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      06-19-2008, 03:21 AM   #39
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Drives: E92 M3
Join Date: Sep 2006
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Originally Posted by jm1234 View Post
I doubt if you had access to the source code that there is a variable that's called spring rate. The point is that the control algorithm is designed to operate in conjunction with the as designed system parameters (including the stock springs).
... AND the system is designed to be robust to a variety of real world operating parameters and very likely a decent range of spring/roll bar stiffnesses.

Originally Posted by jm1234 View Post
Any control algorithm if connected to a system with different parameters will not operate as designed.
Not true. A system can be designed to be able to work with a wide vaariety of physical contants affecting the dynamics of the system. The above is making an ENORMOUS assumption that they did not bother to test EDC with a range of spring and roll bar combinations. I think that assumption is definitely incorrect. Of course they did, seem almost trivially obvious to me. Spring swapping during real world testing occured just as much as it does during testing of a non EDC car.

Originally Posted by jm1234 View Post
I doubt it does because I doubt BMW built this system to be used with any spring. It's a mathematical point, functionally the system may operate exactly the same with different springs.
Want to bet? M5 and M6 also have EDC and vendors have claimed their springs are fine on the system and users have swapped with no deleterious effects. There is no reason to believe the M3 is any different. I care about the math and subtleties myself too, but here that is not what matters. All we care about is does the system work and does it last.

Originally Posted by jm1234 View Post
Lookup tables are not inherently robust or stable. Step changes in any control surface are inherently destabilizing because they introduce a frequency spread of noise into the system. Positive feedback may exist at any frequency. The larger the step, the greater the noise and the greater the likelihood of exciting a positive feedback loop. If a lookup table artificially limits the quantity of control values then this will increase the size of the step change. They could indeed use lookup tables but it would be because the system is inherently stable, not because the lookup table is.
In essentially a 1 DOF mass/spring/damper system with two controlled variables (compression and rebound damping - both in a fairly narrow range)? Don't think so. A look up table or look up function would likley be just fine.

Originally Posted by jm1234 View Post
I would doubt the behaviors are too complex to model practically.
Completely agree on this one. Sure you model will never be perfect nor capture all effects but it would be pretty easy to get a darn good model that is plenty good for realistic virtual testing.