Posted in Tech first, but no one seemed to care, so back to the trusty ITR forum.

I was reading over my girldfriend's VW Cabrio owner's manual and I came across a feature that I found interesting. Though I don't remember what VW's term was, and I don't have the manual here to quote from, the basic concept was as follows.
Using what I assume are the ABS wheel speed sensors, a system monitors the speeds of the drive wheels during acceleration. If the system detects a discrepency between the speeds of the two wheels (as might occur in an open-diff. vehicle when one wheel was on a slippery surface) it applies braking to the spinning wheel, thus effectively sending more drive torque to the wheel with greater traction.

After reading the manual, and with no other information on the system thus far, it appears that it functions very much like an electronic LSD in many respects. I have given it some thought, and I haven't yet determined any disadvantages to this system other than the increased load and wear on the braking system. However, because of its electronic nature, it could be completely tunable and adaptable in real-time.

I am aware that Honda's own ATTS system was not particularly successful (at least in the U.S. market), but although the concept of electronically directing torque was the same, the two systems function in different ways. Perhaps a more simplistic (though properly executed) approach, such as the one VW has taken rudimentary steps in creating, would prove to be a more effective solution.

Just some thoughts.

 

using electronics in a diff is probably better served with a wet-pack clutch type in rheomagnetic fluid - the rear diff on the Acura MDX functions in this manner.

 

It's funny marketing seems to take a perfectly simple concept or feature that is an industry standard...and whip it up into something that impresses even the engineers that designed it! LOL Oh yea...that system you just described is what ALL ABS SYSTEMS DO. LSD is potent because it puts down real torque to both wheels at the same time...so even when the car is turning there's still torque driving the inside wheel even if it slips the outside wheel can will still drive the car. Open diffs don't do that and when the inside wheel slips, there is NO POWER ON THE OUTSIDE WHEEL. That's what makes abs so important, it slows down the inside (slipping) wheel (where most of torque is going to) so it doesn't slip and you lose control.
rmc


[Modified by WundedSaint, 1:35 AM 12/30/2002]


[Modified by WundedSaint, 1:44 AM 12/30/2002]

 

ABS=Anti-Lock Braking System

Standard ABS systems detect when one or more wheels have lost traction (locked)during braking, and then modulate the braking pressure to keep the wheels rotating, thus maintaining directional control and the use of whatever traction is still available.

Such systems don't act during acceleration as the system I described does. The concept of such a system is that even though the car is equipped with a conventional open diff., the tendency for one wheel to spin when it looses traction (since torque is directed to the wheel with the least resistance) is reduced by the braking of that wheel during acceleration (thus increasing that wheel's resistance and directing torque to the opposite wheel).

 

Honda's ATTS only directs torque to the outside wheel when the car is in a turn with the throttle open. The system monitors steering angle, vehicle speed, throttle position, and vehicle yaw. But the ATTS system acts as an open diff in a straight line. You can smoke one tire all day long in a TypeSH Prelude because ATTS does not have any way to monitor wheel "spinnage".

The VW system you describe sounds more like a straight-line traction control system rather than a handling enhancement system.

Andrew


[Modified by aklucsarits, 11:29 PM 12/29/2002]

 

ATTS actually affects both wheels making the outside one spin faster and the inside
wheel spin slower. but youre right it cant act as an LSD.

 

My VR6 GTi had that silly traction system in it. I prefer the lsd in the ITR to the system, hands down. The VW system would help sometimes, and others it was useless. I think there are wheel speed requirements for when it works and when it doesn't.

My parents have a gravel driveway, so snow removal is a pita. There is always packed snow on the driveway and ice. My GTi, no matter how gently I drove it up the driveway could not make it with brand new P700's (with the snows it was no problem of course). The ITR with the bald (I mean bald) RE010's had little to no problem getting out of my driveway in the snow (again the new 185/65 15 snow tires helped).

As for getting the power down out of the corners on dry/wet roads, the VW drove like it had an open diff and would just spin the inside wheel, where the itr just goes.

When doing my best rally driver impression on snow covered roads all I could hear in the VW was the abs relay clicking. A strange metallic smell would come int he car. I believe that smell was the abs pump getting hot. I think that running both the brakes and the throttle at the same time defeats VW's traction system.

As for controlling the traction system in the VW, I think that it might not matter. In a racing situation you might just heat your front brakes up trying to control wheel spin, reducing your overall braking ability.

 

Its not at all an 'electronic LSD' Its just a needlessly complex way of describing a traction control system. A true LSD doesn't limit the torque going to the wheels (as selective braking does) but rather evenly distributes it to the wheels with the most traction. There are 'active' differentials such as the system that the Lancer EVO VIII uses which operates a hydraulic clutch pack to distribute power based on several real-time sensors (including wheel slip) but the VW system isn't that.

I am reminded though about a quote that applies to all this electronic automotive voodo. "Technology, when it becomes significantly advances, becomes indistnguishable from magic" Whether these electronic driving "aids" become good magic or bad magic remains to be seen. Personally, I think that the simplest system that gets the job done is all that is really required. The Germans in particular seem obsessed withing making things needlessly complex (although I have to admit, they do a good job of it)

Mike


[Modified by 92sleepR, 6:22 PM 12/30/2002]

 

Electronic LSD, like they used to brain wash d. zoolander

rob- who is fuggin useless