[DeTomaso] EFI

[Dave Londry]

Dan
Do you remember the label on your old post about control schemes?
dave


On 05/10/2011 8:51 AM, Daniel C Jones wrote:
>> Question: Are any of those EFIs closed loop? That's how OEM works, and if it
>> is, then tuning should be unnecessary
> OEM EFI are combined open and closed loop systems and, even if they
> were completely
> closed loop, would need tuning.  The gains (and limits, deadbands, etc.) in the
> forward and feedback paths are scheduled with various parameters and tuning is
> required to determine the values of those gains.  The reason open loop
> tables are
> used by the OEMs is the sensors (mass air flow, O2, etc) don't have
> the bandwidth
> required (are too slow to react to changes like throttle transients).
>
> There are attempts at automated tuning, either model based or target
> based, though
> I don't know how successful they are.  Model based systems attempt to model the
> engine to determine the fuel (and spark) needs.  I know some of the aftermarket
> systems use a model to come up with an initial set of gains/tables that will at
> least start the engine and serve as a basis from which a tuner can
> work.  In target
> based systems, you defined desired air-fuel ratio tables (the targets:
> ratios versus
> RPM and load as determined by throttle position and possibly manifold
> pressure) and
> the computer adds or subtracts fuel (and spark advance) to iterate to
> towards the
> targets over time.
>
> I'm a flight controls engineer by trade.  There are all kinds of
> controls schemes.
> Implicit and explicit model following, neural networks, etc.  I've even seen a
> Darwinian gain scheduling approach in which you define populations of gains and
> success criteria then run simulations to determine the best (survival
> of the fittest)
> of the gain sets then introduce random variations (mutations) in the gains are
> recompete the resulting sets until the best set is found that
> satisfies the success
> criteria.
>
> One of the problems guys have with aftermarket EFI is picking the
> wrong controls
> approach for their specific engine.  I've made a lengthy previous post
> which detailed
> the three basic engine control system schemes (mass air flow, speed
> density and Alpha-N)
> and which ones are best suited for manifold type (common plenum or IR)
> and cam overlap.
> If you pick the wrong control approach for your engine, all the tuning
> in the world won't
> make it work properly.
>
> Dan Jones
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