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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > Attn: If Interested In 100% Rwd



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      10-31-2011, 01:52 PM   #1
Doyle
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Attn: If Interested In 100% Rwd

All,

If you would be interested in having the capability to select when AWD engages, please make your voice heard here:

http://w w w .n54tech.com/forums/showthread.php?t=13856

It would be great to have the big-league tuners look into this. Hopefully if we make enough noise, someone will listen! If there is a demand, someone will create the supply!
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      10-31-2011, 01:56 PM   #2
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That is a TALL order..the pricepoint and issues associated with it would be mind boggling...there is a reason why the RWD is chosen for the performance and the AWD for traction and driveability in poor weather...you just simply cant have it all
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      10-31-2011, 05:35 PM   #3
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Quote:
Originally Posted by tibra1 View Post
That is a TALL order..the pricepoint and issues associated with it would be mind boggling...there is a reason why the RWD is chosen for the performance and the AWD for traction and driveability in poor weather...you just simply cant have it all
Have you done any research into the TCU and how it communicates with the ECU? Have you had any experience with the logic of the ATC 300? Have you ever coded/tuned an x-drive car? Or are you just spouting off about something that you have based entirely around assumptions? I'm sure you are fully aware of the Haldex controller and how it can "rewrite" how the transfer case reacts in VW/Audi cars...

RWD is for performance and AWD is for traction? I'm sure the Porsche Turbo, Nissan GT-R, Audi R8, most Lambo's, Evo's and STi's would prove otherwise. Can't have it all? I'd point you to the GT-R's Nordschleife wet lap record.

Terry himself has said that it could be very possible. The point of this is to get more attention on this capability, not to shit on every idea and stagnate the community. Take your negativity back to the Raceland downpipe threads.
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      10-31-2011, 10:22 PM   #4
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Quote:
Originally Posted by Doyle View Post
Have you done any research into the TCU and how it communicates with the ECU? Have you had any experience with the logic of the ATC 300? Have you ever coded/tuned an x-drive car? Or are you just spouting off about something that you have based entirely around assumptions? I'm sure you are fully aware of the Haldex controller and how it can "rewrite" how the transfer case reacts in VW/Audi cars...

RWD is for performance and AWD is for traction? I'm sure the Porsche Turbo, Nissan GT-R, Audi R8, most Lambo's, Evo's and STi's would prove otherwise. Can't have it all? I'd point you to the GT-R's Nordschleife wet lap record.

Terry himself has said that it could be very possible. The point of this is to get more attention on this capability, not to shit on every idea and stagnate the community. Take your negativity back to the Raceland downpipe threads.
Easy tiger..dont mean to rain on your parade..but it aint happening ..as you can see by the overwhelming responses to your thread.

Sorry dont take your AWD frustrations out on me.
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      10-31-2011, 10:30 PM   #5
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This would be fun to have

but i have to say the X drive on our cars is nowhere close to as sophisticated and track bred as the GT-R AWD system or even the Evo ACD
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      10-31-2011, 11:02 PM   #6
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Quote:
Originally Posted by tibra1 View Post
Easy tiger..dont mean to rain on your parade..but it aint happening ..as you can see by the overwhelming responses to your thread.

Sorry dont take your AWD frustrations out on me.
Your first comment added nothing to the discussion, not sure why you even posted it

The potential is there for a quick tweak, and the potential is there for a big road block that would prevent such a tweak so it can go either way. Also given the large number of responses in a similar thread regarding XI going RWD like the STI I would say there is a big interest among us XI owners so it certainly could happen!

Anyways...
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      10-31-2011, 11:03 PM   #7
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I read somewhere. You can pull a fuse, and it disactivates the FWD. 100% RWD. Just by pulling a fuse.
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      10-31-2011, 11:07 PM   #8
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Originally Posted by amclint View Post
Your first comment added nothing to the discussion, not sure why you even posted it
Well thats your opinion and your entitled to it..just like I am entitled to mine..and mine is that this is a pipe dream..but hey have at it and reach for those stars..
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      11-01-2011, 12:46 AM   #9
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Quote:
Originally Posted by CrimsonIvy35i View Post
I read somewhere. You can pull a fuse, and it disactivates the FWD. 100% RWD. Just by pulling a fuse.
Yes but the car IMO is dangerous to drive this way, it's not just DSC/DTC disabled with the front wheels but also the ABS and the car drives very differently compared to just manually shutting off the DSC/DTC. At 50mph + it just doesn't feel right and I personally won't do it again.
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      11-01-2011, 07:30 AM   #10
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Quote:
Originally Posted by tibra1 View Post
Easy tiger..dont mean to rain on your parade..but it aint happening ..as you can see by the overwhelming responses to your thread.

