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Re: Adjustable WG actuators
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Posted by Dean (more from Dean) on Fri, 13 Feb 2004 08:37:05 Share Post by Email
In Reply to: Adjustable WG actuators, Jeff in ATL, Fri, 13 Feb 2004 06:29:36
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What is wastegate creep? At high CFMs the boost goes up or down?

On boost the pressure of the boost, and flow drag pushes on the WG valve plug. That changes the characteristic of the WG, as there is now more than the WG spring force to contend with. With your boost jacked up, this effect is stronger.

And at high flow rates, with the WG open, the high flows of exhaust gasses create a larger pressure drop across the WG for any given WG position.

So the WG characteristics are changing with high flows. The MBC is a simple passive thing that has its own control slope. It can only do so much while dealing with the variations in the WC and turbo at high flows. An electronic system with a simple feedback would have similar problems. An electronic controller with fuzzy logic can control things much tighter.

Look at your cruise control as a model. On hills you will loose a little speed and gain a bit going down slope. Our Passat diesel cruise control has a much tigher error band. Most controllers take action on a error feedback. There has to be some level of error or deviation to drive the corrective action.



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