More on XWD and the eLSD [Archive] - Saabscene :: Saab Forum - Saab Technical Information Resource

: More on XWD and the eLSD



Swade
01-22-2008, 04:28 AM
The story continues……


First we heard (http://www.trollhattansaab.net/archives/2008/01/saab-xwd-and-elsd-update.html) that there’d be no eLSD option on 2008 Saab 9-3 Aeros equipped with eLSD. For 2008, the eLSD will be available on the Saab Turbo-X only.


This led to the obvious question: why won’t the eLSD be available on the 2008 Aero equipped with XWD?


The answer from Saab Sweden is as follows:


——


Hello Steve,


Hmmm, - I cannot really agree with the ones saying that the eLSD is the only thing that makes or breaks the XWD system.


I know you’ve heard all this in June, but just to emphasize the major things….


As a summary, the XWD system is an active, on-demand, fully pre-emptive system that optimizes torque distribution depending on driving situation (driver intention, speed and road surface friction etc.)


So you still have all the advantages with continuously variable torque distribution between the front and rear axles, with 0 to close to 100% torque distribution. This counteracts unwanted over steer, under steer and instability and gives better handling, improved stability and a sportier driving.


Then also that the system is completely integrated and works in conjunction with all the vehicle dynamics systems like ESP.


But what makes the XWD system so great is actually the Saab 9-3 itself. It’s the rigid chassis, the electronics and Engine management system all working together with the XWD system, that creates a car perfectly tuned for any condition.


It’s a fully pre-emptive system that is electronically controlled, which means as soon as you turn the ignition key, the electronic oil pump ensures the system has full oil pressure and are ready to distribute full power to the rear wheels. No front wheel slip is needed, so we have programmed the system to start with a torque distribution that mimics the dynamic weight distribution, thus utilizing every wheel’s grip to the maximum.


In normal cruising mode, only 5-10% of torque is distributed to the rear, thus cutting down on internal friction and minimizing fuel consumption. However the system is always active and can in 80 milliseconds distribute 80% of the torque to the rear wheels if needed.


The eLSD then, is “the icing on the cake” to further enhance the driving experience. It’s improving traction.


It improves stability, giving for instance possibilities to drive faster through a curve before over steering tendencies shows.


It also helps yaw damping, that is to reduce the risk for over steering when lifting off the accelerator.


Later when accelerating out of the curve, the inner wheel tends to spin. This is avoided with the eLSD where we distribute more torque to the inner wheel and thus can accelerate stronger out of the curve.


Then it’s also used as you remember from the animation, in split-friction situations, when you have the wheels on one side of the car on Ice or gravel and the other on a higher friction surface, to help a strong acceleration from start. Also to stabilize the car when driving through a puddle or an ice spot affecting only one side of the car.


The tuning of the XWD and eLSD is always made with an aim of a neutral behavior of the car.


The eLSD is at the moment only tuned together with the lower/harder TurboX chassis, which is why we do not offer it on the Aero XWD. We are doing the final tuning on the Aero chassis now and for your information, we will be ready for MY09. How the exact offer will be M09 is not set yet, and can vary by market.


Hope this helps…..


——


So there you go.


Many thanks to Henrik for taking the time to provide the extra info.


How well the system operates without the eLSD has been somewhat of a mystery, so it’s good to get the insight from the people working on it. I just wish it was this plain already, of course, but now you know.


So if you’re looking for the full XWD system as soon as possible, the Saab Turbo X is you vehicle, in all its limited edition glory. Make mine a black one, OK?


If you’re willing to wait, the 2009 Saab 9-3 Aero V6 will have the eLSD available. We heard from John Libbos (http://www.trollhattansaab.net/archives/2008/01/more-9-3-xwd-news-us-market.html) from SaabUSA last week that it’ll most likely be standard equipment on the US version of the 09 model, but we’ll have to wait and see as to whether it’s standard or optional in other markets.


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