Sorry dont take your AWD frustrations out on me.
Why isn't it happening? Explain it to me using your apparent vast amounts of technical knowledge.

"Overwhelming responses"--obviously you don't come to this section often: it's a ghost town. It gets nowhere near the traffic the n54 engine mod section gets. 8 responses in 12 hours (overnight, to boot) is pretty good. Also, if you have done any research, you'll see that one of the longest threads in this section deals exclusively with this issue:

http://www.e90post.com/forums/showthread.php?t=444973

I'm not frustrated with my AWD. In fact I'm looking forward to driving it all winter long

As for your "opinions", you are certainly entitled to them. I would just prefer they be educated. Right now, you are just coming off as an ignorant and unproductive troll.
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      11-01-2011, 12:54 PM   #11
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not a regular reader here and not really an Xi intender, but AWD is a pet technical field of interest.

For those criticizing the XI awd system as being unsophisticated, I respectfully suggest that your technical understanding of AWD systems is lacking, especially if you're contrasting with the nissan GT-R which is a fundamentally very similar AWD system.

They are both using a transfer clutch to couple the front and rear axles together, The only differences are in the control algorithms (and the presence of torque vectoring rear diffs in some R33, all R34 and R35 GT-Rs).

Ultimately, the transfer clutch is just a couple of wires looking for a voltage, and possibly some position sensors to verify function. Either by coding the existing control hardware, or by inserting new electronics between the various inputs/outputs of the system, it should be very feasible to alter the behavior of the AWD system. Especially since sensing accelerations and orientation has become so low cost with modern MEMS type chips.

Just look at things like the DCCDPro, the GRID and other ATTESA controllers, even the MoTec MDC for Evo ACD applications.

Keep the faith,
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      11-01-2011, 01:17 PM   #12
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DannyZRC-

Awesome! Thanks for chiming in. It would be great to get further insight into the system. I agree that in essence "ripping off" the solution for quattro, ATTESA, and DCCD will be the best option. Especially with a TCU that already has the capability of directing 100% of the power to the rear axle.
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      11-01-2011, 01:31 PM   #13
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Quote:
Originally Posted by DannyZRC View Post
not a regular reader here and not really an Xi intender, but AWD is a pet technical field of interest.

For those criticizing the XI awd system as being unsophisticated, I respectfully suggest that your technical understanding of AWD systems is lacking, especially if you're contrasting with the nissan GT-R which is a fundamentally very similar AWD system.

They are both using a transfer clutch to couple the front and rear axles together, The only differences are in the control algorithms (and the presence of torque vectoring rear diffs in some R33, all R34 and R35 GT-Rs).

Ultimately, the transfer clutch is just a couple of wires looking for a voltage, and possibly some position sensors to verify function. Either by coding the existing control hardware, or by inserting new electronics between the various inputs/outputs of the system, it should be very feasible to alter the behavior of the AWD system. Especially since sensing accelerations and orientation has become so low cost with modern MEMS type chips.

Just look at things like the DCCDPro, the GRID and other ATTESA controllers, even the MoTec MDC for Evo ACD applications.

Keep the faith,
I think the main weakness in the xDrive system most of us have on 3-series is the use of individual wheel braking on an open diff to simulate an LSD. It is fine for passenger car applications but start to tune and pump a bunch of TQ through it and you'll be wanting better diffs/TC, and the electronics to make use of them.
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      11-01-2011, 01:56 PM   #14
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Quote:
Originally Posted by ajsalida View Post
I think the main weakness in the xDrive system most of us have on 3-series is the use of individual wheel braking on an open diff to simulate an LSD. It is fine for passenger car applications but start to tune and pump a bunch of TQ through it and you'll be wanting better diffs/TC, and the electronics to make use of them.
From a hardware standpoint, we could really use a rear LSD. That is why M Gmbh put one on the x5/6m.

Software, wise I think we're close. On a road course, it is a bit intrusive on corner exits. For the strip, if we could disengage it mid second gear, that would free up power (essentially just launch control).
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      11-01-2011, 03:43 PM   #15
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if memory serves, the X5/6M models have a torque vectoring rear diff.

Also, I recall having seen at least 1 implementation of the wavetrac in an xi application

The addition of an LSD will likely reduce the activation incidence of the eLSD that BMW is doing through the ABS, but ideally you would either disable or modify the eLSD functionality.
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      11-01-2011, 05:25 PM   #16
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You are correct. For some reason I thought it was a viscous-clutch center diff with 1:1.1 planetary gear on either side.

