RPM approximation-prediction

[Chaxel Frederic (QUALITE)]

Hi DIY_EFI members.

I'm start to design and program an Injection-Ignition ECU for
a simple engine (30 cm^3 mono-cylinder) which is used
for the Eco-Marathon Shell :

  a competition with the less fuel consommation objective
(1200 Km with one litre at Le Castelet in France)

I'm a beginner in Injection-Ignition ECU, and I have one
question by now :


I get some TOP signals from a captor. This information
is used to calculate the engine RPM and to calculate the
Ignition time (by the way of a table).
But of course I get the RPM at T time and used it for
ignition at T+DT time (1 engine round after).

Of course RPM is not the same at T+DT than at T (if the
RPM change, which is often the case).

So if I want to be exact I must approximate (predict) the RPM.

My solution is actually to use RPM(T-1) and RPM(T) to calculate 
RPM(T+1) :
  RPM(T+1)=RPM(T)-RPM(T-1)+RMP(T)=2*RMP(T)-RPM(T-1)

It's a simple linear approximation (and simple to program
in assembly language).

This give good results (much more better than using RPM(T+1)=
RPM(T))

Maybe somebody know a better solution (Kalman Filter
for instance, or ...) ?

Sorry for my dirty English !


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+ CHAXEL Frederic          Email : Chaxel at cran.u-nancy.fr +
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