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Abstract |
Closed-Loop Spark-Advance Control using the Spark Plug as Ion Probe
The spark advance determines the efficiency of spark-ignited (SI)
engines by positioning the combustion in relation to the crank shaft
rotation. Today's spark-advance controllers are open-loop systems that
measure parameters affecting the spark-advance setting and compensates
for their effects. Several parameters affect the best spark-advance
setting but it would be too expensive to measure and account for them
all. This results in a schedule that is a compromise since it has to
guaranty good performance over the range of all the non-measured
parameters. A closed-loop scheme instead measures the result of the
actual spark advance and maintains an optimal spark-advance setting in
the presence of disturbances.
One possible measurement is the in-cylinder pressure which gives the
work produced by the combustion. Another measure is the ionization
current that uses the spark plug as sensor, when it is not used for
ignition. This is a direct in-cylinder measurement which is rich on
information about the combustion.
A novel approach to spark-advance control is presented, which uses the
ionization current as sensed variable. The feedback control scheme is
closely related to schemes based on in-cylinder pressure measurements,
that earlier have reported good results. A key idea in this approach is
to fit a model to the measured ionization current signal, and extract
information about the peak pressure position from the model
parameters.
The control strategy is validated on an SI production engine,
demonstrating that the spark-advance controller based on ionization
current interpretation can control the peak pressure position to
desired positions. The controller maintains an optimal spark
advance under various conditions and in the presence of environmental
disturbances such as air humidity. In addition, a new method to
increase the engine efficiency is presented, by using the closed-loop
spark-advance control strategy in combination with active water
injection.
Lars Eriksson
1997
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Last updated: 2021-11-10
