah, you gotta love Wiki... :thumbup:

But the Wiki description you cite is exactly how I understood the current xDrive (and described it above)... it just stops short of explaining how it manages traction side-to-side (either within a given axle, or diagonally). If what I read previously is true, this is what's improved upon in xDrive II.

As for the DSC button... I JUST got back from a romp in the snow to/from the supermarket, and now I wish I'd checked this thread before I left so I could have tried the press-the-DSC button-for-10+ seconds-trick!!
But I have experimented a bit with just pressing the DSC button once to disengage the DSC, but retaining the DTC. My impression is that, on an xDrive vehicle, the DSC is much less invasive than it is on typical 3/5/7 rear drive models (certainly much less so than on my old 328Ci sport). So there's not a huge difference in 'normal' snow driving with it on or off... but when things get really slick, the DSC will cut engine power and engage ABS as it sees fit to stop what it perceives as an over-/under-steer loss of control. For this reason, in the snow I prefer to drive w/ DSC disengaged at all times (with the exception of high-speed highway travel) to allow for a little xDrive-controlled yaw play. The mix of just traction control - which only limits wheel spin - and xDrive is a phenomenal combination for the snow IMO.

But there are times - when things are REALLY deep and messy - when if you don't just let the wheels spin a bit and keep the vehicle creeping forward, you can still get stuck... as I understand it, this is because DTC is cutting wheel spin, so if none of the 4 wheels are getting sufficient traction, then... well, you get the idea.
Now, the part I'm not sure about is: If you hold down the DSC button for 10 seconds and disengage DTC as well, without traction control's influence, would the ABS still intervene to manage side-to-side wheel spin? (Probably... ) Or would the xDrive's eDiff lock-out and let the wheels spin unencumbered? [Not sure, but it sounds like this is what Audi's mechanical diff does (?)... and I think the Cayenne has a manual lock-out control to accomplish this.]
Most likely, I'd think that xDrive would still function in full, managing torque between axles, and calling upon ABS to manage wheel slip within a given axle.
But to be sure, someone should go out in the snow tonight and test it out! :driver:

At any rate, I think xDrive is a great balance between dry-road performance (where Audi's heavy mechanical system is losing ground to xDrive - and some of the other new eDiffs out there), and off-road traction. But if xDrive II will in fact add the capability of shifting torque from side to side as well (rather than limiting wheel slip with ABS) then it should be a nice improvement.

You have a slight misperception about traction. Once a tire starts slipping (by spinning) you lose traction because the coefficient of friction changes. Slowing the rotation of the tire to prevent spinning actually maintains traction, and a non skidding tire will always provide better traction and better acceleration than a spinning tire, the same way that threshold braking will always stop a car faster than if you lock the wheels up. The only time spinning the tire might be an advantage is if the snow is so deep and soft that you can't get traction, then spinning the tires can sometimes burn down through the snow to the point where it hits pavement.

Quattro really is impressive. My old S6 that I just traded in for the 4.8is was unstoppable in the snow with snow tires.

http://video.google.com/videoplay?do...4614&q=allroad

Allroad in this video vs the others up a ski slope. Cool stuff!

also, I'm guessing that the 10+ sec trick would disable the ABS from braking one particular wheel once it starts spinning. Thus, at most you'd have one front tire and one rear tire spinning at the same time. Kind of like two open differentials front and rear which is essentially the case. BMW is relying on the ABS system to brake one wheel which in turn transfers torque to the other side of the car.

Quattro has front and rear EDL's (electronic locking diffs) as well as a center torsen (TORqueSensing) differential providing automatic and variable front to rear distribution.

:iagree:

No mis-perception here - that's an example of a situation I had in mind... seen it happen several times. I've also (in my snow-tired 328Ci) had TC actually slow the vehicle to a stop when climbing an icy hill b/c the wheels could not find enough traction to keep them from spinning. After switching off DSC/DTC, from a dead stop, I was able to scoot right up and over the hill by keeping the wheels carefully and slowly spinning (like 2-3K RPM).
I'm aware of the physics of traction as well, but I've found that sometimes the real world deviates from academic theory.

Makes sense... that would be very cool, actually. Tough to verify though - unless you enlist a buddy to stand outside the vehicle in the snow and watch what the wheels are doing. ;)

I remember seeing a video of the X5 and a Audi going up a snow covered hill and the Audi won. Do any of you still have the link?

Dude, look 4 posts up... :slap:

By the way, judging from the stock prices rolling across the bottom of the screen in that video, it's circa early-2001... which means that the X5 is not the facelifted xDrive version. I'd like to see a re-test of Quattro vs. xDrive!!

:confused:

Mitch P's post... 4 posts before yours.

Here:

So the BMW 3 and X5 didnot have X drive?

That Audi video looks a bit suspect to me. The Audi looks like it's about to die before it gets anywhere near the camera (tires are spinning and it has lost momentum), then it cuts to a shot of it going past the camera so fast it practically takes air of a bump.

I also wonder what they did about equalizing the tire/wheel combos between vehicles. If they aren't running the same model and width of tires, then the comparisons are meaningless if you're trying to compare the abilities of the AWD system.

It also looked like the Allroad was making a faster approach that gave it an advantage. It sure did not look very scientific.

yep... (3 series didn't get xDrive until the e90 came out in '06)

I noticed that too... I assumed that they were demonstrating 2 different traction modes or something (?) :dunno:
(Maybe one of our German speaking members can translate the narration.)
But either way, it definitely looked suspect the way they cut to a shot of the Allroad streaking up the middle section of the hill :confused:

I do think that Audi has a great system it would be great to see a fair test.

On quattro (it may have been covered):

xDrive is similar to the Haldex quattro system used on the transverse-engine cars (TT, A3, as well as Golf, current Passat). The biggest difference is that it's reversed front-to-rear.

The quattro system used in modern longitudinal-engine Audis (A4, A6, A8, as well as the last-gen Passat) uses a mechanical torsen center diff.

All three systems use some form of "Electronic Diff Lock" which is not a diff lock at all. They simply brake the spinning wheel which encourages it's opposite to move. In most cases the front and rear diffs are otherwise open. The EDL has limitations but is suitable for the road.

I'm not sure if disabling DTC disables the EDLs.

I think that Volvo switched to the Haldex system but the test car didnot have it.