BoostControl (2006-04-24 17:55:47)

Dutycycle table suggestion

After trying to tune the current (1.0.36) firmwares PID BoostControl,i realized that is really a hard one.

Tried different methods and PID settings, but never got a really satisfying bahaviour => write on your page

Because every BIG ECU brands have openloop Turbo boost control, I suggest implementing this 'ASAP' to ours.

A 6X6 or 8X8 RPM / TPS or MAP (selectable) table would be fine, with loggable Dutycycle.

Such an "openloop" (it is not openloop, because the MAP changes and it provides feedback) table is very similar in effect as using only the P component (with I=0 and D=0) if the "refpos" is set right (20, 40, 60 or 80%, whatever gives closest balance for the boost-target) for the given setup.


Overview of boostcontrol

Typical Pneumatic connections


Boost control system layout:

Primary system for internal wastgate:

Primary system for external wastgate:

Improved spoolup and range for external wastegate:

The systems are sequenced, first pressure is applied to the top chamber but if that is not enough (remember EBP pushing on the wastegate valve) the boost control working on the lower chamber will start to bleed off boost. In addition to this the system acting on the bottom chamber is always bleeding off as much boost as possible until the system is getting over the adjustable 'spoolup' threshold.

Note that the atmosphere connection can be replaced with a vacuum connection. A vacuum reservoir will NOT work, it has to be a fairly high capacity vacuum pump. (If a zero break pressure check valve is found and used (never seen one) to atmosphere a vaccum reservoir can be used.)

-Jörgen


Audi external wastegate example - under investigation, no final word on this yet; Actually, text below might be bad ! Please review

Connection

Is this (trying to be) similar as the "boostvalveexternal" example connection ? - Yes, I was wondering if this was the best solution.

Operation - must be verified against the connection

Alternative:

The alternative would be to put the solenoid in between the compressor and the bottom chamber (big pipe), like a regular boost control and let the top chamber vent to atmosphere.

Pros:

Solenoid would only be powered when boost needs to be regulated which is better because with the other configuration the valve would be powered constantly at idle and cruising, not very good.(unless there are different types of solenoid valves? i.e ones that would vent to atmosphere when powered)

Possible Cons:

Very slight loss in performance due to bleeding off boost, the other configuration would theoretically not bleed any boost(not bleeding off boost could cause a problem with the wastegate returning to closed state). Possibly slightly slower actuation of the WG valve due to restriction in the solenoid valve.

After some thinking it seems to me like the regular boost controller style setup would be the best choice. Except I don't get this:

Primary system for external wastgate:

What would make this configuration spool up faster and have an extended range? (this is the config which the above section is about, not the alternative here) And from your text Jörgen it seems to me like the valve would vent to atmosphere in the unpowered(rest) state, contrary to Marcell's correction above.

And just to make clear, the bottom chamber (closest to the valve) is the one where boost would be applied to open the WG valve, top is the chamber with the spring in it and a higher pressure in this chamber would only keep the WG shut harder.


See also