I believe all LSDs that work with RWD models work with x-drives. I believe the quaife will fit in the front (per Harold @ HPA).

As far as the nannies, I wonder what either HPA or Berk have done with them? I don't believe they are running aftermarket ECUs.

I'm glad we finally got a real discussion going on...

Danny: How familiar are you with the x-drive system and it's capabilities? Have any good resources/documents that you could link/post?
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      11-01-2011, 05:38 PM   #17
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I think people are just slapping in an LSD in the rear and doing nothing with the electronics. This bothers me, probably for no good reason. It's just I suspect there are times when the new LSD and e-braking diff + TC software could get confused, and you'd hate to find that out when in a limits of traction/max TQ situation.
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      11-01-2011, 05:39 PM   #18
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I don't know anything beyond the obvious, Transfer Clutch + Open diffs, using electronic brake actuation to perform traction control / slip limiting.

I can't help with any technical documentation on how control is delegated, apologies, I'm just responding to the folk that are acting as though it were an inscrutable magic box that only a gengineered nuclear rocket surgeon could possibly hope to twiddle.
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      11-01-2011, 06:08 PM   #19
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Well one thing I do know (and that's about it) is the e-braking traction AWD xDrive thing is a stand alone module, it works even when DTC/DSC is off. (dynamic braking? there is an acronym for this subsystem which I forget).

When I bought the car I wanted to know exactly what was there and working, it is very hard to separate out the advertising hype and the true system design.

Basically we have an open diff front and rear, and then an unbroken rear drive shaft connecting tranny output to rear diff. So basic rear drive platform with front diff added. Then the TC case is just a drive chain and some clutches hung off the rear drive shaft, one side connected to a front driveshaft, and those clutches engage or disengage between 0-100% according to electronics. So the TC is not a diff, rear diff is always engaged and max TQ to front is 50/50 split when TC is locked up.

Another nice addition would be a true center diff.

edit: Anyway the electronics manages the TQ split between F/R axles via TC clutches (usually 40/60 but can vary from 50/50 to 0/100) and side/side via e-braking to simulate LSD each axle.
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      11-01-2011, 06:20 PM   #20
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I'd be happy with just being able to disable it, similar to pulling the fuse. I'd prefer RWD during the summer and AWD on the few days of winter that I need it.
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      11-01-2011, 08:40 PM   #21
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ajsalida, I wouldn't say that the eLSD functionality qualifies as standalone simply because the DTC/DSC disables don't suspend it's activity. ABS is not suspended, and yet it's all the same electronics/software running that show (I suspect the eLSD as well).

Also, a locked clutch doesn't necessarily mean 50/50, this depends on many things including steering angle and relative traction at the various wheels. locked clutch, rear wheels on ice is going to be very near 100f/0r torque distribution.

akotten, disabling it is probably also the easiest thing to achieve, so that's a plus.. but remember, there is extra drag on the front wheels from the AWD hardware, so making the car RWD won't exactly emulate RWD dynamics. Probably close enough for government work though

This is a link for a modification of an Isuzu trooper with the TOD transfer case (very similar AWD workings to xdrive), the users wanted to go the other way though and lock up the clutches for a more conventional 4HI application off road.

same basic idea would work for xdrive, but of course all the details of the implementation would have to be independently found, and it's possible that the BMW uses some diagnostic mechanism which would be difficult to circumvent. either way, for consideration: http://www.planetisuzoo.com/articles...quipped_Isuzus

they replace the clutch lockup signal with their own from a simple circuit, and the same simple circuit also handles loading the 4wd computer outputs so that it doesn't realize the jig is up.
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      11-02-2011, 05:21 AM   #22
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Danny you are right, stand alone is the wrong word. Foundational would be better, it cannot be turned off just like, and it is intergral with, ABS. BTW the e-diff (DBC) is also on 2WD cars. Very curious to see what can be done here.

As far as the %TQ that can go F/R, we are into marketing semantics here. If the rear cannot be disengaged, and the front can be, then the most the front gets is 50%. In the same manner an ordinary diff, when welded, is sending at most 50% TQ to each wheel.

In xDrive, if the rear driveshaft cannot be disengaged from the tranny, then the least amount of TQ it can receive is 50%. Convoluted scenarios involving what tire/axle has zero traction don't count as part of the machinery.

You do not work for BMW marketing by any chance do you?

edit: said another way the rear driveshaft can never rotate slower than the front, and that means at least one rear wheel is rotating at the same rate as the fronts, always.
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