Thu May 30 05:48:45 GMT 2013
function of air-fuel-ratio (AFR).
1.2.1 --- Constants and variables
AFR: Air fuel ratio
F_gal/hr: fuel flow rate in gal/hr
Sg: specific gravity of gasoline
Sg = 0.74 gr/cc = 46 lb/ft^3
1.2.2 --- Equation
F_gal/hr = (air flow lb/hr) / (air fuel ratio) / (specific gravity of gas) X
F_gal/hr (gal/hr) = A_lb/hr (lb/hr) / AFR () / Sg (lb/ft^3) * 7.481 (gal/ft^3)
F_gal/hr = 0.1626 * A_lb/hr / AFR
Substituting the above equation for A_lb/hr gives,
F_gal/hr = (107.6*Vd) * MAP * RPM * %VE / Ta / AFR
where (107.6*Vd) is a constant and %VE is primarily a function of MAP and RPM.
While this is the basic equation needed to control the injector duration, the
terms should be grouped and normalized in such a way as to make programming
the CPU easier (i.e., the terms MAP, RPM, and %VE could be combined into one
lookup table as a function of MAP and RPM).
1.2.3 --- Determination of AFR
The air-fuel-ratio should be 14.7:1 whenever the system is operating in
closed-loop mode with the oxygen sensor. During conditions of starting, cold
engine, cold O2 sensor, or power enrichment, the system should be operated
open loop. Open loop AFR depends on coolant temperature, MAP, and RPM. (need
more info here --- need to define the controlling algorithm)
1.3 --- Additional terms -- Acceleration Enrichment, Deceleration Enleanment,
and Close-Loop Feedback
1.3.1 --- Acceleration Enrichment (AE)
In the prototype controller, AE should simulate the accelerator pump of a
traditional carburetor. That would make it an additive term to the equation
of (1.2.2) that would add a pre-set quantity of fuel as a function of
throttle change. Additionally, it would have an adjustable "decay parameter"
that would be similar to the hole diameter of the "shooter". In the future,
it may be beneficial to include MAP and coolant temperature into this
term. For now, I will just represent it as a yet to be defined additive
function of AE. (need more info here --- need to define the controlling
1.3.2 --- Deceleration Enleanment (DE)
I don't believe this term is necessary in the first prototype of our
controller. Ultimately this term will lean the engine during deceleration
much as the acceleration enrichment term adds fuel during acceleration. It
should have the same inputs as the acceleration term.
1.3.3 --- Close-Loop Feedback (CLF)
This should be a multiplicative term representing the integrated error from
the oxygen sensor. The conditions for when this term should be included are
yet to be defined. Conditions to consider are cold O2 sensor, cold engine,
acceleration, deceleration, power enrichment. (others?) (need more info here,
need to define the controlling algorithm)
1.4 --- The overall fuel delivery equation.
F_gal/hr = (107.6*Vd) * MAP * RPM * %VE / Ta / AFR * DE * CLF + AE
In this equation, MAP, RPM, and Ta are engine parameters measured directly.
(107.6*Vd) is a constant. %VE is experimentally determined as a function of
MAP and RPM. DE and AE depend on MAP, TPS, and coolant temperature. CLF
is a function of the O2 sensor input. AFR is a function of crank (starting),
cold engine, and power enrichment.
2 --- Idle Air Control
3 --- Spark Timing
This is getting lengthy...
Will expanding this help anyone?
Someone want to start an input/output description or a software description?
John S Gwynne
Gwynne.1 at osu.edu
T h e O h i o - S t a t e U n i v e r s i t y
ElectroScience Laboratory, 1320 Kinnear Road, Columbus, Ohio 43212, USA
Telephone: (614) 292-7981 * Fax: (614) 292-7292
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